to much compression

[monkey joe]

I got a brand new 2700cc engine that I'm bolting a aluminum head on but when I ccd the head and checked the bottom end it comes out to 14.0:1. I have voiced my concern to a few engine builders and get a different answer each time. So I was going to run the regular cheap fel pro gasket I usually run and be easy on the timing I thought about running a thicker cometic gasket but have heard that making the quench area larger can cause detonation quicker than more compression with a thinner gasket. So my question is if this was your engine what head gasket would you run and how much timing would you run. I have never ran this much compression but some say its not that big of a deal but I'm trying to find out from someone that has done this before and not someone that says run it it will be fine Lol. Any help would be greatly appreciated thanks in advanced.

[84Dave]

On my 2.0L SOHC Ford engines, I've always run a minimum 12:1 static compression ratio. I'm currently running 13.25:1. With great success, I've always used a .041" thick/compressed Fel-Pro head gasket, with the piston tops even with the block deck, for the desired ~.040" of quench/clearance. Plus..... I ALWAYS o-ring around the top of the bore with stainless .040" wire. With the wire positioned at the very outer circumference of the 'fire-ring' on the Fel-Pro. And a .030" deep machining groove for the o-ring, which allows .010" of the o-ring diameter protruding above the block deck. Using the above setup, I have NEVER failed a head gasket in 20+ years of building/rebuilding/racing the 2.0L! Works for me. Ignition timing? Engine dyno the completed engine, budget permitting. Using the exhaust system that will be used in the race car, if at all possible. Obviously use a wide-band sensor O2 system in the exhaust for proper initial jetting. I've always used the F.A.S.T. system with its RPM module. No external computer required to log/read the AFR stored data at any rpm. If the dyno is a decent facility, it'll also have an accurate fuel-flow meter in-line with the fuel line to the carb for measuring Brake-Specific-Fuel-Consumption (bsfc). Which is an indicator of how EFFICIENTLY the engine is burning the fuel/mixture. Start the ignition timing @ 32-degrees, watching/logging the AFR/bsfc/TQ/HP. Advance to 35-degrees & repeat. Then advance to 38-degrees & repeat. Adjusting AFR along the way as required. And in my experience, the final jetting on the race track was nearly always a couple of jet sizes larger than the dyno. Why? The airflow/surrounding ambient temp in the engine bay of the driven race car is nearly always different than experienced on the dyno. Particularly if the dyno setup did not use the air-filter assembly as used on the race car. Those little differences do make a difference! -84Dave-

[monkey joe]

Wow Dave you really know you're stuff thanks for the info. I been thinking about running it on a dyno but didn't want to waste the money if it was going to have issues on the dyno. Thanks again for the info.

[Big E tech]

I think I may have talked to you on the phone... Don't be afraid of the compression, but make sure that you have a solid handle on the tune-up before you try and lean on it. As for the head gasket, we recomend the Felpro 8993PT1 on just about everything below 400hp. or so... If the block isn't o-ringed, you should really look into having it o-ringed now instead of trying to chase down a fix during the season when you can't get the gasket to live as long as you'd like. The aluminum head doesn't seem to like the Cometic gaskets.

[monkey joe]

Thanks Big E and yes you were my first one I called . I'm currently trying to get this engine dynoed and I was also looking at the fel pro 1035 but was scared the built in ring in the gasket might damage the head surface. Can you oring a block that is already together ?

[Big E tech]

Thanks Big E and yes you were my first one I called . I'm currently trying to get this engine dynoed and I was also looking at the fel pro 1035 but was scared the built in ring in the gasket might damage the head surface. Can you oring a block that is already together ?

The 1035 will brinell the deck of the head requiring frequent surfacting to maintain a good seal. In order to o-ring the block, we would recomend dis-assembling the shortblock to keep the cast iron particles from potentially contaminating the rotating assembly.

[let-r-eat]

The 8993 will hold what you're doing. The o-ring is excellent but not required on your build in my opinion. A good tune is what you need.

[monkey joe]

Thanks everyone I'm putting it together with the 8993 and hopefully going to sneak up on it on a local dyno before we put it in the car. What do you guys think start by adding some jet from what i ran on a smaller engine and set timing around 26* and then start putting more timing in it

[raabbiitt]

"have heard that making the quench area larger can cause detonation quicker than more compression with a thinner gasket"


in general, is the above statement true? i have not heard of this before

[let-r-eat]

Thanks everyone I'm putting it together with the 8993 and hopefully going to sneak up on it on a local dyno before we put it in the car. What do you guys think start by adding some jet from what i ran on a smaller engine and set timing around 26* and then start putting more timing in it

The larger engine with same induction will require LESS jetting. You'll have more pressure differential across the carb which will pull more fuel through a smaller hole. Leave the jets alone since you have them right. Jet's more often go with the carb not what engine they are on.I hope that made some sense to you. Start at 27* or so and sneak right up.........good deal.

[let-r-eat]

"have heard that making the quench area larger can cause detonation quicker than more compression with a thinner gasket"in general, is the above statement true? i have not heard of this before

Absolutely. The wider piston to head distance slows down the flame front. An efficient cylinder head has a fast flame front. You are squeezing more out with the shorter area and this squeeze is making the flame front faster. There are some cases like in nitrous builds and the like where you must widen this distance between the head and the piston. You widen to slow down the flame front because it takes more time to burn all that mixture and the mixture is much easier to keep burning.

[RACEMAN]

Absolutely. The wider piston to head distance slows down the flame front. An efficient cylinder head has a fast flame front. You are squeezing more out with the shorter area and this squeeze is making the flame front faster. There are some cases like in nitrous builds and the like where you must widen this distance between the head and the piston. You widen to slow down the flame front because it takes more time to burn all that mixture and the mixture is much easier to keep burning.

Can you verify this information with a qualified, verified mechanical engineer with a specialty in combustion engineering? If so, please provide a source for this information.

[return to dirt]

some good info on this subject but one thing i haven't seen mentioned is fuel. race gas, alky or what? what octane? you can have the best tune but the wrong fuel can quickly kill the engine.

olin