• Protip: Profile posts are public! Use Conversations to message other members privately. Everyone can see the content of a profile post.

boost vs pulleys

Rating - 0%
0   0   0
Joined
Nov 10, 2003
Messages
1,066
I have a 2.3L whipple charger it flows 812 Cfm/Rev and the stock comptech flows 565 Cfm/Rev it is bolted on an modified comptech Intake. I am running the 9lb pulley from comptech and i just installed a boost gage. first reading was 5 lbs so i tighened the belt up and the pulled 9PSI. does this make sence? i would have thought that since the CFM is much higher that the PSI would also be.the gage i just installed is an auto meter and came with a very small line 1/8" or so i had already ran a 1/4" line so i used it would that give a false reading? i will start to tune the car next week but was just wondering if the boost seems correct. i will have a set of pulleys made to reduce the slippage i would like to dial in the dia before have them custom made. also would any one else be insressed in a set of COG pulleys if i have them made it could reduce the costif ordering more than one set.
 
Rating - 0%
0   0   0
Joined
Apr 22, 2003
Messages
1,063
Location
chicago
i may be interested. what is a "cog" pulley? what materials? 8 rib ? could they do a harmonic balanced crank pulley?
thanks
woody
 

Yellow Rose

Suspended
Rating - 0%
0   0   0
Joined
Nov 22, 2001
Messages
2,259
first reading was 5 lbs so i tighened the belt up and the pulled 9PSI. does this make sence?

The belt was slipping, thus the SC was not making as much boost…..of course it makes sense.

i would have thought that since the CFM is much higher that the PSI would also be.

Boost will be what it will be, because the more important parameter is CFM.

the gage i just installed is an auto meter and came with a very small line 1/8" or so i had already ran a 1/4" line so i used it would that give a false reading?

Makes no difference what size line you use to measure static pressure against the back of the boost gauge…..there will be no false reading.

also would any one else be insressed in a set of COG pulleys

This will be rather expensive because you will have to make a cogged pulley for the alternator and a cogged pulley for the harmonic balancer. Additionally, it may be a challenge to find a cog belt that can operated at 8000 RPM of the small diameter you need.
 
Rating - 0%
0   0   0
Joined
Sep 28, 2004
Messages
1,743
i would have thought that since the CFM is much higher that the PSI would also be.

Boost will be what it will be, because the more important parameter is CFM.


As andy said, boost and CFM are pretty different, most people do combine them though. in a perfect world, atleast with a factory NSX engine, you would like to have as high of CFM (through the engine) as you can (using other peramiters to detemine what that max would be) with as low of a PSI as you can. This is unforchanlty pretty hard to achieve with the standard turbos and SC's on the market. This is why it seems like a difficult task to FI the car.

look at it like this, if you flow 600 CFM through the engine you will have 400hp, it really doesnt matter if you flow that with NA, SC or turbo, and it doesnt matter if it is 2 PSI or 22 PSI, its the CFM that counts.

before anyone flames on me, these are statements are obviously generalizations, used to make a point.
 
Rating - 0%
0   0   0
Joined
Sep 13, 2001
Messages
323
Location
Lake Mathews (Corona), Ca
2.3 L per/rev = about 0.078 ft^2 per/rev. At 8000 rpm and a standard 1.7 to 1 pulley ratio (blower rpm of about 13,600) that means about 1060 ft^2/minute. At 90% blower VE that would be about 954 ft^2/minute. On an otherwise stock NSX (VE wise) that should give about 19 psi boost! Something is way off if you’re getting only 9 psi unless you’re spinning the S/Cer WAY slower than the stock Comptech setup (or my 1.7 to 1 assumpion). Either that or you got almost 600 hp at 9 psi and don't know it! That would be a record for the NSX I think.

Also, regarding a cogged belt I have the following caution found the hard way. I recently treated my pulleys to a process used in aerospace for increasing the shear capacity of bolted interfaces with oversized holes. A thin layer of tiny tungsten particles are embedded into the surface of the parent material producing a very hard surface with the texture of roughly 200 grit sandpaper. Did it work, you bet . . . too well. During rapid rpm changes (like a bad downshift!) the inertial loads resulting from trying to accelerate or de-accelerate the relatively heavy S/Cer lobes can be tremendous. It's at times like this that belt slippage safely dissipates this energy. What happens when the belt doesn't slip? In my case the coupler connecting the S/Cer drive to driven shaft exploded causing the blower to fail. If the coupler wasn't there to absorb the shock I assume the gears would have torn a few teeth or the lobes would have spun on the gears (the Eaton uses pressed on gears). In either case, it wouldn't have been pretty. So the warning: a bit of slip can be a good thing . . . .
 
Rating - 0%
0   0   0
Joined
Nov 10, 2003
Messages
1,066
Mark thanks for the Calc's. I am running the stock crank and the 3-5/8" or so comptech pulley. how tight should my belts be can you over tighten? after looking into the pulley types and sizes i would like to get a set of the wider gruppe M pulley's or have a set made like yours. I will be fine tuning the car on wednesday. I have a GTech i will get out to try and get a idea of power. It will be several weeks before i will have the time to find a dyno.
Thanks again for your help
 
Rating - 0%
0   0   0
Joined
Sep 13, 2001
Messages
323
Location
Lake Mathews (Corona), Ca
That explains it. The 3 5/8 pulley is huge. It's probably only about a 15% overdrive to the crank. That'll put you around 650 cfm at 8000 rpm (assuming 90% VE at that S/C speed). Note: You might want to find out how efficient that blower is at speeds from 2300 to 9200 rpm, you might not be in the "sweet spot" in terms of VE at the engine rpm you desire. Typically this will net over 400hp and 8 -10 psi (depending on engine rpm) on a stock motor. At 650 cfm the stock TB is probably ok, but I'd keep an eye on your pressure between the TB and the S/Cer if you increase the CFM. That'll tell you when you'll need a bigger TB. See, everything is as it should be . . . . mark
 
Rating - 0%
0   0   0
Joined
Nov 10, 2003
Messages
1,066
I still dont understand the blower is rated by whipple @ 813 CFM/REV. I do understand the pulley size so what size pulley's would be needed to crank out 600HP to 700HP? the motor should be able to hold that kind of power. I have low comp, larger valves, new sleeves and so on.
 
Rating - 0%
0   0   0
Joined
Sep 22, 2003
Messages
451
Location
DC metropolitan area (MD)
ken sampson said:
I still dont understand the blower is rated by whipple @ 813 CFM/REV. I do understand the pulley size so what size pulley's would be needed to crank out 600HP to 700HP? the motor should be able to hold that kind of power. I have low comp, larger valves, new sleeves and so on.
You need to push at least 14 lbs of boost to achieve the results you're looking for... (between 6-700 BHP) Your big blower should do that, its just determining the right sized custom pulley to do it (lots of domestic performance shops do custom pulley sizes) Also with that kind of boost pressure and 8K rpms on a relatively large whipple belt slippage can be a big issue, a thicker belt (more ribs will be needed**). In all, your set-up is unique and should give killer performance when complete. :smile:
 
Rating - 0%
0   0   0
Joined
Nov 10, 2003
Messages
1,066
Thanks for your help I guess what I would like to do is set this up to run 16PSI if anyone knows what combonation of pulley's would be needed this would be great.
 
Rating - 0%
0   0   0
Joined
Sep 13, 2001
Messages
323
Location
Lake Mathews (Corona), Ca
Well, I'll need to correct my last post (which said everything is good) and go back to my original post (stating someything is funny). If you have a stock dia crank pulley (about 5.5" effective dia), your 3.625" blower pulley puts your drive ratio around 1.5. That's enough for 842 cfm at 8000 rpm (assuming 90% blower VE). Roughly speaking (VERY roughly), that'll get a stock NSX around 16 psi (pre IC pressure). Assuming you're not slipping, you need to check a couple of things. 1) pressure between your TB and blower at WOT (disconnect the air cleaner). If it's not zero or very close, you need a bigger TB. 2) Pressure between the blower and IC at WOT. Usually it's a psi or two higher than the pressure in the main manifold (depends on boost level, air temp drop and the IC's resistance to flow). If you see more, like 3, 4, 5, 6, etc, your IC or your manifolding simply can't flow the required volume. 3) Combination of the above. Just some thoughts . . . Mark
 
Rating - 0%
0   0   0
Joined
Sep 22, 2003
Messages
451
Location
DC metropolitan area (MD)
Mark911 said:
Well, I'll need to correct my last post (which said everything is good) and go back to my original post (stating someything is funny). If you have a stock dia crank pulley (about 5.5" effective dia), your 3.625" blower pulley puts your drive ratio around 1.5. That's enough for 842 cfm at 8000 rpm (assuming 90% blower VE). Roughly speaking (VERY roughly), that'll get a stock NSX around 16 psi (pre IC pressure). Assuming you're not slipping, you need to check a couple of things. 1) pressure between your TB and blower at WOT (disconnect the air cleaner). If it's not zero or very close, you need a bigger TB. 2) Pressure between the blower and IC at WOT. Usually it's a psi or two higher than the pressure in the main manifold (depends on boost level, air temp drop and the IC's resistance to flow). If you see more, like 3, 4, 5, 6, etc, your IC or your manifolding simply can't flow the required volume. 3) Combination of the above. Just some thoughts . . . Mark
So based on your rough calculations...the pressure drop from the IC which his set-up does have, other aspects, and possible slippage issues should have him at measurably less than 16psi....my fearless predication would be closer to 12psi with the 3.625inch supercharger pulley. (of course this is just a rough guesstimation being none of us have the actual flow specs/etc. on all the variables that can affect the pressure drop in this particular custom system)
 
Rating - 0%
0   0   0
Joined
Sep 13, 2001
Messages
323
Location
Lake Mathews (Corona), Ca
NSXTASY_MD said:
So based on your rough calculations...the pressure drop from the IC which his set-up does have, other aspects, and possible slippage issues should have him at measurably less than 16psi....my fearless predication would be closer to 12psi with the 3.625inch supercharger pulley. (of course this is just a rough guesstimation being none of us have the actual flow specs/etc. on all the variables that can affect the pressure drop in this particular custom system)


Yea, you might be right. My estimates are based on a big assumption regarding blower VE. Of course flow rate is what's important but you can't easily measure it. Pressure is a direct byproduct of flow so it's a pretty good indicator of flow again making certain assumtions about engine VE. Everyone tends to agree to disagree on both of the above assumtions so like you said, they're just SWAGs. That said, if everything was designed correctly on a stock engine, I'd expect around 14+ psi in the main manifold up to VTEC and towards redline. Probably a pound or two less in between. Based on my personal car, I'd say that would put it close to 500hp if tuned properly. If there are excessive pressure deltas between the air box and TB, TB and blower, blower exit to main mainifold, or exhaust header to exit pipe disregard all estimates as something in the "system" isn't designed properly.
 
Rating - 0%
0   0   0
Joined
May 24, 2004
Messages
96
Location
The Netherlands
The standard CTSC pushes 1,6 liters/ rev, on a 3.2 L engine the used air (NA) is (in theorie at 100% efficiency) 1,6 liters/rev. (Remember 4 stroke engine !)

With a pulley ratio of one crank rev : 1,5 supercharger rev and the standard 2% slip due to (correct tensioned !) drive belt th SC will run 11 760 revs at 8000 crank revs , providing 18816 liters of aiir

Due to the overlap in the valve timing, inlet valve and exhaust valve open at the same time, it is likely that pressure is lost in to the exhaust.

The NA engine will need 12800 Liters (@8000rpm) so the pressure availebale with this setup is 18816/12800 equals 1,47 Bar, a boost of 0,47 bar (= 6,768 PSI)

The temperature of the air will rise (compressing air gives temperature rise) so the amount of liters will be correct but the amount of oxigen molecules will be less ! (and therefore at fuel ratio of 14,6 to 1 less fuel ergo less horses )
 
Last edited:
Top