Post
by foggyjames » 05 Dec 2009 02:31 am
Bump. I found some answers to my questions in the other thread here!
The concept is very, very sensible (keep the boost down and the revs up), and exactly what I plan to do (15psi on a custom T3 - .63A/R Cosworth hotside and CHRA sits on my shelf...compressor yet to be decided)...but I think you're going to need to work more on the application.
I think you'll need to work on both the exhaust manifold and the head (bigger exhaust valves, at least) to get it to make useful power above 5500rpm. The cam will need to be aftermarket (Enem do a particularly wide range for turbo apps...take a look at the K16 Turbo) at that engine speed...even a factory 'K' grind runs out of puff above 6k. And you're going to need something stronger than the 9mm B200. A 13mm rod engine should be ok to 7500 or so, but I'd probably put a set of H-beams in it, just to be safe. The pistons will be fine at that power level...although given your RPM aspirations, you might want to look at making the rod/stroke ratio more favourable by using a longer rod and shorter piston...which might as well be forged, since you're there anyway! This is all getting a bit spendy, so I guess you could always have a spare late B230 kicking around (£150?) just in case, and see how you get on with the stock bottom end.
You can swap a late B230 to a block-mount dizzy easily BTW...just swap in a 240 or 360 aux shaft, and off you go. Personally, I'd ditch it and run coil packs. You're on MS anyway, right? You'll pick up a lot of spark power that way.
Personally, I'd do "mk1" and shoot for 250bhp at say 5500-6000rpm (which the B200 should be safely capable of, with good mapping, at 10-15psi with that turbo), then (if you decide you want more) be working on "mk2" (300-350bhp at 7krpm...rods, big-valve head, cam, tubular manifold, etc) in the meantime. The precise numbers for "mk2" there are kinda bench-raced, as most people put them in agricultural 2/7/900s, where loads of torque is not an issue. For example, my housemate's 740 runs up to 2 Bar of boost on a T3/T4 hybrid, but with a 6200rpm limiter...and that's a pretty standard-issue Turbobricks concept...trading bottom end strength against the lack of a good flowing head.
I'll be very interested to hear how you get on with it.
cheers
James
