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240zBoy

Thoughts On This Fuel System

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So after replacing a wheel cylinder and putting in another r200 differential, I thought my 72 sbc swapped z was ready for the road which it has rarely seen. Backed her out on the driveway and while idling she died. Even more concerning though, the scream of my holly red pump was nowhere to be heard lol. Pushed back into the garage and the fuel pump was rather hot. After some reading I discovered that it likely burnt up due to being ran deadhead style (no return line). Now I never liked that pump, so I purchased the Carter p4070.

 

My plans are to drop the tank to inspect and replace as many of the rotted hoses up there as well. I am thinking about cleaning the tank out but I have had clean filters ever since running a couple gallons through from when she sat for about 13 years. So that is still up in the air....

 

But anyways I was going to switch over to 3/8 hose but have now decided to stray away from that as the only simple solution is to plumb a 3/8 fitting at the drain plug and I do not like that. Plus I am only around 330 hp and don't plan to ever go over 400 so the 5/16 hose should be just fine. I am going to replumb a return line to the original location which I believe is only a 1/4 nipple at the tank but that has been ok according to peoples experiences. So place the Carter Pump right in-front of the tank with a fresh new pre pump filter. Add a fuel pressure regulator (to make sure I am around 4.5-5 psi as I am running an edelbrock 600cfm) with a return line option near the tank as well and have it go right back to the original return line location. Also, I have the vapor line currently plugged closer to the engine bay and it hasn't seemed to cause a problem...?

 

I am new to fuel systems and still learning so if anything sounds like a recipe for disaster please let me know. I did do a bit of research to hopefully get this right and I think this is my most cost/time effective route to be back on the road without cutting to many corners!!

 

 

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Your assumption that the 5/16" feed line for your feed line being adequate for 330 HP is wrong. 5/16" is barely adequate for 200 HP. Even the anemic Chevy engines of the 1970's used 3/8" fuel lines.

 

Do your self a favor and when you have the tank out and cleaned, have the Tank shop replace the feed line with 3/8" and return line to the tank with 5/16" or 3/8". its easy for them to do. Them plumb new chassis hard lines from the fuel tank all the way to the front. 

 

The 5/16" lines will be just too restrictive. They also work the pump harder than necessary. And people forget about acceleration. Fuel has inertia. When you floor it, all that fuel has Mass that is now working against the fuel pump. This drastically reduces fuel flow. Anything that can be done to reduce restriction helps.

 

Top Fuel Drag cars always have the Fuel Tanks up front due to the extreme acceleration they produce. So acceleration forces push the fuel back towards the engine, thus helping the fuel flow. 

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Posted (edited)

Rebekahz might disagree about "wrong".  He seems to do okay with his LS2 powered 240Z.  There are very few absolutes in the world.

 

http://forums.hybridz.org/topic/97623-280z-stock-fuel-tank-with-ls-1-for-dummies/

 

Fuel systems are easily tested with a container and some battery power.  Fit your parts together, apply some power, measure what comes out of the return line.  Put a 5/16" restriction on the end of the line to mimic the return port.  Do some calculations.  Modify if necessary.  You might find that you're already overdoing it with your plan.

 

 

Edit - and don't blend high pressure EFI fuel system knowledge together with carb system knowledge.  Much of what's out there is about problems with high pressure systems on a 240Z.

Edited by NewZed

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You probably would be working the pump harder with a restrictive line, dead heading a pump usually is a big no no as well unless it is one of the newer models with an FPR near the pump that shuts it off/pulses it with a controller. 1/4 inch as a return also does not seem like much, better then nothing for sure.

 

What newzed says is solid. Test your system. You need two fuel jugs, a measured amount of fuel, and a pressure gauge. 

 

The term hose you use is also a bit disconcerting. Really you shouldn't use much if any hose. You don't need to go and buy expensive AN lines, but routing hardline would be a much better idea.  I've got a spool of aluminum in 3/8 kicking around somewhere.

 

General advise would be to go a bit bigger then you plan. Dropping everything is a pain so if you have the option stepping up slightly larger is a good idea, plus if something happens like the rubber starts to deteriorate or you start to clog up a filter a larger line is going to have a bit more room before it clogs.

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Posted (edited)

Holley red pumps can be run deadhead according to a lot of people but I only got 160 miles out of it that way haha If it's going to end up costing me 4-500 just to have the tank cleaned and modified for 3/8 then I'm better off buying one of those custom tanks around the internet (grossly expensive)..Guess I will have to get some price quotes and be safe. The 5/16 is more than likely fine and lightly modified v8s up to 450 sometimes more seem to have no issues but it definitely is a limiting factor there. Like already said, just would be a PITA to later on need 3/8 haha But I do feel that a 1/4 return line is oftly small even for a stock Datsun :/

Edited by 240zBoy

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You might be overcomplicating the issue.  On the progression path of "work" the pump has to do, a small return line is in between deadhead and big return line.  You could just add a return at the tank like Rebekahz describes and probably be fine.  With a filter in front of the pump.

 

That red Holley is rated at 97 gph if it's the one below.  Might be another part of your problem.  There's a bunch of calculators out there that get super specific but the rule of thumb for estimating seems to be 10 HP/gallon.  Get a 40 or 50 gph pump (at 4 spi) and you'll take load off of both the pump and your electrical system.

 

Could also be that the understandings of "deadhead" are different.  No return from the carb is deadheaded at the carb.  But there's usually still a regulator with a return line. If you just deadheaded the pump exit line that would be bad.  Might be why it's been screaming.

 

http://www.tanksinc.com/index.cfm/page/ptype=results/category_id=165/mode=cat/cat165.htm

 

https://www.amazon.com/Holley-12-801-1-Electric-Fuel-Pump/dp/B00029JC5S

 

http://www.jegs.com/i/Carter/180/P4070/10002/-1

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Posted (edited)

Good read, I will dive into that a bit further. Planning on running a FPR with a return line at the regulator with the carter pump. Would like to find one with a gauge port to dial it in right there. I first ran it simplly just pre filter-pump-filter-carb which I learned it what caused it to overheat/scream/die lol a return line will remove strain and lower any heat that would be at the pump by not heating fuel up.

Edited by 240zBoy

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Posted (edited)

The 10gph number is what I had in my head, but apparently V8's run more?

 

Our Carter P4070 flows 72 Gallons Per Hour which can supply a 400 HP engine. 

Our Carter P4600HP flows 100 GPH and will take care of over 500+ HP.

 

Maybe they are just terribly inefficient and require more fuel usage? 

 

Really not sure, I do know it was fairly common practice for old hot rodders to have spare pumps installed inline, Y'd into a separate fuel circuit, or just store spare pumps in their glove box since they tend to kill them. 

 

Completely off topic, where did you get your car painted? Looks pretty darn good!

Edited by seattlejester

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Huh lol I did some more reading and the carter pretty much can be ran unregulated based on an internal regulator that holds it at 7psi which is perfect for a Holly. Now most edelbrocks run less so using a regulator with a return back to the tank will provide that consistent 5ish psi and the return line from that regulator should be a bit kinder to the pump. To add though I believe 5/16 will add strain to this pump as I read that it is meant to work on 3/8. Trying to push fuel through a smaller line is more strain so

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The Holley should have worked fine according to instructions.  Maybe you had it mounted too high and it was running dry.  You should do more thinking on why the Holley failed.  You might just reproduce the same errors, if not.

 

https://static.summitracing.com/global/images/instructions/hly-12-801-1.pdf

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Mounted correctly. Best assumption is not having a return line hooked up but it is possible debris got through the filter. Getting that tank down will tell me more there. Many people have had the same problem as me deadheading these red pumps and it was pretty hot when I touched it after failing. Possible it was something else but most likely due to not having a return line

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Rebekahz might disagree about "wrong".  He seems to do okay with his LS2 powered 240Z.  There are very few absolutes in the world.

 

http://forums.hybridz.org/topic/97623-280z-stock-fuel-tank-with-ls-1-for-dummies/

 

Fuel systems are easily tested with a container and some battery power.  Fit your parts together, apply some power, measure what comes out of the return line.  Put a 5/16" restriction on the end of the line to mimic the return port.  Do some calculations.  Modify if necessary.  You might find that you're already overdoing it with your plan.

 

 

Edit - and don't blend high pressure EFI fuel system knowledge together with carb system knowledge.  Much of what's out there is about problems with high pressure systems on a 240Z.

Speaking of this, the main reason you can get away with the smaller line with EFI is that the pressure drop it induces is less of an issue when you are running the higher fuel pressures that EFI requires.  The regulator is at the rail, and the EFI pump generally has enough over capacity pressure-wise to compensate.

 

What Chickenman is getting at is when you require just 4-5psi at the carb, those losses become a very significant part of the equation.  Putting the regulator at the pump is really not helpful in this case either, since the pressure loss through the line is a linear function of restriction times fuel flow.  So the pressure regulation at the carb would be terrible - if you were to set the pressure at idle to 4psi you would likely end up with 2psi or less at full flow.  Conversely if you tried to set the fuel pressure to maintain 4 to 5 psi at full flow you would almost certainly go over the pressure spec for the carb at idle.  This is why carbs pretty much always need bigger lines than EFI.

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Still, all you need to do is measure.  The pumps seem to be generally set at 7 psi.  Should provide desired pressure at the carb after the pressure drop, easy to confirm with a gauge.  These types of things should always be confirmed by measuring, no matter how expert the opinions are.

 

Just like there's no best on Hybridz, there's no wrong.  If it works as intended.  There might be better, but saying it's wrong is wrong.  Why spend a bunch of money and time if basic knowledge of pressure drops and proper installation, confirmed by measurement, get you where you need to be.  Keep it simple.  He's not building a top-fuel dragster, it's a simple 330 HP V8.  There are hundreds out there.

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No offense intended to anybody in this thread.  I think that we're all nostalgic for the more sophisticated conversations of the past.  But this is just a tank, a pump, and carburetor on an engine that's been transplanted so many times that somebody wrote a book about it.  The solution might even be covered in the JTR book.  I don't have a copy myself, but even if it's not in there, for the Z's, there are thousands of simple electric pump to carb systems out there.  That's why each pump has a full set of installation instructions and recommendations.

 

Slow times on the old Hybridz site...

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