Aftermarket EFI on NA motor...???
10-30-02, 10:50 AM
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Aftermarket EFI on NA motor...???
Straight to the point...
The speed-density method 99% of aftermarket ECU's use works great.
When applying the speed-density scheme to, say, a 6 port actuated motor on paper could be seen as 2 different motors. With the same MAP values, the motor will flow differently whether the 6 port's are open or not. How big a difference could this be?
Working on EFI'ing a 12A, I believe it'd be nice to pick up bottom end torque like the factory system, the engine is only breathing through the first 2 barrels of the carb which only feed 2 ports of the motor. Port velocity must be GREAT when on the first half of the carb! This would be an EXTREME example of 2 different airflow/MAP profiles. Keeping the runners throttled seperately, I also do not see any way to source a good MAP value. I think I'm screwed...Perhaps, like VDI, I should have the second pair of throttled runners controlled 100% by rpm. Wideband dyno tune the car each way, with 2 runners open and with 4, figure the point the 2 torque curves meet, make the 2nd pair of runners open up at that point, then re-tune. A drive by wire throttle body for a GM truck (Escalade/etc) just sold on ebay for $40 so I think I can come up with a relatively simple way to throttle the 2nd set of ports by RPM.
Ideas? Give up ??? on the bottom end and throttle it all together?
The speed-density method 99% of aftermarket ECU's use works great.
When applying the speed-density scheme to, say, a 6 port actuated motor on paper could be seen as 2 different motors. With the same MAP values, the motor will flow differently whether the 6 port's are open or not. How big a difference could this be?
Working on EFI'ing a 12A, I believe it'd be nice to pick up bottom end torque like the factory system, the engine is only breathing through the first 2 barrels of the carb which only feed 2 ports of the motor. Port velocity must be GREAT when on the first half of the carb! This would be an EXTREME example of 2 different airflow/MAP profiles. Keeping the runners throttled seperately, I also do not see any way to source a good MAP value. I think I'm screwed...Perhaps, like VDI, I should have the second pair of throttled runners controlled 100% by rpm. Wideband dyno tune the car each way, with 2 runners open and with 4, figure the point the 2 torque curves meet, make the 2nd pair of runners open up at that point, then re-tune. A drive by wire throttle body for a GM truck (Escalade/etc) just sold on ebay for $40 so I think I can come up with a relatively simple way to throttle the 2nd set of ports by RPM.
Ideas? Give up ??? on the bottom end and throttle it all together?
10-30-02, 11:14 AM
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The 6th ports and VDI open at the same rpm under load all the time. So setting up the ECU should not be any more difficult then say a v-tech honda. If you are talking about a series 4 with pressure activated ports then there may be an issue of consistency, but a series 5 has electronically controlled solenoids to open the port sleeves.
10-30-02, 11:44 AM
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"...Perhaps, like VDI, I should have the second pair of throttled runners controlled 100% by rpm. "
Yes, making the VE% change take place at an exact RPM makes it easy to work with.
I believe I can set up the EFI to have 2 maps that can switch on the fly based on whether it's on 2 or 4 ports.
BUT where do I source my map signal from when I would have seperate throttle bodies per pair of runners, 2 seperate plenums. Averaging them together I believe would not work well as the plenum under the closed throttle would be pulling a STRONG vacuum.
If it DID change from 2 to 4 ports at a set RPM I could tune it based off a MAP reading from just the main throttle. Perhaps move the 2 to 4 port crossover rpm point low enough (likely below the ideal point) that the change in MAP isn't as radical.
I can think of more and more issues that might make me give up on the improved bottom end torque. "Don't need no stinkin VTEC"
Of couse, once we go there it's not so much 2nd gen specific....
Yes, making the VE% change take place at an exact RPM makes it easy to work with.
I believe I can set up the EFI to have 2 maps that can switch on the fly based on whether it's on 2 or 4 ports.
BUT where do I source my map signal from when I would have seperate throttle bodies per pair of runners, 2 seperate plenums. Averaging them together I believe would not work well as the plenum under the closed throttle would be pulling a STRONG vacuum.
If it DID change from 2 to 4 ports at a set RPM I could tune it based off a MAP reading from just the main throttle. Perhaps move the 2 to 4 port crossover rpm point low enough (likely below the ideal point) that the change in MAP isn't as radical.
I can think of more and more issues that might make me give up on the improved bottom end torque. "Don't need no stinkin VTEC"
Of couse, once we go there it's not so much 2nd gen specific....
Last edited by faster7; 10-30-02 at 11:52 AM.
10-30-02, 11:59 AM
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Brain babbling further, I believe I would need to throttle the whole motor through the same main throttle body/plenum. Throttle for the 2nd set of runners drawing from that same plenum, essentially the system layout would be like that of the stock 6 port S4 motors.
Air flow based EFI would make lots of this easier...But we're not going there!
Air flow based EFI would make lots of this easier...But we're not going there!
10-30-02, 02:05 PM
#5
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Measure the vacuum that exists in the secondary ports, and compare it to that in the primaries. I'm betting the difference is negligible, regardless of whether the ports are active or not.
Think about it...the source of the vacuum generated in the intake is an expanding combustion chamber volume inside the rotor housing. This vacuum will present itself equally (neglecting dynamic effects) in both intake ports.
The concern I have with my setup (Megasquirt in '86 n/a) is getting the aux port opening consistent enough to compensate for their effect properly in the VE table. An rpm switch would be ideal.
Thoughts??
Think about it...the source of the vacuum generated in the intake is an expanding combustion chamber volume inside the rotor housing. This vacuum will present itself equally (neglecting dynamic effects) in both intake ports.
The concern I have with my setup (Megasquirt in '86 n/a) is getting the aux port opening consistent enough to compensate for their effect properly in the VE table. An rpm switch would be ideal.
Thoughts??
10-30-02, 02:12 PM
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Glad you found my thread!
I'll have to do some testing and see exactly how far off the vac signal would be. I can see your point!
You're the code MAN, I've looked at the palm stuff/etc. Should be nothing to grab an extra output line on the ol 68HC08 coded as an rpm trigger.
IF I was MS'ing a NA 6 port motor like yours, I'd grab the pineapple 6port sleeves. Should pick up some top end and not have to deal with tuning essentially 2 different motors.
I think if I can get my transition down, a bit of coding would let me make it not interpolate to the next highest RPM bin at the switchover point. With just the 6 ports like you're dealing with, I don't think the fluctuation in vac signal when they open up will be that big a deal.
R
I'll have to do some testing and see exactly how far off the vac signal would be. I can see your point!
You're the code MAN, I've looked at the palm stuff/etc.
Should be nothing to grab an extra output line on the ol 68HC08 coded as an rpm trigger.IF I was MS'ing a NA 6 port motor like yours, I'd grab the pineapple 6port sleeves. Should pick up some top end and not have to deal with tuning essentially 2 different motors.
I think if I can get my transition down, a bit of coding would let me make it not interpolate to the next highest RPM bin at the switchover point. With just the 6 ports like you're dealing with, I don't think the fluctuation in vac signal when they open up will be that big a deal.
R
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