silvea

iTrader: (1)

Ok So today I dropped my LQ4 off at the machine shop to have it bored .030 over. So far this is my build list.

370 iron block
TSP rods
Weisco Pistons -11 dish
Stock LS3 heads
Tick stage 2 turbo cam (it will be a custom grind from tick but that level of aggressiveness)
Stock crank
all being force fed by a comp turbo 7875.

Now here is where my questions for you come in at. Will a 7875 be able to keep a 370 fed? I only have a T4 flange and with my military discount that 7875 comes in at a real deal for me.

The next thing I am worried about is the compression ratio. I already own the LS3 heads so those are what is going on the engine. With that being said my options for pistons become -11 or -25. The -11 put the compression at 9.37 and the -25 put it at 8.24. Which is a pretty massive gap. Thats running an LS9 head gasket at .055 gasket thickness. I am stuck in California in an area where E85 isn't an option so I will be running 91 octane. I do have the option of running a cometic .075 gasket from lingenfelter which would drop the compression ratio to 9.0. I'm just wondering at what compression ratio I can run at safely on 91 pump.

Goal for the car is make at least 650 hopefully 700 RWHP on 91 octane gas. Am I in the right ball park or am I just dreaming. This is a street/strip car, so I want to be able to cruise it to work without issues, yet run respectable times at the track when it cruises out there.

Beanslsxnova

iTrader: (1)

I think your off to a good start, and everything you listed parts and specs will work well together. I would like to see a little bigger turbine on that turbo, but non the less it will work fine for 650-700hp application

svslow

Go with the 9.37:1 CR and run meth injection.

ta02zx10r

iTrader: (19)

Fwiw I'm running 10lbs and made 746hp on 91 my comp is 9.5:1 on a mustang dyno

oscs

iTrader: (19)

9.37 and let it eat. My 9.5:1 LS3 headed 370 @ 14lbs of boost made 650whp through a T56 on 93 and 14* timing. No meth with an A2A. We were having some fueling issues so it could have made more.

oscs

iTrader: (19)

Those are ambitious numbers. Not impossible by any means but that's suggesting the motor was making at least 450whp NA and making 30whp per lb of boost on 91.

DavidBoren

As mentioned, I recommend the combination that gives you 9.37:1 compression. The 7875 will be fine to get everything up and running, work all the bugs out, and should prove to be an excellent turbo to start with. You might outgrow it, as power is addictive, but it will be fine for a cam in the +/- Tick Stg2 range.

silvea

iTrader: (1)

I know how this is going to go, however is it worth the effort to cut my t4 flange off and weld on a t6 and pick up a Borg for like 650-750 bucks. They are 83 mm I think but from what I hear huge! It would be a real chore to get it fit as my headers Y in front of my engine and the turbo mounts below.

DavidBoren

If you have any space restrictions, you will probably have better luck with the 7875, than a Borg. They are big. Your current setup with the 7875 and the stage 2 cam will allow you to get it running and tuned, then you can know first hand if you need a bigger turbo, a smaller cam, whatever it may be.

ta02zx10r

iTrader: (19)

Those are corrected numbers of course but that's what the numbers were. Don't know what else to tell you. I know I've done some rolls from 15-120 and a newer r6 didn't fair so well. I know that dyno numbers can be obscurred, but I don't think they would be that far off.

Realcanuk

LS9 gaskets are .051 compressed, not .055. Make sure all your numbers are right when calculating for compression. You don't want surprises.

MUSTANGBRKR02

iTrader: (91)

The 7875 is a good choice you also have the pt88 if you need more down the road. Borg Warner also makes T4 units for a lot of their units in the 80 and smaller section.

silvea

iTrader: (1)

Ok sorry I actually got the .055 number from someone when I called Texas speed. Anyways... Since it is .051 with a 4.030 bore 3.622 stroke 0 deck clearance 11 cc dish with 68cc heads- I get a 9.45:1 compression ratio. Idk how that fairs for a turbo but it seems a little high. Lingenfelter offers a ls9 head gasket with a .075 compressed thickness which would drop me down to about 9:1. Would I be better off with this lower compression ratio? Also do I have to worry about sealing issues with a thicker gasket.

oscs

iTrader: (19)

Leave it right where it's at. 9.5:1 is perfect. My car preformed extremely well with the exact same setup.

Realcanuk

Its not high. Personally I would shoot for 10- 10.5 to 1, but you will get as many different opinions as answers on the forums on this issue.

ZERO_POLLO

iTrader: (2)

I am working on a similar setup as you , I have a lq9 370 with -15 cc forged diamond pistons and 62cc 5.3 prc heads, not the best heads but im working on a budget right now.

I am at 9.63:1 Compression. I have a huron speed turbo kit waiting to be install and Im gonna go with a Billet 7875 from huron speed, that they are releasing soon. And shooting to be around 600 to 650 hp. I will keep you updated once I finish my build

silvea

iTrader: (1)

Ok so the machine shop called on Friday. He said my block is looking really pretty and it is time to order pistons and rods so he can get my short block assembled. This I thought was exciting news. However I'm back to looking at all of my options as its time to pull the trigger and order some stuff. The issue I'm running into is the piston rod combo I was looking at from texas speed uses scat rods. Since scat means **** and that's what I have heard about them I'm now scared. I can upgrade them to eagle or better but then that 1000-1100 dollar price tag is much higher. Tick performance has a deal for like 1200 for diamond pistons and lunati rods which I think is a better sounding solution? What rods do I really need... I mean I'm half tempted to go buy some Gen 4 rods from the dealership with an aftermarket piston and just call it a day.

DavidBoren

I would personally try to increase the rod ratio while you are at it, go with something like a 6.34" compstar rod and a ~1.079" compression height piston. Gives a rod ratio of 1.75 which is pretty awesome. The Callies Compstar rods run about $700, and have plenty of people running them with good results.

silvea

iTrader: (1)

Now I feel dumb. Why do I want to go with a rod ratio like that?

DavidBoren

Higher rod ratios reduce the working angle of the crank/rod/piston. It also reduces the side loading of the piston against the cylinder wall. Higher rod ratios generally experience less vibration, and in theory, less wear.

A higher rod ratio also increases the amount of time the piston stays at top dead center. The effects of this "dwell" are a slightly more efficient/complete burn in the combustion chamber.