Feeler: Phenolic intake spacers
12-17-2009, 11:12 AM
#62
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For emissions it may be desirable to hit the warm walls of the manifold to get complete vaporization, for power it may be better to aim towards the valve seat. Most EFI systems until recently also fire the injectors on the "off" stroke (valve closed) and pool some gas near the seat at higher power loads, I don't know if the Bosch systems on these do that (I think so since they fire in pairs). The air flow patterns near the valve seat aren't constant over RPM, you have to pick a location and angle for the injector that works well over the entire range on a street vehicle. That may not be the one that gives best peak power.
12-17-2009, 01:10 PM
#64
Rainman
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the injectors are wired in pairs so probably fired in pairs lol
after briefly looking at the 944 intake and the angling of the injector bung (will have to plug an injector in later to be sure) i think the diameter of the port/runner is large enough that a height difference may be ok.
i am working with a local speed shop that many of you are very familiar with
to set up dyno time soon.
after briefly looking at the 944 intake and the angling of the injector bung (will have to plug an injector in later to be sure) i think the diameter of the port/runner is large enough that a height difference may be ok.
i am working with a local speed shop that many of you are very familiar with
to set up dyno time soon.
12-17-2009, 04:13 PM
#66
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If it's a 4 stroke setup as most cars are, then you'd have so much waste that gas mileage would be affected.
In a waste spark setup, 1/ 3 cylinder fire on the power stroke and 2/4 cylinder fire on their power stroke.
Sequential and waste spark are the main firing order today but since I'm new to the Porsche engine, not sure why they would have all cylinders injectors fire on every stroke.
Maybe some more explanation of this would be good.
12-17-2009, 04:17 PM
#67
Nordschleife Master
They don't fire every stroke... they fire every revolution
Meaning the fuel has to sit behind the valve and wait for the last cylinder in the firing order to get to the intake stroke....
....a few milliseconds....
Meaning the fuel has to sit behind the valve and wait for the last cylinder in the firing order to get to the intake stroke....
....a few milliseconds....
12-17-2009, 04:26 PM
#68
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The beginnings of digital fuel injection... the injector circuit is fired from one driver, as such all injectors fire at the same time.
Here is a great post about batch fire:
Here is a great post about batch fire:
I noticed a common misconception in the original posters thoughts –
At full load in either sequential or batch firing the majority of the fuel will hit the closed intake valve – this is actually a good thing since the quite hot intake valve will aid in the vaporization of the fuel. When you see that the fuel injectors are running at or over 80% duty cycle (typical for full load) the 80% represents 80% of the 720 degree cycle (or 80% of two successive 360 degree rotations for a batch fired). Either way – a lot of time squirting on a closed valve.
When you look at the spray pattern of a fuel injector you will also understand that the injector never fires the fuel directly into the cylinder.
If I recall the Motronic unit correctly there are two drivers but they are tied together to run as one batch fired system.
Summary- basically the timing of the injector firing is irrelevant except for a full sequential car that is dead cold – only then will you see a difference. The plus of running full sequential is that you can get a larger injector to idle at the correct mixture since.
At full load in either sequential or batch firing the majority of the fuel will hit the closed intake valve – this is actually a good thing since the quite hot intake valve will aid in the vaporization of the fuel. When you see that the fuel injectors are running at or over 80% duty cycle (typical for full load) the 80% represents 80% of the 720 degree cycle (or 80% of two successive 360 degree rotations for a batch fired). Either way – a lot of time squirting on a closed valve.
When you look at the spray pattern of a fuel injector you will also understand that the injector never fires the fuel directly into the cylinder.
If I recall the Motronic unit correctly there are two drivers but they are tied together to run as one batch fired system.
Summary- basically the timing of the injector firing is irrelevant except for a full sequential car that is dead cold – only then will you see a difference. The plus of running full sequential is that you can get a larger injector to idle at the correct mixture since.
12-17-2009, 08:19 PM
#69
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Thank you Rogue and I now have a better understanding of the 'batch fire' setup over the sequential fire.
This will also get me to better understand how it all works with a future engine build that I'll be doing in which the cam sensor may be eliminated with custom cams and making my other car go from the waste spark system to batch fire.
With this knowledge, I can make a better informed decision on what I'm looking for in the engine build.
Back on topic and thanks again..
This will also get me to better understand how it all works with a future engine build that I'll be doing in which the cam sensor may be eliminated with custom cams and making my other car go from the waste spark system to batch fire.
With this knowledge, I can make a better informed decision on what I'm looking for in the engine build.
Back on topic and thanks again..
12-17-2009, 08:45 PM
#70
Rainman
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after going over the injector again the squirt angle looks like, on an engine without the spacer, it is aimed at the wall of the cylinder head, which someone before said was an emissions type thing. my estimation based off the orientation is that the injector position is in no way a power-making decision. seeing how the injector is mounted and how large the intake pipe is, the injector spray should still hit the wall of the head.
attached is an extremely complex diagram of the injector setup.
attached is an extremely complex diagram of the injector setup.
12-17-2009, 10:07 PM
#71
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Lol, I love the MSPaint drawing... BTW do you have Windows 7? It comes with an upgraded version of paint that actually makes it respectable.
Once again, ideal angle would be to spray directly at the back of the valve.
-Rogue
Once again, ideal angle would be to spray directly at the back of the valve.
-Rogue
12-18-2009, 12:11 AM
#72
Rainman
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Yes, but with the 944 head, the injector would have to be mounted on the underside of the intake to do that. Certainly doable but things need to be moved around and modified obviously.
12-18-2009, 02:20 AM
#73
Rainman
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an idea to throw out there...
while i am basically done developing the phenolic spacer and today drilled and tapped my spare intake and installed my air temp sensors, money is pretty tight for me at the moment.
i have talked with a local porsche speed shop about using their dyno for testing this spacer and the owner has agreed to give me a good rate, and i was wondering if some of the interested people would be willing to put a deposit of sorts down (out of the total) so i can get the dyno done and the results up whether they are good or bad.
if the spacer proves effective, the people that made a deposit would receive an equivalent pricecut for delivery of the spacer. so, for example, if you put down $20 beforehand, if the spacer works out i will honor that $20 and give you another $20 as a thank you for your help, so you would be paying $60 total instead of $80.
if the spacer doesn't prove effective, i can refund you your deposit at a later date if you so wish, but it may take a while.
its a long shot i know but it would potentially get these to you all sooner! PM me if interested.
while i am basically done developing the phenolic spacer and today drilled and tapped my spare intake and installed my air temp sensors, money is pretty tight for me at the moment.
i have talked with a local porsche speed shop about using their dyno for testing this spacer and the owner has agreed to give me a good rate, and i was wondering if some of the interested people would be willing to put a deposit of sorts down (out of the total) so i can get the dyno done and the results up whether they are good or bad.
if the spacer proves effective, the people that made a deposit would receive an equivalent pricecut for delivery of the spacer. so, for example, if you put down $20 beforehand, if the spacer works out i will honor that $20 and give you another $20 as a thank you for your help, so you would be paying $60 total instead of $80.
if the spacer doesn't prove effective, i can refund you your deposit at a later date if you so wish, but it may take a while.
its a long shot i know but it would potentially get these to you all sooner! PM me if interested.