Learning from experience
Thread Starter
Staging Lane
Joined: Feb 2012
Posts: 71
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From: South Mississippi
Learning from experience Well i finally figured out why my brand new 408 had a bust at low throttle and wouldnt make horsepower above 5600 rpm. Turns out it was in the PRC LS3 heads, apparently at low throttle, the intake valve was shrouding and heads would not make any power above 5600 rpm. Just a word of advice dont use these heads on a 4.030 bore. I went to TF 225 and solved all my issues.
Uh huh you didnt do your research on the heads nor choose the right cam with right valve events.
I got the aftermarket 260cc ls3 heads for my 408 and im shooting for 550rwhp somewhere around 6800rpm
I got the aftermarket 260cc ls3 heads for my 408 and im shooting for 550rwhp somewhere around 6800rpm
Thread Starter
Staging Lane
Joined: Feb 2012
Posts: 71
Likes: 0
From: South Mississippi
Good luck, I made 468 at 5600 but there is still room for more, also my tuner had a similiar build a month ago with same heads and he had the same results. And yes everything was bought for compatability but the problem is the size of the bore with the LS3 intake valve. Just trying to help people not make the same mistake i did. People will tell yall that this work on a 4.030 bore with no issues but just beware, i tried it and did not get optomal results.
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You got caught up in the hype despite ALL available information saying they clear a 4.00 bore but really need a 4.065. You tried a 4.030 and then manned up and admitted your mistake and tried to help others but there are going to be those who will never believe, because we all know a huge port and a huge valve always make more power even when the valve is blocked by the bore.
I believe most folks will understand you were stating you bought the wrong heads not that the heads were anything less than quality pieces.
I believe most folks will understand you were stating you bought the wrong heads not that the heads were anything less than quality pieces.
Last edited by 96capricemgr; Jan 6, 2013 at 10:52 AM.
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Verdad Gallardo The LS3 setups look cheap though so LOTS of people are going to keep making that costly mistake in the name of "saving money".
Maybe it wouldn't be that way if more folks would admit their mistakes like you did.
Maybe it wouldn't be that way if more folks would admit their mistakes like you did.
Well i finally figured out why my brand new 408 had a bust at low throttle and wouldnt make horsepower above 5600 rpm. Turns out it was in the PRC LS3 heads, apparently at low throttle, the intake valve was shrouding and heads would not make any power above 5600 rpm. Just a word of advice dont use these heads on a 4.030 bore. I went to TF 225 and solved all my issues.
Yes the more you can unshroud it the better. .4030 is a lot better than just 4, but could obviously be more and better.
But it just depends on a lot of other things too. The ls3 stuff is veerrryyy picky about valve events.
But it just depends on a lot of other things too. The ls3 stuff is veerrryyy picky about valve events.
I'm thinking his issues were more related to other parts being wrong or just plain way out in left field. It's not like this I the first 408 to use L92 style heads. Others have done it and made better power.
Thread Starter
Staging Lane
Joined: Feb 2012
Posts: 71
Likes: 0
From: South Mississippi
iron 408, diamond pistons 4.030 bore, callie rods, callies crank, FAST 102 LSXr intake, FAST 50# injectors, PRC LS3 66cc heads, Caddie lifters, Stock rockers with trunion upgrade, 102mm tb, SD tune, racetronix pump with hotwire kit, comp cam 621-624 lift,duration at .050 235-251, 113 LSA. Kept having a bust at 2800 rpm, until we tuned with SD, fattened it up to make air heavier and fixed the bust. Makes peak horse at 5600, does not drop but levels out to above 7000. Also using NGK TR6 plugs with .032 gap.