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Discussion Starter #1
Guys I have a 468 with stock heads, 10.5:1, street car. Guy wants to put twin turbos on it, but maintain streetability, pump gas 93 octane max. We don't want an intercooler if we don't have to. What size turbos... would 60mm be enough? Also we're talking max boost of around 5psi.... maybe 7? Remember... total street car here, Blow Thru carb.
 

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Chris,
There are some pretty important considerations that need to be addressed first. What hp is he looking for? Is this at the tire or at the crank? What compression ratio? What tranny?

Running pump gas usually means you're going to have to run an oversized turbo(s) in order to make power at lower boost levels. Doing that w/o an intercooler really invites detonation . . . and pump gas makes that situation even worse.

BTW, the .60 A/R refers to the compressor side. Your biggest challenge here is going to be what A/R to run on the turbine side.

Rod Short
Sales Manager
Precision Turbo
 

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Chris Uratchko said:
Guys I have a 468 with stock heads, 10.5:1, street car. Guy wants to put twin turbos on it, but maintain streetability, pump gas 93 octane max. We don't want an intercooler if we don't have to. What size turbos... would 60mm be enough? Also we're talking max boost of around 5psi.... maybe 7? Remember... total street car here, Blow Thru carb.

Chris,

Turbocharging it is not a big problem...just $$. :wink:

The problem I see is the 93 octane requirement being maintained?

With the starting C.R. being 10.5, at 5# boost it would be equivalent to 11.8-11.9 C.R., which would normally require at least 100 octane. At 7# of boost it would be in the 12.9 to 13.0 range and need at least 104-105 octane.

The octane requirement can be somewhat reduced with some creative timing adjustments, but not to the point of 93 octane use. No doubt the engine would be prone to detonation under load. This of course would be more so due to lack of intercooling.

You didn't give much info regarding the current power level or operating rpm range, so I will make a few assumptions.

Lets assume that your 468ci makes approx. 600hp FWHP. I don't know your rpm range, but I was assuming 62-6500rpm.
At 5# of boost it should make in the area of 680-685 FWHP, and at 7# approx. 725-730 FWHP.

As I said above turbo charging it is not a problem, but the restraints due to the higher c.r. does sort of put a damper on the octane issue.

Turbo choices...for twins, the T04's with .69 a/r turbine housing would be adequate based on my assumptions. Of course properly sized wastegates would be required to bypass excessive exhaust gases to maintain the desired boost levels.

If I'm not in the ball park with your current power level, or rpm operating range let me know.

Joe Lubrant

Lubrant Performance
219-838-5213
 

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Discussion Starter #5
The compression ratio is CURRENT.... I'll drop it for him to whatever we need it to be.... so lets not put a constraint on it with compression.

Operating range is 6500 rpm max. Power level.... 650-700 would be plenty.

This turbo stuff is new to me so I'm in a learning curve here.
 

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Chris,

the T04B is the one that Grape Ape is running on his SBC (I dunno if you remember him from the 2nd Gen site. http://www.grapeaperacing.com/GrapeApeRacing/). those seem like a good choice for this (~800 HP). with that big a motor, you might though run into issuez with getting turbin housings that have a good AR so that you can flow enough air.

From what I can tell, a CR of 8.5 to 9.0, seems to be the norm on these forced air motors. sounds like a piston change is in order. also there seems to be a big benifit from coatings (especially piston crowns & chambers).

I would guess if you keep the boost low enough, pull enough timing & do some coating that you would not need an IC.

What kind of car is this going in? the reason to ask is that there are some pretty nice 2 input 1 output air to air IC's out there that might provide some insurance & make more HP when he gets bored with what your going to give him.

Bob
 

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Discussion Starter #9
Awe c'mon now don't tell me that Jim this could pimp the project.... no intercooler!!!

Well.... maybe if I can find a 'cheap' air to air.
 

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Hey guys, thanks. It's nice to be here.

In order to keep the detonation level down, you're going to need a lot of turbine flow with an efficient wheel.

We'd suggest a custom small trim GT4067 with a water cooled Garrett dual ball bearing cartridge. We'd also use a rather special 65.5mm compressor wheel. There would be other combinations that would more or less fit, but this would be the kick ass combination.

This is something that we don't normally sell, but would be custom built to your customer's application so they'd get the best possible performance.

Let us know if we can help.

Rod

2005
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Discussion Starter #13
He just doesn't want to spend the coin and I'm not sure if he has the room.... at the very least, I'd like to see if he could stuff a Cummins Truck air to air IC in there.... this is going in a 71 pro street type Chevy Pick em up....
 

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Oh he has TONS of space. My uncle, my grandfather and I built a '70 Pro-touring type truck, chopped, late model bead, custom frame, etc, so I know the available space. ;)

He will be MUCH better with it, a cooler charge will be less prone to pre-ignition, and make more power due to the cooler charge.

Yes, FMICs can get expensive, but they don't need to be, like you said, you can use a bone yard IC and adapt it, cut it down, rebuild it, pretty it up, etc.

Go for the cooler, it's worth it.
 
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