924Board.org

[924 turbo]

I know this is going to seem like I'm picking on the n/a crowd. That's not my intention. So many questions get posted here about 924 and 924S upgrades, and on the Pelican board 944n/a upgrades are discussed constantly.

I know you guys love your cars. I really liked my 924n/a also. But there really isn't much you can do to make it a fast car without spending a ridiculous amount of money on it.

If your intention is only to make your car faster, which you are not willing to get rid of for personal reasons (love, worship, unnatural attachment ) this does not apply to you. If you are out to prove a point (the "I can make a 924n/a fast and I'm willing to sell a kidney to do so" crowd) this does not apply to you. This also does not apply to classed race cars.

For the rest of you...pick a benchmark for the straight-line performance you'd like to achieve. For me, it is the Mustang. I want my car to be about as fast as an unmodified, new, manual Mustang GT. The Mustang is approximately 3270 lbs and makes 260hp. That gives it a power-to-weight ratio of about 12.6 lbs/hp. The 924n/a weighs about 2600 lbs. It makes about 110-115hp. For argument's sake, let's say 115. That give the 924 n/a a power-to-weight ratio of 22.6 lbs/hp.

So, what are your options? You can modify the engine and remove weight...both will make your car faster.

Let's take the free weight savings Jon McCullough lists on his site, http://come.to/924.org. Back seat, insulation mat, AC system, dampening mat, charcoal canister and luggage cover. In my opinion, this is as far as most street drivers would go. You'll probably keep both front seats, the carpeting, etc. Using the numbers Jon listed, your grand total is around 200 lbs. Your new power-to-weight ratio: 20.87 lbs/hp.

Okay, time to start modifying the engine. Porting the head, using a bigger camshaft, a header, a larger exhaust, a test pipe, a larger throttle body, and bumping the compression should yield around 150hp. It'll also set you back...around $1300 if you port the heads yourself and do your own installations. This is around the theoretical street maximum HP for the 924. There are other small tricks you can do, but none of them will have a great effect on horsepower. After this point, your upgrades are thousands of dollars and include things like stroker kits, 931 heads and intakes with custom pistons, etc. Remember we're talking about street cars here. Anyway, where did that round of modifications get you? 16.0 lbs/hp.

Sounds good, right? So where would you fit in with modern car power-to-weight ratios? You'd be a hair slower than a Toyota MR2 Spyder, slower still than a new Acura Integra GS-R.

If this is your goal, congratulations. You haven't spent a bundle of money, and you're probably pretty happy with the streetability of your modifications.

Do you have a fast car? Not really. That Mustang is still making you look pretty bad, and even the unmodified Integra your little sister drives is faster.

Where does the 924S/944n/a fit in all this? The road here is brighter. You're starting out with better power-to-weight ratios than the 924n/a guys. Let's take a look:

For kicks we'll use the 160hp version of the 924S. At 2734 lbs, your power-to-weight ratio is 17.0 lbs/hp. The early 944 weighs 2675 lbs and is 147hp. That puts it at 18.2 lbs/hp. The later 944 was 160hp at 2844 lbs, or 17.8 lbs/hp. We'll assume that you can remove the same amount of weight from these cars, and adjust the numbers accordingly:

924S: 15.8 lbs/hp
944(early): 16.8 lbs/hp
944(late): 16.5 lbs/hp

A Huntley stage II MAF kit is $1500, a stage I kit is $1200. That's a lot of money. Let's say you find some money in your old jeans and decide to get the stage II MAF kit, a header, test pipe, exhaust, and K&N air filter. According to Huntley, the stage II kit is worth 15hp, probably at the rear wheels. Let's say with the header and other goodies, you get 40 flywheel horsepower. You'd be right around 200hp now. Sure, it was a big investment (around $2000+) let's see how the numbers come out now...

924S: 12.7 lbs/hp
944(early): 13.2 lbs/hp
944(late): 13.2 lbs/hp

Woohoo! The 924S is finally in Mustang territory. Of course, you had to spend a bunch of money to get here. You might have been able to buy a 944 turbo instead at this point.

Now for the best part: The 924 Turbo
For the purposes of this discussion, I'm going to use the Series 2 931 (because that's what I have ). The series 2 931 is 2779 lbs, and 154hp. That puts the power-to-weight ratio at 18.0 lbs/hp. Ouch! What can we do about this?

Okay same weight savings here as with the other cars. We're down to 16.8 lbs/hp now.

Here comes the fun part...

Boost controller: $60
944 intercooler: $200
Piping: $200
Look on the Mustang guy's face: Priceless

The intercooler and associated piping add approximately 35 lbs. But the result is inspiring. At 10psi of boost (0.68 bar) the car makes approximately 210hp. Where does that put you on the power-to-weight scale? 12.5 lbs/hp. Mustang territory, for less than $500. If you're brave enough to run 0.9 bar you're looking at approximately 230hp. That would put you at 11.4 lbs/hp. You could now keep up with a Boxster S, outrun a Honda S2000, and almost catch a 928S4.

A fuel mod would allow you to run 1 bar of boost or more. This would likely put you in the 245+ horsepower range, but it would probably also eat $1000 or more of your dollars.

Of course, your new competition would be Mustang Cobras, the NSX, and the new, 333hp M3.

So which car did you want to modify again?

Long live the 931...

_________________
Jon Furst
'81 931/951 intercooler project

[ This Message was edited by: 924 turbo on 2001-08-09 18:35 ]

[924RACR]

Loved the analysis! How does this change for the Series II, like mine?

I have to admit, drove the car in to work for the first time today... and found a C5 Vette to chase... almost the same plat. metallic as my car! OK, so I know he wasn't totally laying into it, and I wasn't running the ragged edge either, since we were on a public road, but we did have a little fun playing follow the leader for a mile or two...

I'm interested in staying up to date on your intercooler project... how goes it? Have you driven the car yet? I'd like to attempt the install from below, without touching the badge panel, as I don't want to repaint my car yet. I also want to keep the stock headlights. I have no problem cutting and welding underneath/behind the panel. I will have to take another look at your layout and plumbing to figure how it goes again...

(already have the intercooler and boost regulator, just need to deal with some maintenance issues and buy a boost gauge)

BTW, can everybody else hear their turbo spool? Mine's very loud out the tailpipe - and I love it!

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Peter]

Jon, how did you go about fabricating the piping? That is, did you go to a performance shop and ask them to plum everything, maybe a good mufler shop, or did you buy different pieces of tubing and measure and cut?
Vaughan, what boost controller are you using?
-Peter

[924RACR]

I don't have anything installed yet, but have a regulator on hand... just need a boost gauge and the intercooler installed.

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[larso]

924s are not actaully light cars really, some 931s are 3000 pounds from the factoy.

Hondas and small bmws weigh about 2500 pounds fromt the factory, if u weight reducted that car (bmw, civic), u could go fast, thats why there are some rare civics which are actually fast.

IMO people should buy a motor bike...what exactly is the point of buying a camaro when u can just get a motor bike that will blow away camaros????

People talk about if you have a turbo car over an NA car that isn't cheating...FINE, then neither is riding a motor bike against a camaro, so go buy a bike for 3000 bucks and save your 70 000 that you would have bought the viper with.

Another situation is the tranny, sometimes the 0-60 times really give a bad impression of a car...

How often do you actaully do a 0-60?
Where I drive, I usually need to do a 20MPH-60MPH run...not a 0-60.

[ This Message was edited by: larso on 2001-08-10 06:54 ]

[larso]

BY the way JON, turbos are a nice way to horsepower, but they just don't cut it for track, lag SUCKS!

[924 turbo]

1. The pipes are in the mail! I'm totally excited to get them together. I bought a bunch of bends, which I'm going to assemble, cut, then have welded together. I'm going to leave one section on each pipe soft to allow for flexing. Of course, the full and final dimensions will be available to anyone. And I've found out that I have to file the corner off of the passenger side headlight mechanism to make room for the pipe, but it's no big deal. Of course, more info to come...soon (really this time )

2. 20-60, 40-100, i'm not really concerned. The only reason the car would be excessively slow over 60 would be due to bad gearing or poor aerodynamics. As far as I'm concerned, this car has neither.

3. Lag shmag. Yes, a n/a car making the same power would likely be faster. Good luck getting 225+hp out of the 2.5 liter 944 engine, not to mention the 2.0 liter 924 engine. You've also got to remember that as n/a engines make more horsepower, their power bands get narrower and higher, which effectively does the same thing to you as turbo lag. This is especially true for small-displacement 4-cylinder engines. Sound familiar? Can you imagine how narrow the power band would be on a 200hp n/a 924 2.0?

[Rick MacLaren]

Great analysis Jon.

You scared the shit out of me however,...do you mean to say at 15 PSI I should have done something else to my fuel delivery system besides cooling the air with alcohol and water? What else has to be done?

[Dave]

924S RULES!!! Im at about the 200hp now. YA there was lots of $$$$ involved But I always have the HP I dont have to wait for a turbo to kick in I thought the 924 turbos where slower then the 924S??? Im looking to buil a motor for my car that will put out about 225 HP at the wheels IS a 931 A 924T. Im also looking into putting a 944 turbo engine into my 924S.

[924 turbo]

Yes, Rick! The factory fuel system adds fuel to approximately 0.8 bar (11.7psi). If you're not doing anything else to add fuel, you should be leaning out at the top end. Getting an air-fuel meter would verify this.

This is not NECESSARILY true though, since the factory system can add fuel via the air-flow meter as well. Get an air-fuel meter and verify this for us, Rick!

Dave: The 931 is the 924 turbo. Yes, the stock 924S is slightly faster than the 931. However, the 931 is a turbo car, and judging from my analysis above (ok, ok, I know that I'm biased) you can see where modifications get you.

I might be able to dyno my car when it's ready, as there are several local places that have dynos.

[larso]

RICK, get a 928 fuel distrib, mangle it up so that it works on four cylinders...i believe the carreras use the 928 fuel distrib, not sure which ones or if all.

I am not saying u want to get 200 HP out of a 2 litre, a 944 can be 200 HP gettable IMO fairly easily, some of the engines have 160 HP stock, not to mention if you got a 3 litre 944 engine...throw a nice cam in it, put a MAF on it....make it 2.8 or 3 litre...balance it, shave block and/or head, pistons, balancing...or hell, you could just buy the #### 911 and learn how to drive it!

[Vince]

All of the hop ups you describe were done by me a long long time ago. Including lightening the car. What you get is a very finicky car that only wants to run full tilt. I love my 924 and the euro 79 931 but for the street the mod 924 is a bear to tolerate. Don't get me wrong as the owner of a 44 and a 911 I still love my 24 first. As for fast I never jump off the line for fear of losing the clutch. Rolling is fine. On the track it holds its own against 44s and 24Ss. You are correct in that it takes a lot of money to get to the 150 mark. I would now rather buy a 924S and make the changes. But then in 1982 we did not have 924Ss.

[Dave]

Analysis is WRONG guys. Sure your ideas would work but then who is driving the CAR?? You didnt add in the weight of the driver!!!

[Rick MacLaren]

Lars, Jon, do I have to change my fuel distributor? Or can I just hook up a more powerful fuel pump?

Damn!

[Joes924]

150 lb/hp

[ This Message was edited by: joes924 on 2001-10-20 14:31 ]