divided vs. undivided turbines.... What size A/R? Also WG size questions!
I'm building another FD RX-7 to do top speed events/1 mile shootouts/drag racing and be a street car. Engine is an iron 6.0 (doweled main caps) for boost with stock crank/forged rods/pistons, as cast TFS 220cc heads, a Virginia Speed 23x/230x cam, and E85 fuel. Tubular headers that meet up in a single T6 style flange. Setup for the wastegate to vent from both sides of the headers and dump back into a 4" dowpipe.
I'm looking at an S80 or T88 sized turbo but the goal is 1000rwhp and will give up power for faster spool. 7000 rpm redline. I plan to run a T56, Textralia twin disc, and Cobra 8.8" IRS diff with 3.08 gears as my driveline.
What is the difference between a divided and undivided housing?
What size exhaust A/R should I run on the turbo? Is .82 too small or is a 1.06 better suited to this style of racing?
Also is a 44mm wastegate enuf to control the boost at high boost levels running E85? Should I go with a 50mm setup?
Thanks guys... I built a couple Buick GN powered RX-7's in the past but this is new territory with this setup for me. I would like to run some 8's@165mph+. The vehicle should weigh under 3,000lbs with fuel. With approx 580rwhp a 2900lb RX-7 will run easy low 10's@140mph n/a and T56. I think with 400rwhp more my goals are realistic.
I only run divided housings with quick spool valves now.
Actually just made a very good business venture regarding that part, and have a big block red 69 in the driveway to boot. lol (not mine but in for work)
Id run a an sx80 with valve with a divided 1.32 housing.
The valve goes right under the turb of a divided housing, closing off half teh housing, (until boost rises), which causes a higher turbo wheel speed due to increased exhuast gas pressure on the remaining open side.
The turbo van idles at 50-54 kpa....and goes into boost instantly . It doesnt drive around in vacumm at all really unless your coasting.
People talk about turbo lag....I LOL. Its a 5.3 with a 1.10 housing 72, and drives like a stock srt4....if you have ever been in one its funny.
wastegate size really depends on the size of RPM and piping, imo. Some people get away with 44mm on mild setups.
I would use twin 38mm. You will get awesome control and it will only cost slightly more than a single 44mm.
To run the 'quick spool valve' you have to run an 'open collector' ie it cannot be divided.
Jose mentioned a 50mm WG at the minimum to control a turbo this size. He also mentioned the the S80 has come WAY DOWN IN price and can be had for under $1K!
So I'm pretty much getting a 60mm Tial WG and deciding upon a GT88 turbo ($1250) or a dual ball bearing GT47R-80 turbo. Both make similar HP. I'm going for the undivided unit as Forced Inductions said I'll have no problem spooling either turbo with 370ci.
Is it worth the extra $800 for the dual ball bearing unit?
If I'm running E85 all the time I assume that the big WG won't cause any issues as I'm literally going to have it tuned for one set boost level and then leave it alone. Then use an aftermarket boost controller to ramp in the power in each gear or as a time based power ramp in.
My goal is to run 8's@165mph in a 3000lb RX-7 street car.
if you want better spool then the 800 bucks is worth it for the dual ball bearing. I personally always used bb turbos mainly because on a 4 cyl its dead before boost hits, Im sure your setup wont be that bad before boost. Another thing to remember is when you go ball bearing the cost to rebuild the turbo is pretty much the same as getting a new one.
all the waste gate is doing is releasing x amount of exhaust gas out the waste gate before it reaches the turbo. Usually you only experience problems when running to small of a waste gate according to the turbine size, in that case it wont be able to release enough exhaust gas causing boost spike. In your case the 60mm should be perfect
60mm WG ordered. I went with a GT88 turbo... Jose mentioned top end pull like the Space Shuttle . Cost effective and cheap rebuilds if needed. If spool time is an issue I'll spray a 50hp nitrous shot to help it out. 6.0 iron forged shortblock at the machine shop now. That ever familiar whooshing sound from wallet has begun.
divided vs. undivided turbines.... What size A/R? Also WG size questions! 
. Cost effective and cheap rebuilds if needed. If spool time is an issue I'll spray a 50hp nitrous shot to help it out. 6.0 iron forged shortblock at the machine shop now. That ever familiar whooshing sound from wallet has begun.
