LS7 Intake under boost
 

Well my build has changed today to a single turbo setup, either 76 or 88 depending, and the basics will be the LSX block, LS7 heads and an LS7 intake...does anyone have an idea at what power the LS7 intake starts to fade? I plan around 750rwhp on pump gas, then the occassional big boost 1000+ rwhp for the track with race gas. Is the LS7 intake good to go up to that boost? Or should I start thinking Hogans? :cry:

Dude, I'm betting the LS7 intake is good for 1500+ turbocharged hp. It's lightyears ahead of the LT1 intake that's been proven to 1000+ rwhp.

Mike

I dont think 750 on pump gas is realistic.

When the LS7 stuff is making 500 - 550 rwhp on motor alone, I bet you could get over 900 rwhp on pump gas. That is, of course, with the right turbo. The 76 isn't going to cut it. Heck, with my LTx, I'm making 700 rwhp through an auto/loose converter at only 17 psi.

There is a local guy that has a GTO, stock bottom end, stock ported heads, stock intake making 650rwhp on 5psi with a T76...how is 750 not possible? The turbo is good to 1000hp. I might go with the 88...but that's another $1500 basically for the turbo alone.

Good to know the LS7 intake is fine up to 1000hp, I figured it would be, just wondering what's been done on it so far. LS7 heads and intake it is then!

The 76 will create some backpressure issues, depending on the cid. You don't typically install the LS7 stuff on a small motor, which is where the problem comes in. Also, note that the T76 becomes VERY inefficient at low boost and high flow. That's where the 750 rwhp on pump gas problem comes in. You're better off with the T88, hopefully a T6 exhaust side, and a 3.5 or 4" downpipe.

Or. . . if you want to optimize power on the 76, you could built a small displacement engine using the LS7 heads/intake. You could use the 4.125" LS7 block with a 4.8 crank, for 350 cid on the nose. Or, even better would be a 6.0 block with the 4" bore and the 4.8 crank, for 329 cid. That is, if the LS7 heads work on a 4" bore. That would give you very good cylinder filling and a good backpressure ratio on the turbocharger. You could cam it however you want and rev the pee out of it.

Mike

I was thinking LSX block with a 4.125 bore for the LS7 heads and a stock stroke Callies crank, or possibly even go with a 4" stroke and use the T-88 turbo. Thats if it's possible to keep that motor around 8.5:1 compression and keep the wrist pin away from the ring lands. Have to see. So many dang questions! :cry:

So you're talkin' 388 - 427 cid range. The T88 will actually start to see some problems with a motor that size flowing that well. You might consider the S88 from forcedinductions.

LastLS1 is running an LS7 intake I believe, and has gone 8.6's. So he's making over a 1000 crank hp, maybe 1100.

you make 700 on pump gas?

Can you expand on that? Turbonetics recommends that turbo with a .90a/r for motors around this size with a 1000hp goal. I'm curious to pick your brain about this subject, if you don't mind. :chug: Wish you lived in KC so we could enjoy a brew and talk!

I'm running an LS7 setup on my 427 (4.125x4) with an F1C Procharger and made 788 RWHP at only 8 pounds of boost on 93 octane pump gas. Compression ratio is around 9:1.

that is an extremely rare case,most are no where close to that at that psi so thats a poor case to go by.and u need to a remember that just cause a turbo says its good to XXX/XXXXhp doesnt mean on every setup no matter what.

I understand that his GTO may not be the same as all, and I'm not sure why it makes so much power. And I also know that you can't just go buy a turbo cause it says it's good to xxxxhp and plan to get xxxxhp out of it. I was simply stating that, for basics, the T-76 is supposed to be good to 1000hp on a engine around the cubes i'm building. I understand there are a lot more technicalities to look at, but just a general statement is all I was making.

Then let me ask you all this: Let's say with a 4.125 bore, 4.00 crank, LS7 heads and intake, which turbo would YOU put on there? I would like to stick with an air to air intercooler, but most I'm finding are only 1000hp cores. Are there any air to air that will support, say 1200hp? Or should I start looking at....*sigh*....water to air.

I did that through an auto/loose converter at 17 psi. That boost level is borderline for pump gas alone, so I use inject some Methanol also. I think I could tune it to work on pump alone, but it would be on the edge. Also, note that stick tranny's are known to make 120 - 220 more rwhp than auto's with loose converters. So, I could get to 700 rwhp at around 12 psi if I had a T56 even with my LTx junk.

Mike

With around 400 cid and very good flowing heads, turbo selection will be tricky. Let's look at both sides:

Compressor: All turbocharger compressors are more efficient at high flow rates and high pressure ratio's (boost). At 850 fwhp on an LS7, you're only talking about 6 or 7 psi, or a pressure ratio of 1.5. So, even though a T88 may be rated for 1250 hp, its not that efficient at 850 hp and 1.5 Pr. So, in order to get good low-boost numbers on a large displacement, well-flowing engine, you have to size the turbo bigger than what you want. Just for example, a T76 would be only 50% efficient at the same level.

Turbine: Again, the cid and flow make this more difficult than most. You will definitely need a T6 exhaust side. That's why I recommeded the new S series of turbochargers. They are available from S76 up to S88, all with a T6 exhaust side. However, the S88 will support 1500 hp and is about the same size as a GT42 and much smaller than the large-frame T91 that's only good for an extra 50 hp.

Don't take this from me, though, on a serious build like this. Call Jose at forcedinductions.com. He has alot more experience than I do.

Mike

If it were me, I'd talk to Jose to see if he thinks an S88 is a good match. If you have room, a PT91 would definitely work, but they are BIG. Another thing to consider is something like twin PT67's if they'll fit better.

Keep in mind that this combo has some serious parts and will make well over 1000 rwhp on race gas.

Mike