Racing Fuel Systems

***Migrating this thread to the new forum***

It's been a while since I have been on this site. I did a 6464 1050 2 circuit conversion with help from here several years ago and it worked awesome. We have since gone to a mild small block with a blow-thru gt45 turbo setup.

The carb is a "650HP" and I put that in quotes because it started life as a 4777-7 that got a main body swap to get adjustable bleeds and no choke horn. Everything else is still the 4777-7 parts. That means 2 corner idle block and base plate.

We originally had it set up with a T5 and it really worked pretty good because you modulate the throttle a lot with a manual trans. We have since switched to an AOD and have struggled with getting the carb to act right off boost. We are running 8psi and it works good at WOT, but has issues with tip in and part throttle. Converter is a 2000-2200 and is prob a little too tight.

Tip in has a big stumble and part throttle accel is stupid rich. Like 10:1 rich. Cruise in OD is 14-15:1 . Our elevation here is 3600' so the typical DA is pretty horrible.

Ignition is controlled with a Megasquirt and is completely programmable. I also use it to datalog.

Current setup:
IAB 45
HSAB 27
31/32 squirters
2.5 PV / blocked rear
65/78 MJ
pink cams f&r

I dove in and drilled the PVCR to 0.075" following the hangar18 blow thru instructions. In retrospect, this may have been an error. I may drill and tap these for brass set screws.

Anything glaringly out of place? I went down on primary MJ and went from a 6.5pv to a 2.5 to attempt to lean out the part throttle accel.

Car is crazy fun at WOT, but the street manners with the auto trans need to be better.

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It's getting better. The part throttle accel is much better,
PIAB 72
PMAB 25
SIAB 45
SMAB 36
39/32 squirters
2.5 PV front, rear blocked
65/78 jets
Blue cam front / pink cam rear in #2 hole.
0.075 PVCR

It is much happier with the air bleed change, but it still has this irritating lean spike. This is a pic of the datalog right at the spike.

I am at a steady cruise here, then try to gently accelerate and it spikes lean and sputters. The squirters and cam seem big and have not changed this situation much at all.



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I worked on my timing table a bit yesterday to put a lot more in it at the cruise rpms.

I will upload today and see how she runs.

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The timing seemed to help. The stumble is smaller. I am going to continue to play with the timing a bit to see if I can mitigate it even more.

I added a column in the timing table to have better resolution in the idle/low rpm cruise area.


Old pic:

How is your PV's referenced? There is a thread on the old forum, where you have a vacuum side restriction and a boost side restriction to the PV cavity to control PV opening.

Thanks! It is unfortunate that the pics no longer appear in parts of that thread.

Rear PV is blocked (metering block has no provision) front PV is reference is the stock configuration.

I finally got a set of 10-32 set screws so I can fiddle with air bleeds a little more. Previously I was just using what I had available in my box.

The idea is to use manifold vacuum and boost to control the PV opening. On that particular build Dave used a tee to a boost referenced port off the side of the carb. .062 coming from the vacuum side of the carb, .042 on the hat side to start. You can also build it internally with some machine work, drill down inside the air bleed position down to the PV cavity with a .042 restrictors, thread the vacuum passage in the carb behind the PV and restrict at .062. These are starting points, you can manipulate the sizes to trigger the PV to open where you need.