I'm thinking about doing a turbo project, but not sure how to go in terms of turbos. I have a 400 SBC, so would it be better to go with one big turbo vs. 2 smaller turbos? Would they equal out in terms of air flow? I always hear about people using turbos from diesel trucks on bigger engines. Are there any advantages from running 2 vs. 1 turbo? also, would a turbo from an '87 Grand Am be too small and are they the same turbo found on a sunbird GT Turbo? I might be able to get a deal on them, but if they aren't a good selection I wont even bother.

 

You are going to get all kinds of opinions on this subject. It all depends on your available time, money, and experience. From a cost & labor point of view, go with one turbo. From a "it sounds cool" point of view then go twin turbo. For some reason people are more impressed with two turbos on an engine than one turbo on an engine. To me, anything is better than nothing.

Check out Welcome to Turbo Mustangs.com for diesel turbo info. It was the best I could find and I found more than I wanted over there. You can use one on a gas engine. In terms of airflow, you need to learn how to read a compressor map before you look for any turbo(s). With a 400 SBC I wouldn't even consider any 4 or 6 cyl gas engine turbos. Well, maybe the GN turbos as twins are worth a look. Personally, I would buy Master Power, Garretts, or diesel turbo(s) for a 400 SBC.

Not sure if this helps, but I have a 400 SBC sitting (for about 6 years now) that I plan to install a turbo on sometime in the next two years. That may be just a dream to have it running in two years. Since I hate spending any money on aftermarket over-priced speed parts, I chose a detroit diesel 8V92 turbo for it. It is made by Garrett. I got it for a little over $300 brand new. I have seem new ones usually go for $400 and up. It is good good for up to 1000 FWHP or so (just a guess, don't quote me on that). It will spool slow as heck (heavy wheels in it and big turbine). It will probably start to spool at 4000 RPM or higher.
That is just a bit of info. I hope it gets you a little curious and start looking/searching about turbo info for your SBC. I am a relative newbie to turbo stuff so don't take my opinion as anything set in stone.

Twin turbos sound cool, look cool under the hood, cost more, take longer to fab stuff for, fit in smaller spaces. I have two twin turbo setups in the works so I am speaking from experience.

Single turbos can make just as much HP as twins. Cost less, require less fab time, and cheaper to maintain (one rebuild kit instead of two). One possible leak instead of two. They require more leaning on your part if you go the diesel junkyard route.

Oh yeah, what RPM range are you looking for more power in? How fast or how much HP do you want? Both this and money is what will define how many turbos you use and what size they are.

 

cool. thanks for the info. I read an article a while back in I think high performance pontiac where a guy did a build up of a '79 TA with a 455 pontiac. He put in a turbo from a cummins turbo diesel and basically fabbed up all the piping himself. Everything he did, or got from the junkyard. It's a blow-through carb setup but he was getting upwards of 575 hp and 600 ft-lbs torque. I looked up on transamcountry.com since he is a board member there and have been reading up on the setup and blow-through setups in general. I've also been looking on turbomustangs.com. They seem to have a lot of blow-through info.

Basically I'm wanting to do something similar. In the article it says he is running 7 lbs of boost and can make more than 5lbs instantaneously even off idle. He is running a water/alcohol injection system to spray the mixture into the turbo outlet duct. It's non intercooled, but he did try one and decided it was too restrictive. At this state he says he's running high 11's low 12's. All in all the cost he put into it was less than $900. Not bad for a DIY and it doesn't really seem that hard to fab up the piping. It's just getting all the parts. He's also running a 9:1 compression ratio. I thought that was kind of high. I've always thought turbo engines have a lower compression. Isn't the rule the higher compression the lower the boost??

Anyway, this article was my inspiration to do something similar, I'm not looking to squeeze every bit of horse power out of this setup. Even in the article the guy said his setup was not fully tuned, and didn't really care for it to be. As far as what I would like, something at least in the 400 hp range. I'd like to keep a lot of low end torque if possible...not looking to get a high revving engine. If this guy can get 5lbs of boost of idle I don't think lag is much of a problem. I'd like to keep the lag as minimal as possible also. Basically though, this is this what I'm looking at as my base for this project.

 

I came across that article early last year on the web when I was researching turbo info. I seem to remember him using a Cummins diesel turbo. It looked like a Holset 60-70mm inducer which is undersized for that many cubic inch from a max. HP point of view. I could be wrong, but that is what it looked like in the picture that I saw. Like the article said, he wasn't looking for giant HP numbers and just wanted some more HP. So that turbo was just about perfect for what he was after. Low RPM spooling and some more HP.
The good thing is that you are being realistic about what HP and engine characteristics that you want. A good street setup.
The 400SBC could easily be at 400 FWHP in N/A form. From the sounds of it you want something that is slightly undersized for quick spool and low RPMs.

About the spool off of idle thing. Without have a computer (EFI fuel injection) to log the boost PSI and RPM it is very difficult to see when a turbo truly starts to spool. By the sounds of it, a 455ci with a 60-70mm inducer and small turbine would probably start to spool at 1500 - 2500 rpm. It would do it so fast that you probably couldn't tell where it really did start to spool at unless a video camera was on the tach & boost gauge. EFI is nice because it tells you exactly where the boost comes in and where boost is maxed.

The $900 price tag is plenty possible possible for a single if you do the carb mods yourself. Keep in mind that two of everything (twin turbos) will proabably cost more. I would not intercool it for the HP levels you want. I wouldn't even spray it windshield washer fluid. The spray cools the intake air so that higher boost levels can be used without detonation.

 

On a 400 inch motor You need to have a T6 exhaust side if You want to run a single...which causes packaging problems on the majority of street cars, but works great on track cars. Twin T4 turbos are Your best bet on a street 400...sizes and trims would depend on what You want to do with the car, imo...
A pair of T04B-s p-trim with .58 AR would be awesome on a street car, maybe even too much torque too soon on a 400...but could make around 800hp...twin 60-1s can make around 1200hp (flywheel) and still spool decent...for a street driven car with a hydraulic valvetrain I would stick to the 60-1s...inho...