rustbucket

I have the same stupid question - what size turbos. The car is a 2.5 v6 Alfa to be used as a street car that will see some heavy traffic. Low RPM boost is not required,not looking to win stoplight dragraces, max power should be in the upper part of the rev range. There is not eonugh space to bring a pipe under the motor to use 1 turbo - so twins. 20 years ago Callaway set up about 50 cars with twin IHI RHB5s, unfortunately Callaway is not answering questions and the Alfa crew is clueless about WHAT model RHB5s were used.
My plan is to lower the compression from 9.0:1 to 8.5:1 and start with about 8 psi and work toward 14 psi. There is enough space in front for big intercooler. I use MegaSquirt for fuel management/spark control. Callaway built a plenum with an IC on each side, but it didn't cool well as the hood scoop didn't move much air, none when stopped.

I have read Corkey Bell's book and think I understand the compressor flow maps. For 300hp I need about 16.5 lb/min or 227cfm or .122kg/sec per turbo. small turbos. I think the Garrett GT1752 from Saabs have the same compressor maps as the GT2052s and they look like a good choice. Also the MHI TD04-13G that are popular upgrades for Mitsu 3000GT look good on the maps - But I dont know what cars in the junkyard will have them. The map for the Probe RHB5 VJ11 looks acceptable also, they stopped making Probes several years ago - cheap but in need of a rebuild.
Another way to look at the problem is as a 1.5 liter single turbo low compression Honda. Honda guys have put every turbo ever made on those cars - What works well on the street and on the drag strip with about 10 psi and an intercooler?

Sorry for the stupid noob question - but your experience could save me from a big mistake. So - A good junkyard turbo for a twin installation on a 2.5 V6 that revs to 7500

ichbinsobose

two T25s but they might be a tad small... try a flavor of 14b or 16g I'm sure tow of them can flow well enough for 300 horse.

Slo_crx1

I would say the 14b's with the 6cm^2 exhaust housing. They're quick spooling on a 4 cylinder, but with only 3 cylinders it should slow it down a bit and still make the top end rpm you're looking for. Plus tdo5h/14b's are still easier and cheaper to find than tdo4/13g's.

the 13th round

what about a small turbo and a larger one? so it dosent drop off at the top? or is that dumb, i dont know much about multiple turbos really.

ichbinsobose

If you want to go sequential, a supercharger for the low/midrange and a turbo for top end makes more sense. I have yet to see an effective twin turbo setup of differing sizes, and it is very hard to tune. I am sure two junkyard 14bs or something a little bigger would make you very happy.

rustbucket

Thanks for the input.
I made a mistake - Garrett GT1752 and Gt2052 have different turbines so they have different maps. The Gt1752 only has a 44mm turbine wheel.
The TD05-14b looks way too big. With only 1250cc to work with it can't get to the best part of the map.
see: http://www.rbracing-rsr.com/turbo/Tu...s/td05-14b.gif
too bad the TD04-13g is so rare, the central island is at 78% and well situated flow/PR wise.
Anybody have a compressor map for TD04-13C?

Toysrme

Why in would you drop from a 9.0:1 CR? That's completely stupid. You should be able to run 30psi in the manifold before you have a head gasket no problem if detonation is kept in check. If you're swapping pistons, bump it up to 9.5:1. It's free power & economy. Especially off-boost.

Decide what you want for a powerband, and what you want for peak power. Until you've done that. You don't know what the ---- you're trying to do. You could do 300bhp on anything. 300bhp is pathetic for having 6 cylinders.
Pick a bigger number, starting at 300bhp is just ------- rediculous. A week down the road you'll realize you really want atleast 450bhp, and a real powerband. Meaning you fucked up your entire setup from the get-go.


I'm saving you time, take my word for it....

accordepicenter

dont need to lower your compression, 9.01:1 is acceptable for boost and pump gas. Lowering it any further is just gonna cost you power

rustbucket

For a powerband I am looking for a torue peak at 2700 rpm and 300 hp at 7000 rpm. This represents twice the power of the stock 2.50 liter GTV6 motor. As far as the pistons - I would just as soon NOT lower the compression. I was planning to trim the crowns, as Callaway is said to have done, rather than have new ones made (I am cheap). This is my first turbo project, it would be nice to be able to look at how others have solved the problems but all the info I can find concerns the Callaway cars. So I look at published numbers, The WRX and Porche are about 8.5:1, The highest compression turbo pistons J&E make for Honda is 9:1. What do I know? Callaway is my only example and he lowered his cars to 7.5:1. Other than that, there is plenty of talk but not much of it is based upon experience. Most production turbo cars are biased toward low end punch and serve as poor examples. There are few twin turbo v6 examples. Fortunately the 3000GT guys publish based on experience. But that motor is a 4 valve that is 20% bigger(TD04-13G!). If the Suzuki Swift or other 1200cc motor had a 150 hp turbo option I would be looking closely at it. As far as the eternal quest for more power - I don't mind taking multiple steps to get there. Some people regard the "baby steps" approach to development as "chicken ----", but in my experience, it is an approach that produces the fewest disasters - "swing for the fence" and strikeout. I doubt if the first guy to turbo a 1.5 Honda got 250 hp on his first attempt.

aero

Not sure if you are here in the states or not. Here the 3000Gt Vr4 uses the TD04 9b. On that 24v 3.0 they rate it at ~300 in the early models at 11lbs. They can be had cheap from people upgrading, and shouldn't fall off quite as bad with 2v heads and .5l less. You should be able to make a bit more than 300 as a starting point. Upgrading would be easy with the td04 13g ect.

You wont be in the most efficent part of the map for sure, but it will spool up fast and have a fun powerband.

Like you said the 14b is too big for what you want and would be pretty laggy.