RT

Not by simply changing pulley size .....

jerrypeterson

Are you still trying to get more boost ~3-4000rpm? If you'd like to find how it could be done though, check out the GruppeM supercharger for the NSX and pay close attention to the implementation.

KAMcDonald

does anyone have the diameter of the crank pulley for the Comptech SC?

we may not be able to tell the boost in PSI until someone actually tests it out on a dyno, or with a boost guage installed, but using the formula of

(crank diameter / blower diameter) * rpm * internal SC ratio

i made up a quick excel spreadsheet.

the internal SC ratio for the NOVI 1000 is 3.54.

i guessed at 5.2" diameter for the crank pulley, could not really get an accurate measurement. i used the 4.575 stock, and 4.375, 3.875 and 3.5 numbers posted above as alternates.

using the 5.2" estimate shows that at 9k, the stock setup would have the SC turning at 36,212 RPM, with a published 6 lbs of boost. when i did my dyno last week, it showed 6.1 lbs at 8700 rpm. of course, i forgot to get a printout of all the data points, i will get that on the 15th when i go back for a dyno day with the local NSX people who have invited some S2K guys along.

anyway, i think the point is using the rough numbers would show that the SC RPM, and therefore boost of 6 lbs, would correlate as 4.375@8600, 3.875@7600 and 3.5@6900. a diameter of 5.4 would lower the RPM by 3-400.

once i get the complete data point listing, i might be able to extrapolate boost for the smaller pulleys above the 6 lb published maximum for the stock setup.

if any of the people who already have the smaller pulleys have done dyno runs and collected boost datapoints, can you please let me know what they are so i can run them against my spreadsheet? i will post the completed chart once i am satisfied that it is close to accurate.

keith

1Randyc

Hey Keith,
Back in February, Wesmaster found out for me that the crank pulley diameter is 5.5 inch give or take a few.
I am running on 3.4 inch blower pulley and just prior to that I've tried 3.9 inch pulley.
But sadly still don't have the boost gauge installed because I am taking care of other stuff first.
My dyno run was posted a month ago here in this forum.
Here is the thread
https://www.s2ki.com/forums/showthread.php?...1&highlight=341

I've just installed the RC injectors 440cc but having some serious drivability issue.
If I don't get to resolve this before June 15 Curry dyno session, I will not bother putting my car on the dyno run.

Hopely I will see you there Keith.

KAMcDonald

ok, using 5.4" crank pulley and 3.4 blower pulley, my spreadsheet would show you at approximately 6 lbs boost at 6700 rpm based on internal SC RPM's.

i think i may need to go back to curry's before the june 15 event to but some ATE super blue brake fluid because it looks like i am need to take my car in to Honda to have them check out 5th gear, it is rough going in and worse coming out. i am running aftermarmet brake pads and have P+'s for the track, so might as well let them change brake fluid at the same time.

since it is so important for those of us with VAFC's, i will also plead with them to get their A/F monitor hooked up to their dyno so we can plot all the data together instead of having to try and adjust for A/F based on realtime estimates of what the RPM's are.

while there i will get the chart showing the boost datapoints, i cannot remember where the boost started so i cannot extrapolate any figures for different pulleys right now.

i have not made any changes, so will not dyno at curry's on the 15th, but i will show up just to talk and see what other people are doing.

keith

KAMcDonald

well, therein lies the confusion...

SC boost should be the same at a specific internal blower RPM no matter what pulley sizes are being used to drive it.

i am making the assumption that default max boost of 6 psi is delivered at 9000 engine RPM, 38302 SC RPM using 5.4" crank and 4.575 SC pulleys. dropping the SC pulley size makes that 38302 SC RPM available at lower engine RPM, i.e. 8600, 7600 and 6900, but i do not have the numbers in hand to determine the ratio for each 100 RPM increase of engine speed and what the new max boost would be. the progression in boost should be linear since it is a constant belt driven speed, but i need the start point to determine the angle. when i did my dyno run, we captured the boost, but i forgot to get the table printout. from HP charts the increase is negligible up to 3100 rpm, then starts to rock begining at 4k, so it could mean that no boost is developed until that range meaning we cannot start our boost figures at idle speeds and increment up to the 6lbs@9000 rpm, or that the addition is so minor as to not register.

keith

Diddy

Installed the 3.875 pulley and @ 9000 RPMS 7.2 psi
@6000 getting something close to 3 psi

KAMcDonald

Hecash,

well, i guess i was a little closer for the peak with my spreadsheet... 7.5 @ 9000 but i had 4.2@ 6000. Are you using a crank pulley size of 5.4" ?? i do not have a good measurem,ent myself, was using 5.2 but someone else said they thought it was 5.4.

overall my estimates are 4.375=6.3; 3.875=7.5; 3.5=8.55; and for fun 3.00=10.34. of course that is all based on comptech saying stock pulley gives 6.00psi. if that number is a little higher/lower, mine would be proportionally changed as well.

i get more confused the more i look at it.

talked to Paxton direct, they claimed that the novi-2000 should put out 11-12 psi@ 50k SC rpm.

i figure that at 9k we are spinning the SC at 37605, extrapolate it to 50k and using comptech boost of 6 psi, we only get 8.7 psi. using Paxton's 50k 11.2 psi figure would mean we should get 7.6 psi at 9k rpm.

using a centrifugal SC, half the boost should be available at half the rpm, so 6 psi at 9k rpm should be 3 psi at 4500 rpm, and i get 1.8 on my spreadsheet, and 1.4 on the dyno.

must be some magic happening inside that little silver box that no one has explained yet... once we get a few more people doing dynos with the various pulleys we will at least get some realtime data to plug into the spreadsheets and not have to extract it from the vendors...

keith

1Randyc

Hmm, looks like I need to get my butts moving and install the boost gauge...
However, I am now having some issues with just installed VAFC with RC 440cc injectors. I am very tempted to go back to stock injectors at this point but I am willing to give few more tries.
Based on air/fuel meter installed, my car seems to be possessed with unexplainable readings.

I have 3.00 inch pulley coming in about a week. I will report back to you how it behaves. With that I definitely have to kiss my 9K rpm good-bye and stay below 8K rpm before risking seriously overdriving the blower.

Diddy

[QUOTE]Originally posted by hecash
[B]Diddy,

That's the boost that my theoretical spreadsheet predicted for the 4.375 inch pulley.