Twin Turbo Second Gen - Official Project Thread

[Insomnya3AM]

81Daytona - That's some amazing information there! Everything you say parallels the book I am reading, "Maximum Boost" by Corky Bell.

A bigger motor will have a much lower boost threshold, and that is very desirable for the street. I definetly plan on going with a 400 Chevy.

I haven't decided in stone yet to go with a twins or a single turbo, but building my own custom fuel injection is a top priority. Not only is this a car for personal enjoyment, this will be a competition car and it will be a demonstration vehicle for the types of things my shop can accomplish.

We should meet up some time and talk boost.

(BTW- Your post has decided my ongoing discussion between building that 95 T/A and building my 78/72 Camaro.)

[MattODoom]

A couple of thoughts:

2. One big turbo can be better than two small ones - Don't get caught up in the twin turbo bling. Yeah, it looks cool, but depending on how you set your application up, you may not be gaining much other that weight and heat. Smaller motor, contemplate twins. Bigger motor, may not be necessary. There's a potential cost savings here as well.

Right on. Get one big turbo. Likely less cost... less money in rebuilds... less demand on the oil pump... and you dont have to worry about one turbo being worn and the other not.

4. RPMs are not critical for larger motors - Small motors need to spin more (i.e. 2.0L vs. 5.7L) to make up for displacement. If you stick with the V8, I'd doubt you need to turn more than 5000-5500 rpms to make max power. Estimate a 6000 rpm redline max (with a 400sb) and match your cam lobe overlap to match that. Anything much more than that and you're out of your powerband and gasping for air (several factors appy, of course).

This is really just kind of irrelevant. RPMs are critical for any motor, not just small motors. Horsepower is derived from torque times 5252 divided by RPM. Simply saying that a motor doesnt need to rev high because it makes the same power as a small motor at a high rpm really doesnt matter much. The higher you can turn your motor without a significant loss of TQ the more horsepower your going to have. Also, setting an arbitrary redline of 6k for your 400sbc is nonsense. Your redline can be built to whatever you want it to be, it all depends on the parts you build it out of.

5. Computers/intercoolers not necessarily required - You can run carbeurated motors with single or twin turbos without computers or intercoolers. The system is based solely on pressure. Not as tunable as a computerized system, but then again, once you get it set, how many times are you going to tweak it? Just a cost save option.

Computers offer such a vast advantage over a carb, *especially* for boost applications. When you're dealing with all this air it is extremely important your mixture be right on or you are going to run into problems and melt pistons, etc. Even a good tuned carb cannot hope to compensate for things, a fuel injected system is far more forgiving and able to correct for conditions, as well as being more efficient and better running. As far as intercoolers... consider it a must for anything past like 5psi. Past that the air charge will be too hot and you will get detonation and burn up your pistons... see a trend? Might even want to consider water injection onboard for when you race so you can run a couple more PSI.

My $.02.

Good discussion BTW....

I am planning on doing a LSx turbo in my GTA so im pretty interested in this thread.

[81DaytonaPaceCar]

Right on. Get one big turbo. Likely less cost... less money in rebuilds... less demand on the oil pump... and you dont have to worry about one turbo being worn and the other not.



This is really just kind of irrelevant. RPMs are critical for any motor, not just small motors. Horsepower is derived from torque times 5252 divided by RPM. Simply saying that a motor doesnt need to rev high because it makes the same power as a small motor at a high rpm really doesnt matter much. The higher you can turn your motor without a significant loss of TQ the more horsepower your going to have. Also, setting an arbitrary redline of 6k for your 400sbc is nonsense. Your redline can be built to whatever you want it to be, it all depends on the parts you build it out of.



Computers offer such a vast advantage over a carb, *especially* for boost applications. When you're dealing with all this air it is extremely important your mixture be right on or you are going to run into problems and melt pistons, etc. Even a good tuned carb cannot hope to compensate for things, a fuel injected system is far more forgiving and able to correct for conditions, as well as being more efficient and better running.

My $.02.

Good discussion BTW....

I am planning on doing a LSx turbo in my GTA so im pretty interested in this thread.

I need to slightly disagree with you about RPMs and redlines. While the numbers I used were arbitrary, they are likely where this particular project will work out at keeping in mind that part of the requirement is that it's streetable.

Is it possible to build a 455 to run 8000 RPMs? Sure it is.

Is it practical for this application? Probably not.

It's not how many RPMs you turn, it's where and how your HP and Torque readings peak, and managing the system to keep you within those boundaries. Keeping in mind that this motor will be street driven, and will (most likely...depending on parts) hit it's torque peak at 2500-3000 RPMs, and HP to peak at 5000-5500, what is the advantage to run 8000 RPMs? Not only are you out of your primary powerband, when you shift into your next gear, you are STILL out of your powerband. That defeats the purpose both of having big torque and a turbo.

As for the computer, yeah, I'm with you there 100%. I was just throwing out the option of no computer to save money. You could get the car running and add the fuel injection and computer at a later time if wanted.

For your GTA, have you checked out the STS turbo (replaces a portion of your exhaust at the rear of the car)? Very slick with big power. Plumbing is a bit of a nightmare, but people who have 'em love 'em.

[MattODoom]

It's not how many RPMs you turn, it's where and how your HP and Torque readings peak, and managing the system to keep you within those boundaries. Keeping in mind that this motor will be street driven, and will (most likely...depending on parts) hit it's torque peak at 2500-3000 RPMs, and HP to peak at 5000-5500, what is the advantage to run 8000 RPMs? Not only are you out of your primary powerband, when you shift into your next gear, you are STILL out of your powerband. That defeats the purpose both of having big torque and a turbo.

While this is true, your HP peaks is derived from your RPM and torque. There is just plain and simply too many variables. You could have a turbo that spools up at a lower RPM and fades higher up, or on the other hand you could have one that doesnt spool up until late, and in that case your torque peak is going to be higher then 2500-3000 RPM. The advantage to running 8000 RPMs is that with a properly flowing intake you are able to make much more horsepower. Say with your redline of 6000 that you are making 350lb-ft of tq at 6,000RPM. That means that you are making 399 horsepower at that same instant. Now if your able to build a motor with a larger CC intake port and a turbo that doesnt spool until higher up so that way only minimal torque is lost.. say your making 300lb-ft at 8,000 RPM, you are now making 456 horsepower. If your curve was flat from 6,000 to 8,000 and you were still making 350lb-ft you would now have 533 horsepower! So you can easily see how much RPM can help to in essence "multiply" your horsepower.

here is an excellent read:
http://vettenet.org/torquehp.html

It talks about the advantage of not just making more torque, but making more torque longer.

I think you'll find some of the stuff in there very interesting.

EDIT: I would think getting a 400sbc past 6k RPMs shouldnt be too hard. A stock LS1 will do that. Granted it will start to float right around there, but.... its not hard to hit 6,500.

My dads old 426 hemi used to shift out at 7,800 RPM.

DOUBLE EDIT: I'd like to clarify the fact that im not saying the higher you rev your motor the more HP you make. *NO*. Im emphasizing the importance of making a motor that is capable of breathing at high RPMs.

[wezeles]

if your going to go 400sb i would also say go with the 5.7 rods and the shorter pistons... the setup of the 400 does have the stroke but they just toss the shorter rods on it with the regular 350 pistons which kills it off the shelf for its capabilities.. but the advantage to the 400 is almost all your performace parts will be the same as a standard small block and i know there are more than a few threads of single and twin turbo sbc kits on here that are decent price i was looking at bbsdesign for the kits they make and the price its not to bad there twin turbo 305-383 kit is less than 5 grand and its everything you need minus the intercooler i believe but they have had 350's dyno in at 1200hp with a forged assembly, for how much your going to need to toss into parts to even handle the boost your already going to be able to rev to 7,000 rpm atleast for a basic forged assembly might as well use it, the thing that will make it streetable is the turbos kicking in at the higher rpm you dont always need to reach on the street

[MattODoom]

if your going to go 400sb i would also say go with the 5.7 rods and the shorter pistons... the setup of the 400 does have the stroke but they just toss the shorter rods on it with the regular 350 pistons which kills it off the shelf for its capabilities.. but the advantage to the 400 is almost all your performace parts will be the same as a standard small block and i know there are more than a few threads of single and twin turbo sbc kits on here that are decent price i was looking at bbsdesign for the kits they make and the price its not to bad there twin turbo 305-383 kit is less than 5 grand and its everything you need minus the intercooler i believe but they have had 350's dyno in at 1200hp with a forged assembly, for how much your going to need to toss into parts to even handle the boost your already going to be able to rev to 7,000 rpm atleast for a basic forged assembly might as well use it, the thing that will make it streetable is the turbos kicking in at the higher rpm you dont always need to reach on the street

Yeah.... keeping the boost out of daily driver RPMs is where youll score your mileage, even then it wont be exceptional as you will have a large cam that wont be too efficient at low RPM.

And yeah, by the time you have a forged bottom end for boost all thats holding you back from 6,000+ RPM is a nice valvetrain. A forged bottom end with ARP rod bolts and maybe a main girdle if you're paranoid will easily do 7,000.

[MrMojoRisin681]

I've not seen a 2nd gen twin turbo TA run a 301 (with good reason...things go ka-Boom).
Banks build a very small handful of twins, but they were based off the 350 cu in motors. Macho also built a couple of single turbos, but those were using 400-455 Pontiacs.

I was refering to people adding another turbo to their car. DKM used the Pontiac 400 in the Machos until 1980, when they used the 301 Turbo. Which wasn't that much better than a stock TA (if at all). So they didn't sell very many.

[81DaytonaPaceCar]

While this is true, your HP peaks is derived from your RPM and torque. There is just plain and simply too many variables. You could have a turbo that spools up at a lower RPM and fades higher up, or on the other hand you could have one that doesnt spool up until late, and in that case your torque peak is going to be higher then 2500-3000 RPM. The advantage to running 8000 RPMs is that with a properly flowing intake you are able to make much more horsepower. Say with your redline of 6000 that you are making 350lb-ft of tq at 6,000RPM. That means that you are making 399 horsepower at that same instant. Now if your able to build a motor with a larger CC intake port and a turbo that doesnt spool until higher up so that way only minimal torque is lost.. say your making 300lb-ft at 8,000 RPM, you are now making 456 horsepower. If your curve was flat from 6,000 to 8,000 and you were still making 350lb-ft you would now have 533 horsepower! So you can easily see how much RPM can help to in essence "multiply" your horsepower.

here is an excellent read:
http://vettenet.org/torquehp.html

It talks about the advantage of not just making more torque, but making more torque longer.

I think you'll find some of the stuff in there very interesting.

EDIT: I would think getting a 400sbc past 6k RPMs shouldnt be too hard. A stock LS1 will do that. Granted it will start to float right around there, but.... its not hard to hit 6,500.

My dads old 426 hemi used to shift out at 7,800 RPM.

DOUBLE EDIT: I'd like to clarify the fact that im not saying the higher you rev your motor the more HP you make. *NO*. Im emphasizing the importance of making a motor that is capable of breathing at high RPMs.

I agree with everything stated above. However, maybe I was approaching it from a slightly different perspective.

An 8000 RPM redline will broaden both the HP and Torque curves, however the trade off for this is the Torque peak will be pulled slightly further up the scale (i.e. instead of peaking at 2600 RPM you will now peak at 2800 RPM).

Big deal? Probably not. Change how engagement points of the turbo, and you're fine.

However, in order to get to an 8000 RPM redline, you will have to open up the cam lobe angle and (if you're smart) go to a optimized, balanced, and lightened rotating assembly to compromise for the extra stress/mass at that RPM level.

Again, big deal? It's just more money.

Except for the lobe angle.

To get to an 8000 RPM redline, (and I am guessing here) you'll have to go to something like a 114-115 deg lobe angle. Again, no big deal, except now you are venturing into more towards a full race type engine set up.

Engine idle will be increased (unless you go the computer route) to, what, 900-1100 RPMs? Again, just adding cost. Can be done.

Head porting? Upgraded valvetrain? Full roller motor? Sure couldn't hurt.

Eight grand is a fairly large number to do with day-in-day-out reliability.

But more importantly, compression ratio will likely rise, possibly significantly, especially if we keep the goal to be "streetable". And compression ratio will fight what you're trying to accomplish with a "streetable" turbo motor. If you're running a 11:1 motor without boost, that number will be significantly higher under boost. Be prepared for all top dollar parts.

Can it be done? Absolutely. Your costs just went up geometrically, that's all.

And be prepared to run 110 octane gas.

Still streetable? Hell yeah (at least for me). But it wouldn't be something that could constitute as a daily driver (again, unless you're committed to computerized fuel injection).

As for your old man's Hemi, well, that's pretty much the holy grail of big block development . Maybe a Chevy ZL-1. Maybe.

But neither one of those big compression motors ever had a turbo strapped to it.

And neither one of 'em ran a computer.

Long story short, it comes down to how much $$$ you have.

Low cost option is probably around $13K. For everything.

High cost option is probably $7K more. At least. And keep counting if you want to get silly.

Again, maybe we're approaching this from different perspectives.

If I build an eight grand motor, dammit, it's gonna see eight grand...regularly.

Anybody can build a motor that "might" see eight grand.

For reference, check out the grenaded 600 hp Ford 302 that was posted today.

[MattODoom]

Whew so much quote work to do!

However, in order to get to an 8000 RPM redline, you will have to open up the cam lobe angle and (if you're smart) go to a optimized, balanced, and lightened rotating assembly to compromise for the extra stress/mass at that RPM level.

In reality though, *any* performance motor should have a balanced lightweight and probably entirely forged rotating assembly, so its not much if any more cost for a boosted app.

To get to an 8000 RPM redline, (and I am guessing here) you'll have to go to something like a 114-115 deg lobe angle. Again, no big deal, except now you are venturing into more towards a full race type engine set up.

Engine idle will be increased (unless you go the computer route) to, what, 900-1100 RPMs? Again, just adding cost. Can be done.

Must be more like 110LSA. My cam is mild and its a 114LSA. EFI doesnt like cams much below 112LSA without a *lot* of tuning.

Head porting? Upgraded valvetrain? Full roller motor? Sure couldn't hurt.

Headporting, again, something that should be done to *any* performance motor. Same with a nice valvetrain, these are not extra expenses incurred by going TURBO. Also, most 87+ motors are roller, at least the FBod blocks. Trucks didnt go roller till like '95 IIRC.

Eight grand is a fairly large number to do with day-in-day-out reliability.

Agree'd

But more importantly, compression ratio will likely rise, possibly significantly, especially if we keep the goal to be "streetable". And compression ratio will fight what you're trying to accomplish with a "streetable" turbo motor. If you're running a 11:1 motor without boost, that number will be significantly higher under boost. Be prepared for all top dollar parts.

Compression ratio should be low... about 8.5:1 for a boosted app... not good to run boost on an 11:1 motor.

Can it be done? Absolutely. Your costs just went up geometrically, that's all.

Probably exponentially. Hah, but you have to pay to play...

And be prepared to run 110 octane gas.

No. I wont do that, not happening. My motor will be built to run 93 octane.

Long story short, it comes down to how much $$$ you have.

As with most things.

Again, maybe we're approaching this from different perspectives.

Not at all. We both want to go insanely fast with the one and only replacement for displacement -- boost!

-Matt

[81DaytonaPaceCar]

There's so many different ways to do it, your options are nearly limitless.

The STS kits really intrigue me. Hard to believe the power they make from a single non-intercooled turbo, and very little (if any) engine work.

I'm waiting to see someone do a twin application to a LS7.

It's in development...

http://forums.corvetteforum.com/show...756&forum_id=3

[Insomnya3AM]

STS kits are great for street machines and other "bolt-on" cars, but it's severly limited as opposed to a purpose-built kit.

[81DaytonaPaceCar]

STS kits are great for street machines and other "bolt-on" cars, but it's severly limited as opposed to a purpose-built kit.

True.

Just offering options.

Bolt-on-and-go has it's advantages too.

[Insomnya3AM]

Bolt-on and go is very nice.
I think those STS kits are best suited for pickups and W-bodies. There's too many solid alternatives for f-bodies to settle with such a kit.

All this turbotech is too much for one day. Thankgod it's midnight

[SS4Matt]

just my $0.02 as i am not a huge fan of the STS kits...but...

81DaytonaPaceCar There's so many different ways to do it, your options are nearly limitless.

The STS kits really intrigue me. Hard to believe the power they make from a single non-intercooled turbo, and very little (if any) engine work.

the reason for the non-intercooler on the STS kits is because "they say" the charge pipe that is about the length of your car! cools down the boosted air on it's way to your intake! i have seen FMIC STS cars though on LS1tech.com

just my thoughts on the situation. i am going with a GMR turbo kit most likely with a log type manifold (log manifolds are kindof restrictive in exhaust flow and are only good for about 550 hp...but that should be enough for me until tubular turbo manifolds!)

[Insomnya3AM]

Yeah, log type manifolds aren't all bad. Tubulars ARE the better manifold, that's regardless, but a log manifold isn't a horrible thing.