924Board.org

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

I found this site.
http://www.stealth316.com/2-air-fuel-flow.htm
With these calculations I figured the 1984 displacement ,at 1000 rpm,
Natural Capacity 100%,Density ratio 1.=574.07 CFM
If I divide this # by 4 should I have the optimum air flow for one runner?
=143CFM 100% VE
Then by using the results from air flow data from "bolt on Bonanza" below
http://www.geocities.com/the_924_site/BOB1_4.html
It seems that the intake manifold is ported more than than enough to allow for 100% VE airflow.
Therefore the problem lies in getting the right TB to hit that 143cfm.
With the restrictor in, the 108CFM is to small, without it at 158CFM its' too big.
This is why a Larger TB upgrade never had any results in HP.
They were going too big when they actually had to fine tune the TB to narrow the opening just a little from 152 to 143cfm.
The closer we get to that 142cfm the smoother and quicker the entire throttle response will be.
Does this make sense or did I figure this wrong?
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

leadfoot · Posted: Sun Aug 21, 2005 2:53 pm Post subject:

I would think natural capacity would not be 100% as there is a 180 degree bend in the intake, and there is frictional losses due to surface materials.
Most books give an ideal VE of a non forced induction motor to be around 80 - 88% for older two valve engines. All my calculations were adjusted by 15% after I did my supercharger setup and this seems to mesh with the results I get from my ecu, handy having a MAP sensor!!.
Of course I had flow losses from my SC, intercooler and cam as well, but if you gave yourself this margin it might prove to be more acurate.
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

CBass · Joined: 03 Nov 2002 Posts: 2807 Location: Vancouver, Canada

The trick to getting 100% VE is to overcome the inefficiencies inherent to the engine with inertia supercharging. My 924 is modified, but I sincerely doubt I make more than 140-150hp. The head is junk, and either needs to be seriously reworked or it needs to be junked.

One of these days I'm going to hit up a dyno day, and it's going to make me cry...

_________________
'81 931 in various states of assembly

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

I was reading recently that most older two-valve engines are in the 75% to 85% VE range (they were talking about pushrod V8s) and most modern four-valve engines are in the 85% to 95% range.

I'd guess a 924 would probably average around 85%. Don't forget that VE changes over the entire rev range.

The Honda S2000 engine is rated at slightly over 100% VE (a slight supercharge) but then that engine has won SAE awards because it's so insanely amazing.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

I have driven it 2 times, and IMO with 240hp it should accelerate MUCH better, than quoted 6.8s 0-100kph. I totally agree with you Peter about those gear ratios.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

I suppose that the scientific equations are:

big hp/kw = magazine covers

big torque = low ETs

_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Lizard · Posted: Fri Aug 26, 2005 12:40 am Post subject:

that is why the boxster hoses the S2000, torque,

I would rather have 300ft lb and 300bhp as supposed to 200ft lb and 400hp,
but then again just remember that high torque is what causes things to break in the drivetrain.
_________________
3 928s,

CBass · Joined: 03 Nov 2002 Posts: 2807 Location: Vancouver, Canada

The S2000 makes more torque than the 924. The original 2.0 liter S2000 made 150ftlb, so 75ftlb/liter, the same figure which was so impressive when the 968 was built. Also, it has two distinctly different cam profiles, and excellent port velocity, so it's really quite driveable at low speeds. Just don't expect it to pull like it has a 5 liter engine, because it doesn't.

Sure, it's no diesel, but drive any classic sports car and you'll find yourself noting it seems to lack torque.
_________________
'81 931 in various states of assembly

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

Sry CBass, but as a car journalist, I've driven MANY sportscars (including new 997 S at the racetrack on Tuesday

) and S2000 has: 1) a powerband too high for normal street usage 2) no suitable gearbox to use it's powerband on the track. That's a lousy combination IMO. If it had a good (suitable for high revs) gearbox, it would be excellent ride on the track, but with what it has now, how to put it? No fish, no meat, I don't know what it is....
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

leadfoot · Posted: Fri Aug 26, 2005 2:12 pm Post subject:

"Suitable for turbocharging"

"Powerhouse Amuse in japan has strapped a Trust TD06-20G to a standard 11:1 engine and changed the stock 180nM @6000rpm to a more pleasant 240nM @4000rpm at .45bar"

I'd like to see a whipple strapped to it instead, sacrifice a few top end ponies for some really usable torque. You could easilt fit a eunos charger down the side of the engine bay bolted onto the intake.
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

J1NX3D · Joined: 06 Feb 2003 Posts: 1333 Location: New Zealand

i think u guys will like this thread from rennlist
http://forums.rennlist.com/rennforums/showthread.php?t=221549
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'86 944

CBass · Joined: 03 Nov 2002 Posts: 2807 Location: Vancouver, Canada

http://www.aempower.com/pdf/dyno/24-6104%202004%20Honda%20S2000%20Dyno%20Numbers.pdf

Dyno sheet for an original 2.0 liter S2000. It's a bit soggy between 1500-2500rpm, but so's a 931

The least torque you're seeing is still over 100ftlb, which in my 2100 lb GTI feels quite torquey. By comparison, the 3.0 liter 968 has a flat torque curve of 150-160ftlb from 2000-3000, and makes the same peak hp roughly. The S2000 is about as torquey down low as a VW 2.0 16v, which is also mated to tall gears. It won't pull stumps but it's still quite liveable. Keep in mind, any built N/A 2.0 liter engine is going to be lacking in the bottom end, even most built 3.0 liter engines are.

I think we're taking a lot for granted these days... It's a sports car, it's not mean to be practical, it's not meant to haul groceries or pull trailers... It's meant to gobble up twisty roads, and they do that quite well. Sometimes I feel like us 924 owners have been spoiled by our practical and easy to drive cars.

As for the gearbox, where do ya think the quote of "mad tight third gear VTEC" comes from?

_________________
'81 931 in various states of assembly

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

Thought some of you might be interested in this. It`s the VE table from a GM/Delco computer for a Holden Camira (4 cylinder, normally aspired, SOHC, 86mm bore, 1998cc - sound familiar?):