turbo size and cubic inches

nborga87

nborga87

Poor Boy Puller
Joined
Nov 1, 2009
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There is a profarm tractor pulling class around here that limits you to a 2.4 inch bushing size in the turbo. The cubic inch limit is 540 cubic inches. There is also a overall diameter limit on the turbo which is 11 inches from the exhaust mounting flange to the top of the turbo. Generally guys will run an hx 50 with a 25 or 29cm exhaust housing or a comparable charger of other brands. What my question is, being such a small charger has to be used is it most efficient to have the max of 540 cubic inches or would it be most efficient with a smaller cubic engine. If so how would you figure out the most efficient cubic inch setup with your turbo?

thanks
nick
 
With a bigger motor, you're going to be able to drag it down more without choking the turbo out. If there's no exducer limit, only an inducer limit, best to run as big of an engine as possible so you have a broad rpm range.
 
well there is no actual limit on the exducer just a limit on the overall diameter of the turbo. You dont think that at a certain point the cubic inches become a waste?
 
I would build a lot smaller motor , and use high compression close to 20+ 1 to one .


use a very late closing intake event as well.
 
I say go big and use as big a charger as you can, then bush it down. I think it'd be a beast on the low end......
 
With limited turbocharges, engines you only have a given amount of air. Making the engine bigger only makes the engine starver for air up high in this case of extreme large displacement the power peak could be as low as 2500 rpms. Size the motor accordingly. As to the benefit of high compression, it mechanical advantage that makes power. Look at it this way it’s the size of the combustion chamber / swept volume that is critical in the design of maximum effort engines in very limited rules environment.
Limited rule, are the place where hard work and proper use of process engine development really shines.
 
ok so how is the best way to decide on cubic inch that would work the best
 
nborga87 said:
ok so how is the best way to decide on cubic inch that would work the best
Click to expand...

you need to find out your turbo limitations first. charged air is going to be the most important thing before you even think about cubic inches. if the bore rules are vague and open to interpretation...build on the bigger cubic inch. if compressor and cover rules are strict then a smaller cube motor will be more efficient. post a link for the charger rules first before you do anything.
 
5. Intercoolers and water injection allowed.
6. Turbocharger must be under hood. See drawing below for maximum turbo charger
size. Turbo charger must have a 2.4 maximum inlet bore at the compressor wheel,
or a restrictor plate 1/4”thick with a hole no larger than 2.4”in diameter within 2”
of compressor wheel. All air must go through 2.4 turbo inlet. There must be only
one turbo going through one pressure stage.
7. Exhaust must discharge vertically upward above highest point of tractor; with
exception of roll bars; and must be securely attached.exhaust must be at least 18”
above the hood and no curved pipes or rain caps allowed. Exhaust pipe must be
cross-bolted with two 3/8”grade five bolts within 1”of each other in vertical pipe
 
I understand what they are wanting, but with no clearly written restrictions on the MWE groove nor if the wheel needs to protrude into the bore, it leaves the door open for interpretation. With no limit on the turbine wheel, intercoolers being allowed, max A-pump, and a non cut 24.5" tire allowance, cubic inch will be hard to beat.
 
^^^ This.

Run the bigger mill. It is easier for a smaller charger to support a lower pressure ratio at high volume than a high pressure ratio at small volume(smaller CI engine).
 
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