My hood after business will instantly burn and cook your hand if you touch it just from the turbo system alone.

 

Probably from a too small of a turbo being run at really low efficiencies.

The airspeeds in, thru, and out of a turbo are extremely high. 500-700ft/sec going in, 800-900ft/sec thru the wheel, and 1,000+ ft/sec going out. Just not enough time to move heat. Same theory as your cooling system, if you take your tstat out the coolant speed is to high to pull heat out of the motor.

 

It’s really because I pulled the heat shielding off my factory metal hood, I think, but anything’s possible and what you mentioned are facts.

 

BBI your power increase estimates are pretty pessimistic. Power increase is usually better than the density increase because mechanical losses don't increase proportionally. Anyway if the OP says his best motor has 75 hp at 6,000' he only needs power increase of 120/75 = 1.6 or 60%. this is only 50% increase over stock which should be no problem durability wise. It probably won't need a 60% increase in density - perhaps only 60% pressure increase ie 1.6 PR. Absolute manifold pressure would be 12 psi x 1.6 = 19.2 psi. So at sea level it needs 19.2 - 14.7 = 4.5 psi boost. At 6,000' that is 19.2 - 12 = 7.2 psi boost.

 

But is that taking into account the added heat? I can see mechanical losses not scaling proportionally, but there's also added heat and some timing pulled.

 

Agree if timing has to be pulled.

In earlier turbo days (1980's) we built dozens of different engines to run 13 - 14 psi for 100% power increase. They were de-compressed and had water injection I must admit. No intercooling though.

 

1980s turbos were a lot lower efficiency too, so modern turbos with lower charge temps and lower drive pressure would be even better.

With a bit of intercooling, I have no doubt it will make 120+ hp on the boost level I suggested (4.5 psi @ sea level) and plenty of room for a bunch more power when you decide to turn up the wick.

Stock compression will work with half decent fuel. My rule of thumb is 1 lb of boost for each octane number, so on stock compression it will be happy as long as the fuel is 4 or 5 numbers better than stock requirement.

 

Went back through this thread I realized I figured 150hp using his high elevation hp of 75hp. Your 6.5psi only gets me to 109hp.

If he makes 75hp @ 12psi aap, that equals 92hp at sea level. Going from 92 to 150hp means 10psi in the manifold, 120hp @6000 ft. Accounting for pressure drop thru the ic, that's 12psi at the compressor, which is a pressure ratio of 2, up there.

Did you use wastegates back then? The old school way was with big turbines/ ar housings, which produced a really favorable boost: drive ratio.

 

He wants 120 hp not 150. I said 7.2 psi boost at altitude and 4.5 at sea level.

Yes, wastegates in the 80's. Mostly TO4 and draw thru carburettor. Started doing EFI in the mid 1980's - still preferred draw-thru throttle plate and port injection. Mostly manual transmission, draw-thru holds boost through upshifts for vastly better driving experience with those big old turbochargers.

 

I know, the 150hp is sea level power, which at 6000' becomes 120hp. Because compressor maps have corrected intake flow in lbs/min, we have to find the real hp/flow at sea level, then correct it for elevation. His 120hp will be moving the same pre-compressor cfm as if the engine was at sea level power, but will be feeding the engine 120hp worth of lbs/min.

Your draw thru comment brought up an interesting point. Do you think the "held boost better" was because when the throttle plate closed the turbo was effectively spinning in a vacuum with very little air resistance?
Did you ever have problems with pulling oil through the compressor seals?

 

I don't see the problem. Regardless of altitude, if you have 75 hp NA and you want 120, you need a DR of 120/75=1.6

Yes draw-thru has the compressor spinning in thinner air at closed throttle.

Need to use a carbon seal turbo (or twin piston ring compressor seal with aspiration between the 2 rings). Also see much bigger axial loads - some applications wear the thrust bearing prematurely requiring modification. BB turbo is the ultimate solution of course.

 

Thank you gentlemen for continuing this discussion.
I am learning a lot.

To simplify my situation and what I am attempting to accomplish,
let's forget about altitude and the modifications that I have already done to this engine.


I'm now concentrating on a completely stock engine for this project.
The book says that it's 80 HP.
I would like to increase that 50% to 120 HP. using a blow thru turbo. (no intercooler)

BBI suggested a GBC 14 which looks like a great fit. But... $$$ !

I have an opportunity to pick up a GT1544 for a lot less.

I found a compressor map for this turbo and was hoping that you guys would take a look
and tell me IF this turbo would work for me and how comparable it is to the GBC 14.
Thanks!

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The "gt15" part of the turbo would work great. The "44" is on the small side. On that map the compressor is a 33mm in, by 44mm out. Bumping up to a 36ish mm wheel would make it friendlier. Good news is, those wheels are pretty cheap, in fact I have a few on my shelf with housings. Swap and balance and it would be out my door the same day.