Big Heads on a 346...??
Thread Starter
Drifting
Joined: Mar 2006
Posts: 1,489
Likes: 5
From: Atlanta GA
Big Heads on a 346...??
On a 346, If I changed my heads from 205 to 225 (or bigger), what differences in performance should I expect?
What compression ratio should be run for best results?
What compression ratio should be run for best results?
Melting Slicks
Joined: Sep 2006
Posts: 2,041
Likes: 4
From: Rockford Illinois
I would stay under 12:5.1 for compression. Otherwise race gas could be involved.
Thread Starter
Drifting
Joined: Mar 2006
Posts: 1,489
Likes: 5
From: Atlanta GA
You can see significant gains with larger heads, Im used to seeing power levels of well over 50 HP with head and cam. Im not too sure on a number for you with just heads, but im sure it will be over 65 HP.
I would stay under 12:5.1 for compression. Otherwise race gas could be involved.
I would stay under 12:5.1 for compression. Otherwise race gas could be involved.
thx
Melting Slicks
Joined: Sep 2006
Posts: 2,041
Likes: 4
From: Rockford Illinois
Moving up to larger heads would make more power as there will be air, and even a higher red line.
Le Mans Master
Joined: Oct 2001
Posts: 5,577
Likes: 3
From: Southern Maryland Maryland
I was running 240cc heads on a 346 with over 12.0:1 compression on nothing but pump gas. My 346 results are in the sig and speak for themselves. My results were in about 75-80 degree weather not 30s-40s like all the others. If I were to put the iron rear in so I could actually launch the car would probably go 10 teens in the cold air @ 135.
Phil
Phil
Last edited by Phil97SVT; Mar 30, 2007 at 04:19 PM.
Thread Starter
Drifting
Joined: Mar 2006
Posts: 1,489
Likes: 5
From: Atlanta GA
I was running 240cc heads on a 346 with over 12.0:1 compression on nothing but pump gas. My 346 results are in the sig and speak for themselves. My results were in about 75-80 degree weather not 30s-40s like all the others. If I were to put the iron rear in so I could actually launch the car would probably go 10 teens in the cold air @ 135.
Phil
Phil
Why is there such a mixed opinion on this issue? Do you gain power or not? If so, how much?
I road race, so I dont mind sacrificing some low end hp for more at the top end.
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Safety Car
Joined: Jul 2005
Posts: 4,275
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From: Vancouver WA
You will be sacraficing some low end TQ for some top end HP with bigger heads because you lose air flow velocity. That's just physics. How much, I can't say. Higher compression may help recover some loss in throttle resonse. You will also need some high rpm to get the benifits from the bigger heads. So make sure your cam matches your rpm requirments. Also, bigger cam will need more compression so your dynamic compression doesn't drop too low. It's all about matching the right parts. If you are making 480/440, then it looks like you already have a good set of matching parts. I'm not sure if you will gain much more without higher revs.