84bronze

when to use a mounting plate for a sbc mechanical fuel pump

sofakingdom

iTrader: (1)

There isn't one.

There's a "blockoff plate", goes behind the pump, which always has to be used. Without it there'd be a ginormous oil leak.

84bronze

ok, so the metal spacer between block and pump always has to be there no matter what year or application. A gasket on each side. Thank you

84bronze

It's been a long time since I messed with a mechanical pump. I want to convert my TBI to carb by removing in tank pump and adding a block mount pump on a block that originally didn't use one. Debating whether inline electric or mechanical. I want simple and reliable.

sofakingdom

iTrader: (1)

IMO the mech pump is simpler and more reliable; but when it comes to hacking up a fuel system, … gotta be a bit more careful how we go about it.

Just because the "system" is simple and reliable, doesn't necessarily mean that how a swapper goes about putting it into effect, is EITHER simple OR reliable. After all, "reliable" includes things like, the car bursting into flames while our 18-month-old daughter is asleep and strapped into a car seat a few inches (LITERALLY) away from the fuel tank. Let that thought percolate and sink in all the way through the grounds and the filter for a minute.

But yes, the blockoff plate always has to be there; either with the provisions for a pump, or without. Different plates obviously: exactly the same, except different. And, to use a pump, the pump drive rod has to be there, and the cam has to have the "eccentric" to work the rod. All older motors, up until the late 80s, had that. Starting around 87 or 88 or so, different ones started losing those features, as they became increasingly irrelevant to new car production. So, examine carefully, and make decisions accordingly.

A typical EFI car will need the electric pump removed from the tank and replaced with a much more basic sort of pickup; just a tube really, with a "sock" filter on the end. A mech pump generally won't be able to suck fuel through a disabled electric one. For that reason, lots of people decide to retain the electric, and use a regulator. But then you have the issue of controlling the electric pump with the correct logic. Not impossible by any means, or even undesirable; just, requires careful, logical, and COMPLETE thinking through the consequences of each decision.

NoEmissions84TA

iTrader: (1)

You need to use this plate if running a block-mounted mechanical fuel pump. Are you sure your block is drilled and tapped for using one?
IIRC, some blocks are not drilled for the fuel pump pushrod.

84bronze

Thank you for the help. The motor I have is a late 78-79 block. I has a blank off installed so I couldn't picture what was needed to make it work. Seeing the picture is like one of those duh moments. I think it should be ready to go with the correct cam. Fuel line, rod, plate pump, and fittings should get me running, just hope it goes that easy.

Last owner left the pump in tank with a electric Mr Gasket on the frame next to block pump blank then to the carb. It's been nothing but trouble!

84bronze

I have removed the old pumps both in tank and inline. I added a tube to replace pump for a pickup. Took out the EFI frame mount filter.

Thinking about rerouting the fuel lines off the firewall is necessary? I would like to move it from left frame across to the right frame then straight forward to block and pump. Also remove return line off firewall. Would be cleaner if nothing else. Hopefully this will work and be reliable.

sofakingdom

iTrader: (1)

I would recommend leaving the fuel lines alone as much as possible. There's nothing wrong with the factory routing. In the carbed cars, the lines went the same route as they do in your TBI setup, except they continued on over the top of the hump and came down over by the AC evap housing and then frontward along the top of the "frame" to the pump. In your case, I would cut the lines at a convenient point near the left valve cover, double-flare them, get flare union fittings, and use brake line sections to fab up new steel lines to run the rest of the way as described. Use absolutely as little rubber line as possible. Similarly, between the pump and the motor, use either steel line or PTFE braided-stainless, NOT plain rubber. Fuel is DANGEROUS and FLAMMABLE, and your life, the lives of your passengers, and the continued future of the car, are not worth taking a risk on a hack job.

If you use a mech pump, choose one with a bypass return, such as just yerbasic stock AC Delco one for a carbed one of these cars (the stock 305 pump will flow enough fuel for at least 400 HP... guess how I know this...), and hook it up much like they were hooked to the FPR on the FI TB. Just look it up at the parts store for a 84 Camaro 305 or the like. I'd also recommend a light-weight drive rod such as a Moroso, and a heat-insulating blockoff plate (the thing NoEmissions posted the photo of) from Canton.

84bronze

Ok that makes sense and sounds good. Didn't really want to reroute everything anyway just make it work correct. Looking at a pump with the return since it look like it will help with not getting vapor lock.

A 2 line pump with a 2 port return regulator between pump and carb would work the same way. I have a dual inlet carb and that would save some piping. Found a pump for 69 vette that puts 4-9 psi @30 gph.

84bronze

After searching and reading more. I think that I might try the carter 6624 pump (9 psi). Good brand usually and lifetime warranty

84bronze

Thanks for the help. Still in process of tuning as per Sofaking post.

NoEmissions84TA

iTrader: (1)

Look at the Carter M6626. https://www.summitracing.com/parts/crt-m6626

zed-028

2nd'd on the M6626 - excellent unit, certainly doesnt break the bank either

84bronze

6626 is only 5.5-6.5 open line psi. Holley needs 7 psi? 6624 is 7-9 open line psi. Both are of same quality?

Edit: both 9.0 psi depending on which website you look. Carter website shows
6624 is 2 line/9 psi/ 23 gph
6626 is 3 line/9 psi/ 40 gph

The return line makes difference in restrictions of the fuel?

Adding a regulator with return after pump and before carb would be the same flow?

Is this a 6 of one and half dozen of the other thing?

zed-028

I run a 6626 with my 70's quadrajet and requires a hell of a lot less than 7-9psi. I was running a regulator after the pump, however was having strange flow issues and the bowls werent filling quickly enough. I actually removed the reg, reset the float, checked the peak pressure and have been running without the regulator ever since.

If i didnt have the return line i think it would probably present more of an issue.

84bronze

So pump with the return bahaves differently so the extra flow is more than just the return off the pump.

Easier I suppose and keep engine clean with less hoses on top.

Thanks again

84bronze

I bought the 6626 and now waiting for it to arrive. $19 shipped so not too bad. Mounting plate, push rod and pump for $35. Can't beat that!

Tuned Performance

iTrader: (92)

84bronze

This is an older late 70's block. It has a chrome blockoff plate installed. I haven't pulled it off and looked yet though

Be a change of plan if no hole! If no hole than cam probably not correct either?

sofakingdom

iTrader: (1)

70s blocks will all be fully prepped for the mech FP.

Virtually all cams you are likely to encounter in such a block will also be equipped. About the only SBC ones that aren't, are stock LT1 & Vortec ones; which are both roller types, and both would require the retrofit rollers. Not saying there ABSOLUTELY IS a cam eccentric; only, that the odds of it NOT having one, are so tiny that they would need to involve Planck's constant.

A carb does not "need" any particular level of pressure. Carbs don't work off of pressure; they work off of VOLUME. As long as the pump, and the rest of the fuel system (which is usually more of a factor than the pump), can support adequate flow at .001 psi to keep the carb bowls full, then .001 psi is all it actually "needs". In reality, virtually ANY carb suitable for street use, will be perfectly happy if the pump can keep up 3 psi indefinitely, under sustained full power. Which is of course NOT the same thing at all as 9 psi (or ANY OTHER number for that matter) sitting in the driveway idling out of gear.

84bronze

I was under the impression that since all the different carbs list different psi requirements. Holley says 7 psi. Motorcraft 3 psi. That is the pressure that is used to unseat the float? The volume or gph is what determines how much hp can suppy?

Same as electric where voltage (psi) and amperage (gph) determine size of motor it can run?

sofakingdom

iTrader: (1)

Ignore those "ratings". They are largely meaningless.



It's really not that hard. Keep the fuel bowls full, and everything will be happy. That's all that matters.

84bronze

Sorry took too long to respond.

Ok so I got the new ampump installed and got it running. Run much better already. I am planning to set up carb as per sofaking post. I need to spend so time tweaking and learning as per. Thanks everyone for all your help.

NoEmissions84TA

iTrader: (1)

Give yourself a pat on the back.

84bronze

Feels good having it running good! Now to make it better? Hopefully lol...I might be back again