Push through or Pull through MAFS on SR20det

[Jeff240sx]

Originally posted by andrave
well, not done.. that sounds like lotsa work, and I planned on running an S-AFc or an F con.. I would be able to get around those problems with one of those computers, correct?
if the S-AFC solves them with its atospheric BOV setting than that just made up my mind when I finally swap.

The s-afc does have a setting for atmospheric bovs. I don't know about the f-con though.
-Jeff

[Foxcolt]

aish, this is what I didn't want to happen. Now people are gonna think that this stumbling issue is a huge problem. When in reality it's pretty minor.

[Jsquared]

So now that we agree on the pop-off valve, and the bypass valve, and the difference in a bypass valve and a blow off valve, you mention that you have a bpv.
Is that why you don't stumble?

a "BPV" is the exact same thing as a "BOV," the BPV is routed back into the intake stream and the BOV is vented to atmosphere. it's the exact same part, mechanically. i turned the stock BPV into a BOV just by disconnecting the hose that would send the vented air back into the intake.

Just because you have had 2 cars that didn't have problems, it doesn't mean you have solved the issue and that everyone else is making stuff up. 2 cars = 2 data points, which is not enough to pull a firm conclusion.

1) Porsche 944 turbo (dad)
2) 2G Eclipse GS-T (friend)
3) SR S14 (friend)
4) SR S13 (friend)
5) FD3S (friend)
6) FC3S (friend)
7) S14 KA-T (friend)
8) MkII MR2 turbo (friend)
9) Porsche 930 turbo (PCA member, acquaintance)

as well as numerous people on numerous forums...

All stock turbo euro cars be they crapwagons (Sorry! I hate em, no offense intended) or porshes are boost controlled from the ECU. Our cars whether they be ka-t or SR's the ECU has no idea there's a turbo in there. It only reads mafs voltage. In that sense i think it's safe to assume that your porshe ECU has sometype of algorithm to compansate for lost air during shifts.

no. read what i've said. the stock setup has the BOV/BPV routed back into the intake behind the MAFS and before the turbo inlet, thus the ECU doesn't expect anything other than what it sees at the MAFS. and the ECU (fuel, timing) is a separate computer from the TCU (and don't forget, this is 1986 electronics we're talking about). there is no "algorithm to detect lost air."

I think a big reason that the 240's see a stumble with a BOV more htan the porshe is that the porshe most likely has a 1.1 afpr.. where as ace in the hole recomends a 10.1 which means A HELL OF A LOT MORE FUEL when the car is goin into a rich state...

there really isn't that much of a difference in fuel pressure and injector flow...

[Jeff240sx]

Originally posted by Jsquared
no. read what i've said. the stock setup has the BOV/BPV routed back into the intake behind the MAFS and before the turbo inlet, thus the ECU doesn't expect anything other than what it sees at the MAFS. and the ECU (fuel, timing) is a separate computer from the TCU (and don't forget, this is 1986 electronics we're talking about). there is no "algorithm to detect lost air."


there really isn't that much of a difference in fuel pressure and injector flow...

Yea. You're right. Myself, Ace, Dennis, we're all in collusion to get people to stop and think about lost air during shifts. Apexi and other huge companies are just making it up as a marketing gimmick to sell to a niche market. Companies also make blow-through maf setups... and they, of course, are lying.
What the hell do you want to hear? There are numerous people here and on FA that have had stumbling issues during the shift. The larger the turbo, the more air you have in piping and the intercooler, the faster the bov lets the air out.. they all play a role in the severity of the stumble.

Also, there is a huge difference in fuel pressure and injector flow. Read up on the formulas.
Take the square root of the new pressure divided by old pressure. Then, multiply that number by the injector flow rate.
43.5psi to 50psi change gives a product of 1.0721. On 50# (525cc) injectors, a 6.5psi change gives 53.6# of flow. Thats per injector, giving a total of 15.4 additional pounds of fuel off 4 injectors. This doesn't seem so large (actually, it does), but when you are saying that a 1:1 fpr and 10:1 fpr are compatible.. you're severly incorrect. At 10psi, thats an additional 90 psi of pressure. That gives a product 1.752, changing 50# injectors to 87.6# injectors.
Please.. stop spreading stupidity.
-Jeff