Help! Not sure which heads to run due to compression!
07-29-2014, 10:42 PM
#1
Help! Not sure which heads to run due to compression! I am building a boosted l33 5.3 engine. I am going to be running between 15-20 lbs of boost. Blower cam, ls6 intake. I am at the point of needing to decide which heads. I have a set of 317 heads I may have ported but that will only put me at 9:1 compression. I could have them milled a bit but then I may run In to piston to valve clearance issues. Other option is a ported 243 head biggest cc texas speed can do is 65 which will put me at 9.7:1. My target is 9.5:1. I will be running 91 octane with meth. What do you guys think? I could also use ported 241 which would put me right at 9.5:1 but ik a lot of people don't think the 241 heads are that great . I just do to want to have any detonation problems !
07-30-2014, 01:44 PM
#4
Which is why I am so worried about detonation.
07-30-2014, 04:43 PM
#5
At this point, detonation is the least of your worries. Those pistons ain't gonna last long at that boost level even if you have 0 detonation. Might as well do it right the first time cuz you'll be pulling that engine out sooner rather than later and you're going to have to rebuild it at that point.
07-30-2014, 08:07 PM
#7
The ring gaps are opened up for boost , so they will last longer then you think!
All I'm saying is that while you're at it you might as well beef up the bottom end. Sooner or later (more sooner than later) it's going to pop and you're going to have to take it out again and forge it. Why not do it now?
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07-30-2014, 09:41 PM
#8
Well maybe it's time to order some forged pistons! Does anyone know if forged Pistons are available at stock size? these cylinders have already been honed. So I could drop some factory size forged pistons in. Decided for sure today im going to use E85
Last edited by josh4ku; 07-30-2014 at 09:58 PM.
07-30-2014, 10:11 PM
#9
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15-20 pounds of boost is a big difference on whether or not that stock bottom ends lasts a while. My son just put together a fresh stock bottom end with .005 milled 317 heads and LS9 gaskets with a static compression of 9.6:1. He's running 12 lbs of boost and figured he may creep to 15 for margin. With his tune and on 93 octane will live for a while. If I were you I'd look into forged rods and pistons - plan on the costs adding up quickly since you have to balance the reciprocating assembly as well if you go this route. OR drop your boost aspirations while you are on a stock block and just accept the reality that it will eventually eat up the ring lands on those pistons. E85 will certainly help the engine live longer but will require a significant investment in your fuel system. Ask me how I know. LOL
07-30-2014, 10:33 PM
#10
15-20 pounds of boost is a big difference on whether or not that stock bottom ends lasts a while. My son just put together a fresh stock bottom end with .005 milled 317 heads and LS9 gaskets with a static compression of 9.6:1. He's running 12 lbs of boost and figured he may creep to 15 for margin. With his tune and on 93 octane will live for a while. If I were you I'd look into forged rods and pistons - plan on the costs adding up quickly since you have to balance the reciprocating assembly as well if you go this route. OR drop your boost aspirations while you are on a stock block and just accept the reality that it will eventually eat up the ring lands on those pistons. E85 will certainly help the engine live longer but will require a significant investment in your fuel system. Ask me how I know. LOL
07-30-2014, 10:53 PM
#11
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I wouldn't bother with forged pistons if you aren't going to replace the rods and balance the assembly. Keep the boost in check and keep us updated at how long it lasts. You may get a decent length run with it if you keep conservative. ;-)
07-30-2014, 11:06 PM
#13
Which are the ls2 rods that are supposed to be good up to 800rwhp. Is it necessary changing rods also? Or just change pistons?
And if you're going to be opening up the motor for upgrades you definitely should do the rods too. For the price of ARP bolts and re-sizing labor you could've gotten forged steel rods with ARP bolts already there. But that's too late by now, maybe you can get some money back selling those and going with a basic h-beam rod for $500 and some wiseco pistons for $700. Along with balancing that $1500 is going to go a long way in holding your engine together at 20psi. Something that is pure hit/miss with stock parts.
If you plan on keeping this car a while and having fun, definitely spend a little money now to build it right. If you're only going to run it sparingly and will be unloading it soon then keep the engine stock and pray it holds for as long as you have the car.
07-31-2014, 02:54 PM
#14
Well since my L33 is rebuilt and ready to go. it would be a waste to throw that all away. I think i mayb just run it with 317 heads at 9:1 cr , keep the boost at a maximum of 12lbs and run e85. Hopefully run that a while. Maybe Ill turn it up later on and see what it will take!