Compression ratio question

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Steven190

Steven190

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I am considering a head change on my 408. It now has a 10 to 1 compression ratio with aluminum heads.

My question is if I change to the new compression ratio which would be 10.3 to 1.
What effect does this make on drivability? I know the change is small and there maybe not any real effect. The engine now runs on 93 octane gas. Which around here is getting harder for find. I have been doing fuel additives so this is not an issue. The car is not driven that much and I don't mind doing the additive. Since I am doing the additives, the change in compression ratio is not an issue. The reason for the question is the times I can not find the good gas and have not additive to add.
Or am I splitting hairs.
 
Your pretty much splitting hairs here. The only negative effect may be that you will have to take some timing out of it. I would run it under load and listen for any detonation. If you notice any retard the timing a few degrees and check it again. 65'
 
Steven190 said:
I am considering a head change on my 408. It now has a 10 to 1 compression ratio with aluminum heads.

My question is if I change to the new compression ratio which would be 10.3 to 1.
What effect does this make on drivability? I know the change is small and there maybe not any real effect. The engine now runs on 93 octane gas. Which around here is getting harder for find. I have been doing fuel additives so this is not an issue. The car is not driven that much and I don't mind doing the additive. Since I am doing the additives, the change in compression ratio is not an issue. The reason for the question is the times I can not find the good gas and have not additive to add.
Or am I splitting hairs.
Click to expand...
I'm curious to what you're looking to gain from this head change? Is it just for the two points of compression?
 
No.
I am not looking for just a change. When we built the engine we used the Pro Comp cast aluminum heads. The thermostat stuck closed one day and before I could pull over it got real hot.
It seems that it did not hurt the engine, everything looks right, good compression test and no leaks, but I am now not comfortable with it. With the new Trick Flow heads coming out late this year and they are billet heads form what I can find. I was thinking about changing the cast heads out for them. They have a smaller combustion chamber which would raise the ratio some. So hence the question.
 
Steven190 said:
No.
I am not looking for just a change. When we built the engine we used the Pro Comp cast aluminum heads. The thermostat stuck closed one day and before I could pull over it got real hot.
It seems that it did not hurt the engine, everything looks right, good compression test and no leaks, but I am now not comfortable with it. With the new Trick Flow heads coming out late this year and they are billet heads form what I can find. I was thinking about changing the cast heads out for them. They have a smaller combustion chamber which would raise the ratio some. So hence the question.
Click to expand...
Actually... he answered your question, .3 isn't much and might require a degree or 2 to be pulled from the timing. You won't have any issue nor power increase that you can feel from a .3 bump, the flow will be the power increase you feel with the trickflow heads...which if much greater, might add to the compression some.
If it got hot enough to cause damage you would know it.
You just want to buy the better heads and this is your excuse, don't ask us to back you up though...because If your engine or heads had an issue...it would run hot and or leakdown.
Saying you are "not comfortable" sounds like paranoia or materialistic "gotta have the latest" .
Btw billet is great and all, but I'll worry about that when it comes to crankshafts...not heads.

How green are you?
I'd rather read something like "hey I wanna go faster, I'm power hungry, will these heads work without it rattling?"
 
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Thanks for the inputs, There is no excuse to why, just looking into options and I have questions, that is it. I have been at this for some time and when things go wrong there are usually later effects.

I would rater keep my options open than settle for something that I am not comfortable with. What ever you think is your business, this forum is to air your thoughts, not to be judged on them.
 
Steven190 said:
Thanks for the inputs, There is no excuse to why, just looking into options and I have questions, that is it. I have been at this for some time and when things go wrong there are usually later effects.

I would rater keep my options open than settle for something that I am not comfortable with. What ever you think is your business, this forum is to air your thoughts, not to be judged on them.
Click to expand...

Okay, maybe it was choice of wording.
You've been in this game for quite some time, so then you presumably know already.

What kind of power are you making right now?
 
It is a street car, the 408 make 550 horse with 560 pound feet torque. It is just my rod and I take it to shows and the grandkid for rides. I had a idea of the answer but wanted a newer prospective of what is going on today. Sometimes you can be on the edge and a little over has a different outcome. My bother and I had a Division 5 Pro Stock (other brand) Camaro in the late 70's and early 80's. The only engine work I have done is this Dart and the Pantera's I work on. 90 % are high performance street cars, so nothing too exotic.
 
Steven190 said:
It is a street car, the 408 make 550 horse with 560 pound feet torque. It is just my rod and I take it to shows and the grandkid for rides. I had a idea of the answer but wanted a newer prospective of what is going on today. Sometimes you can be on the edge and a little over has a different outcome. My bother and I had a Division 5 Pro Stock (other brand) Camaro in the late 70's and early 80's. The only engine work I have done is this Dart and the Pantera's I work on. 90 % are high performance street cars, so nothing too exotic.
Click to expand...

10.1 on 91 octane over here.
It's all in the tune.
 
Yeah we can not get anything more than 91 octane here too. That is why I am mixing some additive to boost the rating to at least 93. That is why I asked the question I know that .3 is not much but can make some difference. I am running 34 degrees now, with Fast EZ 2.0 injection. It is easy to change the timing and curve on the hand held.
 
Steven190 said:
Yeah we can not get anything more than 91 octane here too. That is why I am mixing some additive to boost the rating to at least 93. That is why I asked the question I know that .3 is not much but can make some difference. I am running 34 degrees now, with Fast EZ 2.0 injection. It is easy to change the timing and curve on the hand held.
Click to expand...

Oh yeah?
Running iron heads with a carb and 28 degrees.
 
With aluminum heads, and tight Q;
I'm speculating
That you might be able to drop the timing back to 30/32" at 3400 and run 87E10, and never know the difference until You hit top gear at WOT.

That's what I did; with a 367, .034Q, and 10.9 Scr with a 230* cam in at 106.....and it still hit 93 in the 1/8th @3467 pounds.She's been swilling that skunk-pee since 1999.

Your results may vary
 
Steven190 said:
No.
I am not looking for just a change. When we built the engine we used the Pro Comp cast aluminum heads. The thermostat stuck closed one day and before I could pull over it got real hot.
It seems that it did not hurt the engine, everything looks right, good compression test and no leaks, but I am now not comfortable with it. With the new Trick Flow heads coming out late this year and they are billet heads form what I can find. I was thinking about changing the cast heads out for them. They have a smaller combustion chamber which would raise the ratio some. So hence the question.
Click to expand...



The trick flow head is NOT billet. You could save a bunch of cash and have the heads surfaced and be done with it.
 
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