I'm thinking about doing a twin turbo set up for my project boat but seem to be having problems getting any of the online turbo calculators to come up with anything.

Wondering if anyone could help me out with sizing ?

The engine will be 555 cubic inches with 8.6:1 compression and AFR aluminum heads. Figuring on a max of 6000 RPM with 10 lbs of boost on pump gas....


Thanks,

Doug

 

id go with 70-76mm compressors

 

How about a pair of the GT45's?

 

the gt45's have about a69mm compressor inducer and a 77.7/88mm turbine wheel, not sure how it would spool up , might be a little slow

 

I've been playing with the Borg Warner Match Bot some more.... Here are my numbers plugged in... Match bot

Seems my biggest issue is the low boost I'm looking to run..

Looks like a 100S71 in the Borg Warner S400sx series may work.. Any thoughts ??

 

i like the looks of the 105s72(72mm inducer) even the 6th pt(6000rpm) is at 76% efficient no just have to figure out what size hot side to run,,

makes sence also, a good match is a 70mm comp inducer on a 302 for, because you are getting close to 2 of those engines put together you would need 2

 

How do I do that ? Move the Turbine Expansion Ratio numbers 'till they all line up on the same phi curve like it says .... And hopefully not have the waste gate "choked" in the process ?

Thanks..

 

scroll to the btm of the page, there is some how to videos,, just guessing you will end up about 64.5/74.2mm or 67/74.2mm aka P or Q trim

 

....Messed with it some more. I changed my 3500 rpm boost to 10 psi and changed the turbine expansion ratios..

Came up with 80mm and a 1.05 AR... Match Bot 2

 

i think the 80mm is the big measurement of the turbine wheel,, i wish they would just put both measurements on the calculator , that is close to the gt45 specs(88/77.5mm)

 

https://www.theturboforums.com/threads/325578-Mike-Walter-s-twin-88-540-BBC-Jet-Boat

I've done a few of these projects. See above.

Long story short, GT47-88's are a VERY nice fit on your engine.

A few observations: 8.6:1 compression is not going to work well. Going to guess the rest of the combo is equally mismatched. I'd be interested in what you are doing with the engine.

 

What compression ratio would you recommend ?

It's going in an I/O and needs to run on 91-93 Octane gasoline.

The engine isn't built yet.. I'm still in the planning process and collecting parts.

So far I have..
A Dart Big M block that needs to go to a 4.560 bore.
Eagle 4.25" stroke crank. (I may switch to an American forging. Still undecided)
A set of Eagle & a set of Carillo 6.535 rods.

I came up with that compression Ratio figuring on using AFR's 325 cc heads with 117cc chambers .041" Felpro MLS head gaskets. JE257954 -20 cc inverted dome pistons. With a 0 deck block.

What would you recommend I do different ?

Thanks,

Doug

 

First things first, put a flat top piston in it. With a 6.535 rod you are going to have a very short compression height piston and that is not really desirable. (9.780” deck, 4.250” stroke, 6.535” rod, 1.120” compression height.) The main issue with any of these applications is the exhaust relief. As you probably are aware, there is next to no free drop in your style cylinder head. Consequently, you need a massive exhaust valve relief and no intake valve relief. The core issue is this, simply X power = X cylinder pressure which in turn equals X heat. Therefore, at a give power/pressure/temp you are going to cause the thin metal around the exhaust valve relief to start to melt, and then upset the compression ring. The solution is to drop the piston in the hole, remove much if not all of the exhaust valve relief and strengthen the piston. The quench distance has much more to do with the behavior of the engine than the actual compression ratio. Now, I’m not going to get into a debate as to what degree and so on. What I will say is that a properly designed piston/rod combo will allow you to run more compression, more boost and have significantly stronger parts all while having a larger tuning window.

Respectfully, if this were my combination I would start by figuring out my max power my drives will hold and what RPM. Then I would ask myself how far do I want to push my equipment. Once you know that information you can build around it. The bore, stroke and cylinder head seem to have been determined in your build. From that premise I would look and see how much lift I need at the given RPM to not be a restriction. Then when I knew what lobe and rocker combination I was going to use, I would look at the actual valve relief needed. Once you know the relief requirements you can start to play with compression height, rod length, piston to deck, and gasket thickness.

 

Sorry, I guess I forgot to mention that it's a tall deck block..... Compression height is 1.520 with the 6.535 rods..

The only thing really set in stone in my build so far is the block.. I'm definitely open to suggestions. That's why I'm here.

The main reason I was thinking of the dished pistons over the flat tops is the latter puts it at 9.4:1 compression with 121 cc chambers.
I thought that was a bit high to run much boost at all ?

My drive will have to be upgraded. Without breaking the bank I can get one built that will handle +-1000hp @ 6000 rpm which is what I'm looking for out of this build..


Again.. Thanks !!

Doug

 

https://www.theturboforums.com/threads/365507-Big-block-ford-turbo

guy using gt45's on a 460 also a video of a chevyII using 45's on a bbc,, maybe something to look at

 

I've found a LOT of builds using the same "Chinese" turbo as that Chevy II. Seem to work OK. I'm just a bit worried about longevity..

I've been looking all over for a "gt45" map. Do you happen to have one ?

Thanks,

Doug

 

Master power gt45 map prob close to what you are looking at #ad


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I plotted my engine data from 2000 - 6000 rpm.

a bit small ??

Do you have anything in a Magnum turbo that would work ?

Thanks,

Doug

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in my opinion that looks pretty good ,, ill pm you some numbers

 

Okay.. Being a turbo newbie let me make sure I understand the Map properly...
On the Masterpower one above.....

RPM Efficiency
3000 70%
4000 74%
5000 74% ?
6000 72%


...and a Borg Warner turbo I've been looking at....

RPM Efficiency
3000 73%
4000 76%
5000 78%
6000 78%

Is the BW too big ?

Again THANK YOU !!

Doug #ad


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