blown 87

They really are works of art, and his engine is scary as to how fast it revs.

928mac

Ok I mean intake , or air filter assembly that sits on top.
Do you have anything like that.

Mike Simard

I'm on my 3rd airbox design. First was aluminum and worked well. Then I made one in CF that had an oval snout coming forward over the radiator to a giant oval filter in the bumper. I wasn't happy with that so am now working on more traditional one in CF. This time I'm having it molded and it might even be a universal item. Those should be here any day.
I'm getting away from the oval snout over the radiator and going with canisters above the valve covers. Keeping everything behind the radiator will make life much easier. The biggest problem when using this kind of induction system is 'what to do for filters'. I'm trying to make that as pleasant as possible for installation and day to day life.

dr bob

Mike-

How much room is there between the tops of the bells and the bottom of the hood? And how far away do you try to keep the roof of the airbox from the bells so you don't spoil the airflow there?

If the height was less of a problem, the temptaion would be to fit a large flat filter element above the bells, so it could even out the distribution of incoming air above the filter before it gets down to the bells. Lateral flow across the bellmouth is the biggest disturbance.


With the height limitations, the ultimate airbox for your ITB intake will likely end up pretty wide. It has a flat filter element over each cam cover, with an end-fed plenum feeding air to each filter from the existing nozzles in the radiator sheet. Flow to the main airbox will be from both sides to minimize crosstalk between the bells. The top of the main box should be tall as possible within the limits of the hood and engine movement. A lexan top center section would make it possible to show off the goodies, and also to put some telltales in there to video airflow paths during hard pulls. Not that there's a whole lot you can do there short of baffling each bell to the filter wall individually.


If I wanted it to pass Cali smog inspection, the top cover would be molded plastic to include "PORSCHE V8" on either side. If it looks like the factory made it, it will pass. Plus it would hide all the obviously non-stock hardware around the fuel rails and the throttles. Good for the smog ***** here but not a good way to display the underhood eye candy.


You'd still be stuck trying to get the cruise control hooked up...

blown 87

Mike, a air box like is on the ITB set up on a M5 would look great on a 928.

Mike Simard

The hood is tapered and there's about 1" at the front and 2-3/4" at the rear. That's to the highest point on the trumpets which are at an angle.
Air enters a trumpet from the sides so a 'low roof' isn't the problem you might think.
I know what you mean about placing a flat filter on top. I did that on my Cobra ITB setup, a flat vette C4 filter fit over the group of trumpets well and there was a hood scoop there too.
That's not practical on a 928 but there is enough room on the sides for canister filters that can feed the rear of the box, that's the plan in the works now. Feeding the box from the front is fine too but it's tricky to not get in the way of radiators etc.
The current box will hang over the fuel rails a bit to keep lots of space around the trumpets. They'll come molded with no inlet to allow design freedom. Being able to tuck everything in behind the radiator but still have good filter area would be the airbox holy grail.
It sounds like you have some good ideas for a box. I did contemplate other ways but yours sounds interesting. One thing to consider is daily life with the box in place. Being able to get at spark plugs easily is nice. It's essential that you not dread in any way working around a part like this. In other words, if you have to do some work under the hood someday, the airbox should be something that you don't even think about as you go about your work.

dr bob

Mike--

Envision the panel air filters almost vertical just outside the fuel rails. Almost-round plenum with hose nozzle facing forward clips on to the filter area. Want to change plugs? A few clips and the plenum is out of the way. The plenum would end up right about where the stock air ducts live now, over the cam covers.

If you don't mind the uneven flow pulsing, you could make a single piece for each side, a round-topped box that would sit down around the bells some. Or on top of them but that may not be best. Anyway, one tooling would work for both sides, and a second tooling for the plenum outside the filters. Inner pieces swap side to side. Plenums roll end to end so inlet nozzes face forward on either side. didin't notice what you are using fro airflow measurement. MAP and TPS, or MAF?

andy-gts

I had to post again as dr bob's post is 666, hahahahahah!!!!!!

I havent heard from Greg except the fact that the second dyno session everything was working as plannned and he would have things ready for pickup . that was end of february......just getting a little fidgety...

Ready for the drive home to kansas ....Greg????


andy

andy-gts

Question for those with much more knowlege....

I currently am running the old devel level 2 headers with their 3 inch cross over and dual exhaust...

I have read and understand louis otts experiment with stock engine.....should I keep the 3 inch dual exhaust.
Am I giving up something. I think Tim Dey is running the 3 inch exhaust....any science to the exhuast we have available.

Mike Simard I am sure you have thought and concluded many things regarding this among other things....anyone have any thoughts ??

Louie928

Andy,
Not sure about science, but this is my thoughts. For HO stroker motor use dual 3". For any 5.0 or 5.4 use dual 2.5". Some people like a single large pipe, but it is quite difficult to get effective mufflers that will fit. I went from the header collectors to 4"OD/3"ID straight through mufflers then an X behind that. I used a 3" in/out Borlas beside the transmission then nearly straight out from there. I had already used the rear muffler space for the engine oil cooler and I wanted a different treatment for the exhaust anyway. The tranny cooler (GT engine oil cooler) is in the rear bumper channel vented out beside the license plate. I figured I'd need the four mufflers and the front mufflers sorta look like cats if anybody looks. I probably should have used larger mufflers than the Borlas because it is still quite loud for the few seconds you have the throttle open. Not bad on the highway at legal speeds. It has a resonant howl at around 3000 RPM and I listen to that rather than the radio.

Louie

andy-gts

thanks for the pictures Louie.

I seem to remember that you wanted the crossover back a little bit to move the peak torque further up the rpm band...did it do this and make it more drivable around town?

thanks for your reply..
andy

Louie928

Hi Andy,
I have no clue as to what effect, if any, the position of the crossover made on my car. I have read that crossover position does have an effect. I wanted the front mufflers and they fit where the cats normally are. I put the crossover right behind the mufflers because it fit better there. It was strictly a "where will it fit" decision. It is not very pleasant to drive around town although it will do it. It runs best at about 40mph on up. I'm convinced the reason is that the cams have the lobe separation angle too close (106.5 deg) for the amount of duration. Probably a lobe separation of 110 to 112 deg would make for a more docile behavior. These cams were ground from S4 cams and it would have been better had they been ground from GT (LSA 110 deg)or S3 (LSA 113 deg) cams. However they weren't, and at the time no one really knew what the outcome would be.

I did an exhaust on a 5.0L GT with the Devek headers. On that car, I kept the crossover up front right behind the collectors just in case someone wanted cats later. I transitioned from the 3" collector outlet with a tapered section to the 2.5" crossover inlet. That worked out really well with 349 lb ft torque at 3000 and 338 rwhp at 6000. Whether it would have made a different result with the crossover further back I don't know. The normal X pipe has the X further back but with the exchange of the stock exhaust manifold to headers it isn't a direct comparison. I don't think I have a picture of the header collector to 2.5" X crossover transition. I do have a dyno result of the car with a regular X crossover and 2.5" rear exhaust vs the Devek headers and 2.5" rear exhaust. The gain is only from the Devek headers and you can see the greatest gain with the headers is from the low end on up. That helps drivability a lot. It seems to me that we were able to get about 10 hp more after tuning, but I don't have the dyno run here at the house. Jim Corenman has the car now and he was able to refine the tuning more after he got it.

Louie

GregBBRD

Yes. Performing the "after dyno" service. Oil filter looked great.

Pan is off and am looking at the rod beaings...everything looks fine. I'll probably "roll" in a new set of bearings and have these looked at by the manufacturer...for any "insights" that they may have. We will also check the rod bolt stretch on all the bolts, to make sure everything is perfect.

Valve covers are off and everything looks fine. I've got one little modification to finish. in there, and we will put them back on.

Engine will go into chassis, this week. Still have to figure out how to make the automatic kickdown work with this throttle linkage and fabricate the pieces, for this. Need to fabricate something for air filters, etc. Need to hook up the wiring loom that we used on the dyno so it works in the car. Once it works in the car, we will then take it out again and have it covered. The engine will need to be "tuned" to compensate for being in the car and not on the dyno.

Doing fine...but none of these things are 10 minute jobs.

Mike Simard

I have done little thinking over the exhaust. A quick calculation for the optimal length of the secondary pies which is the crossover point or in my case the point of the merge into one 4" pipe. That wound up being in a convenient place. The rest of the thought involves fitting the biggest pipe possible in a tidy way and choosing a non-restrictive muffler(s). A poor muffler will take up lots of power.

BC

I can't do anything at all in 10 minutes. It takes me 10 minutes to figure out what I am even thinking about doing....