High performance plenum system for aftermarket EFI ?

[Mark Henry]

Thanks I'll check that out, I hope to have the intake halves by the end of the week then I can see what I have to work with.

Should I get the stubs and fuel rails? Could the stubs be modified to fit a SC head?

I'm asking because I've been offered these parts for free/cost of shipping. If I can cut off the old flange and weld on a new one it would save time. Oddly enough Ihave limited experiance with the 3.6 engine.

[dannobee]

Get them both. You'll need fuel rails. Even if you don't use the bases, you might want them to fab something up.

[Nux]

Do you even need the flap? Why not just run a straight pipe and keep it open all the time?

https://rennlist.com/forums/993-forum/608345-resonance-flap-effect.html

This is of course with non-stock cams, but still interesting.

[winders]

Originally Posted by Nux

Do you even need the flap?

I would say it depends on the build. I had a 3.6L race engine that, due to class rules. had to run a 1995 993 intake and 1 5/8" headers. The flap being open or closed made a difference there.

Soon I will be putting a a 996 GT3 setup on my 369 RWHP 3.6L race engine with AT Power ITBs and 1 3/4" headers. We will do dyno runs with the resonance flap open and closed at 100% throttle to see the differences. We will also do some partial throttle tuning to see what happens with the resonance flap open and closed to how that works out.

I am told that on engines like mine that the flap makes a difference and that difference is not small.

[Nux]

Originally Posted by winders

I would say it depends on the build. I had a 3.6L race engine that, due to class rules. had to run a 1995 993 intake and 1 5/8" headers. The flap being open or closed made a difference there.

Soon I will be putting a a 996 GT3 setup on my 369 RWHP 3.6L race engine with AT Power ITBs and 1 3/4" headers. We will do dyno runs with the resonance flap open and closed at 100% throttle to see the differences. We will also do some partial throttle tuning to see what happens with the resonance flap open and closed to how that works out.

I am told that on engines like mine that the flap makes a difference and that difference is not small.

interesting - be sure to post it here please.

where did it make a difference on your current build? The flap is mostly open on a racecar I guess? Do you gain more torque in low revs (<5000)?

I would really like to find a good solution to our JSR ITBs as well.

[Mark Henry]

I'm going to use some kind of flap but I will remove it if it doesn't do anything.
I won't really be able to make plans till my intake halves get here.

[JoeMag]

Remember too that cup cars from 964 to now (though I do not know about the 992), all had at least one operable resonance flap.

I had 993 plastic intake with single throttle on 3.8 rsr enduro pistons and factory rsr cams 1.75” headers and res flap makes a difference. Though that intake was too small for the motor...

[Mark Henry]

I see some like the plastic intakes, why is that? Thinner? Lighter? more volume? better design?

I want the aluminum, #1 reason is I can weld it, but I was just wondering why some like the plastic.

[winders]

Smooth.....and also light.

[Steam Driver]

I have also heard someplace that there is less heat accumulation in the plastic version (makes sense; less mass) lowering charge air temperature some. Every little bit helps.

[Nux]

964 Resonant Intake

Post #8

Torque is better from 3500 - 5000 with valve closed. Both torque and hp improves with valve open at +5000rpm

[Raceboy]

Why would you need to run TPS only with EFI+ITB's??

Any decent engine management system has at least Alpha-N/MAP hybrid load strategy where you also have MAP as input for fueling thus having much improved driveability and mixture consistency against various air temps+humidity.
Absolutely no reason to ruin nice and clean look of ITB's and hinder their performance (and yes, I recently saw on the dyno with 3.8liter 964 engine that Singer-like intake plenum (looks fancy) held the engine back, after removing the plenum engine picked up nearly 20 hp.

[Mark Henry]

Well...I could make the argument "WHY EFI?" when carbs make more power at WOT.

I've been doing the EFI thing for near 20 years, if I dont like the result I'll do ITB's, no big deal. As far as looks go in a 914 you can't really see much in the engine bay except direct overhead.

It seems a lot of peeps have troubles discerning the difference between a street car and a race car. I daily drive (summer) my 914, it's not a race car.

[targa72e]

The 964 plastic intakes are reported to flow better and more even than the earlier cast aluminum. The early aluminum 964 intakes also had a dual stage throttle body and the later plastic have a single throttle body. Plastic is considered a upgrade on 964 with aluminum intake.

john

[winders]

Originally Posted by Mark Henry

Well...I could make the argument "WHY EFI?" when carbs make more power at WOT.

Why do you think carbs make more power than EFI at WOT?

[Mark Henry]

I don't have time for a debate, I have a dozen or so engine builds to be working on.

[Evan Fullerton]

Originally Posted by winders

Why do you think carbs make more power than EFI at WOT?

Carbs can make more power at WOT due to the intake charge cooling effect. There have been several tests on V8s over the years by various magazines and most support that a well tuned carb can make a tiny bit more power. Cold fuel has also been shown to make more power then hot fuel.

There is no question that EFI is better for drivability, gas mileage, and altitude and weather compensation but for a drag car if you tune it for the conditions a carb might make a bit more power.

[winders]

Evan,

When we used to build engines for my race bikes, around 1998 we started to make as much peak power with EFI as we did with carbs. Of course, we used manifolding that was different and some advances were made in fuel injector design.

With the advances made in ITBs, intake design, and fuel injectors along with much more powerful ECUs and comprehensive sensors than we saw 20 years ago, I don't see any disadvantage to EFI with regards to WOT.

https://youtu.be/CHLB-mkM5qs

I know that a lot more drag racing cars are using EFI these days too.

[dannobee]

It's true, given the two scenarios, the carb will make more power at wide open throttle. Nascar LOST hp by going to EFI. Pro Stock drag racers LOST hp by going to EFI. And I'm by no means a carb fan at all. To this day I hate working on that god forsaken stuff, but they will make the most power. Driveability will be better with EFI, mileage will be better with EFI, tuning will be easier with EFI, and it will likely make more power everywhere else in the rpm range, but in that one area, at wide open throttle, the carb will out power the EFI.

There's a solid reason for it. Because the higher up in the intake runners you can start the fuel mixing process, the more homogenized the mixture will be, and the fuel has a cooling effect as it goes through the intake, too. Like I said earlier in this thread, put the injectors as high up in the intake tract as possible and it'll make the most power. Without a doubt. Might run like stink everywhere else in the rpm range, might be a bear to start when cold, but it'll make more power at WOT. Look at any of the current nascar or pro stock intakes and compare injector location to those on your street car. They will always be as high up as possible or allowed by rule. This isn't by accident.

Now, with all of that said, if you could stick the EFI injectors at the very top of the intake tract (much like the mechanical fuel injection that Porsche used in the race cars), you'd negate the carb's advantage, but not with the injectors spraying just an inch or two from the intake valve. There simply isn't enough time for the fuel to thoroughly mix with the air.

[JoeMag]

Nux -- I just happened to take a look at that post that you pulled off the 993 forum and that was actually my post from a long time ago. What I found interesting is that dyno graph is not what I saw on future dyno's. I had my ref flap actuator fail and went to the dyno (as I noted in post). Saw that the top end HP was down so tie wrapped the flap open. It was a few years later that I noticed that on that dyno that I did with res flap failed closed, my torque was higher in the mid RPM range (no idea how I happened to notice it, but I did). So I got a new actuator and headed back to dyno the next spring...

Bottom line there were mid range gains there. Pic below are the torque differences with res flap open <5.7k (orange), and closed <5.7k (blue). Had to pull off multiple dyno's so put into excel.

I am still puzzled by that original dyno. Only thing I can attribute is Hi/Lo settings of the actuator were mixed up when we were testing.