GlenL

Thanks, Marc!

Ducting from the base of the windshield is the best approach, I figure. Just don't want to cut up the firewall.

Having reviewed Porken's post on this approach, I'm not surprised at the response.

I'm going to do a dyno run with the blower fans off just for John... A chassis dyno like the DynoJet doesn't replicate actual conditions which is a point I've made to folks on other issues. It is about the best opportunity to do a trial under controlled conditions.

I will not be reporting my assometer numbers, even though mine is NIST traceable.

One things for sure, it looks cool when I pop the hood!

John..

I can tell you the stock 4.5/4.7 air filtration system will easily support over 400 crank HP worth of air without any modifications. This is after the air is all shoved through a 2.5" diameter pipe, complete with bends. Contrary to popular belief, you don't need a large intake pipe to make large amounts of HP once you are force induced. All 400+ HP of air feeding my 4.5 liter flows into the manifold through one 2.25" diameter pipe. Of course the air is compressed there and that is the key difference.

To do it right and get meaningful results you would have to be in an environment with moving air and dyno with the hood closed, but there are only a handful of places that have setups like that...I believe Dinan has a setup like this.

I am with you on Dynojet, if I put the new turbo car on a dyno I might do the load dyno this time because you can hold a given load much longer.

Still, we can't discount Porsche's effort with the intake system. It pulls air from the cold side of the radiator outside of the engine compartment. There probably is a better way to do it, but keeping anything that looks normal and increases the performance would be a tough task.

Even the 944's airbox snout pulls air from a cold source, under the driver's side fender. I am not a fan of the cone air filter setup so many people run in an open heated engine compartment these days.

Now let's talk K&N....do you think these increase performance? I had one and got rid of it, but there may be some merit there....I just don't know. Another thread for another day....

PorKen

Simplify, simplify... make it fly!



Note: long ago I removed the engine driven fan and fan shrouds, so some cool air can go over the top of the radiator.

GlenL

Frankly no. But the assometer notices the change from a dirty filter to a clean one!

mark kibort

I vent my air box to the rear and use the stock tubes. then, you get the best of both worlds, and the timing belt gets some venting too.
what the designs show here is that all the air is being fed from the engine compartment. all you need to do, is seal that entire box to the base of the windshield. as we all know, the base of the windshield has almost the same pressure rise as the nose of the car. ( or just below the nose.)
Marc T is right, the real nose of the car would be the best place.
mk

GlenL

(cross-post from email list)

Ran the 1980 Euro S on the dyno today. Results were good but not what I had hoped but still farther than what I'd feared. I didn't get the printout and the shop is going to email the data so I can't be as precise as this engineer would like.

The top numbers for the day were 255 rwhp (SAE) at 3900 rpm. The torque for the run was around 250ft lbs. The A/F ratio tailed down from 13.5:1 to just below 13:1 at 6200 rpm. Two years ago I was at 248 rwhp without any tuning. These are Dynojet numbers.

I spent a few runs tweaking the mixture buit wasn't getting much more my richening the mixture. Any lower than 13:1 and the top-end suffered. I made some adjustment to the timing but it was acting a bit strange. I'm suspecting a problem in the vacuum or mechanical advance. (Steve? Ya out there?) It's around 31 or 32 degrees at 3000 with hoses off.

The really interesting part was the final run where I removed my special open-frame air cleaner lid and put back on the stock cover and venturi hoses. This garnered a 4 hp _increase_. The conditions were a bit sub-standard as the shop had two small blowers that shot directly into the grill and did not provide any cool air to the engine. A moving car may provide cooler air back there. Be that as it may, that there was a decent increase going to stock shows that the stock cover and tubes are not restrictive. I may try the open frame at the track and check some lap times as that's what matters, but I think the data here is nearly conclusive.

Nice to see Mike S. at the shop. Can't miss his pristine '79. Our cars looked a bit out of place at the sport compact tuner shop, but the guys were nice enough!

PorKen

That horsepower peak seems low, especially for a euro cam. Ought'n it be about a grand or more higher, with more power?

My US '81's peak (stock cam advance), was around 5200 on the dyno.

GlenL

Typo! The HP peak is at 5900rpm. Just a bit below the rev limiter.

The stock rating is 300hp so 255 rwhp is exactly 15% down. Decent. Not 230 hp. I did hope for 265 though.

GlenL

The shop sent the dyno runs. Here's the best versus the previous best from 2 years and an engine rebuild ago.

I've put the numbers in DIN horsepower for A) the fun of it and B) that's the way Porsche specs them. It's 255 hp SAE.

You'll note that the fuel mix is much richer this time around and I've got the distributor advanced a few more degrees. (Gotta check that!)

GlenL

Wandered into this old thread looking to delete pics...

Tried the fancy airbox top at the track a few weeks ago and it was noticeably slower than the stock top. In the session I ran it I could only get to 140 mph at the end of a 1-mile straight. The session before I was getting 145 and the session after I was touching 150.

The ambient air was a cool 70F so figured there'd be enough blowing through the engine bay to get just warm air to the filter. No!

My final judgment is that the air is more warmer this way than the intake is restrictive with the venturi tubes. My next approach is going to be straight intake tubes. $5 a side at Fleet Farm...or maybe something better looking.

danglerb

Last time I measured the air temperature coming out of the radiator it was I believe 165F.

Mike Frye

Nice resurrection, thanks.

This post surprised me. I'm pretty sure that the forced induction guys just cap off or ignore the vent tube openings at the top of the timing belt covers. I did the same with mine when I put in the 'snorkel' CAI after speaking with a few forced induction guys.

Does anyone know what this post is referring to? Where in any of the literature does it say what those vents are for? I've never read it in anything from Porsche.

GlenL

This is much debated. Do those vents draw air out or blow air in?

I believe the 944 series went away from using the vent from the belt covers.

I plan to leave them disconnected when going to straight tubes.

Mike Frye

I can see how they would pull air up from the bottom, across the belt (for whatever reason) and then get sucked along toward the rear. I've just never heard of any actual documentation of the purpose of it. Is it to cool the belt? Is it to pull air from down below the engine (cooler air)? The post I quoted earlier seemed to indicate that there was something in a manual somewhere that explained it, I was hoping to find that or someone who might know at least what he's referring to.

hernanca

Wow! Recent postings on this old thread!

I was searching and reading posts on air induction.. This thread or another related one also mentioned that the holes might be used to clear out the Timing Belt "dust"? I guess this could become a problem if neglected over a long period of time? I would also like to know where any of this may be documented.