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Discussion Starter #1
I need some help if any of yall wanna help me out.

I have a 2000 trans am. It has a built motor: 370ci iron block, forged internals, oringed head and block, 8.5:1 compression

eagle crank: 3.622 stroke
wiseco: 4.030"
lunati rods: 6.125"

I have a new HT60 that I would like to use if it'll work with my setup. I am looking for 800+ whp and spool quickly. which is the attraction to compounding. I was thinking of using a hx35 or 40 as the high pressure turbo.

I have heard of a 2jz which is a 3.0L toyota I6 trying this setup and getting full tq at like 2500 rpm, I wouldn't mind that.

I would like to stay under 25 psi if possible. My generation of motor flow alot of air, therefore dont need alot of boost pressure to make alot of power. i.e. 800hp at 13 psi with like a 78mm turbo.


Thanks for any help, John.

Compound turbo GURUs: Help with a setup on a gas motor
 

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78mm is also freakin huge. sounds like a dyno car and not much else.

not sure how many folks will know, seeing as this is a diesel forum and we're used to 50-60psi out of a twin setup.

but bump for you
 

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Discussion Starter #3
78mm is not that big for my motor, the ht60 is a 74mm which is also on the too small side for my app. alot of people run 88mm turbos on my sized motor. I am novice on the math and all of sizing the turbo. isn't it LowPressure PressureRatio times HP PR is the manifold PR?
 

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likely not going to happen seeing how you are still on 4 bolt heads.

The thing with compound turbo setups is well..... it compounds the boost. Great if your motor can take it.... not so great if your motor can't.... and the factory 4 head bolt LS motors LOVE to push water. you would have to be running both turbos on wastegate and hope your motor holds on. the 2jz guys can get away with stuff like that because their motors love boost. from the factory, the ls motor... not as much.

and correct me if i'm wrong but isn't a holeset hx35 just a factory turbo off of a cummins.... I remember them being fairly small.

Why not just get a pt76 or s480? or if you are going balls out, a pt-8847 or 91mm?
 

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Discussion Starter #6
likely not going to happen seeing how you are still on 4 bolt heads.

The thing with compound turbo setups is well..... it compounds the boost. Great if your motor can take it.... not so great if your motor can't.... and the factory 4 head bolt LS motors LOVE to push water. you would have to be running both turbos on wastegate and hope your motor holds on. the 2jz guys can get away with stuff like that because their motors love boost. from the factory, the ls motor... not as much.

and correct me if i'm wrong but isn't a holeset hx35 just a factory turbo off of a cummins.... I remember them being fairly small.

Why not just get a pt76 or s480? or if you are going balls out, a pt-8847 or 91mm?
With the oring setup and 1/2in ARP head studs, my motor should hold more than a stock setup.

The main reason for doing this is because I can have a tiny turbo which spools instantly and then I get the large flow from the big turbo. the PR multiplication is the aspect that is screwing me over.
 

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I've heard all sorts of things like a 75mm being tiny for a gasser..I'd check an ls forum or something. There are a few gasser guys on here though.
 

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Discussion Starter #8
I am more wanting help with the compressor side of things which is universal. like compound PR's. compound map
 

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I wouldnt base anything on a 2JZ Poopra setup, most switch to a big single and are dyno queens. They catch boost at high end, 1000+ hp and run 11's its kinda embarasing. With a big enough nitrous cam and 10lbs of boost is pleanty enough for 800. My brothers 408 forged iron block in his camaro puts down 550 hp and tq at the wheels N/A. Stuff a little boost in it and I think youll be just fine:thumb
 

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Discussion Starter #10
The main reason for doing this is because I can have a tiny turbo which spools instantly and then I get the large flow from the big turbo. I have 8.5:1 compression, which without a tiny turbo to spool up quick, will be a dog out of boost.
 

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You still have a light LS that revs to the moon quickly, the more effecient the motor N/A the more effective it is with boost. Lots of info out there on forced induction on LS motors. I recomend fuel slut, or LS1 tech, both great forums. Prob any combo you can think of has been used there and gone over in exhausting detail.
 

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^ I can make shy of that with my Holset i already own. theres just the problem of it not spooling til like 4500 rpm
 

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With the oring setup and 1/2in ARP head studs, my motor should hold more than a stock setup.

The main reason for doing this is because I can have a tiny turbo which spools instantly and then I get the large flow from the big turbo. the PR multiplication is the aspect that is screwing me over.
You will be MUCH better off to pyramid the head gaskets, instead of o-ringing the deck/block. It's been proven many times that those $300 head gaskets (or however ridiculously priced they are these days) provide more sealing power than o-ring-ing.

The main reason for doing this is because I can have a tiny turbo which spools instantly and then I get the large flow from the big turbo. I have 8.5:1 compression, which without a tiny turbo to spool up quick, will be a dog out of boost.
^ I can make shy of that with my Holset i already own. theres just the problem of it not spooling til like 4500 rpm
A 76 mm on a lq4 will start spooling @ 3250 rpms and be fully spooled by 4000 rpms.

or have a twin 62 mm setup that will start spooling @ around 3000 rpms and be fully spooled by 3750.

With neither pushing the limits of your head sealing power.

and I am very doubtful you can make damn near 1000 rwhp @ 18 psi with a 74 mm on a 370. You would need a ridiculously efficient motor/intercooling system. and if you have a small 74mm on a lq4 and can't make it spool until 4500, you are doing something very wrong.



or you could just re-invent the wheel and do it anyways.
 

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Discussion Starter #15
You will be MUCH better off to pyramid the head gaskets, instead of o-ringing the deck/block. It's been proven many times that those $300 head gaskets (or however ridiculously priced they are these days) provide more sealing power than o-ring-ing.





A 76 mm on a lq4 will start spooling @ 3250 rpms and be fully spooled by 4000 rpms.

or have a twin 62 mm setup that will start spooling @ around 3000 rpms and be fully spooled by 3750.

With neither pushing the limits of your head sealing power.

and I am very doubtful you can make damn near 1000 rwhp @ 18 psi with a 74 mm on a 370. You would need a ridiculously efficient motor/intercooling system. and if you have a small 74mm on a lq4 and can't make it spool until 4500, you are doing something very wrong.



or you could just re-invent the wheel and do it anyways.

My motor is 8.5:1 compression which would lead to longer spool times. If I go with just the ht60 I would be pushing more than 18 psi. more like 25
 

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nevermind.....

I'll let the kid learn on his own.
 
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