I have been kicking around the idea of using 2 Grand national turbos for my IROC's 356. I have researched a bit on a few GN forums and such really didnt find much on the stock turbo. What I'm looking for is 2 turbos that push a 86 IROC into the 11's with 450-500HP to the wheels, Street manners are not really an issue. Mainly going to be a strip car, that can be run on the street, also will have a diet of 92+ octane. Motor specs 356ci Vortec iron heads (port matched to Stealth Ram) Vortec Stealth Ram TPiS TQ secrets cam .495/.495 Forged bottom end Let me know some opinions on these turbos and what you think Jason

Interesting. TPIS TQ secrets cam? You need to list the cam specs in order for people to figure out if those turbos will work. Strip car? why not just a big single?

700-135-Small block
Intake Exhaust
Advertised duration 280 280
Duration at .050 224 224
Gross lift .495 .495
Lobe separation 112

And I went with twins cause i thought they would be decent on the street. Thats the only reason...but I open for opinions

Jason

Here is a guy from turbomustangs.com running two GN turbos. Deep 10's at nearly 130mph. Very impressive IMO. Stock TPI intake with 20+ psi of boost!


LINK

FWIW, like jnkcltr stated a sungle will perform just as well or better on the street and track. Twins are cooler though...

Thats a cool link thanks man...I agree that twins are cooler.

I am buying these turbos soon so hopefully this project goes well!

Jason

a pair would be good for an easy 700hp or maybe a little more, and would be very streetable...

thats pretty much what i was looking for crossfire. Your basing those numbers off of the stock turbos right? That is what I bought so I hope so what is the benifit of using stainless over mild steel? I plan on using mild steel w/ 1 3/4 primarys into a 2 1/2(?) collector. I dont remember off hand what the inlet exhaust size is.

Jason

The stock ones on the cold air GN’s are basically a 60/.63 T3’s that have had the compressor housing machined for a larger compressor wheel that is almost identical to an S3 TO4B.

If you look at an S3 compressor map it tops out at around 37lb/min at a PR of 2:1, and almost 40 at 2.5…

2 will flow 2x that so it should get you to 700hp easy (really, if everything is matched up well it should move enough air to get close to 800hp), but real world a pair would be much happier with a combination making 500-600hp (these are crank numbers).

Doesn’t matter because you won’t need nearly that much to run 11’s. Your average, 3600lb f-body should need about 465hp at the crank to go 11.5

Stainless tends to be more durable and does not conduct heat as well, but also expands and contracts at almost 2x the rate of mild steel so depending on construction techniques can be more prone to cracking.

1-3/4” primaries are overkill… I’ve seen cars make 1000hp with all the exhaust flowing through a section that had the same cross section as a single 2.25” pipe. The inlets on those turbos has about the same cross section as a 2.25” pipe. I usually try to keep my primaries in the 1-1/2 – 1-5/8” range on a small block, of course I’m not a big fan of tubular headers on a turbo setup…

Wow interesting info one the turbo and headers. Thank you! So are you saying that you would go for more of a log style? I have a pair of hooker super comp shorties that I considered using for the build but the flanges are to small. I'll look into log headers. From what I have read it also seems that people sway towards tubular headers opposed to log style, whats the benefit?

Jason

Back from the dead what RPM should I expect these to make power to. Can't seem to find a compressor map...But I have since forgotten how to read one.

I am starting the slow ball rolling again with the recent purchase of a 377 chev. was previously a circle track motor

few specs

destroked 400
GMPP forged 350 crank
chrylser 6.125 (IIRC) rods
9.5 2 relief pistons (dont think they are anything special
splayed main caps
water ports blocked off and machined for vortec 350 heads

I am currently looking into 6.00" rods and am unsure on a decent piston. I have heard/ read that a bit higher compression ie 10:1 is good for a street car. But may play it safe and try 9.5:1. also I am ditching all efi and going to a blow through set-up. Also from alot of research it appears that although it is thought the 377 spins like crazy it really doesnt spin up that fast. more just brings the power band up in RPM losing low end torque. Personally the only racing a I do is a sunday once a month out at the track. I dont give dork the time of day on the street so how it preforms on the street I dont care.

Anyone know of a couple combinations that this particular setup may like?

Stainless steel is the best way to go with turbo setups . I used 304 on my setup. it cost more than rust prone mild steel but will save u in the long run.

If u look at all formula one , indy , nascar you`ll notice they all run tubular headers. you know why ,tubular headers holds heat in better.

primary size depends on the heads u are running. i run 1 7/8" on my single turbo with 3" crossover pipe. i think you be ok with 1 3/4" with vortec heads.

go back to EFI..... forget carbs in forced induction applications.

83 CrossFire had alot of good information there...

You will care how well it behaves on the street... larger primary's will slow exhaust gas speed and slow down spool.

Each stock GN turbo flows 550cfm and supports 350hp.
A TA49 (Next step up) flows 800cfm and supports 550hp.

There is a 2-300 rpm diffrence in spool. (Higher) with the TA49.

Anyway... keep your primary's at 1 1/2inch to 1 5/8 max. 1 3/4 only in much larger hp.
Log or tubular isn't going to make much difference. Downpipes should be free flowing and 2.5" Minimum.
Tuning is 95% of any turbo car. Carbs are fine for WOT but suck everywhere else especially on the street. EFI is the key to making a good power depenable car that get's decent MPG.
~Scott

You should look on turbomustangs.com. There is a guy with a third gen trans am that was running GN turbos. The thread was titled "How long till it granades?". It was even in car craft.