jcorenman

In the original design the MAF is between the filter box and the boot on the throttle. The filter box is attached to the block with a couple of 6mm studs so the MAF is trapped, and can't go anywhere. The clamp at the bottom is only needed to prevent air leaks.

So why not use the original design, and secure the air-box (or whatever is above the MAF) to the engine? There's about 10 in^2 of inlet area into the MAF, at 20psi that's about 200# trying to lift the airbox.

I can't think of any reason that the lower MAF screen is ever needed. Depending on what is feeding the MAF, you may need the upper screen to ensure reasonably uniform airflow through the MAF. For the stock intake the filter is just above the MAF and I think the upper screen can be dispensed with.

Cheers,

ptuomov

I disagree! As I wrote earlier, this is something about which I and the consensus are at odds.

It's true that it will reduce air flow. However, my point is that if the overall restriction at the MAF is much less than the restriction at the most restrictive spot, there will be very little benefit from removing the screen in practice. Even if the flow bench shows a decent gain when the MAF is tested in isolation.

Tell me more. The system cuts fuel if above a threshold rpm when the clutch is pressed?

My car uses the stock '87 ECUs with the JDS PEMS and then an aftermarket boost controller (eboost2).

If the second, lower rev limiter is activated by the clutch, that's how the modern anti-lags work. They I believe seriously retard spark but leave the fueling on when clutch is pressed at high rpms to increase the energy to drive the turbo.

The air box is bolted to brackets that are bolted to the block. When I put the air box back on, I leaned on it hard while tightening the bolts so that it's compressing the rubber and silicone parts between the throttle body and the air box. So that method is being used.

In addition, I still have the stock stainless steel straps holding the lower MAF clamp at a set distance from the MAF housing. The groove/lip on the stock MAF boot then holds the MAF housing in the MAF boot.

Despite all, this this the MAF popped out of the boot.

When I swap the engine, I am going to groove the MAF housing so that the clamp will depress the rubber to the groove.

Bill Ball

George Suennen finally learned not to shut down the throttle suddenly when he's on high boost after blowing the stock MAF boot to bits once during a race and then blowing a very tough silicone alternative he had made off the throttle housing at the dyno despite substantial clamps. The stock MAF boot and clamps are a weak link. I agree it would be best if the boot and MAF had a ridge and groove, but as you improve the clamping expect to see problems with the stock MAF boot. It will eventually split at an inopportune moment from being inflated.

https://rennlist.com/forums/928-foru...take-hose.html

Bill Ball

Are you measuring boost BEFORE the throttle plate and not inside the manifold?

ptuomov

My case is a bit different, since the MAF housing came out of the MAF boot before the throttle was shut off. Based on the boost data, the bypass valves work very well when the throttle is shut, preventing spikes but not bleeding off too much boost.

Here's a question about the silicone boot. How are you guys clamping it? The stock lower clamp and the steel straps, really the whole contraption, assumes that the boot has a lip. The steel straps keep the clamp at a set distance relative to MAF housing. The lip on the stock boot keeps the clamp at a set distance relative to the boot. Since the silicone boot doesn't have a lip, how does the silicone boot keep the clamp at the set distance relative to the boot? Does the clamp sink into the silicone and get held that way? Not saying the silicone boot doesn't work, just trying to understand how and why it works.

In any case, the next MAF sensor housing that I'll install will have a clamp wide groove machined to both ends.

ptuomov

That's an excellent point. I hadn't thought that one thru as far as the dyno data goes.

The dyno data that I've posted this weekend are coming from a sensor that was hooked up to the bypass valve reference line, so those data in this thread are downstream of the throttle plate and therefore uninformative about the boost spike due to throttle close.

The peak hold boost data that I mentioned comes upstream of the throttle plate and therefore is relevant to the boost spike question. So far, there's no evidence of the boost spiking at throttle shutoff.

Good catch, by the way.

PorKen

Yes. When the clutch is depressed, the LH lowers the rev limit. I set mine to 4000 rpm, figuring a 1.5-2k rpm drop per gear. The stock rev limiter powers off the injectors (& fuel pump, 02 sensor) via the fuel pump relay. I was surprised, it is not harsh, or particularly jarring, and the rev matching makes the change effortless.

Oops, I forgot you were using the stock brains. (I made 35 pin Bridgits for them, doh!)

For anti-lag I guess you would just want ignition retard. On the EZK, use the transmission-protection-switch input (pin 25), but lengthen or remove the counter for this feature, if revs are above your expected rpm for the next gear.


It would be nice to program the lower limit to be ~1.5K lower than the rpm when the clutch was put in, but I'm not that good at hex programming, and there's no room for any significant recoding on the 4K LH22 chip, anyway (EZF = 2K!).

Cosmo Kramer

I have a single Bosch blow off on my 7 psi system and it has worked fine so far, duals should be adequate for the TT I would think. I must say a lot of air comes out of it at high rpm with the throttle plate closed. My entire intake system is silicone and you can see it flex under the pressure, but it all stays together OK.

The MAF screens saved my engine when I had my S/C impeller break. I would not remove them in any circumstance on a centrifugal supercharger or turbo system.

John Speake

We will be looking at the code for the EZK transmission protect shortly....

blown 87

Tell us more about this transmission project, in a new thread maybe.

John Speake

Will do when more investigation has been done...

dprantl

Is there no way to relocate the MAF to before the turbos in Kuhn's system?

Dan
'91 928GT S/C 475hp/460lb.ft

ptuomov

Here's my wish list JDS:
(1) EZK map that has enough range in the top end to tune different WOT boost profiles.
(2) EZK powershift feature with an input from clutch position switch, where the ignition is retarded to x degrees ATDC above y rpm if the clutch is pressed at WOT. Reasonable values for x would be 30 degrees ATDC and for y 4500 rpm.

Number (2) needs a big warning label on it. "Your exhaust manifold may glow like Columbia and your turbo may blow like Challenger. Your shifts will feel and sound like you've strapped yourself onto a booster rocket."

Bill Ball

Regardless of exactly when it came off, it was probably being worked off by elevated pressure shocks at throttle closure despite blow-off valves. Eventually it will come off or in the case of the stock boot, it will split at some point. George uses T-bolt clamps:

http://www.034motorsport.com/hardwar...zes-p-123.html

tveltman

Relocating the MAF prior to the compressor inlet introduces the problem of (I think) lag time between the actual delivery of air and the calculated amount of fuel. Under constant load operation, this isn't particularly problematic, but when you are opening and closing the throttle plate, that can play havoc with the system. Also it provides more places for inaccuracy since any leaks AFTER the MAF don't show up as corrections in the fueling, and the more piping you have, the more chance there is to develop a leak. In the boosted operation this would cause enrichment, so you wouldn't have to worry about detonation, but under non-WOT situations, where the manifold can suck air in through any gaps, this air won't be metered and will result in a lean condition, which could potentially be dangerous