I've been building a twin turbo 402 and it will be nearing completion soon. It's a 402 with 9:1 comp, ported 317s, 236/236 115 cam, fast 90/90, and twin gt35r's with .82 internal gate housings. This is in a 6 speed with 3.45 rear gears.

Any idea's what this will be like to drive on the street and how much power i can expect to make with anywhere between 12-15lbs boost?

 

750+ to the rear wheels would be my guess..

 

750 and up would be my guess also. as far as drivability,mine drive's like a head's,cam car around town.I love the way it drive's, just be prepared to hang on when you mash the gas!!!

 

what rpms should the turbo's start to spool?

 

I don't have full boost until 3600 or so.It all depend's on your setup and tune.There is alot of variable's that come into play.I would say 3200 or so on your's.It all depend's.

 

GT35R being ball bearing might do a bit better would think you should get full spool 3500 to 4000. I doubt it would be by 3000 those are fair size turbos.
I am hoping my smaller aps modified 20gs can hit full at 3000 on a 408 or 427.
Anyway they are just going to blow off the tires in the first three gears for sure anyway! But it should be fun! Can hardly wait for my kit now.

 

So when do you actually start to see positive pressure in the intake manifold? I'm trying to get a handle on how 'lively' this will feel on the street.

 

Also what effect would changing the compressor housings over to T04E housings like ls1speed use in their twin kit? Apart from being smaller would this also make them more responsive?

 

There are several variables that can affect spool up.flywheel in manual cars, tuning can affect spool up by playing with timing and air fuel. Size of engine. AR of the turbos for sure affects things.Size of the turbo. Ball bearing types tend to spool a bit faster and hold the boost better between shifts in manuals. Autos help get boost off the line with a good stall and stay spooled thru the shifts. Would expect to start seeing boost most times 1000 or so rpm under the full boost rpms.

There may be a disadvantage having them come on real early. Traction is one problem and fuel mileage if you are in boost wouldn't be as good. Also if you have laggy turbos you can downshift it you are in higher gears. Off the line two step launch help or stutterbox as its sometimes called and something called antilag is common at least in the import circles.

 

If i give it say 1/2 throttle and just let the car pull to where I can watch the boost gauge, I can start seeing boost as low as 2500rpm but when I go wot and as soon as it hits 3800or so it is full boost.
As far as how "lively" it will feel,just make sure you are going in a straight line when you hammer it.On my car if I am cruising and then hammer it it feel's ok until 3800rpm or so and then it is like a 300shot of nos!!!