Half bridge and stock intake questions
10-27-15, 05:02 PM
#1
Half bridge and stock intake questions
I got this S5 halfbridge (5/6 port only is bridged) that I need to put together and have some questions. This is a 24 Hours of LeMons/Chumpcar type track car. It needs to look reasonably stock.
1. The housing are not notched for the bridge and somewhat shadows the bridgeport. If I notch the housing for the bridge, does that mean that when I put it together, I need to put the rear apex seals in upside down (i.e. the corner piece towards the middle iron). Do I bother notching, is the downside greater than the upside? How far into the housing can I safely notch? Any guidance towards good example pix would be appreciated.
2. Since it's been half-bridged, I can't make it idle at all under 2800RPM. I'm running essentially a stock intake with the 5/6 ports and mechanism's completely removed and the VDI wired open. I'm running an Rtek with 460/550 injectors with RB headers, single presilencer and dual cat back. I have not done the TB mod (seems to be mixed reviews on doing it) and am pulling intake air from the (since removed) headlight area. It's dead nuts lean at low RPM and I'm supplying all the fuel that the Rtek allows. If I go to 550/550 injectors, It's better but I'm still too lean at low RPM but then it's dead rich everywhere else and sputters it's way till 5000 rpm when the afterburners kick in. If I have 460/550 injectors in it, it runs fine and pulls well pretty much everywhere it's needed. It's still a bit rich and I'm still slowly taking fuel out at high RPM but am taking baby steps since we're often racing for hours in 100+ degrees temps and I'm trying to manage engine temps. I realize that a standalone and probably a different intake could fix this but that's not really a direction I can take. Is there a way to fool the injection into supplying more low RPM fuel? Like can I disconnect the coolant temp sensor in the back of the thermostat housing and stop the coolant from going through the TB to try to fool the engine into thinking it's cold all the time? It would be nice if it idled but if I can't have it both ways, we can live with it.
3. Most of the mised TB mod reviews seem to be centered on street cars. What about a track car?
1. The housing are not notched for the bridge and somewhat shadows the bridgeport. If I notch the housing for the bridge, does that mean that when I put it together, I need to put the rear apex seals in upside down (i.e. the corner piece towards the middle iron). Do I bother notching, is the downside greater than the upside? How far into the housing can I safely notch? Any guidance towards good example pix would be appreciated.
2. Since it's been half-bridged, I can't make it idle at all under 2800RPM. I'm running essentially a stock intake with the 5/6 ports and mechanism's completely removed and the VDI wired open. I'm running an Rtek with 460/550 injectors with RB headers, single presilencer and dual cat back. I have not done the TB mod (seems to be mixed reviews on doing it) and am pulling intake air from the (since removed) headlight area. It's dead nuts lean at low RPM and I'm supplying all the fuel that the Rtek allows. If I go to 550/550 injectors, It's better but I'm still too lean at low RPM but then it's dead rich everywhere else and sputters it's way till 5000 rpm when the afterburners kick in. If I have 460/550 injectors in it, it runs fine and pulls well pretty much everywhere it's needed. It's still a bit rich and I'm still slowly taking fuel out at high RPM but am taking baby steps since we're often racing for hours in 100+ degrees temps and I'm trying to manage engine temps. I realize that a standalone and probably a different intake could fix this but that's not really a direction I can take. Is there a way to fool the injection into supplying more low RPM fuel? Like can I disconnect the coolant temp sensor in the back of the thermostat housing and stop the coolant from going through the TB to try to fool the engine into thinking it's cold all the time? It would be nice if it idled but if I can't have it both ways, we can live with it.
3. Most of the mised TB mod reviews seem to be centered on street cars. What about a track car?
10-29-15, 12:06 PM
#2
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1. dunno, i guess the easy answer is just to flip them, the hard answer would be to put the seal on the housing and see what you can get away with. more reliefs seem to be more like a bevel, you do want to keep some material around the water seal, although it depends on the size of the port.
2a. who cares about the idle speed? its a race car.
2b. TB mod, you probably want to remove the second set of throttle plates and the shaft, more for simplicity than air flow. it does help airflow, just not enough to notice. i'd also remove the thermowax, again for simplicity.
2c. lean midrange. i've seen this too, you might try 550/460 injectors, just based on past experience, you want an AFR around 13:1 everywhere*. for a street car you could go a little leaner, for a road race car you probably want to be richer. the butt dyno won't notice any power difference between 13:1 and 12.5:1 so its a good idea to be a little fat.
2c1. the turbo guys used to add a potentiometer to the coolant temp sensor (or maybe replace it?) and if you get the ecu to think the engine is cooler it will add fuel. not sure i like this in a race car.
2c2. you could raise the fuel pressure.
2c3. if you live with the lean spot, you might pull a degree or two of timing in that area.
3. for a track car we can remove the thermowax, because we're not using it, and its simpler without. we can also remove the second set of throttle plates mostly for the same reasons, although it also adds an insignificant amount of air flow. everything else you can just leave alone, and go have a sandwich
*offered as a guideline, feel free to take it to a dyno and see what your combo really likes
2a. who cares about the idle speed? its a race car.
2b. TB mod, you probably want to remove the second set of throttle plates and the shaft, more for simplicity than air flow. it does help airflow, just not enough to notice. i'd also remove the thermowax, again for simplicity.
2c. lean midrange. i've seen this too, you might try 550/460 injectors, just based on past experience, you want an AFR around 13:1 everywhere*. for a street car you could go a little leaner, for a road race car you probably want to be richer. the butt dyno won't notice any power difference between 13:1 and 12.5:1 so its a good idea to be a little fat.
2c1. the turbo guys used to add a potentiometer to the coolant temp sensor (or maybe replace it?) and if you get the ecu to think the engine is cooler it will add fuel. not sure i like this in a race car.
2c2. you could raise the fuel pressure.
2c3. if you live with the lean spot, you might pull a degree or two of timing in that area.
3. for a track car we can remove the thermowax, because we're not using it, and its simpler without. we can also remove the second set of throttle plates mostly for the same reasons, although it also adds an insignificant amount of air flow. everything else you can just leave alone, and go have a sandwich
*offered as a guideline, feel free to take it to a dyno and see what your combo really likes
10-29-15, 06:25 PM
#3
This is something I've wanted to play with but all the FPR's I've seen for the RX7 are removable ones. The NA one is integrated into the fuel rail. I'm making the guess that the TII uses a completely different setup. Keeping in mind that nice anodized cheaty looking parts on top of the motor draw scrutiny, is there a workaround with the stock bits or failing that, is there someone who makes a NA fuel rail with replaceable/adjustable FPR?
10-29-15, 07:13 PM
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This is something I've wanted to play with but all the FPR's I've seen for the RX7 are removable ones. The NA one is integrated into the fuel rail. I'm making the guess that the TII uses a completely different setup. Keeping in mind that nice anodized cheaty looking parts on top of the motor draw scrutiny, is there a workaround with the stock bits or failing that, is there someone who makes a NA fuel rail with replaceable/adjustable FPR?
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