92rs85berlintta

iTrader: (1)

i was told i have too much comp. its 10.5/1 . with iron heads. it sparks and detonates when total adv is 34 and the timing is between 8-10. does this mean i have too much comp for 94 oct fuel? and iron heads.

Damon

Depends on more than the static compression ratio but my experience is that 10.5:1 with iron heads and a small street cam is usually a bit too much for pump gas. You can get by if you back the spark advance down but that's not really the best way to go. You'll make more power with lower compression and full spark advance than you will with high compression and retarded timing.

As a diagnostic procedure you might try throwing a tank of 100 Octane Sunoco unleaded in it (try to do this on a near-empty tank so it doesn't get diluted) and see if it goes away. If it does then you're probably just borderline high on compression. If it doesn't then you might have other problems CAUSING the detonation- like a lean A/F ratio or maybe a bit more timing than you think you have. Or perhaps you miscalculated you actual compression ratio slightly and it's actually higher than you think it is.

Also, if your engine was originally designed to run an EGR valve and you have defeated it the part-throttle calibration will be wrong and almost always cause some detonation at part throttle (shouldn't affect WOT, though).

You have engine and cylinder head specs? Many here could do a quick sanity-check on your compression ratio for you, including myself.

89RsPower!

also.. what engine/induction system?

F-BIRD'88

If you're car is borderline try a little cooler plug.
I use a cooler than stock, non projected tip plug in mine.
Champion RV8c chevy 305 heads 350 12.65:1 runs on sunoco 94.

Ukraine Train

to add on the spark plug post, i've read that for each point of CR you go up, go down one heat range. in your case i'd start two heat ranges colder than stock then check your plugs after a couple hundred miles. if they're fouled then move up one heat range

nedry

A few days ago, I had posted a question about a theoretical buildof a thirdgen engine/drivetrain for max fuel economy. Vader recommended 10.58:1 compression, using a GM 10134371 aluminum block, GM 10134359 aluminum cylinder heads, 3.98" cast-alooy pistons (with me thinking of maybe substituting hypereutectics), and CPI fuel-injection with a MAF sensor, all to burn 87-octane. I'll openly admit that I just barely know a crankshaft from a camshaft when I see 'em, so I defer to the board's collective wisdom, since you guys know a lot that I don't. To y mearger bit of knowledge, 10.58 on 87-octane seems counterintuitive, or is this another of those things you guys already know that I still have to learn?

Anyway, thanks much in advance.

nedry OUT

92rs85berlintta

iTrader: (1)

my engine is a 355. with 58cc heads 2,02 1.60 valves.edelbrock torquer cam.hypereutectic ft pistons,edelbrock rpm intake and a 600 cfm 1406. im gonna try to get thicker headgaskets
[54$ ouch) .readjust my rockers(i tightened them 1 full turn not knowing with this cam i can only turn them 1/4 turn)and a 750 dp holley. but first im gonna try cooler plugs.anthing else i should do?

92rs85berlintta

iTrader: (1)

also how much compression will .50 thick headgaskets shave off?

Morley

The key there is he said Alumnium bolck ,heads, etc. Alumnium has much better heat rejection properties than iron which will allow you to run much higher CR's than you could with iron. Also being an injected engine helps to keep detonation under control.

Morley

That depends on what thickness and bore gasket you are using now. If you are using a .041" gasket and go to .050 you won't be lowering it much (couple points maybe, .1 or .2) If you are using a .016" shim gasket you'll be lowering it quite a bit more by going to .050".

92 zzz28

Just to add to the ideas of too much compression for iron heads and street bound gasolines, an old combo of mine had about 11.3:1 CR and Sportsman II heads. I only ran 93 octane once to see what would happen and she detonated pretty badly at mid to high rpms. I usually only ran 110. It was built for drag racing so I didn't care that I had to buy gas at the track..

I would do what was mentioned earlier about changing to colder plugs. Maybe also try one of those octane boosters. I have never used one but maybe they work. Like said earlier, changing to thicker head gaskets is probably not going to yield much lower compression. If the plugs don't change enough try to lower your timing a degree or two until the detonation is gone. Then save your money and get some aluminum heads and turn the timing back up...

Twilightoptics

The only way to truely tell is to check Dynamic Compression.

http://members.uia.net/pkelley2/DynamicCR.html

Best Compression ratio/dynamic compression ratio calc ever.

But you need to know some very important things.

Piston CC, Head Gasket Thickness, Deck Height, etc

92rs85berlintta

iTrader: (1)

i beleive my gaskets are .023 or .022 ? does that sound right? so would a .050 even help enough to make it run good? or will i have to start saving for alumium heads?

thanks guys!!

Morley

Plug your current numbers into the above formula, then try it with the thicker gasket.

But just as a guesstimate.. DD2K says you'll drop your CR .74 by going from .022 to .050 thickness. If you were at 10.5:1 this will net you 9.76:1 , a tad high (IMO) but with 94 octane (and proper timing) it should be streetable. Just remember, this is with everything operating properly, good tune on the engine and all. As things come out of "spec" it may start to have problems again.

NastyL98_T/A

FWIW, I'm running aluminum heads with aproximately 53cc chambers, a .030" overbore, stock replacement hypereutectic pistons with a -.014' deck height and a small cam ( GM ZZ4 ).........which all calculates to around 11.0-11.5 CR. I'm running Autolite 103 plugs and premium gas with no detonation. I would guess 10.5 would be pushing it with iron heads. Although some of the late model Impalas and Buick Roadmasters came with LT1's with Iron heads and ran 10.2 CR from the factory.

Morley

Yeah, thats the beauty of injection, it lets you run right on the hairy edge.

I forgot to ask the origional poster if he was running FI or carb. The 9.7 with FI should be perfectly fine for street use, with a carb it should be ok, but nearer the edge of detonation.

92rs85berlintta

iTrader: (1)

my engine is a 355. with 58cc heads 2,02 1.60 valves.edelbrock torquer cam.hypereutectic ft pistons,edelbrock rpm intake and a 600 cfm 1406.

its a carbed 1406 but i just bought a 1407 and havent gotten to adjust the valves or put the 1407 on yet.

Twilightoptics

Remember that gasket thickness changes quench. For best performance and least possability of ping/knock/preignition you want quench to be between .35 and .45; .4 being ideal.

Closer to quench you are with your current compression setup, the better you'll be.

92rs85berlintta

iTrader: (1)

how much do you think i could get out of these.

iron 2.02 1.60 3 angle valve job swirl polished valves 58cc hardened valve seats rated for .588 lift screw in studs. i want to sell them. they have low miles too. what could i ask for them?

Air_Adam

Doesn't seem that high.. the L69 has 9.5:1 CR and runs perfectly fine on 87 octane with iron heads. I think 10.5 or more is pushing it for pump gas though. 10:1 seems to be a happy medium for 91/93 octane though.

Twilightoptics

You have to remember the cam differences in the way that the engines run.

9.5:1 is doable, with knock sensor, good timing, plugs etc.

10 is getting close to the edge. At that point you really need to check your technical figures and physical figures to find out what your compression is going to be. I can move myself almost a full point just by changing the deck height from .025 to .0.... that's not much in height, but lots in compression.

at 10 you also have to figure your dynamic compression. Go to the link I gave it expains it much more than I.

rx7speed

I have read the link you gave and some things about it I don't agree with

first it says that dynamic compression will never go above static compression

that is false
there are N/A motors out there that are tuned very well to work on the ramming effects of the intake as well as very good with scavenging that are able to pull more then 100%VE which would make more higher dynamic compression. above that of static compression


second he says taht dynamic compression does not change at any point during the operation of a motor

at different rpms the motors dynamic compression changes all the time

hence the name dynamic compression
cam/head/intake/exhuast flow all have effects on volumetric efficiency (VE) on a motor.VE is what makes up dynamic compression
and some combos work very well at one rpm but not at another
volumetric efficiency is the % of fill your cylinder gets

lets say you are driving a 350. you are not going to fill the whole cylinder up with air most the time. VE is the percentige of air that does make it into the motor.
so lets say on that 350 each cylinder has a volume of 43.75 cubic inches
now if your VE was 80% (about normal for stock if I remember) you are really only pulling in about 35cubic inches of air/fuel.... another arguement that there is a replacement for displacement as well

like your TPI will work great at low rpms and VE% can do fairly well.

but once you start revving that thing up it chokes and can't breath
VE goes down

that is going to change your dynamic compression


and vise versa with a large cam

at low rpms the intake charge will end up getting pulled throuh the exhuast and then also end up in reversion going back up the intake manifold

this is going to make your VE suck.
but at higher rpms man that VE is going to go way up there
and this is the part where you can pull better then 100%VE mean higher dynamic compression then static compression


and with dynamic comression all you can really do is make a close estimate as to what it would be

but in all reality you can't do it too well by just math alone
and then to figure out what your dynamic compression is going to be along the lines off all your rpms points

UGH too much work

Morley

I was going by a carbed engine, iron heads and no computer controls. For a CC engine it should be fine as long as everything is working properly.

Air_Adam

Thats true... but when I had the L69 in my car, I've driven it around with the computer turned off (unplugged actually) and it had no issues with running on 87 octane. Neither did my dad's '73 Z28, which had a 9.5:1 CR 350. He ran that on 87 octane with no problems, and that had no computer controls whatsoever.

Twilightoptics

Computer has nothing to do with whether you knock/pin or not.

All the computer does is retard the timing if it senses knock *Hense Knock Sensor* that knock will be there reguardless of Computer controls or not.

When the Computer retards timing from knock, you lose massive performance.

rx7speed

not sure about carbs
but with some computer controlled cars it does make a difference


the computer aided system will allow for better adjustment of a/f ratio allowing for a smaller chance of detonation


and with fuel injection it allows an even better chance due to better atomized fuel mixture

8Mike9

Since the heads will be coming off, CC the chambers...I think my preference would be to remove 4-5cc's from each chamber, polish the sharp edges, and run a standard gasket. I assume these were 416 or 081 heads? Should be plenty of material in there to work with.

John in RI

iTrader: (167)

Hi Jeff

Remember me ???

I'm the guy you screwed out of $100......... you remember - I sent you the money for some parts back in MARCH and never got anything. You might not want to remember - but I do.



What happened to your E-Mail address,.......... Not accepting E-Mail from me anymore ??? I've sent you a total of 2 messages since 4-28 asking for my $$ back. Did you just get sick of feeling guilty or what ?

In your last message to me (received over a month ago) you said you would be sending "some" money back to me as a result of a radio you sold here on ThirdGen ----- Now you are refusing to accept my E-Mails !?!?!

I Wonder,...... Did you screw that guy over too ??

Your words :


You are the only guy I have ever met on this site that has screwed me over - I don't appriciate that.

Since it's been over a month since I got an E-Mail from you; & since you are now refusing to allow any contact from me - It is obvious that you have no intention of paying back the $$ I sent you for the parts.

:nono:

I'll be looking into what type of prosecution I can initiate for the Internet fraud I have fallen victim to. I recall that a federal law was recently passed to address this problem - I wonder if this matter will qualify ???


jeff clark
19909 alta vista dr
panama city beach
florida 32413

(850) 249-9485


I'll be in touch, You can count on that -----> kid !

John in RI

iTrader: (167)

Here is the warning I placed on the classified good/bad sellers message board back in MAY. It gives details regarding how I was burned buy Jeff ---->



The Seller that screwed me over ------>

NastyL98_T/A

Wow, seems to me like you should lay low for a while or make ammends with John in RI.

Jim85IROC

iTrader: (2)

getting back to compression ratios...

I'm running flat top pistons along with 461 fuelie heads, which have a 64cc combustion chamber. Their old-school design tends to make them detonation prone. My compression with my pistons and heads should put me somewhere between 10:1 and 10.5:1. I'm running around 6* or 8* of base timing, and using a slightly modified APYP bin, which has agressive timing characteristics. I get no knock counts with the 93 octane gas that I use.

92rs85berlintta

iTrader: (1)

i have never ripped anyone off i am going to school to be a police officer and am an honest person. the only thing i did wrong was pay for shipping on his items wich i shipped uninsured....ask the last guy i sold to or check my ebay feedback wich is 100% Get a life.jonh in ri..and dont use this website to blacklist or harass others who use as they should....


anyway about compression.

8Mike9 ''Since the heads will be coming off, CC the chambers...I think my preference would be to remove 4-5cc's from each chamber, polish the sharp edges, and run a standard gasket. I assume these were 416 or 081 heads? Should be plenty of material in there to work with.''


.

so i could still use these heads? is removing 4-5 ccs gonna change flow characteristics? they just need some machining then right? i adjusted my valves like i said and it did nothing. im putting a bigger richer carb on here this weekend that should help i hope.


Jim85IROC whats your total advance?and @ what rpm?

John in RI

iTrader: (167)

Don't use this site to rip people off !!!!!!!!!

Since you have set your E-Mail to reject my incoming mail I have no other way to get 'the message' to you than this forum.

I don't care about your E-Bay feedback or the last guy you sold to. All I care about is that some kid has ripped me off. One hell of a way to "make it right with you".

YOU were the one that qouted me a price WITH shipping included. YOU should have paid the extra $1.10 for insurance instead of being cheap. The fact that you didn't insure it was YOUR problem. You never provided me with proof of shipping anything and your PayPall account was even cancelled as a result of thier finding YOU at fault.

Here is my last E-Mail to you after you wanted some one else to take responsibility for paying me :

"Hi Jeff, DON'T have him pay me !!!! That could lead to more problems & That is the last thing I want to come from this ! Let him pay you ---- THEN you can deal with clearing up our dilemma !"

Now you claim that you were going to pay me until I started being a *ick ????? How do you figure ----- I sent you 2 E-Mails in the last 2 months asking for the $$ YOU said you were sending - then you block my E-Mail and I'm a *ick.......

Dumb kid !

Here are a few interesting links for you to review in your spare time Jeff. Don't be surprised if you are contacted by the police or the FTC in the near future. I'm sure a felony charge for internet fraud will be a big help in your attempts to be a cop....



http://www1.ifccfbi.gov/index.asp

http://68.166.162.20/repoform.htm

https://rn.ftc.gov/dod/wsolcq$.startup?Z_ORG_CODE=PU01

http://www.fraud.org/internet/intset.htm



Anyone reading this post can review the classified good/bad feedback board to see a COMPLETE history of this deal....... You decide for yourselves who is wrong here !

92rs85berlintta

iTrader: (1)

anyone on this board is here to dicuss .. about the compression..not play your games. so stop disturbing my post and disrespecting me and other thirdgen users.

92 zzz28

Its not disrespectful to me...

Just clear up your issues with this guy and he will leave you alone...

Vader

It's unfortunate when business cannot be conducted to the satisfaction of all parties. However, when that occurs, there are methods and means available to pursue remedies. ThirdGen.org isn't among those.