I need to validate our blow shark's turbo set up using a stock ECU and BEGI rising rate FPR. At first, I thought the turbo would have its own cold air intake and feed forced air into the throttle body after the MAF like this:
Airbox -> MAF -> throttle body
and seperately
Turbo air intake -> charged air -> intercooler -> throttle body (with recirculating valve back into turbo)
But my teammates who know a lot more about turbos than I do want to run it all through the MAF. So the setup would be as follows:
Airbox -> MAF -> turbo air intake -> charged air -> intercooler -> throttle body
Which is the better setup and what are the implications of each? Keep in mind this is low boost (7-10psi) with the stock ECU (it's a knock off perf chip actually) and a BEGI rising rate FPR.
We have the turbo mounted up to the headers built from cutitng and welding the stock parts to keep within our paltry budget. Photo here (further welding still being done):
And just for fun, here's the dynamically adjusting rear wing that I built:
Airbox-> MAF -> everything else. The MAF may not be designed to experience the high pressures and it certainly is not designed to take any oil contamination that may make it into the intake system.
mooseheadm5 wrote:Airbox-> MAF -> everything else. The MAF may not be designed to experience the high pressures and it certainly is not designed to take any oil contamination that may make it into the intake system.
Neither setup has any charged air going into the MAF. But one is pulling air through the MAF into the turbo and the other has the turbo pulling its own air seperately and joining the stock air at the throttle body. My question is which is better. I assume if the turbo is pulling air through the MAF, at some point the MAF is wide open. Does the ECU do anything different when the MAF is wide open? I would assume the ECU would manage the correct A/F ratio until the MAF is wide open at which point extra air would be matched by the RRFPR. Someone tell me if I have this right. Also, if the MAF air is going through the turbo and intercooler before it gets to the throttle body does this introduce a lag in the air / fuel timing?
Generally, I don't know what the implications are of the two different setups. So if anyone has insight into which is better, I would be grateful.
I am not sure what you mean by meeting stock air at the throttle body. Absolutely everything after the turbo intake pressurized. The turbo does not draw air separately- everything that goes through the turbo ends up going through the motor one way or another. I suggest you read Maximum Boost by Corky Bell, as well as any number of other turbo reference books. It really helps with overall system design.
You want the AFM after the turbo and before the throttle. The RRFPR will take care of manifold pressures above atmospheric. The AFM will continue to work as designed, and the RRFPR will take care of air density. Another benefit of a blow through system is the intake air temp sensor reading the temperature of the air thats actually going into the engine. Pre turbo air temps can be way off of actual manifold temps, which can cause big problems.
I ran mine like that for several months. The AFM doesn't mind at all. Car ran great, putting down 230 rwhp and 260 foot pounds of torque, approximately 276/320 at the crank.
That is if he is using a VAF, not an MAF, though. I suspect he is using a VAF, which can be used in the fashion you describe so long as it is properly air tight (if the seal at the shaft where it goes to the sensor is still good.) OP, please clarify this point.
Granted I don't run crankcase vapors back into my intake charge, my journal bearing turbo hasn't blown any appreciable amount of oil into the charge pipes. This could be an issue though if the turbo was tired. I agree completely that MAFs get angry when you load the hot wire up with an oil film.
Big Bronze Rim wrote:Granted I don't run crankcase vapors back into my intake charge, my journal bearing turbo hasn't blown any appreciable amount of oil into the charge pipes. This could be an issue though if the turbo was tired. I agree completely that MAFs get angry when you load the hot wire up with an oil film.
It burns up the sensor, but I'm going to assume that on their pathetic budget, they are using the AFM.
I never had any problems with the Split Second MAF, but I didn't have any oil in my chargepipes either. But, since this is an AFM and none of our cars came with MAF's its all a moot point anyway.
Big Bronze Rim wrote:Granted I don't run crankcase vapors back into my intake charge, my journal bearing turbo hasn't blown any appreciable amount of oil into the charge pipes. This could be an issue though if the turbo was tired. I agree completely that MAFs get angry when you load the hot wire up with an oil film.
It burns up the sensor, but I'm going to assume that on their pathetic budget, they are using the AFM.
turbodan wrote:I never had any problems with the Split Second MAF, but I didn't have any oil in my chargepipes either. But, since this is an AFM and none of our cars came with MAF's its all a moot point anyway.
turbodan wrote:You want the AFM after the turbo and before the throttle. The RRFPR will take care of manifold pressures above atmospheric. The AFM will continue to work as designed, and the RRFPR will take care of air density. Another benefit of a blow through system is the intake air temp sensor reading the temperature of the air thats actually going into the engine. Pre turbo air temps can be way off of actual manifold temps, which can cause big problems.
I ran mine like that for several months. The AFM doesn't mind at all. Car ran great, putting down 230 rwhp and 260 foot pounds of torque, approximately 276/320 at the crank.
OK. So I got wrong both times and confused MAF with AFM! Just to confirm, it should be:
Turbo intake -> charged air -> intercooler -> AFM -> Throttle body
And the BEGI kicks in when the AFM is wide open, yeah? Also, I assume that requires a recirculation valve to relieve back pressure when shifting gears, or can we get away without it for a single race? The budget is brutal!
Apologies for a being a bit slow. My turbo education has only just begun.
The AFM might not be wide open when it sees boost, but it doesn't matter where is at as long as the BEGi is hooked up correctly. It'll handle air density. The adjustments you have are rate of gain and initial pressure. Rate of gain is the factor by which fuel pressure increases relative to boost and initial pressure handles the lean spot some cars exhibit between manifold vacuum and boost.
I didn't use any adjustment on the initial pressure and I didn't use much gain. If you're using the stock eta injectors you probably wont need a ton of extra fuel pressure. The eta injectors are relatively big and flow lots when you crank up the pressure. You may need a restrictor in the signal line to avoid overfueling.
The blow off valve relieves the load on the turbo caused by compressor surge. I'd install one since you can get a good used Saab/Audi/Porsche diverter valve for under $50. I can even send you one for less than that. I've got some extras you can have for the price of shipping. Install the diverter valve somewhere between the turbo and AFM and you'll be good to go.
The AFM might not be wide open when it sees boost, but it doesn't matter where is at as long as the BEGi is hooked up correctly. It'll handle air density. The adjustments you have are rate of gain and initial pressure. Rate of gain is the factor by which fuel pressure increases relative to boost and initial pressure handles the lean spot some cars exhibit between manifold vacuum and boost.
I didn't use any adjustment on the initial pressure and I didn't use much gain. If you're using the stock eta injectors you probably wont need a ton of extra fuel pressure. The eta injectors are relatively big and flow lots when you crank up the pressure. You may need a restrictor in the signal line to avoid overfueling.
The blow off valve relieves the load on the turbo caused by compressor surge. I'd install one since you can get a good used Saab/Audi/Porsche diverter valve for under $50. I can even send you one for less than that. I've got some extras you can have for the price of shipping. Install the diverter valve somewhere between the turbo and AFM and you'll be good to go.
Thanks for the info and for the offer. Much appreciated. Will PM you about the diverter. May have to put a turbodan credit on the car somewhere. I assume that you tweak the BEGI with the wideband O2 looking for the right mixture.
Big Bronze Rim wrote:Granted I don't run crankcase vapors back into my intake charge, my journal bearing turbo hasn't blown any appreciable amount of oil into the charge pipes. This could be an issue though if the turbo was tired. I agree completely that MAFs get angry when you load the hot wire up with an oil film.
It burns up the sensor, but I'm going to assume that on their pathetic budget, they are using the AFM.
Ya, it can fry a sensor. Most OE MAFs have a "burn off" regime coded in which superheat the hot wire on shut down to burn off moderate amounts of contaminants.
So,
I guess I may be following properly, are we adjusting the AFM so it will measure the total airflow properly or are we just letting it pegg wide open and let the FMU handle enrichment?
I dont know if it pegs wide open with boost or not. Its still getting a certain volume of air, its just denser air than its expecting. It probably works the same way it does when its metering atmospheric air. Boost shouldn't blow the flapper open because it'll apply the same amount of pressure to both sides of the flapper.
If you dont tighten the spring in a stock AFM, boost will peg the unit wide open. Air flow is increased under boost. Jim Confortti and Steve Dinan always make the point the stock ECU really needs to measure the full air flow properly, "or your hosed but good"
RussC
turbodan wrote:I dont know if it pegs wide open with boost or not. Its still getting a certain volume of air, its just denser air than its expecting. It probably works the same way it does when its metering atmospheric air. Boost shouldn't blow the flapper open because it'll apply the same amount of pressure to both sides of the flapper.
As I stated earlier, I believe blow through is better because it reads actual IAT's. You also eliminate any problems with air leaks through what can be a shit load of plumbing and couplers by metering air just before the throttle body. Draw through also tends to cause a stronger vacuum before the turbo, which can draw more oil into the intake plumbing and reduce compressor efficiency.
The best my car ever ran was with the stock injectors, stock AFM with the stock spring tension and the BEGi 2025 RRFPR. A few times I've considered building another turbo car with those exact components. It works very well.
While that works, most turbo system at the inception are well past what a stock inj can deliver, so AFM adjustments are a must with bigger inj.
RussC
turbodan wrote:
The best my car ever ran was with the stock injectors, stock AFM with the stock spring tension and the BEGi 2025 RRFPR. A few times I've considered building another turbo car with those exact components. It works very well.
