Racing Fuel Systems

Hi guys,

For some time now i have been working on my Holley 1850 and the car is running pretty good. With the current speed limits over here most highway driving is done on the transfer slots @ 2000rpm. I would like to try en get some mileage improvement. Therefore i have been increasing the PIAB up to 1.9mm (0.075") This provides a 15.2 AFR on the highway, yet on the on ramp the vacuum drops and the AFR hits 16.5 and that's to lean.
Highway 100kph (63mph) @ 2000rpm is transfer slots and gives 17" Hg
Highway 120kph (75mph) @ 2400rpm is main jets and gives 15" Hg
Highway 130kph (81mph) @ 2600rpm is main jets and gives 15" Hg
Onramp is about 10"Hg, AFR 16.5-17
As soon as the power valve opens the mixture gets rich again.

I did pull a plug and its really white, so more fuel is needed.
Would it be a good idea to reduce the PIAB and install TFSR in the primary side ? My reasoning is this would keep the mixture richer and only limit the actual amount that's available.
It might also help to flatten the fuel curve a bit.

Thanks

Nick

what value PV is in there? tried a quick opener 105? what size is the engine?

The current pv is the stock 6.5.That would be a easy fix.
The engine is a SBC 355.
With a Lunati 60102 @0.050 219 int./227 exh.
The heads are Trickflow super 23 175cc head, resulting is 10.8:1 compression.
2.5inch ramshorn Manifolds and 2.5 inch stainless exhaust with mufflers
The distributor is a MSD 8360 with vac advance. 14* initial and 33* total @3500 vac advance is 10* this is a very slow curve to prevent part throttle ping.
I do use e5 (98 Ron) fuel.

The best way to improve mileage is to replace the Holley [ use it for a door stop ] with a Carter/Edelbrock 600 - 625 cfm AFB. Or the new Edel 650 AVS2.
All of these carbs have an 'Economzer' jet inside the primary booster, to improve low speed cruising economy. Carter took out a patent on it.

A little known FACT. Before Edel started re-making the Carter AFBs, they were selling modified Holley carbs. Yes, Holleys! At that time, the Holley period, they tested a 6619 600cfm Holley against a 625 Carter AFB on a Chev engine. The AFB made 17 hp more, 17 ft/lbs more & used less fuel doing it.
once

Can you give us a little background on this. What year was Edelbrock selling Holley carburetors? Did you mean quadrajet carburetors?
6619 Holley was an emissions carb in the 70's.

GTO Geoff ,

Thanks for the information. Could you provide some more? I do have a Edelbrock 1406, but that one never ran as "sharp" as the Holley. It did run OK at best, but never really impressive even after a lot of jet and needle changes.
Making more power with less fuel is always a good thing, it means the engine efficiency did increase by quite a bit. Though I'm not surprised that the Edelbrock tested by Edelbrock did out perform their direct competitor.


I did change the power valve for a 10.5 one. I did notice a odd thing, the old one came with the Holley rebuild kit and was stamped 65, yet using my vacuum gauge it would open around 4 in Hg. The new one isn't a Holley product and does open at the specified point.

Thanks,

Nick

Seems to me with the AFR at 15.2 you are too lean as it is and, therefor, you aren't going to get better mileage. If you want a hotrod SBC then it'll take 'X' amount of fuel to make horse power, leaning it out will just break things you don't want broken. Its all about physics.

Oké, I didn't know that the way you apply the vacuum changes the opening point.
spark plug

Yes this shows the car is running lean.

Hi Nick
was this plug sooty before you leaned the carb?

Tp