towerhand

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.

3500lt

iTrader: (1)

thanks

Tainted

iTrader: (9)

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

towerhand

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.

Tainted

iTrader: (9)

because its not the optimal bore size in reality. The aftermarket ls3 heads have a splayed valve angle that unshrouds the valves and gives better ptv clearance.

Jimbo1367

I find it hard to believe that the PRC heads are the culprit for your low numbers/problems. So you merely swapped the heads ? Did you ever contact TSP regarding your soft numbers/disappointment?

towerhand

Believe what you want, i can assure you they were the problem, but it was not the PRC heads , like i said before it was the bore/ LS3 valve problem

96capricemgr

iTrader: (1)

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.

towerhand

That is correct, just trying to help people so they wont make the same costly mistake

96capricemgr

iTrader: (1)

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.

KCS

iTrader: (20)

What was the rest of the setup? It's just hard to believe it was "shrouding" holding you back when people have made over 500whp with a stock 6.0L shortblock, 4" bore and all.

NOS327

iTrader: (30)

Radial gain of .0175 of 4.065 from 4.030 is enough unshrouding to make them useful tho??

Tainted

iTrader: (9)

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.

KCS

iTrader: (20)

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.

keith102371

iTrader: (20)

x2.......

towerhand

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.

Tainted

iTrader: (9)

Thats a huge split, it doesnt need that much. I know a lot of people will preach 12* or more but thats bad info.

towerhand

Thats the second camshaft, first one was 612-621, 232-242, and a 112 LSA, with same issues

towerhand

Did the earlier model PRCs have issues that were corrected with present castings. These heads were bought in 09 and been new in box since then.

Tainted

iTrader: (9)

How were you picking these cams? Its not all about the specs, the lobes make a huge difference too. And still a large split