Which really would not be running out of breath. Unless you are a fuel tank
running out of breath in the 1/4 mile
- Thread starter diymirage
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But really, if this was an issue , it should turn into a lean condition which should lean to a short term popping condition.
diymirage
HP@idle > hondaHP@redline
I have had no issues, until I started running her down the track at full bore for a while
ive been doing some reading, and at my 423 HP, I should need a pump that can flow about 35 GPH correct?
I cant figure out the GPH rating on the stock pump I have on there now, but it sure looks like there are plenty of mechanical options out there that run 2, 3 times as high a GPH
ive been doing some reading, and at my 423 HP, I should need a pump that can flow about 35 GPH correct?
I cant figure out the GPH rating on the stock pump I have on there now, but it sure looks like there are plenty of mechanical options out there that run 2, 3 times as high a GPH
famous bob
mopar misfit
3/8 line, check p/up, elec. fuel pump, pressure reg. on front fender well. your running out of fuel no doubt. gotta have a small vent too. do it and forget that problem.
My 68 383 Formula S would do the same thing. Ditched the Carter electric fuel pump and put on the Carter HP mechanical pump. Problem Solved.
nm9stheham
Well-Known Member
Yes, your number is in the right ballpark, so aim higher. The pump has to flow that AT rated pressure. The stock pumps are rated in the 25-30-ish GPH range at pressure, so you are right on the margin with those. Yes there are a lot of pumps that can do a lot better, but be careful to look at the flow rates AT pressure. I have found a few that look just like standard pumps claiming 80-120 GPH, but when you dig down in the manufacturer's specs, that is free flow, not flow into 5-7 psi pressure, and the flows at pressure are just the plain stock numbers. So if is looks like the typical stock pump, my advice is to avoid it.
The Carter mechanicals seem to do well. The Carter 6270 is easy to get, but will put out higher pressures that most carbs like, so plan on a regulator inline after that one. The Carter 6902 has the right regulation level but I don't think they are made anymore. I think Mancini got/gets them on special order, but they show out of stock right now, as do other distributors.
The Carter mechanicals seem to do well. The Carter 6270 is easy to get, but will put out higher pressures that most carbs like, so plan on a regulator inline after that one. The Carter 6902 has the right regulation level but I don't think they are made anymore. I think Mancini got/gets them on special order, but they show out of stock right now, as do other distributors.
Free flow in the 100-120 GPH will be what you are looking for. I always use the free flow number, because different applications require different PSI to operate under, so the free flow number makes it less confusing.
Do it right. Do it once. Don't try to skimp on it or you will be chasing your tail.
Do it right. Do it once. Don't try to skimp on it or you will be chasing your tail.
Off topic car, but my '74 Firebird recently had the double whammy of a defective replacement fuel pump and a clogged charcoal canister. The result? Zero fuel pressure under load. If it's not venting, you're getting no fuel.
Tee in a fuel pressure gauge and see what you have.
Tee in a fuel pressure gauge and see what you have.
nm9stheham
Well-Known Member
BTW, as for the fuel pickup..... Hmmm, it is a restriction but all the restrictions in the line add up to to a total inlet pressure drop. If you go to 3/8" main line, then the pressure drop of the main line will drop waay down, almost to nothing, at your flow rates. If 'twere me, then I would stick with the present pickup, put in a better pump, and 3/8" line to get rid of that inlet pressure loss and see how it works.
If you do want to change pickups, then IMHO 5/16" will work for your flow levels since the pickup length is short and subsequent pickup pressure loss will still be low. The pickup can be removed with the tank in car. BUT....keep the old original pickup retaining ring!!!! The new ones are soft and bend and don't seal consistently.
If you do want to change pickups, then IMHO 5/16" will work for your flow levels since the pickup length is short and subsequent pickup pressure loss will still be low. The pickup can be removed with the tank in car. BUT....keep the old original pickup retaining ring!!!! The new ones are soft and bend and don't seal consistently.
nm9stheham
Well-Known Member
Well I thought so too, but I got to looking at the actual Carter specs on the stock looking pumps that Mancini calls 'Muscle Car' fuel pumps. Mancini shows 120 GPH free flow, but the Carter specs show 25 GPH maximum flow rate. It is the same old thing.... distributor specs need to be verified.
Carter M6866 Mechanical Fuel Pump | Carter Fuel Systems Online Catalog
And I agree 100% on the "do it right, do it once" sentiment.
Isn't that one ^^ a stock replacement, sort of?
The one I'm using does say 120gph free flow.
http://www.summitracing.com/parts/CRT-M6270/
nm9stheham
Well-Known Member
Yes, it is. But the M6866 is implied to be some sort of 'performance pump' in the Mancini site and they do say 120 GPH free flow, despite the reality being otherwise. The actual Carter specs nowhere say 120 GPH for that pump; just 25 GPH . So if people buy this M6866 pump thinking that the 120 GPH free flow rate on the Mancini site means it will support 400-500 HP, they are going to be sadly mistaken. We have had one person posting here in the last year that found this out.
I suspect that is a mistake on the Mancini site, but that is my point: don't believe everything you see on a distributor's site. They have some lower paid person who may never touch a car in their life typing the data into the web pages.
Of course to make things complicated, the M6270 Carter spec shows NO flow rates anywhere! Where the 120 GPH free flow rates for that pump come from that the distributors show... I don't know. We just all know that it will support 400+ HP..... and at least there is some real test data out there that shows it will do an honest 40-70 GPH over the RPM range at 4.5 psi pressure:
Mechanical Fuel Delivery for Mopar LA Engines
And notice that the above report shows the M6270 with a free flow rate of 80 GPH.....I'd believe that before the Summit website's 120 GPH rating.
FWIW, I did find the M6902 specs on the Carter site once and it did show the flow rates.... but that is not there anymore.
I suspect that is a mistake on the Mancini site, but that is my point: don't believe everything you see on a distributor's site. They have some lower paid person who may never touch a car in their life typing the data into the web pages.
Of course to make things complicated, the M6270 Carter spec shows NO flow rates anywhere! Where the 120 GPH free flow rates for that pump come from that the distributors show... I don't know. We just all know that it will support 400+ HP..... and at least there is some real test data out there that shows it will do an honest 40-70 GPH over the RPM range at 4.5 psi pressure:
Mechanical Fuel Delivery for Mopar LA Engines
And notice that the above report shows the M6270 with a free flow rate of 80 GPH.....I'd believe that before the Summit website's 120 GPH rating.
FWIW, I did find the M6902 specs on the Carter site once and it did show the flow rates.... but that is not there anymore.
KnuckleDuster
Well-Known Member
What's a good regulator to run with the M6270?
Is a return line really necesarry?
Is a return line really necesarry?
nm9stheham
Well-Known Member
We don't run a return line on our 340. Never have run one on any carbed race setup (just FI) and never had any issues.....so far! IMHO, the usefulness of fuel returns has all changed with the ethanol gasolines, and a return system will indeed keep the fuel cooler and less likely to boil. But we seem to be having more issues with hot underhood air temps than fuel boiling, now that we put a Holley composite material heat shield under the carb; that cured the fuel boiling in the bowls.
FWIW, I can remember 'back in the day' when sometimes fuel heaters were rigged up to help the vaporization of the fuels of the past. Things do change....
FWIW, I can remember 'back in the day' when sometimes fuel heaters were rigged up to help the vaporization of the fuels of the past. Things do change....
straightlinespeed
Sometimes I pretend to be normal
Im running a $25 Quick Fuel non return regulator. It holds a steady pressure and never fluctuates.
diymirage
HP@idle > hondaHP@redline
So I ordered a fuel pressure gauge to help me figure this out
If I run the car in neutral, will it used close to the same amount of fuel as under load ?
(I want to review it for 10 seconds or so and see what the fuel pressure does)
If I run the car in neutral, will it used close to the same amount of fuel as under load ?
(I want to review it for 10 seconds or so and see what the fuel pressure does)
some will scold me for this, but I make several trips "out of town" to do some tweaking before going to the strip. I know the strip is the place for it, but I'm a little too far away and the cost of it all, well, I just can't go down without knowing how the car will respond......
Carter M6866 Mechanical Fuel Pump | Carter Fuel Systems Online Catalog
I liked the Carter fuel pumps. I will also throw out this reminder that the 440 commando's were fed by a mechanical fuel pump, and those could be floored for a mile and not have fuel delivery issues
nm9stheham
Well-Known Member
Not even close.... not trying to pee on you, but it won't tell you what you need to know. That is the issue with the fuel pressure gauge. Best thing you can do with it is to CAREFULLY run a hose out of the engine bay and tape the gauge on the windshield and run down a side road for 1/4 mile or more. But of course you might burn your car down if things go bad with that setup! You really need a remote fuel pressure sensor. Sorry.
nm9stheham
Well-Known Member
Makes all the sense in the world to me to do so. So help me understand why you posted the link to the M6866...?
Just saying I like Carter fuel pumps.... and that the big boys of old all ran just fine off of mechanical fuel pumps feeding a lot of cubic inches and around 400 hp. My brothers '68 GTX with headers and a couple of other upgrades could be floored for a 1/2 mile and no fuel issues..... No, I'm not saying mechanical is better than electric, just saying that they work easily into the 12's
If you tee the gauge into the fuel line and tape it to the windshield, have a friend ride with you to watch it. If you have a fuel delivery problem that results in the car nosing over before 70 mph, briskly accelerating in high gear up to the freeway speed limit should let you know if you have a problem. Fuel pressure at idle should be in the 5-7 psi range, so the needle will drop pretty quickly and not recover if you have a delivery problem.
I'm not sure if you mentioned your tank venting situation, but by temporarily removing the fuel cap and retesting, you can eliminate that variable.
Be very careful how you tee in your pressure gauge, like nm9 just said. Carry a fire extinguisher and double check everything if you decide to go that route.
Of course, if you have a bad fuel pump, your idle pressure may be low and you can avoid the nuisance of testing it under load.
I'm not sure if you mentioned your tank venting situation, but by temporarily removing the fuel cap and retesting, you can eliminate that variable.
Be very careful how you tee in your pressure gauge, like nm9 just said. Carry a fire extinguisher and double check everything if you decide to go that route.
Of course, if you have a bad fuel pump, your idle pressure may be low and you can avoid the nuisance of testing it under load.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Would this be with a vacuum secondary type carb? Just throwing it out there.....
I might be inclined to put a vacuum gauge on the intake and see what's going on at the nose-over.Or actually, what's going on just before the nose-over.
'course you could just cut the ignition, when it pukes, pull over, and check the bowls.
'Course at 5500rpm this is 92 revolutions per second. A good system with a mechanical pump would at least half fill one bowl, having pumped 120gph(freeflow) x 32 ozpergallon/60minutesperhour/60secondsperminute = 1.07 ounces/second. Multiply by 1/2 cuz the cam pumps once per 2 engine revolutions =.533 oz per second. Then say an estimated 3.5 second shut down time; 3.5 x .533 =1.86 oz.I think that's about 50cc or nearly one holley-type bowlfull.
So if the bowls are empty, or very low,it would be a bad pump or system. But if the bowls are full, it could be either or.
If some amount of the fuel in the rear bowl was stacked up against the backwall of the bowl, exposing the secondary jets, you wouldn't know this, cuz you have already backed off the pedal, and are trying to recover on the primaries.So recovery time on the primaries might be 2 to 3 seconds to where the engine begins to respond again, and another 1 or 2 seconds to to fill the secondary bowl,and then it will take full throttle again.
I can agree with others as to the Hi-po pump, and a 3/8 line all the way into the tank, as being adequate for my 367 cuber, which goes 93 in the 1/8. Doing the math backwards this calculates to about 420 hp.
As to tank venting; consider that at .5 lb per hp per hour(you do the math, using average output for the run) this equates to pulling just a few ounces from the tank, per run. If you start with a half a tank of gas this will not present a problem for the Hi-po pump, if unvented. It will probably have enough power to collapse the tank.
I might be inclined to put a vacuum gauge on the intake and see what's going on at the nose-over.Or actually, what's going on just before the nose-over.
'course you could just cut the ignition, when it pukes, pull over, and check the bowls.
'Course at 5500rpm this is 92 revolutions per second. A good system with a mechanical pump would at least half fill one bowl, having pumped 120gph(freeflow) x 32 ozpergallon/60minutesperhour/60secondsperminute = 1.07 ounces/second. Multiply by 1/2 cuz the cam pumps once per 2 engine revolutions =.533 oz per second. Then say an estimated 3.5 second shut down time; 3.5 x .533 =1.86 oz.I think that's about 50cc or nearly one holley-type bowlfull.
So if the bowls are empty, or very low,it would be a bad pump or system. But if the bowls are full, it could be either or.
If some amount of the fuel in the rear bowl was stacked up against the backwall of the bowl, exposing the secondary jets, you wouldn't know this, cuz you have already backed off the pedal, and are trying to recover on the primaries.So recovery time on the primaries might be 2 to 3 seconds to where the engine begins to respond again, and another 1 or 2 seconds to to fill the secondary bowl,and then it will take full throttle again.
I can agree with others as to the Hi-po pump, and a 3/8 line all the way into the tank, as being adequate for my 367 cuber, which goes 93 in the 1/8. Doing the math backwards this calculates to about 420 hp.
As to tank venting; consider that at .5 lb per hp per hour(you do the math, using average output for the run) this equates to pulling just a few ounces from the tank, per run. If you start with a half a tank of gas this will not present a problem for the Hi-po pump, if unvented. It will probably have enough power to collapse the tank.
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diymirage
HP@idle > hondaHP@redline
I seemed to have a vague recollection of consumption under load being different then free RPM consumption
I'm not planning on doing anything crazy as far as extending the fuel line to the windshield to see the gauge...but I might consider popping the hood, doing a 12 second burnout and having a buddy watch the gauge
best I can tell, this is a mechanical secondary carb
ill have to dig out the paperwork to see for sure (or maybe post some pics for people who know)
I did have a look at the lines in the engine bay
the flexible line running from the steel line to the pump is 5/16
does any of this look like it may be restricting flow?
(the steel line running from the pump to the filter maybe? )
replicaracer43
Grumpy Old Man
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The fuel T at your carb has a allen head plug in it, remove that, get a nipple that fits, run a hose from there to a gauge at the windshield. Even doing a burnout is not going to load the engine the same as a all four barrels open run through the gears.
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