Hows the progress going?
I am curious as well. I've been getting slow played by Innovative for much of my stuff. If that is where you ordered from I am guessing you are probably having the same luck and hence no update of the thread. I ordered over 6 mos ago and still waiting for parts to show. Tim at innovative has been helpful, just really slow in producing any parts.Hows the progress going?
I agree totally that turbochargers are fantastic and most all cars I have built have been turbo however its just not a good form of power for a mid-engined well balanced car designed for turning.Chris,
From my experience with forced induction and the K-series trans I'd advise you to use a supercharger rather than a turbocharger in your Exige. Couple of reasons: Its well known that the gears Honda builds aren't that strong (especially 4th in the K-trans), and while cryo-treating can extend their lifespan the bottom line is you really need to look at the kind of torque curve different methods of FI produce. Worst case scenario for drivibility and time to distance is a centrifugal compressor, because boost and therefore torque production are directly linked to engine RPM. Conversely this rather weenie torque curve, where the torque peak is generally right at the redline, is good for trans longevity since drive-train parts only feel torque and not HP. Torque production in a turbocharged engine is weak at low RPM simply because turbine housing sizing is always a compromize, and to get great low-end torque the rising backpressure kills the top end. Using a bigger turbine housing is great for top end power but makes the engine lazy until spool-up and then watch out because the torque curve is going to climb like a Saturn rocket. Most all of this is negated with a VT (variable turbine) turbocharger, but the turbo manufacturers have been thrashing on making this setup work reliably for about 35 years without a lot of success. Its the spool-up part of the torque curve that's troublesome for the trans because that torque spike is always somewhere in the mid-range, and then the torque falls off as engine RPM increases. (This can be negated to a degree by using very agressive boost control, but its expensive and take a lot of dyno-time to get it right.)So in most cases your peak HP production happens at an RPM where the torque is far lower than at its peak, so the trans is taking a lot more abuse than it needs to for the HP generated. Best case scenario from a drivibility standpoint is a positive displacement supercharger. Bottom end and midrange torque production is higher than with a turbo without the spike, and since it keeps making more boost as the RPM climbs the torque curve stays relatively flat all the way to the redline. Secondly, its a whole lot easier to drive a supercharged car fast because there are never any surprising spikes in the torque curve so the HP production is very linear relative to RPM. An example you'll be able to relate to: The 2,308cc "K23A" (M90 supercharged) engine I have in my Elise makes 454 [email protected],000 RPM with 12 psi on Arco 91, and is only producing a maximum of 288 lb/ft of torque. If that engine were turbocharged and making the same HP the torque peak would be more like 340 lb/ft and the trans would last nowhere near as long. I started turbocharging cars in 1975, and I LOVE Turbochargers, but I've never even considered using one in an Elise or Exige and I've been converting them to Honda Power since 1989.
Torque curve manipulation is really what engine building is all about, and if its done properly you always get the most HP from the least Torque.
Take care and have fun,
Here's a dyno chart from back in July '09 when I finally got around to putting my "K23" on the dyno. I machined 4 differently sized 8-rib pulleys, but only 3 of them are on this chart. 12 psi came from running the M90 at 58% overdrive, 14 psi at 69% overdrive, and 16.5 psi at 81% overdrive. This was done more for personal data gathering than anything else, so we didn't even rev the engine to its redline which is 9,200. Basically I wanted to see what shape the torque curve would be with the little IPS supercharger cams since they're small enough to give really sweet mileage at a cruise. Its my street car so that's important, and with the gearing I'm using I'm hoping to see somewhere close to 40 MPG at an 80 mph cruise. From other S/C dyno testing I've done bigger cams would flatten the torque curve out above 6,500 and make substantially more top-end HP, but considering the car only weighs 1,820 lbs I think this setup will be OK as a starting point. The 12 psi run was done using Arco 91, so that's the street setup. The other runs were done using MS-109 since I had some and that's our standard dyno fuel for N/A and low boost testing. The highest post intercooler temp in the manifold was 138 F. but since this was done on the dyno the airflow through the heat exchanger was piss poor, so it'll be substantially lower with 80 mph airflow.
On the subject of centrifugal compressors, you'd need a drive system that would be variable relative to crank rpm to achieve what you were talking about, and as far as I know nothing like that exists. I saw engineering drawings of one that used a planetary drive to get the wheel up to a usable speed quicker, but there was no consideration given to maintaining that speed as the engine rpm increased. Generally with a crank driven centrifugal compressor the torque and HP peaks are at the same rpm, right at the redline, so the torque curve is often curved in the wrong direction, concave rather than seriously convex like with a positive displacement blower. Centrifugal compressors need to be driven by something other than the crank to make a decent torque curve. Something like really hot exhaust gas.
Take care and have fun,
138 at 16.5# is even more impressive. I can only imagine what kind of core/heat exchanger that was. I'm surprised you were able to package the core in the S2 Elise. Were you running the heat exchanger up front?WhatsADSM,
It was 138 degrees at 16.5 psi.
Now I see where you're going with the Rotrex thing. I'm basing what I've said on the experience we had with Hondata's Bonneville RSX. Oscar supplied the biggest thing Rotrex made and it simply wouldn't flow enough air to get the job done, so in the end they ended up using 2 of them. Even with 2 Rotrex's the torque curve was concave! Max torque was something like 390 lb.ft. at 9400 rpm.
Now if you were only interested in an extremely mildly boosted engine I'm sure what you talked about would work OK, but you'd still get a sweeter torque curve with a positive displacement blower.
I've taken broken Rotrex's apart and its obvious what their problem is, they're appealing to people with limited available space so their compressor housings are small in diameter. Good marketing but poor engineering. The compressor wheels they're buying are designed to be efficient in MUCH larger housings, so overall its a very inefficient package.
Quite a few of them went into self-destruct mode at as little as 5% over what they say is the safe RPM. The shaft snaps off where the diameter is reduced to accept the compressor wheel, and the dummies in England who make them say its just fine to produce that part with a zero root radius even though there's plenty of room for a very generous root radius. Not an impressively designed or built unit in my opinion.
Take care and have fun,