Fuel pressure and pumps

[b4black]

What's the minimum pressure I should see at WOT with a Quadrajet?

Are there any performance, mechanical pumps available?

 

[b4black]

What happens if an odd-fire pump is used on an even fire?

Is odd-fire pump the same as the 350?

 

[Freddie's Buick]

I can't answer the questions but I'm looking into buying an electric fuel pump with higher pressure. (Takes a load off of the cam).

I believe that the OEM fuel pressure is 2.5 to 4 LBS for the N/A's. But I don't know if this is at idle or WOT. I do know that the one I'm looking into is rated at 5-7 LBS@72 GPH.

In anycase, the xtra push can't hurt. In fact I theorize that as one ups the power on these engines the fuel pressure requirements are probably also gonna go up. I bet either Fred C or GB could better answer these questions.

Anyway, my modified Q-Jet would probably get a kick out of the additional pressure since the pump shot sizes have been increased.

 

[b4black]

Roe's book says something like 4 psi at WOT, and some Buick manual were saying 5. Then others said a Quadrajet is fine with as little as 2 psi. (I had about 3 pis at WOT.)

Then I found a site that says it's not pressure, but flow that's important. That the carb's fuel bowl can't hold enough for a ¼ mile run. Whith good flow, 2 psi is enough.

In case my pump was bad, I swapped it with a new one I already had (brand unknow). The WOT stumbling improve a little, but was still there.

Then I removed the internal filter in the carb inlet and replaced it with a much larger external filter. (less restriction = more flow) NO STUMBLE!!! 3 psi before the filter dosn't mean much. It's the pressure/flow after the filter that's important.



SOME OTHER THINGS I FOUND OUT:
Odd fire V6 pump are the same as Buick 350 V8 pumps
GM performance still sells a high performance odd-fire pump for ~$67. (Maybe it could be changed to even-fire?).
Carter no longer makes it's high capacity pump.
Odd-fire/V8 pump on even-fire will provide low pressure.



So while I'm OK for know, I still want to upgrade my fuel pump in the near future. I would like to find the part # of the Carter HP pump or find out if the GM HP pump can be converted to even-fire. Otherwise I might just go high-tech - electric

 

[Freddie's Buick]

Rich,

On pg. 23 of the Ruggles V-6 book he breifly mentions the H.D. fuel pump originally designed for the 350. I think he means that the design will only work on the V-6 if one uses an odd fire cam.

He gives the fuel pump part numbers on the bottom of page 30.

Odly enough though, throughout the book they keep showing a fuel pump block off plate. Does this mean racers prefer the electric ones?

It seems to boil down to fuel flash/vapor lock. The electric pumps have less tendency to cause this. On page 116 of the Row book Roe gets into the Q-jet fuel pressure requirements that you read about. I guess 7-PSI would be overkill?

Anyway my guess is that there must be an advantage with less drag on the cam eccentric with the electric ones?

Questions....just more quetions....

 

[Freddie's Buick]

Originally posted by b4black
Then I removed the internal filter in the carb inlet and replaced it with a much larger external filter. (less restriction = more flow) NO STUMBLE!!! 3 psi before the filter dosn't mean much. It's the pressure/flow after the filter that's important.

Very interesting....makes sense. Would the larger filter be available in a clear canister with a replaceble element?

Originally posted by b4black
I would like to find the part # of the Carter HP pump or find out if the GM HP pump can be converted to even-fire. Otherwise I might just go high-tech - electric

I don't know if this might help...but http://www.partsamerica.com/PartDet...=CTR&MfrPartNumber=M60003&PartType=52&PTSet=A

I too have looked everywere for a Carter HP mechanical pump for the Buick V6 but no one seems to make one. Perhaps this one is but no info or data is available for it yet, (possibly too new an item).

I wonder if any of our forum parts techs could find out?

 

[b4black]

That's the standard Carter pump number. Good price though.


I have a clear cannister filter on now. I'm gonna add a gauge fitting after the filter and see what pressure I'm getting.

 

[Freddie's Buick]

Need input....

Well I reconsidered the electric fuel pump idea based on some of the experiments you did Rich.

After gathering much info on electrics I concluded that for a dragster it's a must but for street/strip the payoff is minumal at best. Too much work and money involved for little or no gain.

Also, heres the OEM GM high performance mech/pump you mentioned Rich: http://www.gmproparts.com/product_i...d=139&osCsid=e67ddc5b6cad5d20cc8a08a3cd7e2668

At that price and needing the eccentric it's seems a waste of money for little gain.

Here's what I'm thinking about doing based on what you wrote and what is written in the Roe book:

First, I think I'll go with the Carter pump and some add-ons. I can get a cheaper pump but Carter has a good name behind it.

Summit offers a mini-inline fuel gauge for $16.95, (SUM-G3122). One will need SUM-G1710 to make it work for another $5.99. In addition, prior to the gauge I think I'll install Edelbrock's 10-Micron in-line filter with replacable element, $12.95.

And finally, remove the OEM internal paper filter. According to Roe a good in-line filter prior to the carb will handle the internal paper element's job just as well. (In-line has less restriction then internal and the flow will increase Just like you wrote about Rich). And yeah, the bronze filters are the most restrictive of all the OEM filters, stay away from them.

Cost-wise this cost less than an electric, easily do-able, and will probably give more gain since the N/A's don't require too much pressure anyway. What do you think Rich?

 

[b4black]

I connected the fuel gauge up. I'm seeing 3 psi AFTER the external filter. This is same as I was seeing BEFORE the internal filter.

I'm finally rid of that stumble. I chased that for a long time. I assumed that a Quadrajet, the same carb GM puts on big blocks, could handle the fueling of a little ol' V6. Maybe the CCC carb, with the extra electronics, has a smaller fuel bowl than the early carbs.

I agree, the electric seems like a lot of work/wiring. A good mechanical makes more sense. I like either a Delco or a Carter pump and the external filter. I like having the fuel pressure fitting. Maybe not having the gauge connected at all times, but checking it every so often.

It would nice to flow check a bunch of different fuel filters and see what's the best.

 

[pat83t]

OK here is what I know. The stock replacement Master brand pump is rated at a minimum psi of 5 1/2 lbs and a maximum of 7 1/2 pounds. I have also been thinking of going with an electric pump which would be real easy to do because a chevy big block block off plate will bolt right in place. I hope this helps some of you out.

 

[Freddie's Buick]

Originally posted by b4black
It would nice to flow check a bunch of different fuel filters and see what's the best.

I saw on the Summit catalog that the more expensive fuel filter/canisters have very high flow rates. I don't know if they're just made for electric fuel pumps or can be used with a mechanical. In any case, they cost more or just about as much as an electric pump.

Most of the smaller filters don't give too much info about flow rates but some do give micron/filter rates. I agree, if only they would give flow rates.

Thanks anyway Pat! But think about the electric pumps. See if you can come up with something to counter my doubts about them. What can they truly offer that's better than the mechanical to offset the cost and labor involved. (They really are'nt that easy to set up).