Is anybody here running over 10:1 in a daily driven cast head street machine on pump gas?

I plan on running aluminum heads, but I want to know what margine i have.

------------------
1985 Iroc-z, 14 second 305, new engine in the works.

 

I was running close to 10.5:1 with Iron Eagle heads in my old 400ci Malibu. Too high for pump gas. Had to dial back about 6 degrees of timing to get it to run on pump gas. The only iron heads I'd take to 10:1 would be Vortecs since they have much more detonation resistant chambers. Beyond that, not even Vortecs will save you.

This is assuming a streetable cam, typical rod/stroke ratios, etc. Certain purpose-build motors can exceed this in some cases, but they aren't often found under the hoods of real daily- driven cars.

With aluminum heads you can get up to 10:1 pretty easy on pump gas, but once you're beyond 10.5:1 you're getting back into the danger zone.

 

All things blue printed I'm going to be running about 10.3:1.

I can either build the engine soon and run on some ported/polished GM cast heads (not vortec) or I can wait for the aluminum heads. I was just wondering if it was possible with the right timing etc. The cam will be between 210-220 duration @.05 .500 lift, and 112 lsa.

thanks

------------------
1985 Iroc-z, 14 second 305, new engine in the works.

 

I would follow Damon's advice. Get your engine guys to get it down to 9 1/2 or so. That additional point of compression isn't worth all that much, you know. On a big block it might add 20 hp. On a small block, not as much.

So what do you value more?

Bragging rights and a pain in the *** engine, or an excellent running daily driver?

 

I have an engine running 10.5:1 with cast iron heads, but I wouldnt advise trying it unless you do everything possible to the engine parts to help prevent detonation from occurring.

 

it all depends on your setup, a big heavy car with low stall and gears will start pinging at about 9.5, a light car much more, my freind has a 4-speed vega with a 327 aluminum heads and 3.73 gears about 11.5:1 compression and it runs on 93 all day, there also a while back was that nova with 14:1 with a 4,000 stall and 4.56 gears running on 93 in car craft. if you have a loose converter and gears your compression will be able to go higher, everyone allways says 10.5 is it as thats a average figure but every combo is diffrent

[This message has been edited by TempesT68 (edited December 10, 2001).]

 

well from what the guy told me that sold me my motor.... with normal pistions i should get 10.5-11:1 with 64cc heads but i am puttin on 58cc heads so i will be at 12:1 i think or close to it but i am runnin aluminum vette heads.....btw its a 350 4 bolt main with scat crank and 6 inch rods...

[This message has been edited by 86IROCTHD (edited December 10, 2001).]

 

if there flattop pistons then you will be in the 10.5:1 to 11:1 area with a 58cc head, it **should** be ok on 93 octain but one wil know forsure once you get the engine running

 

I'm thinking a 2,600 stall, 3.73's, and 10.3:1 on aluminum heads isn't going to cause all THAT much trouble. Especially with prom tuning.

------------------
1985 Iroc-z, 14 second 305, new engine in the works.

 

Put in a couple pints of that Redline Water Wetter and it will help prevent detonation. It apparently works well at drawing heat from the combustion chambers, especially on iron heads.

 

I have about 10.1:1 w/ 58cc alum. AFR 190 heads w/ flat top pistons and I use 92-94 octane with no problems. The cam is 219/219.

------------------
89 IROC-SuperRammed 355 w/ AFR 190's and LPE 219/219 cam-http://www.geocities.com/buckeyeroc

 

Are you running tpi?

If so what chip?

------------------
1985 Iroc-z, 14 second 305, new engine in the works.

 

I have another car running 10.3:1 with vette AL heads and it will run on 87 octane most of the time. The car I have with 10.5:1 is 10.5, not an 'average figure' as someone above is assuming. Some of us here actually know how to calculate things like that after measuring displaced volumes and check that sorta stuff and state what it is.

 

A recent combination I ran had 10.3:1 cr
with milled iron "882" heads. It would only run on 94
Sunoco with full advance (36 deg). Spark plugs were 2 heat ranges cooler than stock
and the air/fuel ratio is critical. But after much test & tuning, it worked well.
Then I changed over to vortecs and picked up
50 hp and at least as much torque. Cr is now 10.03:1 and never detonates.

 

Max: take it easy on him man


Since I've already got a thread on compression I'm going to ask my next question here. People mention cams with compression as though different cams will cause pinging sooner than other or something.

Is this true? Is it more overlap makes it more prone to knock or less overlap? Whats the physics behind it?

------------------
1985 Iroc-z, 14 second 305, new engine in the works.

[This message has been edited by tpi_roc (edited December 11, 2001).]

 

Yea I'll take it easy.

Anyways, compression ratio only applies as a engine building calculation. Once its together and you fire it up, static compression means nothing. Cam duration, lift, and timing can affect the actual 'dynamic' compression taking place in the cylinder and affects the engines' tendency to detonate. It would be difficult to determine how far you can go on a piece of paper, its better to see what people have done and go from there.

 

Thats understood, but at least give me the theory.

More overlap would create more A/F mix entering at higher RPM's creating more dynamic compression correct?

Thus if there's a knock issue at higher rpms the last thing you want is more dureation and less LSA, right?

------------------
1985 Iroc-z, 14 second 305, new engine in the works.

 

This might explain my neato knock I get after I changed cams


Although it was such a little change I didn't think it would cause a problem.

------------------
1985 Iroc-z, 14 second 305, new engine in the works.