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Old 06-21-2014, 04:56 PM   #36
realcanuk
 
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Drives: 2007 Corvette C6 983 RWHP
Join Date: Dec 2011
Location: Montreal, Canada
Posts: 679
Quote:
Originally Posted by jessrayo View Post
Thanks for putting the dyno sheet up, that actually helps me quite a bit. Impressive sheet on a auto trans.

Okay first on the blower speed. There are different ways to calculate this stuff but for me the easiest way to find this is to divide the diameter of the bottom pulley by the the diameter of the upper pulley. This gives you the pulley ratio of upper revolutions to one lower revolution. If you started with a long equation calculating the exact circumference of the pulleys you could cancel all of the constants and you end up with the same thing. Okay so on your car you have an 8.66 lower and a 2.75 upper giving a pulley ratio of 3.149. So every rotation of the bottom pulley gives 3.149 rotations of the upper. Since the bottom is on the crankshaft it is easy to figure max rpm this way. 6800 rpms on the crankshaft times 3.149 = 21,413 rpm on the blower at peak rpm. Lingenfelter says 23,000 is the limit on these blowers. I have seen people that build a blower car for drag racing go a bit higher. A close look at the dyno sheet can sometimes give you a good idea if there would be any benefit in spinning the blower faster. Just because lingenfelter says 23,000 is the max doesn't mean your car will operate best at that speed.

I can tell you from trying many combinations on my car that all top mount superchargers will hit a point where the efficiency starts to drop off rapidly. To make more power you have to get more air in the engine. All forced induction engines compress air. The problem with all compressed air is that you get a rise in temp. The basic physics of air, which is a gas, is that if you put twice as many molecules in a space without any other changes you will double the pressure. Also if you leave the exact same number of molecules in the space but double the temp, you double the pressure. So in basic terms, heating air will raise the boost just as much as increasing number of air molecules but will give no gain in power. That is why the heat is the enemy of all forced induction systems. This transition where the boost is coming from heat instead of more air is not instant and you will usually get the most power where the blower is out of its optimum efficiency and it is generating some serious heat. Good cooling lets you drive a little further out of the blower comfort zone.

Okay so looking at your dyno, the first thing I look at is the slope of the power curve (blue line) on the dyno, particularly at the very top of the rpms. Your slope is just about perfectly flat at 6600 it is not really dropping but it clearly isn't climbing like crazy. If it still has some upslope, you can give it more pulley, if you have a lot of downslope at redline you would have less heat and close to the same power if you reduced the pulley ratio. It depends on your heat tolerance. If you only race with ice and do 1/4 miles then it may be okay, if you try to road race the car the heat at high rpms will cause major problems.

Also on your dyno, looking at AFR, air fuel ratios, the yellow line on the graph, it is rock steady at 11.5 right up to 5750rpm. Then the AFR start to rise. Assuming the tables are linear this means at 5750 the car is starting to get more fuel than air..... The fuel rise is linear so the air is not keeping up... This is because the blower is losing efficiency and more of the "boost" is starting to come from heat rather than increased number of cool air molecules.

Same with the boost graph (red line), boost is rock steady at 12psi to 5250rpm and then it starts to waver and climbs all the way to about 14.6 at the redline. Since the pulley ratio is constant all the way across the rpm band this increase at the top is all related to heat.

So based on everything on your dyno sheet it looks to me like you have your car dialed in very well for peak power on your current build. I don't think giving your car any more pulley ratio would help any more, I suspect if you push your car for more than a 1/4 mile now you are going to have a lot of blower heat. Unless you have a very good cooling system you would probably start to lose a lot of timing to high IATs if you were road racing at these pulley ratios. I do the standing mile, 1/4 mile and road racing and road racing is where the blower temps really start to be a problem.
All good information and I agree with most. I don't do any road racing or standing mile. This is mostly a street car and once in a while I got to the track and run 1/4 miles.
The blower speed according to my calculations... damper 7.96 / blower pulley 2.75 x 6800 rpm comes to 19686. I spoke with the eforce engineer at SEMA last year and he says 20k is the max safe rpm.
The increase in boost at high rpm is apparently caused by the runner design which are more efficient at lower rpms. Truth is that even with the most aggressive street driving, there is no real reason to run this thing over 6500. I stretch 4th out to near 7k at the track, just to avoid another shift.
After that dyno run that I posted, I added a little fuel up top for safety even though she makes the best power and seems to like high 11s AFR.
As far as heat goes, there is no question that the faster you spin the blower, the more heat it produces. On that posted dyno run, which was the 4th or 5th in a short time the IAT's got to 126 which is great. I have not run the 1/4 with this setup yet but I expect to see IAT's somewhere around 150 which is ok.
All in all the setup is working great, but in my opinion the eforce is maxed out. If I decide to look for any more power than I have I will go a different route later.
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2007 C6 vert, auto, F55, LT3
LME LS402 , WCCH 245 Heads, Pat G. Custom cam
YSI / 3.0 pulley, ARH 1 7/8 headers, NPP
Dewitts / dual spals, A&A dual pump fuel system.
3.42 polished gears, hardened shafts, Alky control meth, Cartech line lock, ECS axle loops, Trans brace, 6L80 built by me.
ID 1000 injectors, comp rockers, Morel lifters, BT springs, Trend 3/8 pushrods, ATI 10% OD Damper
Circle D Triple Disc stall
1009 RWHP @ 7000, 817 RWTQ @ 6000, Built & Tuned by Seth at FEDERAL PERFORMANCE
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