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Old 05-19-2006, 09:58 PM   #1
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Quench Distance vs. DCR

I'm again wondering which one matters more, and to what degree. Some say that having a perfect quench distance is more important than having low dynamic compression, for detonation resistance. Others disagree.

I'm limited on knowledge of some of the specs in my engine, but I know that with the .015 thick head gaskets and the .018 deck height I have, it comes out to around a .033" quench distance, which actually has some decent quench properties with the D-cup pistons and the same shape combustion chambers (of the stock L98 heads).
I also know that the static compression ratio is (insignificantly less than) 9:1 with the current bore, stroke, piston dish, gasket bore, gasket compressed thickness, deck height, and combustion chamber CC's (about 61.9 because they've been milled slightly, I actually estimated that number from taking the specs & clearances of a totally stock '89 L98 with 64CC heads to get the rated 9.3:1 CR, vs. my current specs & clearances...something like that, it's been a while, but the numbers are probably slightly off).
I don't know the dynamic compression however, because oddly enough I can't seem to locate detailed enough numbers for a stock '89 L98 cam to calculate it. So, I have to go by the SCR for now.

If I put in some .039 gaskets it raises the quench distance to an un-ideal .057, but lowers the SCR to 8.6:1.
If I go even further and install .051 gaskets, the quench goes out the window at .069, but the SCR goes down to 8.4:1.
What I'm wondering is if that would be worth it in terms of detonation resistance, as I ideally want to run about 15psi on 93 octane since the rest of my setup can handle that much boost. I'll be using a 24x12x4 bar & plate air/air IC core with a lot of aluminum piping.
If I lower the SCR a lot, I won't make quite as much power on the same boost and I'll lose some low-end torque (oh darn) all else being equal, but it may be easier to accomplish this goal. However, if it's pointless due to killing off my excellent quench, I may as well not even waste my time lifting off the heads (which have no other reason to come off at this point, especially when I don't want them to).

If you're boosted, aren't incurring detonation, and you know your engine's specs, what's your quench distance, SCR and/or DCR, and your boost level?
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Old 05-19-2006, 10:43 PM   #2
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Quote:
Originally Posted by Steven89Iroc
I don't know the dynamic compression however, because oddly enough I can't seem to locate detailed enough numbers for a stock '89 L98 cam to calculate it. So, I have to go by the SCR for now.
Not sure if this correct, but do a search for "camshaft" at:
http://www.thirdgen.org/tech-data
It lists the camshaft specs. It gives enough info to calc. the dynamic compression.


Quote:
Originally Posted by Steven89Iroc
If you're boosted, aren't incurring detonation, and you know your engine's specs, what's your quench distance, SCR and/or DCR, and your boost level?
You are probably tired of me posting by now, but here it goes:
355ci
.028" piston in the hole
7cc dish piston (valve reliefs)
76cc GM 993 heads polished chambers (big and inefficient)
.028 GM composite gasket
216* @ .050" duration, 110* LSA, 105* ICL
8.6:1 - 8.7:1 static compression
7.8:1 DCR (from memory)

NO IC, 7PSI, 23* BTDC timing, 93 octane, IAT 150* F, 11.6ish AFR, no detonation

NO IC, 9PSI, 23* BTDC timing, 93 octane, IAT 170* F, 11.4ish AFR, no detonation

overall, bad quench, low compression. Not that I wanted it that way. It just came out that way. I have no idea which is better, quench vs. lower SCR.

I wouldn't pull the heads if I was you.

Last edited by junkcltr; 05-19-2006 at 10:49 PM.
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Old 05-20-2006, 09:08 AM   #3
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I've been setting up my engine for an ideal quench, which is around.045". I'll be running a .005 deck with a .041 gasket. I'm having the pistons milled to give me around 9.3-9.5:1. What I am told, is that an ideal quench is a number 1 priority. It's hard to maintain anything else without it. You could run rich, less timing, but if the quench is way out of whack, you may still incurr detonation. And under boost, the likely hood of that happening would most likely increase.
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Old 05-20-2006, 10:10 AM   #4
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I used to run 10.1:1 compression with a .043 quench and let me tell ya, I used to run all crazy types of advanced timing and could never get it to detonate. I've used 3 different timing lights to make sure what I was reading was correct and had many motorheads sratching their heads wondering why it wouldn't detonate. You can even search my old posts about it probably. So yeah, my vote is for a good quench distance.

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Old 05-20-2006, 12:36 PM   #5
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Quote:
Originally Posted by Tom91Bird
I used to run 10.1:1 compression with a .043 quench and let me tell ya, I used to run all crazy types of advanced timing and could never get it to detonate. I've used 3 different timing lights to make sure what I was reading was correct and had many motorheads sratching their heads wondering why it wouldn't detonate. You can even search my old posts about it probably. So yeah, my vote is for a good quench distance.
Was this on an engine with forced induction or was it naturally aspirated? If forced, how much boost was this with?

I'm considering running a thinner head gasket to get a bit more quench, but it's certainly going to give me a good increase in compression which I may not want.
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Old 05-20-2006, 01:32 PM   #6
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Quote:
Originally Posted by Jeremy_84_F41
Was this on an engine with forced induction or was it naturally aspirated? If forced, how much boost was this with?

I'm considering running a thinner head gasket to get a bit more quench, but it's certainly going to give me a good increase in compression which I may not want.
Sorry, it was an N/A motor.
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Old 05-20-2006, 03:51 PM   #7
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junkcltr, not tired of your posts at all. Your setup is probably as close to what I'll be running as I've seen on here, the more info the better!
No detonation at 9psi with that setup sounds good. You had a 20* increase in IAT's from 2 psi and .2 less AFR, that's quite a bit. Was it a hotter day? Makes me wonder how much more it would raise from adding 6 psi on top of that. My IAT's shouldn't be that high, but I wouldn't have thought going from 7 psi to 9 psi would hurt that bad in any case.
I don't want to pull the heads unless some better ones are going on, that's for sure, it's akin to pulling teeth. I was thinking that if I could find some aluminum L98 heads for cheap, if there's a way to open up the combustion chambers some to bring it to around 64-67cc, it might be worth it because I could port those (and take 50 lbs from the car). I'd need a real cc'ing kit though, but I don't even know how possible that is to do.

For testing and tuning purposes, I raised the stock timing tables up across the board with the $8D after I got this engine broken in, most everywhere seemed to respond well to a few more degrees (but I have no solid results other than seat of pants). I could only raise WOT timing about 2-4* before it started showing appreciable knock counts, but I had pulled a little fuel as well. This was in about average ambient temps (60-70) I don't know how much you can tinker with the timing and fuel on a completely stock L98, but this didn't seem like very much being that it has less compression and much better quench (as well as smoothed edges in the combustion chamber and in the piston dish to reduce hot spots). That is of course much more timing than I'll be running with boost.

Jeremy, I haven't seen you post on here in a while. Is your Formy running right yet (or at all)? If so, how is it doing with detonation and such? How much boost? Sounds like you're on the other end of asking the same question as me.
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Old 05-20-2006, 04:47 PM   #8
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Quote:
Originally Posted by Steven89Iroc
No detonation at 9psi with that setup sounds good. You had a 20* increase in IAT's from 2 psi and .2 less AFR, that's quite a bit. Was it a hotter day? Makes me wonder how much more it would raise from adding 6 psi on top of that. My IAT's shouldn't be that high, but I wouldn't have thought going from 7 psi to 9 psi would hurt that bad in any case.
I can't remember if one was a day run and one was a night run. I will look at my notes for the ALDL logs and let you know the ambient temps. My air cleaners get very fresh cold air. They are enclosed in steel boxes in front of the tires and have a 4"x4" or bigger hole cut in the bottom of the inner wheel well with a small scoop that draws in air. There is no IC and the coolant fan and radiator dump hot air on the compressor to TB pipes.

This thing rocks: http://www.gnttype.org/techarea/turbo/turbocalcs.xls
It is very user friendly and gives very close results as to what my ALDL data reads.

Quote:
Originally Posted by Steven89Iroc
I don't want to pull the heads unless some better ones are going on, that's for sure, it's akin to pulling teeth. I was thinking that if I could find some aluminum L98 heads for cheap, if there's a way to open up the combustion chambers some to bring it to around 64-67cc, it might be worth it because I could port those (and take 50 lbs from the car). I'd need a real cc'ing kit though, but I don't even know how possible that is to do.
I looked around at head gaskets for a while before setting on the GM .028" composite ones. I think I read GM rates them for 400HP. I am a little over that, but I like the composites better than the steel shim. I could have went with the .015" FelPro steel shims and had a quench of about .045". I chose to go with the GMs for better head gasket sealing with a .055" quench. I did it more for the sealing aspect than the quench vs. DCR. I didn't want the FelPro .039" due to the really bad quench. Normally I run the FelPros.

The GM .028" would have worked decent with your setup. Here is the part number for anyone else interested. I took me a while to find it.
GM P/N 10105117 (.028" composite). They were $14 each from gmpartsdirect.com w/o shipping.

As for the CC kit, I use an old CD-ROM cover with a hole drilled in it. I had a syringe I got from the vet/pet store. I used mineral spirits for the fluid. It wiped out the syringe rubber seal. A graduated cylinder would be better. I checked the local suppl stores but couldn't find one.

That is a lot of material to remove from the alum. head. I have never found a cut-view of that cyl head to see how material could be removed. I am guessing that there wouldn't be enough material left. Maybe some one will post if they know. Removing that much material gets into CC reshaping and requires some researching first.
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Old 05-21-2006, 09:45 AM   #9
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A .039 quench would have been alot better than the .055. With .055, your inviting trouble. Also, for every .010" of HG thickness you only change your CR by .28, which is peanuts.
And I would have gone with the steel gasket. Properly torqued, it will seal and hold up to boost better than the composite one will, although it depends how much boost, but under 15lbs it should be fine, but the better quench is what would be in your favor with that route.
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Old 05-21-2006, 09:54 AM   #10
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Quote:
Originally Posted by Cruz'N Bruz'R
A .039 quench would have been alot better than the .055. With .055, your inviting trouble. Also, for every .010" of HG thickness you only change your CR by .28, which is peanuts.
I agree that the .045" would have been better than .055".

Quote:
Originally Posted by Cruz'N Bruz'R
And I would have gone with the steel gasket. Properly torqued, it will seal and hold up to boost better than the composite one will, although it depends how much boost, but under 15lbs it should be fine, but the better quench is what would be in your favor with that route.
I have never used the steel .015" and every one I talked to said use the composite. I have read more stories on the web about the .015" leaking more than composites leaking. I am interested in why you say the .015" would seal better. Please post the real world experiences or the physics behind why the .015" would seal better than the .028" gasket.

What do you mean by properly torqued?
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Old 05-21-2006, 12:22 PM   #11
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Dude email me... zooki11@hotmail.com or trevorVFA146 on AIM...I'm in Lemoore and have a blue 89 Iroc....its not very fast but it would be cool to check out your car......sorry to jack your post

350Z
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Old 05-21-2006, 01:44 PM   #12
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Quote:
Originally Posted by junkcltr
I can't remember if one was a day run and one was a night run. I will look at my notes for the ALDL logs and let you know the ambient temps. My air cleaners get very fresh cold air. They are enclosed in steel boxes in front of the tires and have a 4"x4" or bigger hole cut in the bottom of the inner wheel well with a small scoop that draws in air. There is no IC and the coolant fan and radiator dump hot air on the compressor to TB pipes.

This thing rocks: http://www.gnttype.org/techarea/turbo/turbocalcs.xls
It is very user friendly and gives very close results as to what my ALDL data reads.
Cool, knowing ambient temps would help too. How do I use that program? I'm not sure what to open an .xls file with.

Quote:
Originally Posted by junkcltr
I looked around at head gaskets for a while before setting on the GM .028" composite ones. I think I read GM rates them for 400HP. I am a little over that, but I like the composites better than the steel shim. I could have went with the .015" FelPro steel shims and had a quench of about .045". I chose to go with the GMs for better head gasket sealing with a .055" quench. I did it more for the sealing aspect than the quench vs. DCR. I didn't want the FelPro .039" due to the really bad quench. Normally I run the FelPros.

The GM .028" would have worked decent with your setup. Here is the part number for anyone else interested. I took me a while to find it.
GM P/N 10105117 (.028" composite). They were $14 each from gmpartsdirect.com w/o shipping.
I had heard the same things about sealing problems with the .015 steel shim gaskets, but I think the problems may have come from the surfaces not being smooth and flat and/or not using Copper Coat (or copper Spray-a-Gasket). I have about 2500 miles on my engine and have no sealing problems at the heads (the rest of the engine is a different story, heh). My heads were milled, though pretty roughly. I just used an electric sander to smooth out the surface some (ghetto I know, but it must have worked), and I also used the Copper Coat as per directions.
I didn't know about the .028 gaskets at the time, I may have done that instead. Oh well.

Quote:
Originally Posted by junkcltr
As for the CC kit, I use an old CD-ROM cover with a hole drilled in it. I had a syringe I got from the vet/pet store. I used mineral spirits for the fluid. It wiped out the syringe rubber seal. A graduated cylinder would be better. I checked the local suppl stores but couldn't find one.

That is a lot of material to remove from the alum. head. I have never found a cut-view of that cyl head to see how material could be removed. I am guessing that there wouldn't be enough material left. Maybe some one will post if they know. Removing that much material gets into CC reshaping and requires some researching first.
Okay, I'm not sure how much and where there is to remove material, either. It sounds like too much work for the gains though.

Quote:
Originally Posted by Cruz'N Bruz'R
A .039 quench would have been alot better than the .055. With .055, your inviting trouble. Also, for every .010" of HG thickness you only change your CR by .28, which is peanuts.
And I would have gone with the steel gasket. Properly torqued, it will seal and hold up to boost better than the composite one will, although it depends how much boost, but under 15lbs it should be fine, but the better quench is what would be in your favor with that route.
.010 for .28 might be a rule of thumb, but every engine is different. Unlike geometries and other clearances will change those numbers.
I would hope that all heads are properly torqued! Heh



350Z (I bet that pisses off the Nissan guys, hehe), I sent you an email.
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Old 05-21-2006, 02:19 PM   #13
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Cool, knowing ambient temps would help too. How do I use that program? I'm not sure what to open an .xls file with.
The 7PSI data was with an ambient temp. of 50* F from a bank time/temp. sign. The 9PSI was with an ambient temp. of 60* F from a bank time/temp. sign. I am not sure what the temp. was at the inlet to the air cleaner because I don't have a sensor there.

Clicking on that link will bring up a spreadsheet using Microsoft MS-Excel if you have it installed. If it doesn't open up the spreadsheet then I suggest downloading OpenOffice 2.0.2. Go to
OpenOffice.org: Home
and download the Windows version. It is a fee program that can read and create MS-Office documents/spreadsheets/presentation. Or you could buy MS-Office for $300. I suggest the OpenOffice program.....it works great. I think the download file is about 50Meg. If you have dialup, download it overnight.

Quote:
Originally Posted by Steven89Iroc
I had heard the same things about sealing problems with the .015 steel shim gaskets, but I think the problems may have come from the surfaces not being smooth and flat and/or not using Copper Coat (or copper Spray-a-Gasket). I have about 2500 miles on my engine and have no sealing problems at the heads (the rest of the engine is a different story, heh). My heads were milled, though pretty roughly. I just used an electric sander to smooth out the surface some (ghetto I know, but it must have worked), and I also used the Copper Coat as per directions.
I didn't know about the .028 gaskets at the time, I may have done that instead. Oh well.
I don't know if the .010" leak thing is true. I really don't know if the steel shim or composite is better. I have always used a composite gasket (Felpros) and never had a problem with N/A. So I stuck with the composite. I have never used the steel shim so I don't have any real world experience to give.......just hear say and recommendations from a decent machine shop. Also, the block I have has not been decked, but the heads were re-surfaced.

I searched for quite some time to find that GM gasket. I will post if I run into problems with the GM composite gaskets.

Quote:
Originally Posted by Steven89Iroc
Okay, I'm not sure how much and where there is to remove material, either. It sounds like too much work for the gains though.
For the cost of the heads and possibly junking them, I wouldn't try it until you found some decent info that it can be done or has been done reliably. If I can across a set of those heads for next to nothing I would try it.

Quote:
Originally Posted by Steven89Iroc
.010 for .28 might be a rule of thumb, but every engine is different. Unlike geometries and other clearances will change those numbers.
I would hope that all heads are properly torqued! Heh
True, geometry matters.
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Old 05-21-2006, 03:16 PM   #14
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Okay, roughly 10* higher ambient makes 20* IAT increase closer to understandable, being slightly leaner with 2 more psi. I'm sure compressor efficiency has some to do with that as well, you do seem to be slightly off the map at those boost levels with ~25 lb/min coming from each turbo (est. from your hp est., lot's of ests.).

I might try Open Office depending on how much $$$. Haven't looked at it yet.

The only experience I have with the .015 gaskets is my own. I also had not decked the block, but the heads. Before I rebuilt it, the block had actually ingested a decent bit of water and bent turned the #8 rod into an 'S' at 120k due to a heavy rainstorm and my own stupidity. If anything the deck was slightly worse off, but probably not.
I don't see why your gaskets would be any worse than mine though. I will also post if I have problems with the steel shim gaskets.



Now, DCR...
I have seen the link that you posted about the stock cam specs and they don't include all the info I need to calculate DCR, but I did find a nifty downloadable calculator along with a good article here Dynamic CR , that let me figure out some more info on my own. However, I still need the ICL of the stock '89 L98 cam. If it's somewhere between 105 and 108 then it calculates my DCR as being somewhere between 8.56 and 8.62, but that doesn't sound right according to the article (especially when the SCR is 9:1), and I don't know why unless the stock cam specs posted have the duration @ .050, which messes everything up because I need to know the seat to seat value instead. That would make sense why the DCR is so much higher than it probably should be. In that case, I still don't have enough stock cam specs. :/
It also got me thinking about getting (once I figure out the DCR) an adjustable timing set to retard the cam some to lower the DCR a bit more and also raise the powerband up every so slightly. That sounds like win-win, other than the price of an adjustable timing set, heh.

Anyone know more stock '89 L98 cam specs? Maybe the factory manual has them? My factory manual is where my Camaro is unfortunately, 1500 miles away in a dark room.

Last edited by Steven89Iroc; 05-21-2006 at 03:22 PM.
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Old 05-21-2006, 03:42 PM   #15
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Quote:
Originally Posted by Steven89Iroc
Okay, roughly 10* higher ambient makes 20* IAT increase closer to understandable, being slightly leaner with 2 more psi. I'm sure compressor efficiency has some to do with that as well, you do seem to be slightly off the map at those boost levels with ~25 lb/min coming from each turbo (est. from your hp est., lot's of ests.).
It calculates out to about 22-23 lb/min taking into account the IAT temps.......over at the 70%-65% efficiency area on the map. Once the IC goes in it will get worse, but at the same time I will up the boost so in that respect it should keep me along the 70%-65% eff. lines (hopefully).

Quote:
Originally Posted by Steven89Iroc
I might try Open Office depending on how much $$$. Haven't looked at it yet.
It is completely free. It has been around for years. I started using it with a non-Windows computer and now use it on Windows too. Once you try it, you will see there is no reason to dump money on the MS-Office stuff.
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Old 05-21-2006, 07:48 PM   #16
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I was talking about a steel gasket in general over the composite. IMO, I wouldn't build your motor resorting to a .015 shim gasket. they are like a last ditch effort to get a higher cr/better quench value. If your block deck, or head deck are off, even by .002-.003" then your gonna have problems sealing a shim gasket. The properties of a steel gasket mimic the block more accurately than a composite when thermal expansion occurs. i haven't used a completely steel gasket myself, but motors we've built at the shop that endure higher compression due to either natural means, or forced induction/nitrous, insist on the copper gaskets to be used.
Also different gaskets have different torque specs, a shim gasket for example should come with it's own specific torque rating dependant on material thickness/type. Alot of people just torque all heads down at 85ft-lbs, and then ensue possible problems.

Just my $.02
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Old 05-23-2006, 03:38 AM   #17
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Quote:
Originally Posted by junkcltr
I looked around at head gaskets for a while before setting on the GM .028" composite ones. I think I read GM rates them for 400HP. I am a little over that, but I like the composites better than the steel shim.
I’d be surprised if they failed at 400hp… for that matter it’s not that simple, failure happens from loss of clamping force and peak cylinder pressure, you can’t say that when you have 400hp you’ll have X peak cylinder pressure. I wouldn’t be surprised if those gaskets live to the same pressure as the typical composite fel pro’s would.

FWIW, MRG makes a similar composite gasket with a compressed thickness of .026”

Quote:
I could have went with the .015" FelPro steel shims and had a quench of about .045". I chose to go with the GMs for better head gasket sealing with a .055" quench. I did it more for the sealing aspect than the quench vs. DCR. I didn't want the FelPro .039" due to the really bad quench. Normally I run the FelPros.
From the factory these things usually come with steel shims. The GM PN is supposed to be .016” thick, but I’ve never checked it. I can’t imagine them resealing correctly on anything that does not have a fresh factory machined surface (machine shops don’t use the same equipment).

The fel pro’s are steel shims with a rubber coating to help them seal, MRG also makes similar gaskets. I have no idea how reliably they seal, to what level, if they’ll work with non virgin heads/blocks… I can’t seem to find any real data on them or anyone that has used them in a performance application.

Quote:
Originally Posted by Cruz'N Bruz'R
I was talking about a steel gasket in general over the composite. IMO, I wouldn't build your motor resorting to a .015 shim gasket. they are like a last ditch effort to get a higher cr/better quench value. If your block deck, or head deck are off, even by .002-.003" then your gonna have problems sealing a shim gasket.
Just like you would with any shim gasket. I wonder if you could get away with using them with a coat of spray copper or hylomar like you would with some copper and other alloy gaskets to get them to seal (or the old school solution, silver spray paint).

Quote:
Also different gaskets have different torque specs, a shim gasket for example should come with it's own specific torque rating dependant on material thickness/type. Alot of people just torque all heads down at 85ft-lbs, and then ensue possible problems.
Gaskets should act as basically a solid piece once they are compressed to their compressed thickness, and shouldn’t effect torque settings. What does greatly effect what things are torqued to are the bolts/studs used. They need to be stretched enough to properly preload everything to ensure proper tension on the gasket and on the bolt to keep it from backing out, but not enough to yield the bolt, where it looses it’s stretchiness and will not maintain tension, even before the bolt breaks.
----------
FWIW, to answer the original question, the small difference in detonation control you’ll get in compression will be insignificant compared to the results of proper quench.

Last edited by 83 Crossfire TA; 05-23-2006 at 03:39 AM. Reason: Automerged Doublepost
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Old 05-23-2006, 11:42 AM   #18
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Quote:
Originally Posted by 83 Crossfire TA
I’d be surprised if they failed at 400hp… for that matter it’s not that simple, failure happens from loss of clamping force and peak cylinder pressure, you can’t say that when you have 400hp you’ll have X peak cylinder pressure. I wouldn’t be surprised if those gaskets live to the same pressure as the typical composite fel pro’s would.

FWIW, MRG makes a similar composite gasket with a compressed thickness of .026”
I felt the same way about the 400HP ratings. It is all about peak pressure. According to the ALDL data, the CFM and injector BPWs put the car at about 450FWHP. Using the ALDL data in the GN turbo calculator puts the engine at about 450 FWHP. In reality, it is probably in the 410 FWHP to 490 FWHP range. Anyway, I am not worried about the head gaskets. If I went into the 600 FWHP range than I would start to question them.
I went with the composites on my block because it was used and had not been decked. And I always use composites anyway.....because they always worked for me and they are cheap.

Who is MRG? Mr. Gasket Racing? I would like to check out those gaskets. Although, for some reason I always thought of Mr. Gasket Racing as the "Wal-Mart" brand of racing parts.....it seems cheap, but then they break and you have to buy it three times over and ends up costing more. Maybe it is time I took a serious look at Mr. Gasket parts. They might be better than I think.
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Old 05-24-2006, 04:52 AM   #19
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Yep, Mr Gasket…

They do sort of make everything, and cheap, but if you start looking you’ll find that their stuff is the same stuff as say transdapt and a few others sell for a few $$$ more. And I mean exactly the same. Some of it is that they own a whole ton of the other product lines out there... check out their web site, you'll be suprised.

WRT to gaskets they make some good stuff, never had an issue with it, I’d probably put most of their generic, nothing special gaskets between the normal felpro and the felpro hp stuff…
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Old 05-25-2006, 08:34 PM   #20
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Thanks for the info everyone. I'm not going to mess with anything before I at least know how things are going to work as is, I'm just being unreasonably impatient. I think I'm getting that way because I'm so close to getting my Camaro back. This place is desolate and boring (and my Talon is sitting idle waiting for it's built tranny). It was refreshing to get a ride in POS350Z's mint 12-second IROC though.

If I have any problems once boosted with the rubber coated (forgot about that) .015 steel shim gaskets that I sprayed with copper seal I'll be sure to post about it.
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Old 05-26-2006, 03:32 AM   #21
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As a matter of fact, I just ordered myself a set of these into the shop, I’ll experiment with them on my truck before I decide if I dare use them on “the other” 350 (turbocharged)

http://store.summitracing.com/partde...5&autoview=sku
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Old 06-02-2006, 10:37 AM   #22
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I'm another one who'll keep the quench tight, rather than trying to lower the compression with the head gaskets. Have the quench as tight as you dare (at the least, keep it under .040), without contacting the piston/head deck at high rpms.
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Old 05-21-2008, 01:52 PM   #23
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Re: Quench Distance vs. DCR

So sorry to dig this post out of the past for all involved but I am having a problem that I believe may be answered by the statements above.

I built a 383 last march and have had detonation problems with it since it was built. Specifics are : .030 over block, 5.7 rod, 76cc world torquer heads with a nominal (assuming 9.025 deck height) .066 quench distance. This is with FPP-1003 head gaskets .041 thick.

Ive calculated my nominal SCR to be 9.2 and my DCR to be 7.8 with the cam I'm running. Both of these should be ok to run 93 octane which I always use.

I get very reliable detonation above 3000 RPM and no amount of octane boost (tried avgas 100 and octane boosters) seems to make it go away. I am currently running less than 30 degrees total timing and the det is still there.

I now have the heads off an am polishing the chambers to eliminate any potential hot spots I may have had before I send them off to the machine shop for ovehaul (broken valve spring damper - world springs)

I am now looking at quench distance for a solution to the knock. If I use the .028 MRG part, I need to get the chambers to 79 CC (basically there with a good polish) to keep SCR and DCR the same. If I went with a steel shim I would have to enlarge chambers to 82 CC. These options would give me .053 or .040 quench distance respectively.

What head gasket should I go with? and if its a shim should I have the machine shop put an additional polish step on the heads? I have copper spray gasket and have used shims previously with good success.

Thanks for the great post - just looking for confirmation to use the shim gasket.
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Old 05-21-2008, 03:34 PM   #24
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Re: Quench Distance vs. DCR

Your large quench distance is what's causing the detonation. I think if you went as thin as possible on the shim to get the quench to .035-.038, you'll be much better off, even with a slightly higher CR.
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Old 05-21-2008, 05:42 PM   #25
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Re: Quench Distance vs. DCR

Quote:
Originally Posted by askulte View Post
Your large quench distance is what's causing the detonation. I think if you went as thin as possible on the shim to get the quench to .035-.038, you'll be much better off, even with a slightly higher CR.
Great - now just one question, do I spray the copper gasket permatex stuff on the rubber coated FPP-1094 or not? Or shoud I just get the non rubber coated one and spray that?
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Old 05-21-2008, 09:39 PM   #26
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Re: Quench Distance vs. DCR

i ran 10.6:1 with a .064 quench.. AL heads though.. on 92 octane.. people said it was demolition waiting to happen.. but thats what my best time were on..

now i'm at 11.1:1 and .044 quench.. and still on 92 octane.. much better IMO..
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