blow through turbos questions

[evilzee28]

Sorry if these questions have been asked before, but I'm contemplating fitting turbos to my 350 sbc. I read an article in a Pontiac magazine called "Turbos for tightwads" regarding making a home built blow through turbo system & it seemed relatively straightforward. Before starting this though I thought I'd better ask you guys as to the viability of what I want to do. The engine will be fully rebuilt using premium parts. It currently has worked 2.02 iron heads fuellie heads.

Is it best to run twin turbos or a single?
What compression/pistons should I use?.
What camshaft?
what intake would you recommend?
What carb size?
Which turbos (I've been told that T3's or T4's would work best)?
Would it need an intercooler?
What is the difference between a wastegate as opposed to a BOF?.
How do you regulate/change boost pressure?
Anything else I'd need to know?

I have full machine shop facilities so any fabrication work is possible.

The car weighs 3200lbs, manual trans & is street driven. I'm not looking for crazy hp, somewhere in the 500-600hp.Please don't advise to just fit nitrous, any other help is greatly appreciated, thanks

[Martin71RS]

Hi, best is to go to http://www.turbomustangs.com (not just stangs there) and do some reading there.... you will find all the info you need and more.

Martin

[shmoov69]

Also go to www.toohighpsi.com and check out some of his pages. Espically the budget tt 302 setup. There is a couple books you need to read also, Maximum Boost by Corkey Bell and Turbocharging by Hugh Maccines (sp?).

[evilzee28]

Thanks for the info guys, plenty to read there. I was hoping someone here could answer my questions though. Has anyone built anything similar to my intended plans?? All help appreciated, thanks.

[shmoov69]

Thanks for the info guys, plenty to read there. I was hoping someone here could answer my questions though. Has anyone built anything similar to my intended plans?? All help appreciated, thanks.

Only on my car right now! Quick answers now though.

Is it best to run twin turbos or a single? Preference and packaging
What compression/pistons should I use?. 9:1 or less
What camshaft? Get a turbo grind from Comp or whoever you like
what intake would you recommend? Single plane
What carb size? 650ish DP
Which turbos (I've been told that T3's or T4's would work best)? What can you come up with, there are WAAAY too many variables between "T3 & T4"
Would it need an intercooler? Need? No. Better? Yes.
What is the difference between a wastegate as opposed to a BOF?. Two totaly different things. Wastegate regulates boost and a BOV dumps excess boost when the throttle closes to keep the turbo's from wanting to surge, or go backwards so to speak.
How do you regulate/change boost pressure? Many different ways from vacum fittings to computer controllers.
Now go out and do some reading!
Anything else I'd need to know?

[ProStreet R/T]

Great advice on the books and TM forum, spend a lot of time there reading and you can learn quite a bit.

Few things that will help decide how you build this thing.

What RPM range do you want to keep it in? Judging by the heads i'm thinking it will be around a 6500rpm max.

Do you plan to crank the boost up and run on race gas, or will this be a 100% street car?

How adequate is the fuel system in your car?

What ignition system are you using? Just a basic distributor, or a nice adjustable electronic setup (msd digital 6-7 etc)?

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Single vs Twins. Entirely up to you, your packaging requirements etc. The whole twins spool faster debate is moot. If you like symetry, go twins, but a bigger single is easier to plumb.

I would keep it around 8.5:1 static compression max. This will keep it from feeling lazy when off boost, and safe on pump gas. Seeing that you are using iron heads I may even drop it to 8:1.

Cam. I'd like to look at your head flow numbers, but off the top of my head. 224/224 @ .050, 114 lsa Base lift on what the heads will take. Turbo motors don't need a ton of cam to spin decent rpm.

Intake: Pick a nice single plane and go with it. W/E you can find a decent price on. Isn't going to make a huge difference either way at this power level.

Carb size: You'll have to do some research on whats available for blow-thru's. I'm by no means a carb expert (efi all the way ) but 650 is a good starting point.

For a daily driver I would absolutely run an air:air intercooler. It's not a huge added cost, and will reap great rewards. While I don't recommend it, quite a few people have modified stock diesel pickup truck intercoolers. You can find some decent cores on ebay, if you're handy with a tig making the end tanks isn't a big deal.

Wastegate is a valve that controls the amount of exhaust gas spinning the turbine, which is used in part to adjust your boost level.
A Blow Off Valve is on the cold side, and used to relieve pressure when you close the throttle to prevent a pressure surge. BOTH are required.

You can regulate boost many ways. Via waste gate springs, a manual boost controller (which adjusts wastegate pressures) or an electronic boost controller.

Now for the big one, which turbo. There are many questions you need to ask yourself here. How responsive do you want it to be? And be truthful. Lots of people whine and cry about "lag" but if done properly a slightly laggy setup is fantastic on a street car. On our viper we purposely built it so the boost wouldn't come on hard till about 3600rpm. Granted it's a much more extreme setup, but the principles are the same. Around town, through traffic, even driving in the rain, the car feels as smooth as it did stock. My point is, for a street car lean on the larger side for the turbos and it will make the car much more drivable, plus with the power coming in smoother it will lay the power down much better on street tires.

That being said with some rough calculations, i'd start my search with a pair of Garrett T04B-62-1, or any others of similar size/trim etc. This size was chosen figuring you'll be running about 12psi, but will have the ability to turn it up to low 20's should you want to.
If you want to check out various parts, turbos, etc. www.forcedinductions.com is a pretty killer site.


If you have any other questions don't hesitate to ask.




Has anyone else noticed that many turbo companies no longer publish compressor maps? Sure does make it a royal pain the ass if you're trying to compare them.

[evilzee28]

Excellent advice guys, that's set me on the right tracks to start with, as you say, best to read up on a whole load of stuff now, but at least I know which direction to look

What RPM range do you want to keep it in? Judging by the heads i'm thinking it will be around a 6500rpm max.

Yes i don't want to take it beyond 6500rpm for obvious reasons.

Do you plan to crank the boost up and run on race gas, or will this be a 100% street car?

It'll be a street legal car (yet another '69 Camaro), but I intend to run it at sprints/ circuit racing, so keeping boost up is important whilst shifting gear. I was thinking to have it spool up at 3000 rpm, which will allow it to run under that for ordinary road use. 3000rpm =70mph in top gear, & for it to kick in from that point onwards??It'll have to run solely on pump gas.

How adequate is the fuel system in your car?

Hasn't got a fuel system yet as car is still being built, any advice would be appreciated

What ignition system are you using? Just a basic distributor, or a nice adjustable electronic setup (msd digital 6-7 etc)?

I was thinking MSD 6?

I know it's a dumn question, but at 12psi,what sort of power would this thing be putting out?? ok I know it's like how long is a piece of string, just curious. If the boost was high teens low twenties what sort of increase over 12psi. Is there some mathematical equation that tells by how much the increase will be percentage wise per psi increase??

Thanks again, time to read some more I think.

[evilzee28]

I've been doing some reasearch regarding this & I've read somewhere that the turbos from a Volvo 740/Saab/Lotus will work well. Trouble is I've lost the page on the 'net that I found with a listing of compatable turbos on. Does anyone know if Volvos/saabs/Lotus use T3/T4's as there are a few Volvos/Saabs in a wrecking yard fairly local to me? Sorry for the dumb questions, thanks.

[TurboLark]

I've been doing some reasearch regarding this & I've read somewhere that the turbos from a Volvo 740/Saab/Lotus will work well. Trouble is I've lost the page on the 'net that I found with a listing of compatable turbos on. Does anyone know if Volvos/saabs/Lotus use T3/T4's as there are a few Volvos/Saabs in a wrecking yard fairly local to me? Sorry for the dumb questions, thanks.

t3/t4's are a hybrid concocted by the aftermarket. turbos that came on cars will be either t3 or t4. you can buy inexpensive t3/t4's off of ebay, but just keep in mind that they are NOT the highest quality, but rebuilding them every couple years is easy.
It sounds like you want to do this on-the-cheap, so you may want to look for a pair of t3 turbos from turbo t-birds or SVO mustangs. easy to find and get parts for.

[nitrorocket]

I would use a pair of 60-1 hi-fi turbos. I am making 25 psi per # of boost. Probably more now with the new turbos I just ordered! You can do the same with some really good heads.