MikeH

iTrader: (10)

We have tried to run over 14* in the chip. 20* as shown on my auto-xray the car will detonate on the topend with anymore timing. IM running 93 octane..IM not sure of the compression its at least 11.1. The motor has flattop pistons 2 valve reliefs,64cc aluminum heads,a 224/234* cam.

The AFR is right around 12.5 IM trying to decide if it would be worth the effort in terms of power to pull the heads and open the chambers to lower the compression so i can run full timing?

What can I do to stop the detonation to allow full timing? The motor is making decent power now. But I was expecting about 50 more at the rear wheels. IM not the first one to say that I bet. I do have a problem with weak spark but i dont think that would cause the car to detonate. would it?

Any thoughts or comments would be helpful!

Thanks for reading!


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90 IROC
SuperRamed 406
Trickflow 23* heads

J's86ROC

Have you had the heads milled or the block decked? If not I would say 11:1 would be about right for the compression ratio maybe even 10:1. I could be wrong it's been a few years since of done any major heart surgery or transplants on a Chevy. What I would try is maybe you can tinker with the advance curve. I'm not sure of your ignition setup but if you can it's worth a try. Otherwise you might try higher octane, that would probably get the problem squared away. Otherwise I'm not sure what else you could do except for lower the compression ratio. Hope this helps and keep me posted.
Jason

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Jason Lodder; 86 IROC-Z, 305 TPI/700R4, Flowmaster Exhaust, Hypertech Thermomaster Chip, K&Ns, Throttle body airfoil.

F-BIRD'88

Water Injection..... Not just for turbos.
Works on Hi-compression cars too.
Do a search on the internet. If I was running EFI I'd inject it behind the throttle valve and also to each port
before the head. That way you'd be sure to get even spray to each cylinder. You'd need less water. A mix of methanol/water seems to work the best.

Grim Reaper

Yes, high compression and small chambered heads (especially those designed to induce a quicker burn), will start to show knock incidences at fairly low timing AND if you were to "cap" the Max Knock Retard to 0* and tried to advance your ignition further, you'd most likely HEAR detonation occurring at a fairly low timing level (26-32*).

Newer heads are DESIGNED to require less timing than older large chamber heads (that typically took 36* of SA). The newer design makes the same power with less SA. A good example are L98 heads, after 26-30* (effective spark after the knock retard), they will usually have audible detonation.

With my L98, I found capping my Max Knock Retard vs RPM (in PE) to 1* and getting a good spark curve allowed me to get a few more degrees (and a few more HP)...but I still can't run more than 29* of SA before I HEAR detonation. Prior to his with an "open" Max Knock Retard, I was lucky to get 24* of EFFECTIVE spark advance.

Just be aware that nullifying the Knock Sensor (even if only during WOT) is a dangerous practice. If you DO go this route, I encourage you to "back off" the timing a degree or two from the MAX before you hear detonation.

Also, detonation during an "upshift" is another common observation.

MikeH

iTrader: (10)

Th block has not been decked...Glenn we have the knock sensor disabled for now. I dont hear any detonation at the 14* My scanner is Showing 20*. I guess the scanner is adding the 6* base back in. 20* doesnt sound bad based on what you are saying about the faster burn heads. Ive read similar things also. I just hate the thought of losing alot of power to retarded timing. When I can do something about it,If thats the case.

I can pull the heads and open the chambers maybe do some port work at the same time. But I just got the motor in and running decent. So unless it would be worth it in terms of power to get say 8/10* more timing I dont want to bother.

What if I ran some 108 race gas and bumped the timing up to see what kinda of numbers I get? I wonder if that would be a fair comparision to droping the compression and advancing the timing?


I know the headers IM using are killing the topend some. IM going back to the dyno in a week or so. IM hoping for some better numbers this time. I think I have my ignition problem corrected now. IM going to replace the distributor so that should correct any problems there.

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90 IROC
SuperRamed 406
Trickflow 23* heads

Grim Reaper

By your post, I was assuming the Scan Tool was showing the detonation. Do you EVER hear the detonation and at what timing?

As for running 108 Octane, hate to say this, but you may squeeze a degree or two; but it's the head design IMO. And this is the direction all head manufacturers are going to....as it is actually easier on an engine to develop the same power with less spark advance than with more (excluding the detonation issue with people using "old school" tuning techniques).

If you can get the engine to "release" all/same of its energy with only 20* instead of 36*, you have less time where the piston is "working against" the growing spark front. Or so the theory of fast burning heads go.

Setting the spark advance to 36+* is really only necessary with heads that have chambers like 76cc.

I would just start tuning your engine and realize that you won't be able to add too much timing. You do have the Prom Burning Equipment don't you or am I confusing you with someone else?

MikeH

iTrader: (10)

Glenn...I can hear the motor detonate on the topend. It starts building alot of cylinder pressure around 4000. If the timing is advanced 3* more from where its set now it will detonate on the topend steve said. Ive tried to advance the intial to see for myself. But anything more than 8* and I can hear it. Its set at 6* to keep from hurting the motor.(Ive looked at the plugs and there was small specs of gray). Mostly if the car sits at a lite for awhile and i get on it hard. The cars runs pretty cool though.

Steve at tunetechauto.com is burning the chips for me on the dyno. He said when i go back he will try and tweak the curve some more.

So you think the timing is enough?



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90 IROC
SuperRamed 406
Trickflow 23* heads

Grim Reaper

Again, it all depends on what the engine wants. If the engine wants low timing, then it wants low timing and there is really not too much you can do about it.

From the sounds of things, the motor just doesn't want a lot of timing. There are a few things that could (or should) have been done to help get a little more timing like decking the block may help a couple degrees, going with slightly lower compression, playing with the spark curve and AF ratios. But these will only yield a degree or two more, so unless you go to large chamber heads (which can be a step in the wrong direction), you won't be able to run a lot of timing IMO.

Think of it this way, it's not that a lot of spark advance yields more power, but that large chamber heads NEED more timing to get the power. Your smaller chambered heads just don't need that extra timing to develop the power. New technology.

F-BIRD'88

The compression ratio is just too high.
Never mind this small chamber/fastburn theory."Fast burn" is a function of high quench and swirl and mixture quality, not the size of the chamber. Plug position is the major influence on timing required. Run the motor on 110 octane gas and advance timing to 34/36 max and you will see the power you're missing. Make sure the motor is getting all the fuel *it wants* for max power and ignore the air/fuel gauge. just don't get too carried away. Quench clearance should be .040' to .045" including the gasket. there is power in that and detonation protection too. Run cooler plugs. Check the timing marks on the balancer. Mine was out 4 deg. Consider the water injection, it works.

[This message has been edited by F-BIRD'88 (edited November 10, 2001).]

Damon

The advances in swirl/tumble of the mixture from modern heads will not make a very big difference in the engine's timing needs. Older heads usually liked 36-38* of total WOT timing, newer heads may want 32-34*. But if you're detonating at only 26* (6* initial + 20* the ECM is adding) you've got too damned much cylinder pressure, period.

Put in high octane stuff or reduce the compression.

Rule of thumb- an engine with too much compression and reduced spark advance will make LESS power than an equivalent engine with lower compression but full spark advance.

85transamtpi

I say pull the heads, maybe open up the chambers a little, run a thicker gasket. I think that will help.

HiTech5

iTrader: (4)

This what I would do:
1. Back the timing off so that there is no chance of detonation until the motor is broken in.
2. Do you have large enough injectors? Are they new? Do you have a new fuel pump?
3. Retard the cam 2-4 degs. This will lower cylinder pressure.
4. Put in a larger cam with a tighter lobe seperation angle.
I personally like to run as much compression as possible. My motor has 11.6-1 compression and I run 37-38 degs total timing. Compression makes power!
By the way, what intake are you using?
www.geocities.com/dzperf

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D&Z Performance
"Putting Power to the Pavement"

F-BIRD'88

I highly dought you have an actual 11.6:1 cr even with aluminum heads and 11.1 advertized cr pistons, unless you have 1. power robbing retarded ignition timing. 2. power robbing exessive rich fuel mixtures (fuel dumping)
3. power robing incorect cam timing. (retarded, oversized cam with too tight LSA. Which will at best only allow full throttle power at low rpm with out detonation. or light part throttle cruising.)
4. You are at very high altitude. (Less power)
5. a power robbing very restrictive air filter
6. Water/ alcohol injection
7. Your name is FUELING and custom make your own cylinder heads with super high swirl combustion chambers and centered spark plugs
5. Very power robbing leaky valves or pistons rings.
6. don't know how to proper measure and calculate compression ratio.

MikeH

iTrader: (10)

Thanks for the comments and suggestions guys...The timing that IM running now is showing no signs of detonation with 93 octane. There is 14* in the chip plus my 6* initial at wot. My scanner is showing 20* so I assume I have a total of 20*. I think I read somewhere that 400s like around 32/34*. The paper work with the heads suggested 36* or so for maximum power. I know every setup is a little different. But why would they suggest so much timing if the heads didnt like it? The car really is strong I finally think I have my ignition working good now. I go back weds the 21st steve is going to tune on it some more now that the ignition is working well.

The injectors are new 30# svos,and I just installed a walbro 255lph fuel pump. There doesnt seem to be any fueling problems. IM using a SuperRam intake with an Accel base, 58mm tb, Stock air box thats been gutted with K&N filters. I know the headers are holding it back some I didnt even get the chance to port the welds or the airtubes out in the primaries. One thing that gives me hope is the spark was so weak from the Bad coil/MSD box that steve had to lean the motor to around 13.5+ (12.5 on the topend) to get some good power out of it. The spark was so weak that it wouldnt show any data on the dyno screen between 2300 and 3500. So maybe he can richen it up and put some more timing in it.

I want to see what it does weds. If I can get my hands on some good gas I would like to see what it will do with more timing also. You can really feel the motor come alive when I advance the base and drive it around. But when I get on it you can hear it detonate and feel it misfiring. Thats why I think it would run so much better with more timing.

If I pull the heads would it lower the compression enough if I just open the chambers up to match the bore size? I could do that myself. I think they are sized for a 4" bore out of the box. I could kick myself for not getting the 72cc cnc ported ones.

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90 IROC
SuperRamed 406
Trickflow 23* heads

[This message has been edited by MikeH (edited November 12, 2001).]

HiTech5

iTrader: (4)

First of all, you don't know me or anything about my car so keep your expert comments to yourself!
So, just to shut you up. My motor is a 4.030 bore and 3.75 stroke with flattop pistons cc'd at 2.8cc. The block is zero decked with a .039 FelPro 1010 gasket and the heads are milled to 62cc. Now you do the MATH!

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D&Z Performance
"Putting Power to the Pavement"

[This message has been edited by HiTech5 (edited November 13, 2001).]

HiTech5

iTrader: (4)

F-Bird88, I'm waiting for your reply!

www.geocities.com/dzperf

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D&Z Performance
"Putting Power to the Pavement"

Grim Reaper

I am not FBird88, but I calculated your CR and I DO NOT get 11.6! I get 11.7:1 (based on the specs you stated).

I should add that my Compression Ratio calc program does not account for the space between the piston and the first land of the rings. Hence, why I get a slightly higher compression ratio.

As for the whole topic, I also think HiTech that you made a good point about a bigger cam needed. Something that has not been discussed is that higher compressions and cam shafts do go "hand in hand". The larger cam helps bleed off pressure at lower rpms and higher compression is necessary for large cams. You can't bump the compression and run a stock cam as the cam will build too much pressure up at lower rpms. This indeed may be the problem here as you suggested.

Also, while the cam looks fairly large (for a 350), with a 400 the cam behaves more mildly and doesn't bleed the pressure quite as much.

F-BIRD'88

HiTech5: I checked thru your previous posts
and relying on exessive fuel mixtures (fuel dumping) and computer/knock sensor induced
spark retard that reduces the power output
that you should and could have, to mask the detonation from trying to run too much compression ratio for the fuel octane and engine design you are using is what they call "junk science". Not to mention having to constiently fiddle with the fuelmap and timing etc.
A larger camshaft will cause lower cylinder pressure, but will not stop the inevidable
detonation thats going to happen at or around
peak torque (peak cylinder pressure)at full throttle. Detonation is caused by the heat of compression, exceeding the auto-ignition point of the fuel air mix. NOT the pressure.
When the inlet charge is compressed, it is heated a constant amount that increases
at a steady and known rate (gas laws). Extra cam timing will bleed off pressure (mostly at low rpm) but will not decrease the heat.
(heat of compression).
Internal cooling (fuel dumping, water injection, high humidity) will lower the heat in the chamber and get the temps back under the auto-ignition point BUT always at the cost of power, volumetic effeciency, ring and cylinder wall wear, carbon build up (rich mixture) and increased emissions. The carbon build up caused by fuel dumping will always eventually lead to pri-ignition
and more detonation problems, let alone increased engine wear. All of these methods
will get you by (short term) but will not get you more or
even equal power than what you would have
by running the max allowable compression ratio combined with optimum max power airfuel
ratios and more optimum cam/valve timing.
All this has been researched and tested
and documented (S.A.E.)in hundreds of dyno and in car tests by car and airplane manufacturers the world over. Much of it long
before you and I were even a glint in our mother's eye. There is a couple good books by
Ricardo you might want to check out on this
subject. There has been interesting research
by people like Feuling using exotic combustion chamber shapes and super high
swirl etc. But what he is using is nothing like the wedge combustion chamber you and I use. No two engines will need exactly the same compression ratio for max performance
for a said fuel octane but will not vary that much. thats why I don't need to know
your exact combination or tune up.
Please don't take any of this as an attack,
it was not and is not ment to be. I checked out your link to the pics of your car and it looks like a sweet ride to me. You run it and tune it the way you want. It's your car.
But we all live under the same laws of physics. Is trying to bend them worth the trade off in reduced power, effictancy and engine life? Is that sound advice to a bud,
trying to get his project sorted out?
Not in my opinion.... Fill up with some high octane gas, recurve your fuel map
to optimum ratios for max power. bump the timing up to what the motor wants and unplug the knock sensor. now you'll see the power you've been missing. Without hurting your motor. Then re-adjust your compression ratio to something that will work with 93/94 octane
gas (around 10.0 to 10.6:1) and you'll still be making more more power and safer than with the high cr before. Try it, the most it will cost ya is a couple gallons of race gas.
Just my .02, Have a nice day

http://www.feuling.com
http://www.sae.org
water injection
http://www.carrollsupercharging.com


[This message has been edited by F-BIRD'88 (edited November 15, 2001).]

HiTech5

iTrader: (4)

88FBIRD - Again you assume that you know something about my car that you don't. The car was tuned on a chassis dyno using a WideBand O2. The A/F ratios are right at 12.3-12.5 WOT. The motor has 11.6-1 compression and yes I run 38 degs total timing when using high octane fuel. When running 93 octane, I set total timing at 36 degs.
www.geocities.com/dzperf

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D&Z Performance
"Putting Power to the Pavement"

F-BIRD'88

And what about the computer? How much knock retard? What AFR are you able to run when on
93 octane. A little extra is ok (keeps ya out of trouble). How does it perform
at the drags compared to on high octane.
Not concerned with ET cause that can vary too much, just the MPH. How much knock retard in actual use? Not on the dyno. Would really have to see it to believe it. And see the data.

HiTech5

iTrader: (4)

88FBird - I'm still waiting for your calculation of the compression on my motor!
The fact of the matter is, the motor is a 383 with 11.6 compression and I run a total of 38degs of timing for best performance.
By increasing timing from 36 total to 38 total, the car went from 116.2mph to 117.51.
This would not happen if the motor was detonating. There are two of my friends that have very similar combo's to mine they also run 38 degs total. Check out "BadBowties" at the bottom of my web sight. By the way, what does your car run? Does it run?
www.geocities.com/dzperf


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D&Z Performance
"Putting Power to the Pavement"

F-BIRD'88

HiTech5: I guess you don't want to tell me about how much knock retard your computer has to kick in to keep out of detonation
while on 93 octane. Or the AFR used while on 93. That's ok guy I think we got the point.
Not bad MPH thou. A lot of people try to claim to be able to do this or that. But when
someone questions their claims, they do the same thing. Skirt and evade the test,
or question. Like I said before It's your car you run it the way you want. Have a nice day.....

HiTech5

iTrader: (4)

88FBIRD- I disconnected the knock sensor on the motor when I went with the Solid Roller cam. Too much noise sent false readings.
When I tuned the car on the dyno, it had 100 octane in for ultimate performance. On the dyno, the motor would only accept 36 degs total timing due to the engine heat after 16 dyno runs. I am not skirting any issues but you are. What does your car run? Have you ever built a motor or tuned a motor? Well I have and when I answer a post like this one my answers come from experience and education. You slammed my response big time and it pi$$ed me off!
www.geocities.com/dzperf

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D&Z Performance
"Putting Power to the Pavement"

F-BIRD'88

HiTech5: My car is listed in the readers rides pics on this site. It is what it is,
and serves me well. It is completely home built from parts, on a budget. I've had a lot more powerfull and faster cars in the past. I have been building chevys, fords and chryslers, dirt track, drag and marine motors for some 30 yrs. So you could say I've skinned a few knuckles in my time. I have no doubt your 11.60:1 motor performes great on the dyno and on the street on 100 octane gas. Good job and more power to ya. But I know the limitations of 93 octane pump gas in actual in the car street/track performance even with direct-port,computer controlled fuel injection and alumium heads under the best of conditions. What I am trying to get at is
under real world conditions, you or I would have to compromise the tune one way or another to let the motor survive on 93. I don't know what gas is available where you are but here we all use 94 Sunoco. The 92 and 93 pump gas sucks. When we want to run a 11+ cr motor we mix a few gallons of 114 race gas
in with the 94 for any thing other than easy street cruising. I recently helped a guy try to get the best possible tune on a 11.5 cr
400ci cast iron head camaro. The best we were able to do was 29/30 deg with a little over fueling. The car runs .55 sec and 4 mph faster on the proper octane gas with full timing. That's life. I seen tons of people claim to be able to run that kind of compression but when it comes right down to it, the story is the same and their motor
usually self destructs in short order or won't really perform as stated or they made an error when calculating or measuring their
CR. Or they're full of it. If you are able to run a true 11.60 cr on the street real world on 93 octane gas WITHOUT compromising the tune with out knock, great, But like I said I highly doubt it and would have to see it.
Lots of peole who have actually built and tuned motors over the yrs are going to question that claim so don't get all bent out of shape. Guess you better go down and help the origional poster with his, before he scatters it. Good Luck

[This message has been edited by F-BIRD'88 (edited November 16, 2001).]

8Mike9

F-Bird, do you feel a set of Al heads would help you buddy out to get more timing on his 400?

HiTech has AFR 190's (Al heads) according to his webpage.

Have you looked at his engine specs?

You really can't compare an iron headed 400 to a Al headed 383.

F-BIRD'88

You're right, it is not a good direct comparision, just and example.
Alumium heads usually will allow about .5
of a ratio over cast iron. The aluminum heads
usually need this .5(+-) CR more to make equal power compared to cast iron, all else being equal. Alumium has different thermal properties than cast iron.

BadSS

I've built a number of 11.2:1 406s for folks,,, with aluminum heads and had NO problems running and dialing them in on 93 octane gas. However,, there are only TWO stations in town that has "good" gas --- not all gas station's gas is equal. I do knock the sharp edges off the valve reliefs and make sure the chambers are "clean",,, but these particular combinations wants no more than a lazy 32 or 34 degrees depending on a few variables. Maybe it's a bad tank of gas,,, the guy burning the chip is having a little problem with the compression,, or there is some other problem. I really doubt this is a "compression problem" per say.