Just curious on how mcuh boost one can run before needing to upgrade the fuel system... i read on here somewhere that someone is running 10psi on the stock fuel system? This possible and or reliable?

 

if you want a piece of mind, when running real fast, I strongly recommend upgrading.

10PSI is possible. Fuel system is good to around 300HP. I had run as much as 16PSI (boost spikes), but for a very short time, 12PSI on numerous occasions when just built my turbo and wanted to go fast, and 10PSI regularly for a while after that, but as I got wiser, I lowered the boost to 8-9# of boost, rolled the sleeves and learned to tune the engine rather than just razing boost and dumping a whole lot of fuel into it. In my particular case, the car is DD. 100 Miles a day are driven with the stock fuel system with no problems. However tuning, or not, if you have the means - upgrade. The only thing that is holding me back from upgrading at this point is the $$, or rather the lack of it.

 

the stock fuel system is pretty stout. The fuel injectors can support near 300-rwhp, but getting near that you want to replace them.

The stock fuel pump is pretty good- can support north of 320-rwhp. The only real "bolt-in" replacement hi-flow fuel pump I know of is the Mazsport pump, too.

 

the stock system as I understand supports around 300HP as said above, BUT is it 300 WHEEL-HP or 300 FLY-HP, as there is a fair difference?

 

300 whp.

 

The limiting factor on the stock fuel system is actually the fuel pump, it will run out of flow if the stock injectors are used to their full capacity. The injectors are good for 300whp and the fuel lines/rails for way more than that. The stock fuel pump actually allows the fuel pressure to drop at anything over 7psi when the engine revs past 6500rpm(the pressure drop increasing with rpm). I actually monitored the fuel pressure and saw this. The reason people can use it up to 9psi is because although the fuel pressure drops it still retains enough differential pressure to allow fuel to flow into the engine. However, the atomization goes out the door because of pressure loss and the car will exhibit different behavior on higher gears. In first and second gear you might notice no problems whatsoever because you are above 6500 for less time than say, 4th gear, the car revs so fast in the short gears that it doesnt give it a chance for the pressure drop to take a big effect. In 4th and above it takes the car longer to rev out which means you are sitting under boost with the injectors opening alot for a longer amount of time, this allows the system to loose more pressure and you will find yourself in a situation where you may have a perfect car on lower gears but it detonates when sustained on the higher gears and under load(boost). Mi recommendation is dont go above 7-8psi on the stock pump. If you do a pump upgrade(it doesnt matter which one, just one with more flow) you can probably get to 10-11psi on the stock injectors, maybe even more if you really use all six of them to their fullest. Hope this sheds some light.

Chris

 

Thanks, Chris!

I thought the lesser performance in higher gears was due to different load, which means a good tune for low gears might be too lean/rich for higher gears so you need an ECU that can be tuned per gear to address this issue?

Do you have any recommendations/links for which fuel pump to go with? Is there an inline one that isn't too noisy/expensive?

 

If you have a good wastegate that doesnt allow a boost variance of more than 1-2psi there is no difference in load between 5000rpm in first and 5000rpm in 5th at the same psi, at least from the EMS's point of view. We all know the engine has to work harder to pul the car in 5th than in first but this is independent of the air and fuel requirements of the engine an a given psi. You should tune to a specific AFR and this will not change with the gear, 5psi at 5000rpm needs the same fuel in all gears. There are only two reasons why a car would detonate relative to the gear its in. Either the car is tuned marginally(lean) and when it is forced to accelerate slowly due to a higher gear it detonates(which is a simple fix, just ad fuel in the range where it detonates) or the fuel system is insuficient to supply and you dont notice until you force the engine to stay under load for extended periods of time(ie. higher gears). The latter is a little harder to fix, if you keep adding fuel to the area where it detonates you will continue to enrich the lower gears with no effect in higher gears because the system is still running out of flow so it doesnt really matter if you open the injectors more because that will just drop the fuel pressure further.

I would not recommend an inline pump for a few reasons. First they are noisy and you really cant do much about that, usually the less noisy the less powerfull which works against you. Second the car has a very nice and effective fuel line system with special connectors that ensure zero leaks, it would not be a good idea to disrupt this. Also, the regulator for the fuel pump is inside the fuel tank and if you were to mount an inline pump you would have no way to regulate fuel pressure, not to mention the fact that the RX-8 has one of the most accessible fuel pumps a car could have with no need to take the tank down. My recommendation is to either get a higher flow intank replacement or a complete ulgrade assembly such as is offered by Mazport.

We offer an upgrade but for now it is only available with our turbo kit. I hope this helps.

chris

 

It helps very much indeed. Thank you!

My regrets that I spent all my mod money on a GReddy (and had to rebuild the engine), else I would definitely go with your kit; it looks tight.

 

Dont we already have a 240 lph pump? i dont know what makes me think that but i seem to remember....damn old brain.
One thing to remember also is we have a 2 stage pump. Operates on a low hi demand. Would it be adventitious to get a fuel pump controller and operate the pump outside the ecu parameters? ( it goes into a low pump mode if throttle is less than 50% or you are are not accelerating)
At least we have good wiring to the system and get great voltage to it.
I am still not sure if it is a pump or a filter problem. It would be interesting to see an oem assembly that bypasses the oem internal filter and uses an aftermarket external one.
good thread.
olddragger

 

good job.

beers

 

I just think we should show some "love" to mazsport. They do have a fuel pump upgrade, injector upgrades, and definitely know about FI and turbo.

http://www.mazsport.net/shop/index.p...category&id=32

 

so sad mazport is in florida, they should open one here in CA

 

i concur here,

upgrade injectors, upgrade pump.. simple..


beers

 

mazsport has a good up grade no doubt. One of it's mods that make it much better is a rising rate fuel pressure reguator.
olddragger