Okay, so I was all set to do a 355/single turbo buildup when I kept hearing other suggestions. I am now seeking the advice from those in the know. First of all, my car is a 1978 Corvette with an LT1 and 4L60E. I will be changing my rear ratio to 3.55 or 3.73 before all is said and done. My goal is to build a low 11/high 10 second car and maintain some shred of streetability. Thus the turbo 355 idea. In speacking with the turbo shop, they recommended a single turbo that would put the motor at 685 hp when maxed out. My question is, are there more options out there that will put me in this range while being less costly, or more importantly less hectic? I am still leaning heavily on the turbocharging, but thought I would gather some other opinions.

 

Have you thought of nitrous? It's definitely cheaper & less complex to tune- plus you'd be plenty streetable as long as you didn't hit the magic button.... :cheers:

 

Yeah, I have kinda thought about the nitrous route. The only crappy thing there is that you need to refill the bottle. I kind of like having the power available all the time, but I guess all that power is kind of overkill on the street. How streetable would a moderately built 396 be? Just build a stout motor with a little cheater juice for the track?

Bryan

 

IMHO you could go low 12s high 11s on a streetable NA 396. If you want low 11s /high 10s I think you need to call one of the many supercharger Co. Boost will do the job, then all you need is traction!
Rick

 

LT401 has gotten his LT4/1 into the tens on the motor. If your only goal is to go 10s or 11a, or have 600+hp there are much easier ways.
If your set on a turbo, thats cool too. Hearing the release of a BOV in a vette is certain to get you lots of attention, even from ricer boys. It would deffinately be the coolest route if thats what your after. You seem apt to big projects, so I'd say go for it if you've researched it and are prepared.

A turbo that only supports 685hp is on the small side for a 355. The upside is that it would spool probably at idle and make massive torque. I think you'd be just as good with turbo that could support 800+. I know the Supra guys really like turbos from Sound Performance. They spool at lower rpms and generally make more power than a similar sized garret turbo. I think the SP63 or SP66 would be ideal. Those are larger turbo's for a 3.0L but they would spool very quickly on a 355. You should deffinately consult with Monty as well.

 

In talking with Patrick over at Precision Turbo, he recommended an SC61 turbo with the optional T04S compressor and a .68 A/R tangential v-band style clamp housing. He also recommended a 3" downpipe (even though I could run up to 3.5". I am still researching the project, and the only thing that really scares me is the price of paying someone else to do it. I am a fan of "big projects" and lots of trick designs, but the LT1 has taught me that there are VERY few people that can actually do what you want even though most will take your money and slop something together. This has caused me to consider doing most of the rest of the work on my car myself. The only thing I don't really feel I can do is build the headers, etc. for the turbocharger. Now, having no automotive training or skills per se, I might find that most of the things I want to do to my car will be beyond me, but I think I owe it to myself to at least try. Maybe that is why I am hesitant on the whole turbocharging route. I am also still trying to learn about different combinations on Desktop Dyno, but that is kind of hard when everything looks like it was written in Greek, lol! Anyway, thanks for the advice!

 

What's an LT1's compression ratio? Around 9.5:1 on aluminum heads? With that, you can run a small amount of boost. Maybe 4 psi on pump gas, 6 psi with an intercooler. But because you have a SBC, I believe there are head gasket options from Felpro. You may be able to drop it down to maybe 9 or 9.1:1. Another idea is to have the heads worked for the improved flow, and while you're at it, have the combustion chambers cleaned up, unshrouded and enlarged, and see if you can get compression down to 8.5:1 or lower. Then you can run some better boost. At least 10 or 12 pounds.

What about the pistons? Are they forged? If not, keep your boost on the conservative side.

The advantage to such a big turbo is that your car will feel fairly normal in around town driving. You'll have a lot of lag too. I'd guess your turbo wouldn't come on strong until around 4000 rpm. But when it does, it'll hit hard. Very hard. Turbos are totally passive until they sense a load being put on the engine, which is why you wouldn't see significant boost just sitting in the driveway revving.

If you get two smaller turbos, your lag will be a lot less, and your midrange will be a lot stronger. But the single turbo will be similar to a centrifugal supercharger in feel, except with a more exponential power increase.

I agree with you, I like turbos!
:rofl:

 

A 61mm turbo is small for a 355, hell it's a medium size turbo for 3.0L Supra.
I don't necesarily agree with you 100% Bearcat, a centrifugal supercharger builds boost exponentially. A turbo builds boost more linearly, and sooner than a comparable centrifugal supercharger. Futhermore a twin turbo setup that support a certain amount of power should spool at the same time as a single turbo that supports the same amount, everything else being equal. The only way a twin setup would spool sooner is if they turbo's were setup sequentially.

 

Last Ride-Super or turbo charging is probably the best way to achieve your goals.
Dan :chevy