Fuel pumps and injectors

Red_Bullet · Postby **Red_Bullet** » Sat Sep 19, 2015 11:04 pm

Ok, I've just done my first track day on the MS3PRO my logs from Willowbank have alarmed me. Running an MS3Pro, rx8 440 injectors, rotrex c30-74 SC. 170 KPa max MAP.

First trackday after fitting MS3PRO, I'm running out of duty cycle around 5500 RPM. AFR is going lean, pulse width is at 23mSec. :shock:

Original Fuel pump (probably), probably needs new fuel filter too.

Doing my home work with a higher pressure fuel pump my problem should be solved. 65 PSI fuel rail should cover it. Any recommendations on fuel pumps. I figure the fuel pump will solve it but not leave much margin for error. Bigger injectors might be a better option. What are the options for injectors around 550cc, Is there anything plug and play?

Postby **NitroDann** » Sun Sep 20, 2015 12:22 am

13b rx7 purple tops but they are hopeless, you get better spray pattern from your old fella after a night out.

ID725's. Stock pump, done.

Red_Bullet · Postby **Red_Bullet** » Sun Sep 20, 2015 8:16 am

Thanks Dann,

Looks like I've under-fueled it...dammit...anybody wanna buy some refurbished rx8 yellow injectors, only done about 500 km since installation.

Red_Bullet · Postby **Red_Bullet** » Sun Sep 20, 2015 8:55 am

Hmmmm...been thinking and looking around the net, why not go for id1000 instead, even more headroom, if you believe the advertising there should still be no idle problems. Not much difference in price. I have no plans to go E85 so far.

TrackAttack · Postby **TrackAttack** » Sun Sep 20, 2015 11:11 am

ID1000's would be the pick. They can be tuned to idle just as well as a 725.

But in all fairness, I would of thought the RX8 440cc injectors were big enough for a Roxtrex setup...?

Red_Bullet · Postby **Red_Bullet** » Sun Sep 20, 2015 1:23 pm

TrackAttack wrote:ID1000's would be the pick. They can be tuned to idle just as well as a 725.

But in all fairness, I would of thought the RX8 440cc injectors were big enough for a Roxtrex setup...?

About the 440's....Yep, that's what I thought too, that's why I bought them after much research online with various calculators and opinions from miata turbo board. So maybe I should get my fuel pressure checked out first.

Prior to fitting the megasquirt the car had the stock ECU with an Exedy piggyback running a 5th 550cc bosh injector as will as the original Mazda (285?cc) injectors. It produced 141 Wheel KW back in 2011 with this setup.

so..... 141 kw = 185 Wheel HP = approx 213 HP at the crank, so 440 cc injectors "should" make it..

Red_Bullet · Postby **Red_Bullet** » Sun Sep 20, 2015 2:07 pm

Injector Size calculator

http://www.deatschwerks.com/resources/f ... calculator

Magpie · Postby **Magpie** » Sun Sep 20, 2015 8:39 pm

Whilst no forced induction, here is a screen shot of data collected at QR on Saturday night (from about 30kmh at the start of the straight from Turn 6 to the finish line.

ID725 injectors (blue line), E65 fuel (98 and E85 mixed) and 255 walbro fuel pump. Speed in purple and AFR in green.

Injectors did not exceed 67% duty cycle and fuel pressure at about 40 PSI.

Duty Cycle by Eipeip, on Flickr

Red_Bullet · Postby **Red_Bullet** » Mon Sep 21, 2015 6:09 pm

Hey thanks Mark, but I don't really understand that log, if speed is purple then your speed is decreasing and wavering as you run down the straight???

I thought speed would be increasing is a more consistently gentle rising curve rising more quickly from the low speed entrance to the straight then tapering off to accelerate less as speed increases.....

But I take your point on the injector duty max

cheers

Keith

Magpie · Postby **Magpie** » Mon Sep 21, 2015 6:27 pm

That was from Saturday Roll Racing. We started at about 30 coming out of turn 6 then accelerate (2nd gear for me) to the finish line hence the short acceleration.

madjak · Postby **madjak** » Mon Sep 21, 2015 7:29 pm

I'm running the xspurt 1000cc injectors (ID1000 based) with e85. I'm not even close to the max duty cycle given I'm N/A but they idle and tune fine.

One day when I slap on a blower I might start using them closer to their potential.

I'm sure the 750's would be fine too but who knows what you'll do with the car later.

Red_Bullet · Postby **Red_Bullet** » Tue Sep 22, 2015 12:13 am

Just ordered a Wallbro 255 fuel pump and new fuel filter, hopefully that'll make it behave. If not then it's back to injectors......

madjak · Postby **madjak** » Tue Sep 22, 2015 2:02 pm

Red_Bullet wrote:Just ordered a Wallbro 255 fuel pump and new fuel filter, hopefully that'll make it behave. If not then it's back to injectors......

I ran my stock 330cc injectors at 65psi fuel pressure to eek a bit more out of them until I purchased the 1000cc ones. You get another 15% or so more flow a the higher pressure.