Hey Guys,

I have a built 5.7 LS1, currently running 13psi with a single 7665 turbo. I am currently using 317 heads from an Avalanche (year unknown). I read that using these heads would lower the compression ratio allowing for the engine to hold more boost. While I found this to be true, I also found this to simply be not what I want. The engine was built so that it could spin to 7500 RPM. I don't visit the drag strip as much as I do the road track. The issue with the 317's is that they stop flowing well right around 5800 RPM. The engine has a lot left in it but I am forced into a higher gear because the heads just back up. I would like to actually run LESS boost and a higher compression ratio with some more efficient heads, as I feel this would suit my needs. The intake is from an LS6, so it is all cathedral style stuff.

The question I have is, what would be a good set of heads I could get that would support my 7500 RPM needs?

Please keep in mind that I am not looking for any extra HP, or any other performance gains. Which means I don't necessarily need more cc volume in the chamber or anything like that. I have looked at some regular old 241's, and some CNC'd 243's, but I wanted to get some opinions off here as this forum pretty much rocks. Input in the comments
Thanks in advance

 

More details would help. Without knowing your valvetrain specs, or post turbo exhaust setup, it is difficult to picture how you can place all the blame on the heads.

 

I am just going off what the tuner was explaining to me. He was very confident the head flow was the issue. What I know about the valvetrain is that the springs are .690 lift and the cam was spec'd for higher RPMs. I don't have the exact numbers, but I trust the builder on that as well.

 

Without exact numbers we can only speculate, but a quick search of what has been done with bone stock 317 heads, not to mention ported ones, will show why I doubt that they are the problem.

 

Interesting. The post turbo set up is the downpipe comes off the turbo, does under the engine and stops under the passenger seat. No cats or anything, just pipe. Which makes me feel like the post turbo action is not the issue either. I will see if I can get some numbers from my builder on my cam and valvetrain and when I do, I will post them here.

 

If the cam is large enough with that small turbine you could be running into a backpressure issue.

 

put a more bigger turbo

 

You'd need to give more details.....so presumably this is not a stock 5.7 bottom end ?

A strong 7500rpm on an LS6 intake is probably doable, but also not the ideal choice. An aftermarket shorter runner intake would make more sense, ProFlo or something.

And camshaft/valvetrain need to be suitable too. 690 lift springs seems a tad odd for a relatively mild motor and mysterious camshaft. In fact...seems just wrong.

But heads...what is your budget ? there are any number of heads these days.

 

Has a 65mm turbine wheel and wonders why it won't rev to 7500??? You need a new tuner if he thinks it's the heads fault.

 

Lol, I was just about to say the same thing.

 

You want rpm but not hp? FYI - HP is directly related to rpm. What is your hp goal? What is peak torque? @ what rpm?

Head flow not the problem (possible spring setup may not ideal for rpm) Who spec'd turbo and cam to support it?

As mentioned, turbine too small for rpm goal. Would you expect a 427 to run 6150 with that turbo? Can't expect 350 to run 7500. How much gate pressure to make 13psi? or measure pre turbine exhaust pressure to know where your at. No surprise that it's >2:1

Talk to turbo suppliers to sort out combo and needs to meet goal.

 

Turbo is almost positively the reason.

At this point I wouldn't trust your tuner anymore.
My stock 862 heads make peak torque at 6800. You should see my HP curve lol.

 

Stock crank and block, but forged everything else. I could see myself getting a new intake, but I am not sure it's needed. Still in the process of getting my cam/valetrain specs from builder. Cost is not an issue. I always pick fast and reliable and leave the cheap to whoever wants it. If the cost gets high that just means I don't get what I want as quickly, but I will get it

It's not that I don't want HP, I just don't need more power than I have now. What I need is the ability to apply it to the road for longer periods of time. I want to be pulling hard in each gear from 3000-7200 RPM, instead of 3500-5800. It just makes more sense to be able to put the power down longer, then to be flying through gears. It is a 6-speed after all

HP goal = 700 @3000 RPM and hold it through the power band (all the way to 7000). The smaller turbine was to support spooling to such high numbers so quickly. Would also like peak torque a little earlier, but hold it through the band. Unsure about the gate pressure, but there is a manual boost controller.

I have attached a dyno graph to try and portray what I am going for. I am aiming for the SHAPE below, not necessarily the numbers.


I am not opposed at all to talking to some suppliers about a good combo for my needs. I would like to use Precision, but don't have any previous experience with them.

The big thing here is I think that the car can be sportier. Trying to keep up with the STI's around town. On the highway it's no contest, but from light to light it's a little embarrassing. I don't have to crush them, but it would be nice to be in the race. Maybe even win one if they make a mistake.

Please keep in mind that I personally don't know what I am doing. If I did, I wouldn't be here looking for help LOL. I just have the info of the people doing the work that I myself can't do.
The turbo came off an old build and it was just an On3 ac delete kit, bigger fuel pump and injectors, on a stock everything else. Now that the motor is built, it would not surprise me that the setup needs to be changed.

Hopefully this can provide some clarity to those of you following along. I do appreciate all of the comments here, even the not so helpful ones

 

700 HP at 3000 RPM is 1225 ft-lbs.

Your turbo is improperly sized, and camshaft will play a major role.

That amount of cylinder pressure also wont happen on pump gas.

 

If you spend a couple hours looking at dyno curves on Google, you'll likely not find but better understand what your asking for. I don't think you'll find much at all on smaller cubic inch motors. Maybe compound turbo stuff? To get closer to your goal, you need to connect with someone that has done it and have pocket $$$ to get it done. A complex boost/power mgt system will help too. BTW - the trans is used to get or keep you where needed in the power/torque curve.

 

A larger turbine wheel turbo like a 7875 will hang on longer at high rpm and will spool fast enough if tuned properly. That said if you're getting killed at stoplights with that small turbine then you should be looking at the rest of the setup and possibly a twin screw supercharger that'll give you max torque right off idle.

 

Google is where I got my example dyno graph. Most graphs are gradual upward slopes, which is not what I am asking for.

I do believe that I need to consult with someone from a turbo manufacturer, if anything else definitely to get educated

 

It has also just dawned on me that many of the replies here are coming from much lower elevations than I am. I am located in Denver CO and so the air up here is a bit thinner LOL. If that changes anyones ideas or throws into the mix some other possible issues sorry for not brining it up sooner

 

Run a single T4 billet S362 and you can make 700 at the flywheel throughout that rev range.

Your expectations of "flat HP curve" don't make sense at all, but if that is what you want..

 

This is just going to be one of those bizarre threads.