the Mazda spec for the old old race cars was 1.5 Liters in 30 seconds. Mazda specs the fuel pressure at 4.3 psi, give or take the weber is ok with that.

your setup should meet or exceed that

the stock pump does ~700cc in 30 seconds, and about 2.7psi....

 

Yea,,,I think were well above that at 4psi...

 

1 Any chance you have a suction leak up high, accidentally resulting from when changing the fuel mat?

2. Make sure your Holley floats are "dropping" all the way, to let the needle hang low.

 

We did verify the fuel pick up tube is "sealed" so I don't believe that to be a problem. We have experienced that before...

Do you mean the float in the Weber? It's adjusted so that it's just below flooding when the pump is on and the engine is off.

 

So a bit of an update: Last night I put in 245 main jets and swapped out the front barrel's air correction from 160 to 170 since AFRs showed that one going leaner faster than the rear. Took it out for a spin and found it now pulls all the way through 5th...I got up to 99mph before running out of road. It's definitely rich so some more fine tuning is needed but it's nice to make such a step forward. AFRs were at 10s from anything more than 1/4 throttle. Next will be 240 mains and 180 airs

 

This is on an IDA? I run 195 Mains and 120 Airs in mine. Will see if that changes on the dyno but the Pyrometer has always been happy with this jetting.

 

Yea...48 IDA. We were running 205 mains for the last year and half or so and now suddenly its way thirstier. That seemed to be common last weekend at the reunion too. Bradshaw Motorsports street ported 12a EP FB Rx7 had to move up from I think 205s to 245 to run right. Maybe the air in the NW suddenly got way more dense...lol...

https://www.bradshawmotorsports.com/

 

Its a ratio. You are adding more gas and have to add more air. The net effect should be the same.

Charlie Clark and his mechanic typically ran jetting more like yours. My jetting numbers are from a different E Production racer in KC. Of course, this may go out the window once dyno pulls start.

 

Ratio: Your talking about the the mains VS. the air correction jets right? That's what is weird is we hadn't changed anything but suddenly it wouldn't run what we had. Bigger main jets with same air jets is it's taking to run out...

I'm curious what your dyno results will be as well. I'm hoping to get ours on the dyno as well before our next race to do more fine tuning.

 

Update #2:
Ran the car last night at an SCCA TT event. 3 20min sessions.
First session started with 240mains, F7 tubes and 170 air correction jets. The car was able to complete the session but was hitting 10s on the AFR on anything off idle pretty much but was able to pull complete rev range.

2nd session: Swapped the 170 air jets for 180s. Car ran better. Much cleaner up top but still some hogher rpm break up and not feeling full power. Still hitting 10 on AFR above idle. A couple seconds a lap quicker than first session.

.

3rd session: Swapped out 180s for 200 air correction jets. Car ran clean with what felt like full power. No break up at high RPM. Driver came within .5 second of his fastest lap time ever at that track. AFRs now showing 10.5ish at full throttle.

So, the drastic change in jetting has gotten the car back to operational however still a bit rich. From 205 mains and 170 air to 240main and 200 air, its almost the sane ratio between the two jets just a little more rich but when I ran 235 mains with 170 airs I was still seeing max lean on AFRs and lacking power. I'm happy the car is working again but perplexed as to why this drastic change was required. I hate not knowing why something worked or didn't work, makes it hard to belive it wont happen again. Is this just a carb thing and the reason people invented fuel injection?

If we can score dyno time I'll play around going back towards the original set up to confirm that no longer works...

Scott, I know you said you've gone years without having to adjust anything, have you ever had jetting needs drastically and suddenly change? Also, another question on your dual fuel pumps. I know you said that the set up you were taught but what is the advantage? With them feeding in parallel do you get an increase in GPH with the same pressure or is it just to pick up fuel from both ends of the cell?

 

Regarding the Fuel Pumps.

I run dual pumps because the cell has two pickups and I don't think a single pickup would ever let me use all the gas in the cell at the end of a race. Holley fuel mat is a fairly recent development and not available when I bought my cell in 2006. I have never considered using it because I have heard it doesn't play well with pre-mix. Besides the dual pickup arrangement works fine.

Individually, the P4070 pumps are spec'd at 72GPH at 4PSI. I don't think the way I have them plumbed improves on these specs. But I believe they offer more than enough gas flow at a pressure that works for a weber. For example on a prior V8 application with a Holley carb we used a different part number pump with more GPH and pressure.

 

Dyno Update

Got the car on the JPM Dyno this morning. Jesse Prather is amazing to work with and frankly performs miracles. He found and corrected more general wiring fuckery on the distributor, welded the advance weights and tweaked the timing to his liking. I told him that bringing a car to him is allot going to confession.....race car confession. I was guilty of not paying close enough attention to something that "had always worked great and the previous owner built it...so why pay attention to it now." I am healed and will do better moving forward.

The Numbers (because that is what you really want anyway) with 44mm chokes and the air box fitted:
HP = 204 @ 7900
TQ = 144 @ 6500
AF Ratio = 12.8
AF Curve = flat from 5500 to 8250
Pyrometer = 1500F (probes 6" from the ports)
Ambient Air Temp = 78F
Jetting = 195 Mains, 120 Air Correctors, F7 tubes, 60 Idle jets Per Jesse, the jetting is perfect

The car picked up 2 HP by installing the 44mm chokes and 10+HP when the air box was installed and a blower was placed in front of the T/S opening to simulate the car moving down the track. Cold Air is good. The extra choke size did not make a very big impact. However, the 44mm chokes didn't change the engine's characteristics or AF Ratio/Curve. There were no jetting changes made between the 42mm and 44mm chokes.

Jesse suggested that I could install the 45mm chokes for ***** and giggles at Indy but it is doubtful that they would make much difference. We also discussed going to 190 main jets to lean out the engine a little to get a little more power but what I have in there now is safe.

The engine has a nice curve and makes over 180HP starting at 6500. The way the transmission is geared I don't spend much time below RPM that so this works out pretty well. Also happy with the way the engine stayed cool during all of the testing and that the drive shaft vibration issue is gone.

 

Awesome report!

 

Hey Scott, do you know what Jesse ended up setting the timing at?

 

You know I forgot to ask. I will check it this weekend and let you know.

 

Thank you!

 

Looks like you're getting well prepared for the runoffs. I usually watch several of the classes with interest. I crewed on a two-car RX7 GT2 team for 20 years.
I'll be rooting for you.

 

Thank you, I appreciate that! It looks like I am the lone rotary in the class and for sure the only dude with a carburetor.

Don't forget Kurtf, he is #40 E Production. I know he is working hard to get ready and will be making the long trip to the middle of the country. E Production, and all of the Production classed always puts on a show. Lots of SAs amd FBs this year in the grid this year. Heck, back in 17, E Production was heavily populated with RX7s.

I am getting super excited about the Runoffs. I missed out when the Runoffs were at Heartland Park and getting to race at Indy again is very special. I guess I am a Hoosier want-to-be at heart and it is hard to explain how much this track and town touches my inner racer. The Indy 500 has always been my can't miss race and most of my racing heroes raced there. Crossing the yard of bricks, even from the "wrong" direction is something every racer should get to do.

 

Looks like Leading is 22 and Trailing is 17. Fired up the car today after making some JPM recommended distributor wiring updates and it sounded so crisp and immediately settled into a nice brap brap brap.....

 

Thanks for the nod about kurtf in EP. I was rooting for Wayne Graham and Dennis Golden when it was at Rd America several years. Dennis was the first one I called when I was looking for an SA shell. He said he'd give me one about a month after I found one in Nevada. Wayne now owns one of the the GT2 cars that I used to work on.

Good Luck.

 

Thanks for the props. Will be hitting the road 3.5 weeks from now, ready or not. And I’m most definitely not ready yet.

Scott, where did you end up for paddock spot? I’m pretty much right in the middle of the Mazda group in the Hulman paved lot.

 

MU42 - Museum Lot on a paved section. Wanted an end spot because we aren't arriving until Sunday. So pretty happy with the location. Yep more to do over here as well but I am checking things off the list.

 

Wiring updates? Is this secret sauce stuff or can you share?

Update on our car: Removed leading ignitor for MSD 6AL, Fuel system is now Holley Blue fuel pump with Holley regulator to 4psi. Got the car on the dyno and went from what it took to make it run 240 mains with 205 air correctors (100hp) to 195 mains and 130 air on rear and 140 air on front and 138hp. A/F gauges still showing 10.5 a WOT but we went bigger air correctors to lean it further and lost 10hp so went back to 130/140correctors. We didn't play with timing as it's as advanced as we have adjustment for and if I remember its close to what you are set at. It is supposed to be a street port so I don't know if we should have more power available or not...

We had a race this last weekend at the Ridge. Series of races 6hr, 2.5hr, 2.5hr, 3.5hr and 1hr. We had the trailing ignitor fail during the 6hr taking us from 4th to 15th after repair. Spin/mild contact in first 2.5hr dropping from 7th to 16th. 2nd place in both second 2.5hr and 3.5hr. Lead almost all of 3.5hr but a luckily timed pit stop by the winner brought them from 4th to 1st by a lap. For the last 1hr we got bumped up a class along with the rest of the top 7 in our normal class. We were running in the top ten and then got T-boned in the driver door (damage to just the door) and dropped back to around 20th but fought back up to 7th at the end.

We dropped mains down to 190s after the 6hr and found AFRs reading into the 11s at WOT and didn't feel any less or more power but used less fuel. If we could find another 10 to 20hp I think we'd be golden

 

Nothing secret. For the longest time the leading Ignitor had been removed and a pair of pins were stuck in the socket that was left behind. It was all held in place with a homemade connector and some tape. What I did is remove the OE plug that was there for the ignitor and splice on longer leads with bare butt connectors and heat shrink wrap. Then created a seal that is held in place by the distributor cap.

 

Your previous set up is basically what we have now...and I don't really trust it. I wanted to do what you described but there is so little wire/space to work with I'm not sure I can do it successfully...