Going 408 Soon,what Are The Best Heads For It?

[allballz57]

So,I am picking up my new shortblock this weekend and I am trying to figure out which heads to go with.So I thought since there ae plenty of you who have gone this route,maybe you could tell me the best heads for my application.

 

 

Here are the specs,Forged eagle crank,compustar forged rods,dished SRP pistons,the hole assembly has been studded,and the cam is a 236/236-.617/.617 114+4.It was built for 8.8:1 comp. but I would like to see a bit more,So I want to go with 59cc heads.Not lookng for the best bang for the buck,just looking for the best head,also I will be running my D1SC and looking to make 20 lbs of boost.

 

Soooo......what do you guys think?

[misterp]

I would have bought the cam *after* the heads, especially on a FI application. On that much boost all the GM heads are out the window (deck not strong enough) you're going to need a set of aftermarket heads. I would get a set of either CNC ported AFRs, or custom ported Dart 225s (not the Dart company ported heads, they're ho-hum). Make sure the valve job is done right, and that the valve seats have WIDE margins for heat transfer. The heads you want will require a bit more exhaust bias than seen on N/A heads. The valve events on a centrifugal motor will make or break your economy, not all 236/236 cams are the same, if the actual valve events are in the wrong place (for the stroke employed) you will be blowing raw gas out the tailpipe and/or be down on power - a N/A or nitrous optimized cam will be 50-60 hp less than one with valve open/close points intended for a centrifugal; great heads won't make best power with a cam that long anyways. Also *critical* decision is going to be intake manifold, its effect on the intake ports is even greater (on the LS motor) than the port itself, I would be considering the TBSS 90mm intake & TB, we don't have a very good selection of intake choices yet. Smart selection of upper-end on your application will be the difference between 700+ hp and 800+ hp end result.

 

Mr. P.

Edited February 2, 2009 by Mr. P. (see edit history)

[zippy]

Due to the low compression pistons you are somewhat limited. I would either recomend looking into some Trickflow 225's and having them milled or go with some PRC stage 2.5 5.3L heads. Link It would be nice to know the piston part number though as I think he is under estimating the compression with that small of a head. 20+psi has been done on stock heads, but I agree with Mr. P in that aftermarket heads with a thicker deck would be alot better way to go.

[allballz57]

I would have bought the cam *after* the heads, especially on a FI application. On that much boost all the GM heads are out the window (deck not strong enough) you're going to need a set of aftermarket heads. I would get a set of either CNC ported AFRs, or custom ported Dart 225s (not the Dart company ported heads, they're ho-hum). Make sure the valve job is done right, and that the valve seats have WIDE margins for heat transfer. The heads you want will require a bit more exhaust bias than seen on N/A heads. The valve events on a centrifugal motor will make or break your economy, not all 236/236 cams are the same, if the actual valve events are in the wrong place (for the stroke employed) you will be blowing raw gas out the tailpipe and/or be down on power - a N/A or nitrous optimized cam will be 50-60 hp less than one with valve open/close points intended for a centrifugal; great heads won't make best power with a cam that long anyways. Also *critical* decision is going to be intake manifold, its effect on the intake ports is even greater on the LS motor than the port itself, I would be considering the TBSS 90mm intake & TB, we don't have a very good selection of intake choices yet.

 

Mr. P.

 

The cam is aready in it,I didn't build it but I am getting it second hand with 0 miles,It was built it for a turbo car and I was told the cam would work very well with my setup,so I don't feel the need to change it.And the tbss ls2 manifold is actually coming with it ready to bolt on x-link and all.

Edited February 2, 2009 by allballz57 (see edit history)

[misterp]

The cam is aready in it,I didn't build it but I am getting it second hand with 0 miles,It was built it for a turbo car and I was told the cam would work very well with my setup,so I don't feel the need to change it.And the tbss ls2 manifold is actually coming with it ready to bolt on x-link and all.

Cool; consider the ported AFRs - go to DPE Corvettes, spend a 1/2-hr browsing the videos, that car has almost exactly what you are assembling (4" crank & ported AFRs & D1SC).

 

Mr. P.

Edited February 2, 2009 by Mr. P. (see edit history)

[allballz57]

Cool; consider the ported AFRs - go to DPE Corvettes, spend a 1/2-hr browsing the videos, that car has almost exactly what you are assembling (4" crank & ported AFRs & D1SC).

 

Mr. P.

 

I watched the video's,they were pretty badass! I thought it looked familiar as this is the guy I got my 2.5 bar map sensor from.He is on ls1tech quite a bit.

 

It looks like the AFR's might be the way to go,I really don't want to lift a head with some stock castings.I am also gonna look into the trick flow 225's I have heard a lot of good things about them.

Edited February 2, 2009 by allballz57 (see edit history)

[mean05]

why not go 317's...they will handle 20+psi and already have, parish's truck did it no prob as will mine...i have seen it first hand along with the L92's hitting the 20psi mark...no reason to spend a few grand on heads when some stock ones will do fine with a little work done to them

[misterp]

why not go 317's...they will handle 20+psi and already have, parish's truck did it no prob as will mine...i have seen it first hand along with the L92's hitting the 20psi mark...no reason to spend a few grand on heads when some stock ones will do fine with a little work done to them

I stand corrected then, I was under the impression the stock castings were only good for about 15-psi.

 

Mr. P.

[allballz57]

why not go 317's...they will handle 20+psi and already have, parish's truck did it no prob as will mine...i have seen it first hand along with the L92's hitting the 20psi mark...no reason to spend a few grand on heads when some stock ones will do fine with a little work done to them

 

 

Do you know the specs on the stock 317's,chamber size,flow?

[misterp]

Do you know the specs on the stock 317's,chamber size,flow?

I do know people have better luck using the 243s or L92s as a starting point... I would have to search, I am under the impression the 317 heads max flow is somewhere around 260-270 CFM. For a stroked motor the least factory-based head I would put on it would be ported 243s or L92s; again that's my opinion I don't have any hard figures to back it up with. The L92 is proving a great head for stroked apps provided you get the camming right. It's also a difference in values, the way I see things there are some areas of the engine you do not skimp on, and I would certainly buy the best heads you can afford so I would buy the AFRs.

 

Maybe time to start over from a different approach - just what exactly are the goals? I would expect that blower on stock 317s to put the truck down in the mid-11 to upper 11's, is that in line with your performance goals or were you looking for low-low 11's or all-out max-effort?

 

Mr. P.

Edited February 2, 2009 by Mr. P. (see edit history)

[zippy]

why not go 317's...they will handle 20+psi and already have, parish's truck did it no prob as will mine...i have seen it first hand along with the L92's hitting the 20psi mark...no reason to spend a few grand on heads when some stock ones will do fine with a little work done to them

 

 

He'd have to go to 243's due to the ultra low compression. The quickest truck on this site if I recall is still running stock 317's.

[mean05]

see i disagree with the L92's not being a better head, they flow in the 360's for $1800 for a complete head, my 317's flowed 300 at .600....he could also mill the 317's and use a thinner gasket...just use a nice ARP2000 head stud

[Krambo]

Interesting thread guys. I would like to add my thoughts on the subject.

 

allballz57, you state you are going to be running 20PSI on a 408 correct? Have you given thought to running that much boost on the street with pump gas? I think you will run into IAT and knock issues at those levels on pump gas without topping off with race gas and/or running Methanol (even with your low comp). That being said, head choices / porting will be one of my top priorities since you will most likely be tuning to the limits of the fuel before even reaching your 20psi boost goal. I know alot of people say porting isn't a big deal on a boosted application however basic mass flow diagrams show running a ported head, you open up both your intake and exhaust flow allowing air to enter and exit more easily. Easier to get air in = less restrictive = drop in boost pressure, which means you take in the same amount of air with less heat generated and have a more dense air charge. That means more power with less given PSI (lower IAT's) and less potential for knock and also less chance of lifting a head (i.e., you are processing the same amount of air through the motor per given PSI). You may actually make more power with less boost and more streetable truck if you raise the boost IMO. If you then get the urge to increase boost with better fuel / meth, its that much more power IMO.

 

As for heads and boost, talk to a pro engine builder for assistance and DO ask more than one to draw your own conclusions. I like and always have liked the 243's / 799 GM castings due to their dual quench area which promotes a better burn by forcing the mixing of the air and fuel at the center of the piston during the compression stroke and typically are less prone to knock. How does the dual quench areas perform under boosted applications?...I don't know but I tend to think the same principles are involved. So if you were to choose a 243, I would leave the chamber porting alone to keep compression from being any lower and get some port work done. The downfall is the 243's are not cheap and after some port work, they may be only a smidge less than the fat decks of TEA and AFR's. Its a toss up but some ARP head studs are a must for your build.

 

All in my humble opinion of course.

Edited February 2, 2009 by Krambo (see edit history)

[allballz57]

Interesting thread guys. I would like to add my thoughts on the subject.

 

allballz57, you state you are going to be running 20PSI on a 408 correct? Have you given thought to running that much boost on the street with pump gas? I think you will run into IAT and knock issues at those levels on pump gas without topping off with race gas and/or running Methanol (even with your low comp). That being said, head choices / porting will be one of my top priorities since you will most likely be tuning to the limits of the fuel before even reaching your 20psi boost goal. I know alot of people say porting isn't a big deal on a boosted application however basic mass flow diagrams show running a ported head, you open up both your intake and exhaust flow allowing air to enter and exit more easily. Easier to get air in = less restrictive = drop in boost pressure, which means you take in the same amount of air with less heat generated and have a more dense air charge. That means more power with less given PSI (lower IAT's) and less potential for knock and also less chance of lifting a head (i.e., you are processing the same amount of air through the motor per given PSI). You may actually make more power with less boost and more streetable truck if you raise the boost IMO. If you then get the urge to increase boost with better fuel / meth, its that much more power IMO.

 

As for heads and boost, talk to a pro engine builder for assistance and DO ask more than one to draw your own conclusions. I like and always have liked the 243's / 799 GM castings due to their dual quench area which promotes a better burn by forcing the mixing of the air and fuel at the center of the piston during the compression stroke and typically are less prone to knock. How does the dual quench areas perform under boosted applications?...I don't know but I tend to think the same principles are involved. So if you were to choose a 243, I would leave the chamber porting alone to keep compression from being any lower and get some port work done. The downfall is the 243's are not cheap and after some port work, they may be only a smidge less than the fat decks of TEA and AFR's. Its a toss up but some ARP head studs are a must for your build.

 

 

Great reply kevin,I am actually going to run an adjustable wastegate after the intercooler to keep boost respectable on the street,but that was a whole different thread coming up.I just wanted to express that it was my goal to see 20 psi.I was told the shortblock is fully studded,so I assume head studs are already installed.

 

Thi is great stuff guys keep it coming!

[dozer]

A D1SC on a 408 with a big cam, ported heads, and high flow exhaust you will not see more than 14-16psi at max blower rpm and no belt slip. Your Hp levels will be up from all the air you are flowing since boost is just a measure of restriction anyways. But if you are determined to make 20psi you would need to step up to a F series blower.