317s vs l92s
 

This past year I ran a stock lq4 with exception of head gaskets and studs. The engine has 317 heads on it and I've heard nothing but good things about these heads. The motor performed awesome on e85 and 20 lbs of boost with an a2w I managed a 6.15@114 in the 1/8 and 9.63@143 in the 1/4. I've got the car apart doing various suspension/chassis upgrades and came across a deal I couldn't pass on an 08 van. It has the ly6 with l92 heads. My first thoughts were to swap the square ports and truck intake on to my motor. But after talking with a few people, everyone seems to be against putting the square ports on my motor and thinks I should sell them and spend that money else where due to the fact that I won't see much gains out of the l92s from the 317s with my boosted application. So what do you guys think? Should I sell the square ports or run them? I can't seem to make up my mind

You should really get a new cam if you swap heads. I was always under the impression the square port was a better higher flowing design. I have no first hand experience with the 317's and boost though.

A cam is definitely on the list this winter. Wanting to go with a jfr cam

This was just covered a few days ago.

https://ls1tech.com/forums/forced-in...317-s-why.html

If you're wanting to go with a JFR cam, most of his are designed around the heads you already have. Just cam swap it and put the money into something else.

It's a tough call. The 317's have small light valves that are easy to control under boost, and the small ports offer high velocity for a balance of good NA tq and still respond well to boost. The L92 heads offer a lot more airflow and port volume, at the expense of low speed velocity, and heavy valves that need ~180 lbs of spring pressure to control effectively at high RPM and boost. The L92's are going to lose a little response and spool but if cam and setup are right they will make more power on lower psi than an unported 317. In the end tho the 317 head is thicker and could hold more cyl psi. If it were mi I would prob stick with the 317's and do a little work to them, unless planning on going 400+ CI. The L92's really start to come alive on the larger engines.

I can say that my L92's preform quite well on my 370. I'm not really "out of boost" much so i don't notice a lack of N/A torque. I have a twin setup behind a glide so lag is virtually nonexistent for me. Stock 48 is right, You probably wont notice much of a difference.

Well I've decided to stay with the 317s. Gonna sell the l92s to help out my winter budget lol. Stock48 could you pm a number or email that I can reach you at to put in an order for a cam?

ls3 intake flows a lot better then the ls1 as well. works with a 90mm tb too. im not sure how it does in terms to the ls6, but its damn near half the price as a ls6 too.

Have you ever done any testing personally that demonstrated that a turbocharged engine needed more spring pressure than a naturally aspirated car with all other things being equal?

Yes. It's not a crazy amount but the boost can try to blow the valve open to a point. The larger the intake valve the more surface area you have, and normally a large valve is heavier. Same can go with exh of back psi is high.

That is interesting. I have never seen this. I cannot even imagine a scenario where this would happen although i have heard people say it many times. It can't happen on the power stroke because there is more pressure in the cylinder than in the intake or exhaust, on the intake stroke, by the time the valve closes, there should be just as much pressure in the cylinder as in the intake tract, on the exhaust stroke there is more pressure in the cylinder the whole time until maybe the very end if any scavenging is happening. I just don't see it.

Well I typed out a big long explanation and my piece of shit fuck computer erased it all while I was trying to post it lol..... I'm thinking positive psi in the intake causes valve to bounce on the seat. I've had my mild 218/.570 cam and pac 1218 single springs in NA 2'' truck valve 6.0l make pk power at 5800~6200 then slowly descend after but rev clean to 7K rpm before valve float... Same engine with 20 psi of boost would float valves hard at 64~6500 RPM. Add .060'' of shim under the intake and .030'' under exh springs bring seat psi to 150~155 and it would rev to 6700 RPM then float hard. Added a set of BTR dual springs with ti retainers set up at 175/380 and it would rev clean to 7200RPM + @23psi with zero float.

Thanks stock48, great info!

Thank you for sharing that experience Jarrett.