Optimum Fuel Pressure for Thermoquad

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74Dusted

74Dusted

Stock Piler of 340's
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I need to dig my Blown '73 340 Duster out of hibernation to attend a friend's wedding on the 1st, so this is a bit of a rush to get everything perfect again.

At the end of summer I installed a set of 850 Thermoquads (in place of a pair of 750 AVS's), but didn't drive the car any more. The Pressure (8psi) was way too high and it was dumping fuel out everywhere on both Thermoquads.

I'm going to be borrowing the Adjustable Holley Regulator from my Cousin's Supercharged 318 Mazda RX-7 (or as we call it, the Mazdodge RX-318) to get my car running in time for the wedding. Rather than beat my head against the wall testing various pressures, I figured you guys would be able to give me a straight answer that would save me some unnecessary work.

What's the optimum pressure for a TQ (or in this case, a pair of TQ's)
 
Hopefully the thermoquads don't have dried out gaskets.
I would think that 8 psi. Would have been too much for the AVS' s, too.
 
Wasn't too much for the AVS's, actually ran very well (but suffered from the Off-Idle "AVS" Flat Spot).

Both TQ's were rebuilt the day I installed them on the car, I figured the pressure was too high because it was pushing fuel out of places where fuel should never come from (especially at cranking/starting rpms). I recalled something about the TQ's being picky about pressure, but couldn't remember the pressures, since most of my vehicles (with TQ's) ran a stock style fuel pump that didn't pump near as much as the 120gph Edelbrock Pump does.
 
If you have a good fuel pressure gauge I would try 6 psi when you get the Mazdodge's regulator on.
That is interesting. ..putting a smallblock in a RX7.
 
Carman340 said:
If you have a good fuel pressure gauge I would try 6 psi when you get the Mazdodge's regulator on.
That is interesting. ..putting a smallblock in a RX7.
Click to expand...

Did that a few years ago.





A lot of Looong nights, a lot of beer consumed.

It all started because my cousin said to me "Dude, I'm thinking about buying the parts to convert my RX7 over to a 13B Turbo."

"Really? Sounds cool. How much is that gonna cost."

"Couple grand in stuff, but when its done I'll have about 210 horsepower." :wack:

"210? The bone stock 318 in my dumptruck has more power than that and they're a dirt cheap engine you can find everywhere."


Well it spiraled downhill from there. It started as a hopped up 318/727 swap (in the picture above) to a Blown 318/727 (not pictured). I did the fabrication (motor mounts, transmission mount, brainstorming, etc), supplied the necessary info. We built the motor (mostly a learning experience for him).

Then he had to move out of state, and we were about 2 days worth of work away from firing it up for the first time. It's been sitting in his dad's garage for about 3 years untouched. Nowdays there's a company that sells a Small Block Mopar "Conversion Kit", but back when I dropped the engine in that car, it was uncharted territory. Nothing "off-the-shelf" existed, everything was hand made (a lot of runs to the parts store to "eyeball match" parts). Transmission Crossmember for example is a custom built Crossmember, that uses a 1960's Chevy Transmission Mount (I wanna say it was for a Nova?) to mount to the 727 and not stick half a mile down below the car.
 
Lots of measuring and fab work no doubt.
I remember talking to a guy at the Norwin Hills car cruise last year about the same project.
Putting a mopar smallblock in a Mazda RX7 and adding a supercharger. That wouldn't have been your cousin, would it?? I mean how many people in Pennsylvania would think to do that.?
 
Carman340 said:
Lots of measuring and fab work no doubt.
I remember talking to a guy at the Norwin Hills car cruise last year about the same project.
Putting a mopar smallblock in a Mazda RX7 and adding a supercharger. That wouldn't have been your cousin, would it?? I mean how many people in Pennsylvania would think to do that.?
Click to expand...

Not sure where Norwin Hills is, is that near Pittsburgh? My cousin moved to Chicago, then relocated to Pittsburgh about 10 months ago (slowly working his way back to our hometown as his fiance finds openings for her job closer to home)

He'd be a stocky guy in his mid 20's, missing most of his hair, works for a car dealership in P-burgh. Probably wearing a worn brown leather jacket and a beret-style hat
 
Norwin hills is fairly near Pittsburgh. But I don't think it was your cousin.
So they even came out with a conversion kit now. That's nice...after you guys had to do it the hard way
 
With elec fuel pump I ran my Carter thermoquad at 5.5 , I think max allowed on carb was 6.5 , mine ran well at 5.5 was not 100% confident with the regulator I used so I kept it 1 lb lower
 
That depends on modifications.
None, 5 5.5
A member recently posted using a .120 seat orfice (stock .093)
At 9 psi on a hot 340
Extra fuel flow and power were noticeable
 
Like any other Carter 4bbl. 4-7 psi. The Carter chart goes go 10 psi & I have run 10 psi at the strip to richen the mixture slightly, zero problems.
The Carter/Edel 4bbl float design has a tremendous amount of leverage of the float on the inlet valve [ needle & seat ] allowing for higher fuel pressure.
 
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