Hey guys, I am toying with the idea of compounds on my truck, but I am worried it will be miserable to drive with the 110hp injectors I am currently running. I plan on going to 150s down the road, but probably no bigger than that as I do tow with the truck and would really like a very clean running truck with power to spare! I think my current charger would make an excellent top turbo, but what would I run on the bottom? Spool up is definently a consideration. Thanks for any ideas or answers!

 

S475 or a 26cm ht3b.

 

My twin combo works no to bad with my smallish sticks. I have more air, less egt's and about the same spool-up as when I used a single GT3782R.

 

A k-31 has a tighter turbine housing and will have the same size compressor inducer at the S-475 or BTH-3B. The 3b, spins in the opposite direction, so its abit more work for the air tubes. How much power you thinking about building? If you're plans is to max out with the 150's, you could put on a smaller primary. I'm building a new twin set-up. GT3582R over S366, with a large external gate to get that S366 to lite up. Should spool like a rocket.

 

does it rum hot now? i run 150's and a drag comp with a 62-71-14 and mine is as clean as you can get with the box off and will clean it all up with it on whan the turbo lights. i can tow anything and it never gets over 1,000 deg.

 

I daily drive my 150hp injectors and it's not miserable to drive at all (note: these are F1 injectors in a truck with a manual trans and the stock HX35).

If you want good towing response, I'd highly recommend the stock turbo as your top turbo in a compound setup.

You'll want to think about where you want the engine to perform best. Sure, you can you gain a lot of major low-rpm grunt with a lot of fuel and a small turbo-- say, even smaller than stock. But is this even a good thing?

Not really. I personally would not want to have my truck's cylinder pressure go crazy high at low rpm. At low rpm, your coolant and oil circulation is low and the engine's ability to move heat out is more limited. Instead, I'd rather have a setup that pulled strong enough on bottom, but could really put on the power with controlled EGT in a band from 2100-2700rpm. This is the peak power (not torque) range of the engine's mechanical design.

So I'd recommend that you shoot for a "stock like" power curve, just bigger. You can realistically build a CTD to meet a power demand of up to 375hp when towing. Now it might be a 500 hp engine, but you won't be able to use more than 375-400hp of that for towing. Which is fine-- that is a LOT of power for towing anything a pickup truck would be mated to. Heck, there are 15L ISX ratings of 425hp going in trucks rated to 80K!

Note: 900 lb-ft carried up the the stock "Rated" rpm of 2700rpm is well over 450hp!


So I'd use a large(ish) big turbo to minimize restriction in the system, as you really only need the big turbo to be engaged over 2000 rpm. A larger big turbo will help initial spool up (because there's less restriction for the small turbo's exhaust [think potato in the tailpipe])

So I would choose the stock unit for a top turbo (or another unit in the same size range, up or down a little). The bottom turbo would benefit from being the smallest cold side that will do the job, mated to the largest hot side (large housing, etc) that still will operate. This keeps drive pressure low and helps keep EGT under control.

Justin

 

I took mine new twins out for rip yesterday. With little sticks, I got to 50psi and maxed out my egt at 1050 deg's. The spool-up is abit slower than the single GT3782R that I drove last week.

Hohn, the external gate is the secert to limiting the drive pressure. I'm building a new set of twins that will spool-up faster than anything that I've drove as of yet. There are a few more secerts to faster spooling twins.

 

Agreed. That external gate takes a lot of restriction out of the system and when it pops it will hit the big charger and get it rolling.

My latest "vaporware" twins idea involves using a garrett GT3076 on top of a S366 or 372. Heck, a Silver Bullet would probably make a great primary, it's just not the best fit, imo.

 

Another good primary is the HX-55 with VGT. Which housings would you use for both turbos? The compressor size on the GT3076 is decent sized, but the turbine disk and housing is on the small size, I hate to see the rpm of that turbo at idle. A 42mm gate would be a hot ticket. Hohn, you got to build a set one day and see. Its isn't that difficult. This latest set of mine have a hand built exhaust manifold. We are adjusting the diameter of the tubes in the exhaust to maximize exhaust velocity. Even with these big turbos, spool-up is as good as stock HX-35.

 

Hey Mike, you think the S475 would work well for me? The reason I am thinking of going to twins is because I have an auto and I am finding it very difficult to find a happy medium on EGT and smoke control while towing. It seems that the EGTs climb faster than the turbo can cool them, which makes me have to drop out of overdrive and rev the crap out of it to bring temps down. I just feel that if I had more air, towing and driving in general would be much more pleasureable! Thanks for all the help!

 

A S475 is a good choice. My max egt's is around 1100 deg's F at wot and 50psi of boost. K-31 is another good choice, as it has a tighter turbine housing.
Are you planning on putting in larger sticks down the road? You might want to have an external gate available, just incase. I don't know how well that a S300 turbo internal gate is designed. I've modified mine, so I can increase the flow thru the wastegate and that you can put a decent load onto the S475.

110's are abit small for S475, so there is room for larger sticks. I'm gonna hook-up my fiver this weekend.

 

K-31 has a 71mm inducer and a 1.25 housing. 475 has a 75mm inducer and can have .9, 1.10, 1.32, 1.51 ex. housings right out of the box. 3B is the easiest to fit in an auto truck and easiest to make cold pipe for. (no flange)

PS- you wont like the 366 as a primary, it is too small and will heat the air too much in the first stage.
Try a 3582R w/.82 housing over a 4202R w/1.15 housing for a fast/powerful set.

 

Dodge 24- what gears are you running w/the 35s? Also be sure the "pucks" in the wastegate are still seating as HTT has had issues with the SS housings and has an upgrade for the Wgate arms to keep them from bending.

 

There is different set-up on the k-31. The one that I looked at was 74mm and a/r of 1.15, just go thru the borgwarner catalog. They do offer different configurations for different trucks/engines.

As for primary, its all depends on how much fuel that you have. For a 500rwhp truck, you really don't need a 74mm inducer primary, but that depends on yourself. Right now, it would be difficult to break over 1100 deg's F on this set of twins. With the S475 with an A/R of 1.32, its takes awhile to lite up, but once it does, its a fun ride.

 

Thanks Mike. Do you know the part # on that K-31 off hand?
FWIW, I had a 475/1.32 primary last year and a 480/1.10 this year and the 480 lites FASTER/stronger but runs warmer down low.