924Board.org

[morghen]

here is my solution for sizing and general design of the IC...none about mounting it on the 924 yet.

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Supercharger and EFI kits
https://www.the924.com

[ideola]

It never ceases to amaze me the resources that are available to an average guy like me if you just make the effort to reach out. Earlier this morning, I called Bell Intercoolers, fully expecting to get some sales schmuck on the other end of the line. Nope. It was Mr. Gerhard Schruf himself!!! I about fell over!!!

Anyway, we had a good 45-minute conversation about my build and my questions regarding IC design. He helped clarify a couple of things that I think will add a lot of value to this discussion.

First of all, the one point that is not immediately or intuitively apparent in Chapter 5 of Max Boost is that you have to strike a balance between flow efficiency and cooling efficiency. The point Gerhart made was that while a vertical flow IC will have superior flow efficiency (and therefore a theoretical lower pressure loss), a horizontal flow IC with the same frontal area will have superior cooling efficiency. Furthermore...and here's the important point...the tradeoff between flow efficiency and cooling efficiency is NOT a linear relationship; therefore, when balancing flow vs. cooling, superior cooling should always weigh more heavily than superior flow, provided that the pressure loss doesn't exceed 1.5 psi of boost (this is a so-called rule of thumb).

The upshot is this: all other constraints aside, a horizontal flow unit is usually preferred because it can be made to cool more efficiently with an acceptable pressure drop (1.0-1.5 psi) than a vertical flow unit. As an example assume a core with a frontal area of 10"x18" and a depth of 3". A horizontal flow configuration might experience ~1.5 psi pressure loss, but could cool as well as 75-80% efficiency. Conversely, a vertical flow configuration might experience ~1.0 psi pressure loss, but might only cool at a 60% efficiency. In that scenario, the 15-20% cooling gain at the expense of .5 psi of pressure loss is well worth it.

Apparently, ICs made with tubes ~18" long will typically experience <1.5 psi of pressure loss, while delivering excellent cooling efficiency, everything else being equal. Therefore, unless space constraints or plumbing arrangements dictate otherwise, for cars in our size and HP range, it's probably better to go with a horizontal flow IC because the pressure loss difference would be marginal, while the cooling potential could be significant.

Next we discussed my specific engine and BHP goals. To make a long story short ... ok, to make a long story not quite so long ... Gerhart recommended that I go with a horizontal FMIC positioned in front of the radiator (I'll come back to this momentarily) with a frontal area of 10"x18" and a depth of 3". Regarding placement, I questioned him about the impact to the radiator's ability to cool. His feeling was that for my specific application (which is a street legal car that can also be tracked, but will NOT be raced competitively), there shouldn't be any problem placing the IC in front of the rad, particularly if I upgrade the rad to a highly efficient aftermarket alternative to stock (which I was planning to do regardless). The reason is that my on-boost driving will probably be limited to fairly short bursts (i.e. street driving). I don't know how many seconds the back straight is at Waterford Hills, but full laps are typically less than 2 minutes. WH and Mid-Ohio are probably the only places I'll track the car, and then only for club / DE events; I don't see the FMIC in front of the rad being an issue for my intended use.

On the other hand, if I were going to be racing competitively and running all out for long periods of time, the location would be a significant concern, and he would recommend looking at other alternatives (different location, different size, different ducting, messing with rad placement, etc. etc. etc.).

Morghen, based on all of this and your stated HP goals, I think you're right on the money with your IC specs. It also explains a lot how Bass GT is able to achieve 73% efficiency with his modified 951 unit. I'm still concerned that the 951 unit might be a bit undersized for 350 BHP, but it certainly still looks feasible if I can execute placement, venting, and plumbing anywhere near as well as Bass GT. The real question for me now is to compare the cost of a 3x10x18 horizontal flow FMIC with a modified 951 unit. More homework
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erstwhile owner of just about every 924 variant ever made

[bass gt]

Dan,

Sorry, i was thinking your car was a track only car, hence my concern for the placement in front of the rad.
Now, as for your goal of 350BHP.......
In my opinion, to achieve this you ae going to need a fairly hefty huffer. Now this tends to result in pushing the power band up, making the delivery fairly severe. The result is that you can end up with a car that although has 50bhp, is actually slower, due to the chassis being unable to cope withthe power characteristics. I reckon 280-320 is idea for these cars, with the 3+ figures being on prpoer race cars, not using road tyres.
Simon, (Simsport) will confirm there was a 944 in our championship running 350ish BHP. But was a nightmare to drive,due to a tendency to throw the tail out whenever the power came on.
I run my car at 250, and although it is very much lightened, a road car with 280-300 would be equally as fast i think.
To ask the little old 2.0 8 valver to start pushing these figures is a bit much, especially when you consider you are doubling the stock BHP. we know these are not the most efficient engines, so to compensate, we need more boost. More boost= more heat, more stress ect.
I think you would be amazed at the performance of these cars with 260-300bhp, when you consider the Carrera GT had 210!!
One question, have you found uprated head studs. I'm not sure what you have over there, but the ARP studs for the Ford Cosworth Escort here in the UK fit a treat. If you need any info, give Arrow Engineering a call here in the UK. Measure the bolts and they will match them up for you. They are based in Hinckley.
Good Luck,

Steve
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Front Wheel Drive is the Devil's work.

[ideola]

Steve
Yep, frankly, 350 BHP may be pushing the envelope a bit ... more than 2x stock power. However, I think I have the huffer piece sorted out. Details are here.

My goal is to break 300 BHP at least, if for no other reason than just to do it but you bring up really good points about drivability. I have a race-prepped (rebuilt) snailshell with a rebuilt LSD. I've also acquired some suspension bits that should help me keep the 10"-12" of rear rubber I plan to run on the ground (the rear arches will accommodate up to 12" )

As for head studs, absolutely, I'll be going with Racewear studs. The plan right now is to have Eurorace (in Cali) prep the cam/head, and the racewear hardware will come with it. I have to check with them to make sure they can do the fitment of the solid lifters, if the Piper group buy goes thru

Even though this will be a "road car", it too will be significantly lightened...don't know if I can achieve <1000KG, but I'm definitely shooting to shed some weight. I plan to run all lexan except for the windscreen (already have most of it including the hatch), all FG body panels (already have the entire kit), and I'll be putting the chassis on a major diet (carpet, seats, sound deadening, stock rear arches, etc). It'll be bloody noisy in the cockpit, but I plan to be having too much fun to care! I'd like to see ~2100-2200 lbs if possible, which at 300+ BHP gives me a pretty favorable power to weight ratio

Thanks as always for chiming in and looking out for me!
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erstwhile owner of just about every 924 variant ever made

[endwrench]

Steve, nice info on the ARP head studs. I can usually buy them cheaper than what I paid for the Raceware studs.

Ideola, sounds like pretty sound advice from Bell. I wouldn't worry either about cooling with a front mount IC. I have this monster on the front of mine:

By endwrench at 2007-07-28

The core is 18"x12"x3" basically covering the entire front of the radiator. When I first mounted it I did have some heating problems on hot days. I decided the radiator was not big enough so I replaced it with a 951 unit. This definatly cooled me down! Afterthought tells me it was not all the FMIC's fault though. I believe it was the way I mounted it. It was sucked up tight against the stock radiator and because the "bars" on the IC ran in the same direction as the cores on the radiator, they blocked atleast half the cores from getting ANY flow accros them! It's amazing it didn't overheat all the time. The new radiator happened to mount up about 3\4" away from the IC allowing the air to flow thru the entire radiator. I sealed the edges so it would not flow around. keed this in mind while mounting yours.

Todd
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'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[leadfoot]

I like your ideas dan,
I will add this. Cooling to the engines is greatly improved over stock by
a) changing the coolant crossover pipe design
b) having electronic control over the thermo fans
c) having a decent oil cooler

You have pictures of a lower mounted intercooler, the design of having baffles to trap the air through the coolers is a good idea.

I took a slightly different approach when doing my setup and it worked well for me.
That was to have a large oil cooler mounted up high receiving fresh air and ducted out through the header panel.
Have a baffled intercooler mounted lower to trap most of the air though it and vent it down to the ground under the engine.
Leaving a gap between these two to receive a direct supply of freah air to the radiator and vent over the engine using the hood scoop to
a) vent excess heat off at stops
b) create airflow under the hood from front to back by creating higher pressures around the nose of the car and keep the lower pressures well to the rear of the engine.

If you spent a little time in setting up ducting to your coolers through sealed traps you would also be able to measure temperature drops.

There was also a good article online about filling your intercooler with parrafin wax for short burst heat soaking ability...as the energy required to turn a solid to liquid was quite alot, that's if you wanted to get really tricky.
Stuart
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Raceboy]

Breaking 300hp is pretty much a nobrainer when you have basics covered like pistons, engine managent, cooling (both water and air) and turbocharger.

Can't help myself reminding that I got 208 rwhp (about 240 at the flywheel) from stock, not overhauled (300 000+ kms on the clock) Euro 924 NA engine simply by adding turbo, 951 IC and proper engine management.

And those numbers are verified by brand new (6000 kms on the clock) BMW 740 that measured the same time and had nearly stock hp figures (less than 5% difference that can be counted in measuring error).

Not to mention my setup has last no for more than 15 000 kms and that includes several track days, onw top speed challenge and about 10 local dragraces And all of that with crappy NA head.

Getting power out those engines is easy, getting powerband as wide as possible is hard and getting that power to the ground is also hard.

Remember, GTR's lasted 24hrs of LeMans with around 400hp sporting the same engine block and basically the same head (my bet is that many of us have better 931 heads for now than those back in 1980/81).
Gearbox was the weak spot.

You are building a hell of a 931 and like Steve, your engine will be capable for much more than 350, just you won't have to push it and that 300 is perfectly safe hp for those mean machines

Good luck!
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'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

[ideola]

Just arrived today:


Now I can start working on the mounting brackets for everything up front: rad, intercooler, headlight buckets, header panel, and hood pins.

Question: I'd like to paint this to dress it up. I'm thinking either flat black (for stealth mode) or bright silver (why not show it off...the body paint is already going to be a ticket magnet!). Can I just paint this as-is with regular off-the-shelf rustoleum, or will paint on the fins affect the performance?
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erstwhile owner of just about every 924 variant ever made

[flosho]

Dan, I don't think its a good idea to paint the actual intercooler core with regular paint. I've heard that can hurt the cooling efficiency.

Instead having it anodized is better.

Of course this is just what some joe-blows have said on the internet..
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[This Space For Rent]

[tuurbo]

I personally wouldn't - I'd paint everything but the fins. Why mess with success?
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1980 924 turbo, MSD, Meth. Inj, otherwise stock.

[ideola]

Anodizing is out because the end tanks are cast, and anodizing doesn't work well with cast alu.

Maybe I'll just give it a good bath in POR15 Marine Clean and Metal Ready. That stuff is pretty good at cleaning stuff up, and I bet with a good power wash, it would come out looking much spiffier than it does at the moment.
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erstwhile owner of just about every 924 variant ever made

[bass gt]

Dan,

A useful add on to better the IC's efficiency would be a high pressure water spray system. If you had a tube similar to the camshaft oiling tube mounted in front of the IC, with TINY holes to achieve good atomisation, you would see massive increase in the IC efficiency. Add to this, if you can vent the IC through the hood as i have done, i believe the951 unit is ideal, especially in your circumstance. ie, a road car with occaisional track use. The higher the pump pressure, the better the water atomisation, the more marked the cooling effect. Try obtaining an Aquamist water injection pump or similar, and you will be on the money!
Trigger this through the ECU or a standalone logic board from the air inlet temp. on at a set temp, off at a set temp, perhaps with boost present as an added condition. if you configure the system to come on before the charge air gets too hot, you should be able to up the power nicely!! The water tank can go anywhere, so it's an easy system to implement. And yes, this will be going onto my car!!

Steve
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Front Wheel Drive is the Devil's work.

[ideola]

Hood vent is definitely in the works! I have a fiberglass hood now, so creating the vent will be much easier, especially with what I have in mind. Bwahahahah!

I may add the water spray as a stage II at some point...need to get the basic tune sorted, which I expect will take me several weeks or months once I get the motor built. Another approach I'm looking into at the moment is a Peltier-effect second stage intercooler. I need to determine what my 160 AMP alt will be able to handle, but it's a very interesting approach.
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erstwhile owner of just about every 924 variant ever made

[!tom]

[Rasta Monsta]