[SSandman]

Pretty close to pulling the trigger on this turbo build after some heavy consideration to ditch the procharger (long story, nothing against the Procharger...I actually plan to use the head unit on another project in a few years).

I'm running into some obstacles being that I am A) new to turbos and B) up till now I was building the car for the blower, but overall I don't think I am running into anything major.



What I've got:
396 cid LT1, Eagle 4340 forged crank, Eagle forged H beam rods, SRP forged pistons. 9:1 C/R
Advanced Induction 200cc heads/ported manifold
LTCC
Dual feed fuel rail
Aeromotive Phantom 450lph Flex fuel system (will be running gasoline)
Siemens Deka 60# injectors (think I'm going to have to upgrade to 80# to be safe, but I have seen guys make around 700rwhp with 60's).
Cahall pro race 4l60e w/ billet output shaft
3.73 rear with eaton post/moser axles and 1350 yoke
Car will sit on 335/35/17's (25.7" tire)
Vigilante 9.5" Converter

Here is what I plan do for the turbos

AGP custom housing Borg Warner S256sx turbos. 56mm, .82 AR with T3 flange /V band outlet
Precision Turbo 46mm wastegates
TIAL 50mm BOV
I'll be building the turbo headers and intercooler piping myself from t304 16 gauge stainless
intercooler- unknown yet as I can't take measurements yet, but I was planning on going with something from a more budget friendly brand with a good reputation like Treadstone


The Goal- 650-700rwhp (whatever my fuel system can deliver safely without having to upgrade to a boost-a-pump...for now at least).

Here are some areas where I am a little questionable as to whether or not the parts I already have will work. I am sure none of these would be huge problems, but hopefully I run some of it as is...

Cam- obviously I'll need AI to spec me out another cam for the turbos. That's not a problem, just hoping that I don't have to swap valve springs as well. I'm assuming seat pressure would be about the same for either cam given the boost?

Converter- my converter was restalled by precision industries for the blower setup. Not sure how the turbos are going to like that. I'm not too concerned with cutting perfect 60 foot times, more interested in it feeling great on the street.

Gears- Obviously I never would have used 3.73's with a 26" tire if I knew I was going turbo. I think I have weight on my side as the car will be pig heavy, so hopefully there will still be enough load to spool the turbos up nice. I am thinking that with such a short first gear, I may not build up boost very well with the 3.73's....but first gear will probably be useless anyway. Second gear in the 60E's have a huge drop off, so perhaps the turbos will feel more at home there and the steep gears won't hurt me too much. The 3.73's should still help with making the feel car more nimble in turns and what not, I just wonder how much it'll hurt me acceleration wise vs going with a longer gear like a 3.23 (not to mention the added benefit of more comfortable highway cruising).

Any input from you turbo guys would be well appreciated! Help me build this up the right way, and if there is anything I missed feel free to add!

 

[The Bolt-On Terror]

Well, I see very little response here for you
I'm totally ignorant on turbos.
But, and you probably already know this, converter selection for a centrifugal blower car is going to be really close to what it would be for an NA application, usually much higher stall than the turbo car would want.
Centri blowers need that rpm at the start to generate boost; turbos don't.
If Vigilante set that converter up on the mild side, then you may be ok; probably more dragstrip friendly than driver friendly though. What kind of info from them do you have on it?

I think you're OK on gearing. At least leave it for a while and see how you like it. Yes, the turbo setup should have no problem with that 1-2 ratio drop! Are you still running a force motor in the 4L60E? If so, you need some serious editing to the line pressure tables based on TPS.

 

[defdaboss]

i have seen some people use the cast manifold/shorty headers on the passenger side that runs underneat the oilpan into the driver drive. the turbo would rest right above the driverside header and you can still keep your a.c. if you build a nice driver side header for single turbo i would be really interested.

for what you already have i think you will be fine. leave the gear and torque converter as is and see how it runs before you switch them out for longer gear or lower stall.

56mm, .82 AR sound about right. i went with a T70 .81 AR. for single rear mount setup.

 

[94SSman]

i have seen some people use the cast manifold/shorty headers on the passenger side that runs underneat the oilpan into the driver drive. the turbo would rest right above the driverside header and you can still keep your a.c. if you build a nice driver side header for single turbo i would be really interested.

The setup you are describing sounds like the old Turbo Technologies kit.

 

[erenaud]

Ok, I'll wade in. Almost everything that was in the setup for a supercharger is completely wrong for turbo engine. A properly setup wastegate turbo will have a nearly flat torque curve, from way down low until it runs out of volume capacity somewhere up top. So you don't need to run the engine fast to make torque, it makes the same everywhere. So while higher gears might give you more tire-torque, they shorten the length of the single gear torque sequence, and you can loose boost and power on the shift. So the upshot is that you want to keep a low stall converter, and the gearing should be such that you can get as much of the 0-60 time on 1st gear as possible. Other than that, decide what you want: top speed, fast 1/4 mile, or quickest 0-60 times. All are different setups. The top speed calls for high airflow, which means a big turbo, but it will suffer poor efficiency at low flows, and may even stall, so a higher TC stall may be needed. For 0-60 you want a smaller turbo, so that you get good full boost with minimum back pressure right off the line, but a small turbo is going to run out of capacity long before the cam does. So decide what you want, put some torque curves together, and play with a desktop simulator to see the effects of size, gear, and TC stall. There is no "right" answer, you will need to design the system for what you want.

For starters, compare to the GN: Single turbo 3.8L, set up for 15psi boost, 2060 stall converter, 2.74:1 1st gear (200R4) and 3.42 rear end, mid 4s 0-60, mid 13's in the 1/4. To get similar results out of an SS (4400 lbs vs. 3600 lbs) you would only need about 12 psi, and a 3.08 rear end, with the 3.059:1 4L60E 1st gear with a similar 2060 converter (like the S-10 converter). If you put in low compression pistons (~9:1 or maybe a little more with the cool heads in the LT1) you can easily go to 15 psi, maybe more on good gas (as long as you intercool). With the larger displacement (5.7L vs. 3.8), you need 1.5 times the flow with similar shift points, so that would be like a TA44 or TA49. That setup would give you an almost 20% higher torque/weight ratio than the GN. I guarantee it would get your attention, yet off the throttle it would be docile as a baby.

Stick with the stock cam and rockers: you really don't want too much overlap with a forced induction system. The stock grind is actually not bad for a turbo. Replace the springs if they are over 100k miles.

Lastly, forget about peak HP. What you are looking for is the maximum area under the torque curve, stall to shift point. Worry about your airflow, then make sure your fuel system is up to the task (may need to upgrade both the injectors and the pump). You WILL need a custom tune, consider a wide-band O2 to aid set-up. And don't forget that your going to be doubling the torque you are putting through the 4l60. Make sure it is up to the task.

Oh, and skip the "blow-off" valve. They aren't really needed, and just makes you sound like a 19y/o rice boy.

 

[SSandman]

Well, I see very little response here for you
I'm totally ignorant on turbos.
But, and you probably already know this, converter selection for a centrifugal blower car is going to be really close to what it would be for an NA application, usually much higher stall than the turbo car would want.
Centri blowers need that rpm at the start to generate boost; turbos don't.
If Vigilante set that converter up on the mild side, then you may be ok; probably more dragstrip friendly than driver friendly though. What kind of info from them do you have on it?

I think you're OK on gearing. At least leave it for a while and see how you like it. Yes, the turbo setup should have no problem with that 1-2 ratio drop! Are you still running a force motor in the 4L60E? If so, you need some serious editing to the line pressure tables based on TPS.

Tell me about it! Where did all the turbo guys go?! I really need to figure out what Precision Industries set my converter up for flash stall wise. They never told me, just took the specs I gave them and restalled it.

erenaud, I appreciate your reply. I totally understand the concept of turbos and load, and also realize much of the stuff I had for the blower isn't IDEAL for the turbo setup, but I am wondering if some of it may be adequate or how much it will really hurt me. My biggest concern is for the gears. I am thinking I will swap them out as much of a pain as that would be...but another part of me is saying to try them out and see. With a 3.06 first gear, 3.73's and a short tire will probably make 1st gear useless and the turbos probably won't see enough load to spool, but maybe that isn't such a bad for trying to hook up. When the big drop off for second hits, the turbos should have a nice long gear to build boost with even with the 3.73's.

As far as the car goes, it's already well past a Grand National. The 396 made over 520fwhp all motor and with the blower setup I was planning to hit in the mid 600's to the wheels. With the turbos, I'm hoping I could squeeze 700rwhp out of it between the efficiency factor and bumping the boost up a little. I am thinking the car should trap in the mid 130's. I'm not looking to build a drag car, but I am thinking optimizing the gears for the 1/4 mile rpm/trap speed wise would be a good idea.

 

[Jeff Green]

First I'm not a turbo guy, so in no way am I going to try to tell you what to do.

Next is my golden rule, unless you have seen that persons car/engine run with the setup you are taking about then do what you want with that information. I'm guessing you too can read a book and relay what it said. If it were that easy then all the shops, car builders and engine builders would be out of business. They are in business because people try to build stuff from a book and it either has issues or it just doesn't seem to make the power it should. Those that are good and just trying to help will always point out they are not the experts on the subject. All my point is listen to those that actual have done it.

What little I know, because I have not done a turbo setup, it is total different than superchargers. So you have to be willing to change most of your parts to get you where you want to be or to be correct for turbos. It's FI but it's totally different the way turbo's work.

For the power you're wanting there are setups you could copy, proven to work. Even if you paid a few hundred dollars for that setup knowledge, it's not just the parts but the clearances and little tricks needed for it to be happy, that get you what your expected. Trial and error is the most expensive way to do things unless you are wanting something no one else has and it does not sound like that's what you are doing.

An LT is really just a SB Chevy for the most part. You can find what you are looking for by seeing what other SB Chevy builders have already done and apply that to your LT.

I know you have been working on your project for some time so hope you get what you want and make it happen!!

 

[SSandman]

First I'm not a turbo guy, so in no way am I going to try to tell you what to do.

Next is my golden rule, unless you have seen that persons car/engine run with the setup you are taking about then do what you want with that information. I'm guessing you too can read a book and relay what it said. If it were that easy then all the shops, car builders and engine builders would be out of business. They are in business because people try to build stuff from a book and it either has issues or it just doesn't seem to make the power it should. Those that are good and just trying to help will always point out they are not the experts on the subject. All my point is listen to those that actual have done it.

What little I know, because I have not done a turbo setup, it is total different than superchargers. So you have to be willing to change most of your parts to get you where you want to be or to be correct for turbos. It's FI but it's totally different the way turbo's work.

For the power you're wanting there are setups you could copy, proven to work. Even if you paid a few hundred dollars for that setup knowledge, it's not just the parts but the clearances and little tricks needed for it to be happy, that get you what your expected. Trial and error is the most expensive way to do things unless you are wanting something no one else has and it does not sound like that's what you are doing.

An LT is really just a SB Chevy for the most part. You can find what you are looking for by seeing what other SB Chevy builders have already done and apply that to your LT.

I know you have been working on your project for some time so hope you get what you want and make it happen!!

Jeff, I appreciate your advice as always! I agree with you 100% in finding out how other setups have actually worked out for others first. Taking that advice, I posted on Yellow Bullet which seems to have one of the highest population of turbo small block guys and I got some interesting feedback on the build.

There are actually many guys running 3.73 gears with 26-8" tires in turbo cars pushing over 3800lbs. Most guys said that the gears worked great for the heavier cars, but a couple of them said that swapping out to a lower gear helped mainly to alleviate traction issues. They reported that the car also felt better and pulled harder when swapping out to a numerically lower gear, but for the most part nobody had anything terrible to say about running the 3.73's. One possible perk of the gears is that it should put less load on the transmission which is probably going to be a weak spot pushing this much power through a 60e. I'm confident that Cahall Transmission built me a great piece, but it's still a 4l60e after all.

I did, however, discover a tire that should fit fine under my car and on my ROH 11.25" wheels that gives me some additional height to effectively drop my gear ratio to the equivalent of a 3.42 with the old 25.7" 335/35/17. The tire is a 27.7" Toyo Proxes 345/40/17. The price is great and the reviews seem to indicate they are good for street driving and hook decent. I'm just having a hard time finding a tire that will be close to matching in height up front but is also wider than a p275 as I want the car to be very well balanced handling wise.

As far as the turbos themselves go, I am forced to rely on LS builds as I haven't found many LT1 twin turbo builds (probably due to LT's being mainly in F bodies where the single turbo is easier to package). I went with those turbos at the recommendation of a vendor who has put together many twin turbo kits for LS motors and tells me that they should be the best option for my budget. Seeing what they do on similar power LS motors, I think they should do the job.

For tuning, Sherlock9c1 gave me a heads up on a newer 24x conversion company called Torqhead. I emailed the owner trying to find out as much as I could about the product, how it worked and whether or not it would be a suitable alternative to say an EFI connection kit. The owner, a B body guy himself, was a great help. With me not using a double roller (I have an LT4 extreme single), I wouldn't need the billet timing cover with the EFI connection kit. Doing the wiring myself then, it comes out to a bit cheaper than the Torqhead kit. The benefit to the Torqhead kit is that it is plug and play with no rewiring required. I think I am leaning towards Torqhead simply it'll be less time consuming for me not having to rewire the harness. I already have hundreds more hours of work cut out for me to finish the car, piling on more doesn't seem like a good idea.

 

[FaSSt9602]

I've got the TH kit coming once his beta testing is done. I was going to be a beta tester, but my project got put on the slow boat for a while, so I wasn't going to get him the feedback he needed.

It is a VERY slick kit.

 

[JetJoe]

Hey Kris, glad to see you going turbo. We definitely need more turbo B-bodies. Here is my well read but unapplied thoughts, so take it for what its worth.

I think your HP goals/estimates are conservative. I say this because I here story after story of how boost is addicting. Projects start out with a 8-10 psi goal end up turning it up, especially with a turbo since it is fairly easy to do. I understand you fuel system concern, which is very smart indeed. However, at no more than 15 lbs of boost, you should be able to make over 1000 fwhp, putting you closer to 800 whp. 80 lb injectors and that fuel pump at 14 volts should get you there.

I said all of that to say that I think you choice of turbos is on the small side for a 396, especially the 64 mm turbine exducer. They are not a bad choice, I just think a 66 mm or 68 mm exducer might be a better choice for a 396. Of course turbo sizing is a give and take proposition. Too big makes it lazy and hard to spool; too small makes boost hard to control and chokes hp at higher RPM. In the end, a slightly bigger turbine is easier to deal with than one that is too small. A good tune and slightly looser converter will help light off a larger turbine. Besides, that 396 will have plenty of bottom end anyway.

You didn't list any specs on your AI cam, but if it is like their usual NA grinds it is probably ground on a fairly tight LSA, which is generally not optimal for a turbo set up. If you had it spec'd for your blower set up, it might be acceptable. A good custom turbo cam will not only take into consideration your basic engine parameters, but also your entire hot side from the exhaust port to the downpipe which is why turbine selection is important. Ideally, back pressure would be measured with a cam that is close and a custom grind developed from that. An engine with a hot side with less back pressure will tolerate and benefit from a cam with more overlap. Besides AI, you might check with Bullet cams as they seem to do a lot of turbo cam work.

Your converter will of course be dependent on all of the above. I would think Precision could give you an idea of how it might work. If not, you may just have to try it and see. A lot of turbo builds use Pro Torque converters. You could check with them and maybe sell your Vigilante if Precision can't give you a good answer.

As far as the gears, I would wait and see how the 3.73 work with the larger tires and how your converter turns out. Since it is not a dedicated drag car, it is the last thing I would change.

Lastly, have you checked out The Turbo Forums? I would post your inquiry in their GM section. There are some smart and experienced turbo guys over there.

Good luck with your build. Be sure to post pics of your hot side construction.

 

[Jeff Green]

I think that's all on track. One thing to consider, any of the LS builds have 11 to 15 degree heads compared to the LT's 23 degree. Because of that whatever turbo size they are using you need to bump your size up to get the same end result. Not a lot but still some and a good turbo guy would know what the turbo size difference would be from a 23 to 15 degree head.

FI is a great equalizer when it comes to cylinder heads but you still would see a difference, just not as much a difference as you would if it was NA.

Jeff, I appreciate your advice as always! I agree with you 100% in finding out how other setups have actually worked out for others first. Taking that advice, I posted on Yellow Bullet which seems to have one of the highest population of turbo small block guys and I got some interesting feedback on the build.

There are actually many guys running 3.73 gears with 26-8" tires in turbo cars pushing over 3800lbs. Most guys said that the gears worked great for the heavier cars, but a couple of them said that swapping out to a lower gear helped mainly to alleviate traction issues. They reported that the car also felt better and pulled harder when swapping out to a numerically lower gear, but for the most part nobody had anything terrible to say about running the 3.73's. One possible perk of the gears is that it should put less load on the transmission which is probably going to be a weak spot pushing this much power through a 60e. I'm confident that Cahall Transmission built me a great piece, but it's still a 4l60e after all.

I did, however, discover a tire that should fit fine under my car and on my ROH 11.25" wheels that gives me some additional height to effectively drop my gear ratio to the equivalent of a 3.42 with the old 25.7" 335/35/17. The tire is a 27.7" Toyo Proxes 345/40/17. The price is great and the reviews seem to indicate they are good for street driving and hook decent. I'm just having a hard time finding a tire that will be close to matching in height up front but is also wider than a p275 as I want the car to be very well balanced handling wise.

As far as the turbos themselves go, I am forced to rely on LS builds as I haven't found many LT1 twin turbo builds (probably due to LT's being mainly in F bodies where the single turbo is easier to package). I went with those turbos at the recommendation of a vendor who has put together many twin turbo kits for LS motors and tells me that they should be the best option for my budget. Seeing what they do on similar power LS motors, I think they should do the job.

For tuning, Sherlock9c1 gave me a heads up on a newer 24x conversion company called Torqhead. I emailed the owner trying to find out as much as I could about the product, how it worked and whether or not it would be a suitable alternative to say an EFI connection kit. The owner, a B body guy himself, was a great help. With me not using a double roller (I have an LT4 extreme single), I wouldn't need the billet timing cover with the EFI connection kit. Doing the wiring myself then, it comes out to a bit cheaper than the Torqhead kit. The benefit to the Torqhead kit is that it is plug and play with no rewiring required. I think I am leaning towards Torqhead simply it'll be less time consuming for me not having to rewire the harness. I already have hundreds more hours of work cut out for me to finish the car, piling on more doesn't seem like a good idea.

 

[Caddylack]

Stick with the stock cam and rockers: you really don't want too much overlap with a forced induction system. The stock grind is actually not bad for a turbo. Replace the springs if they are over 100k miles.

Are there no friction concerns with a stamped steel rocker?

Oh, and skip the "blow-off" valve. They aren't really needed, and just makes you sound like a 19y/o rice boy.

Can you elaborate?

Audi uses diverter valves that recirculate the excess air, and people are generally afraid to "downgrade" to a blow-off valve. What is the alternative?