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I'm starting to lean towards building the most efficient NA motor that I can and then adding a low pressure turbo combo to get the horsepower where I want it in the 4k to 6.8K range. I'll play with it on my Dynomation software and see what I come up with.
It will be interesting to hear what you come up with. Just what did you have in mind for efficiency?Longer rods? Thinner rings? Cryogenics? Piston oil coolers? Better intake manifold? Drilling the block/head for additional cooling? Ceramic or other coatings? Use a block fill? Tall blond and a pint of Dewars? Demented minds want to know!
I know you already have a head and cam coming from Bo. Which cam did you get? Any idea on what the air flow will be?
I'm starting to lean towards building the most efficient NA motor that I can and then adding a low pressure turbo combo to get the horsepower where I want it in the 4k to 6.8K range. I'll play with it on my Dynomation software and see what I come up with.
Bob
Talk to 8T6 SVO. At Knott's he was telling me that he was making some crazy HP and TQ with his motor. I'm seriously considering having the guys who built his engine, build me one too...or at least point me in the right direction.
....
Remember guys, I'm limited to a certain maximum amount of HP and Torque and need to keep the revs below about 6,800 to keep reliability.
Bob
I think it was the guy I bought my car from, Bob Canepa said that he or someone he knew, would hook up the turbo boost regulator to the emergency brake handle. Need more boost, pull on the e-brake a little. Of course when your doing your dyno runs, they are going to want the e-brake off so you'll register lower HP numbers...
I... said that he or someone he knew, would hook up the turbo boost regulator to the emergency brake handle. Need more boost, pull on the e-brake a little.
That's silly. You have more options with the fan switch!
(That should keep folks up through a sleepless night or two)
Remember guys, I'm limited to a certain maximum amount of HP and Torque and need to keep the revs below about 6,800 to keep reliability.
Bob
are you limited to HP/TRQ by rules, or for reliability? what thought has been done for computer? if you wanted to get sneeky and stay within the rules, get an aftermarket computer that can do boost control based on RPM. then you can tune the car to have the max torque allowed up to 5200 rpm, and then ride max HP out to 6500.
note i never said that would be easy to tune in.
[edit] then you can do stupid stuff, like computer controlled overboost (push to pass), which, as opposed to the hand brake trick, doesn't leave physical evidence. toggle it on and off using the premium switch or what not.
are you limited to HP/TRQ by rules, or for reliability? what thought has been done for computer? if you wanted to get sneeky and stay within the rules, get an aftermarket computer that can do boost control based on RPM. then you can tune the car to have the max torque allowed up to 5200 rpm, and then ride max HP out to 6500.
note i never said that would be easy to tune in.
[edit] then you can do stupid stuff, like computer controlled overboost (push to pass), which, as opposed to the hand brake trick, doesn't leave physical evidence. toggle it on and off using the premium switch or what not.
I think Bob is racing in NASA's American Iron, where there is a 9.5 lb/horsepower and 9.0 ftlb torque/lb (vehicle weight) limit. His car is way under the 3000 lb raceweight, so all he'll need is around the 280 hp or so.
That's right, CP86SVO, there are the class limits. Then we have been playing around with how much horsepower we could have and have the fuel last for 1 hour and 1/2 which further constrains the amount of HP we can make without a substantial decrease in BSFC.
Right now I'm thinking 10:1, intake and exhaust tuned 6,250 rpm for peak HP. Tube header with wastegate priority and a very efficient Turbo that wouldn't need to come fully on until at least 3500 rpm. Low back pressure, low boost. Probably under 10 psi with the ARCA head and a tuned intake.
What's more efficient and has less backpressure, small turbine with a big AR or a large turbine with a small AR? Probably the large turbine, right?
Playing with turbos, it looks like Mike was pretty right on with the GT 28 series, running it at about 8psi really pumps up the torque curve, although it could use more. Wastegate priority header is going to be important.
What's more efficient and has less backpressure, small turbine with a big AR or a large turbine with a small AR? Probably the large turbine, right?
2 different things entirely. efficiency is dependent on the design and size of the compressor wheel and housing. backpressure, the size of the turbine wheel and housing (and force required to spin the compressor wheel). since you want flow and are not going to be pushing too much boost, a small / medium sized compressor wheel that will flow your required CFM @ PR at its highest eff % (think you already mentioned the GT28 series as fitting the bill), and a turbine that is as large as possible, with an AR as large as possible, that will still met your required boost thresholds.
the closest GT28 that my (untrained eyes) could find is the GT2876R - 705330- 2, has a big fat 75% eff area from 20lb/min @ 1.5 pr to 35lb/min @ 2.5PR. good eff, but PR is way too high for your application. running 35lb/min @ 1.7PR gets you way outside the overspeed line. going to a gt30 series, the GT3076R - 700382 - 12 could be a very good choice. flows 30lb/min of air from 1.7PR to 2.25PR @ 77% eff. not sure if that 1.02AR exhaust housing would be too big for you or not, but they offer 3 exhaust housings.
since you are doing endurance with such a low boost setup, and fuel economy does have something to do with it, you _might_ be able to get away with no inter cooler at all.
i think i just typed a bunch without saying much. ask your turbo guy!
intake and exhaust tuned 6,250 rpm for peak HP.
would it be better to tune that down to 3500 rpm for peak torque (better boost response, more compact headers, and you could possibly run a larger AR turbine housing as well), and let the turbo handle shoring up the top end HP? you're already talking about running in crossover with a top end optimized turbo, make your NA systems make low end torque before the turbo spools up, and let the turbo do its job up top.</iamnotahardcoreracer>
Bob, you should get w/ Bo also. He will have some invaluable insite on port configuration with regard to what will complement the head you have and what designs will work best for you. I would love to hear what he has to say on the combo you are looking at.
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