When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
nothing's wrong with it, it's just not covering the reasoning behind why IC vs non-IC need different pressure levels to get the same air mass into the cylinders.
it does seem to be modeled around achieving an arbitrary temperature in the cylinder though.
Can you summarize the link for me? :-)
The only temperature calculation involved is using the gas law to compute the charge temperature rise for the non-IC case.
The calculation also implies you need a smaller blower with IC to get the same HP as a non-IC setup. As far as reasoning, there is no reasoning other that the first HP equation, its valid or its not. To me its a simple conservation of mass equation which is hard to argue against. The rest is gas law (which is also hard to argue against).
Its the blower "CFM" thing I am still hung up on. If that CFM is input CFM then the mass flow rate into the cylinders should be the same with IC and non-IC, the only difference will be the plenum pressure. That's is where I am 'stuck'.
Corky is supposed to be very good about tech help, please share what he tells you.
the link is an investigation into the effect of pressure ratio and rpm on volumetric efficiency of a roots blower.
goes into explanation about the clearances between rotor lobes and between rotors and casing causing boost leak-back which lowers the VE of the blower as pressure ratio goes up.
boost/hot air gets caught by the rotors on their "Downswing" and that mixes with the incoming air in effect diluting the new intake air with hot air (raises charge temp/lowers density).
basically the pressure on the outlet side of the blower finds its way back to the inlet side and partially displaces the incoming "cfm" - the blower is fighting itself re-compressing a portion of the same air over and over reducing effective CFM output.
I created a SC design spreadsheet based on Corky's Chapter5 root's blower application chapter.
Put in your engine specs and desired HP it will calculate the rest including supercharger sizing and pulley ratios for both IC and non-IC configs. I still want to tweak it a little, consider it a work in progress.
bumping this up for anyone interested in trying their own 944 Sc project...these two aluminum parts are for sale.
left is the inlet to an early (oval port) Ford Eaton M90 supercharger with a 2.5" inlet tube.
right is the top "outlet hat" for any year Ford Thunderbird SC M90 (89-95) also with a 2.5" tube.
$75 shipped for the pair, will sell individually if desired.
i also have a disassembled early model M90, ready for rebuild, to match these parts if interested.
Just an update:
VE tables are dialed in and smoothed by hand a bit.
Timing has been put back while monitoring knock, knock action is now enabled.
Boost is 6psi, peak power is 2500-5200, I have a pulley upgrade coming in, expect 10psi soon.
MAT are very good now, only +3 to 6 above ambient after improving the air flow to the 951 IC
I did a recent compression test and scoped the cylinders, all good after about 5,000 miles.
Target Lambda was reduced to .86 and re-tuning the VE really brought it to life.
I have no clue to how much more power is being produced, but it feels like a 75 NOS shot.
What I am learning is the real squeezing of the power is the full control from a standalone...hands down the best part of the entire set-up.
After I get the pulley in, I might be forced to really put in the water/meth injection. Looking at the numbers on a 9.5 CR it might be required.
Just an update:
VE tables are dialed in and smoothed by hand a bit.
Timing has been put back while monitoring knock, knock action is now enabled.
Boost is 6psi, peak power is 2500-5200, I have a pulley upgrade coming in, expect 10psi soon.
Awesome.
I am curious if you tried my spreadsheet and plugged your numbers in to see if its close to predicting what you are seeing?
I tried but the goal of the sheet seems to be more meant to estimate thermo. Including the efficiency percentages greatly impact the calculations......those are assumed. The PSI is not a real great indicator of gain. I was getting the same amount of of boost through my tuning and that meant really nothing other than I did not have a major leak and the SC was in the general ballpark of being sized right.
My two cents is....correcting the air temp is critical, being able to add fuel on boost and retard timing only on boost/rpm is as important as the air temp.
ON top of all that, being able to monitor and review the data as you tweak and drive it harder is what will keep you out of trouble. I reviewed the drive data as I increased the rpm soft limiter, it took two weeks before even WOT and a month before I hit above 4500 rpm. I was overly cautious, but this was a learning experience for me....watched and read tons of tuning tips and articles.
I tried but the goal of the sheet seems to be more meant to estimate thermo. Including the efficiency percentages greatly impact the calculations......those are assumed.
I am suggesting putting in numbers for your situation (efficiency is a guess but a starting numbers) and see what HP gain it predicts. Then estimate your HP by the quarter mile or time to 60mph dyno....then compare the prediction to your 'measured' hp.
I agree that boost pressure is not important, is how much fuel you are using per rev at WOT that matters.
I ended up replacing the crank pulley with a small block ford aluminum pulley (same crank bcd) to get 6 ribs, swapped out the alt pulley for a 6 rib and upgraded the SC pulley to a custom 2.7" for $50. Found a Honda S2000 Gates RPM Racing belt that fit. Getting roughly 8psi, had to back down on the timing of course, but it feels fantastic. Cannot wait for the SCCA season to start. Currently waiting for some upgraded boost hose clamps as the cheap T-bolt clamps are not holding up and starting to deform and strip since I used a cheap ebay universal pipe kit. I did not know that well made hi-torque worm clamps actually do a better job and only $3 a clamp that are SS, lined and hold up to 150lbs. I expect the boost to rise a bit as there are leaks at the hose clamps. Also the air dam adjustments to improve the air flow to the IC have fixed the air temp creep. About 10k miles so far.
Details on that Ford pulley?
By same BCD you mean the Ford pulley matches the bolt holes on the balance shaft gear, that the 944 accessory pulley bolts to?
Details on that Ford pulley?
By same BCD you mean the Ford pulley matches the bolt holes on the balance shaft gear, that the 944 accessory pulley bolts to?
Yes the BCD is the same, the difference is the 4 bolts or fastener diameter bore for each, the ford ones are larger. I searched out steel sleeve spacers to fill the gap and used longer grade8 metric bolts. The advantages are low cost aluminum crank pulleys that are bigger in diameter as the 5" oem crank is way to small to match up with the smaller SC pulleys.....if you want to max. the SC potential and not run into belt grip issues. I would get a 7" if I was to buy another one.
01-08-2018, 08:45 PM
