Hey all, my names Chris and after reading through countless threads and seeing the wealth of knowledge that is on this forum I figured I would join. I'll probably ask a myriad of questions so pardon me in advance.


Currently in the process of putting together a 408 stroker for my 04 Silverado SS. Decided to try out the Summit pro ls line for the rotating assembly, if its good enough for 1200hp it should be fine for my goal of around 600 to 800. I have their +20 cc dished pistons, and currently have 317 heads. My one problem currently is that i want to be NA for a little bit but trying to figure out that with the 317 heads and such low compression is that may be harder than im currently attuned to.


I'm looking for a book or some great reading so I don't have to ask as many questions because I'm not trying to be that guy.


Thanks for reading and I can't wait to learn even more.


Chris

 

Welcome. I would consider making a trip to the local You Pull it Yard and find a pair of 799 or 243 heads from a 5.3l truck. Find a good machine shop to have them freshened up and burn some rubber!

 

Welcome 🤗
you could always do an LS3 top end 😈
5.3 heads on a 408 seem a little too small, on a 6.0 yes 6.7 ehhh
not discrediting jetech whatsoever
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Would these heads be able to be taken off after and work for boost? Or should i just plan on doing work on the 317's i have?

Would these heads work with boost later on? With my current set up on the pistons at +20cc dish, with a 65cc combustion chamber I'll be at 9.8:1. At 70cc it's down to 9.4:1.

I always imagined that doing it this way (N/A to FI) I was going to have to do a head and cam swap when I decided to make the switch. My original motor got water in the number 6 cylinder so it prompted this to happen a year before I was originally planning. So bulletproof motor then add boost later on seems like a solid plan

 

I mean boost is gonna love both no matter what lol, and you don't technically need to change all that out, the 408 is gonna make loads of torque to begin with
Technically every cam is a boost cam - Richard Holdener
But if I was in your shoes, I'd get my CR to the mid 10s and still throw boost with some E85

 

It sounds like i should swap out the pistons for a smaller dish to raise the compression. They are still in the box. Unless there is another way to raise the compression that I missed. I have books coming so I'm hoping to not be as clueless

 

Seems like a shame to me shooting for 600-800hp from a 408 with a turbo. That hp level can be achieved using sbe engines with not more than cam,springs ,fuel system running e85 + boost.
Your combo should be very sturdy.
I would consider finding a different piston setup. Have fun with the build, that is part of the FUN we have doing all this stuff

 

I'd build it for the boost and stick with the 317s. You may be down a little on the NA side but I wouldn't think your losing much versus a 243/799 head.

 

Will the difference in compression Vs reliability be that large? I just don't want the 408 to be a complete dog before it gets boosted. Also, I'm sure knowing myself, that as soon as I hit the levels that I'm shooting for 600-800 I'll probably want more. I'll also probably break some **** because it's in an awd Silverado ss that's 5600ish pounds.

Will it be a dog on the na side though?

 

I don't think so. My 03 Silverado truck has a 6.0 with 317's and it's very responsive. I'm thinking it would be evem more responsive being stroked to 408 and aftter reading your post it's got me thinking that's what I should do with the old work truck. I'd probably be the only land surveyor in Texas running between jobs in a turbocharged LS 408 stroker.. I'd keep my 317's on there but replace the valves, especially on the exhaust side of things due to the extra heat they would see from a boosted application.

 

I've decided to do the work on the 317s. So far I've got trunnion upgrade, and installation kit, pushrod length checker, and trick flow springs (TFS-2500287P). As I keep reading I'll decide further on exhaust and intake valves also if any other upgrades are worthwhile

 

LSA Heads with that many CI, but if you want to stay under powered have at it.

 

In an article by Motortrend the 706 heads made more hp and tq then the 317s in a turbo application. Keep in mind that this was on a 5.3 engine where the small bore heads have smaller valves, combustion chambers and flow less than the larger 317s so my guess is I'd see similar results from a 317 over an 821 or 823 head on a 4.03 bore. I do know however that rectangular heads will make more hp than cathedrals on the larger bores which is why I decided to run them on my LS370 nitrous build. I also don't think that Motortrend's comparison was fair because the lower compression offered by the 317's would allow for additional boost.