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Okay, PACECARTA pointed out that the Return down-pipe from FPR and the frame mounted line are not the same size. Obviously I didn’t measure the two lines but my theory was derived after putting the same o-ring on the end of each pipe. Neither fits snug but below the engine, the o-ring falls off quite easily. So Paul I owe you yet another beer. (This project gets more expensive every day.)

Anthony thanks, interesting read on the link you provided. After Tori switched to a DW200 pump, although different brands, our pumps have the same flow capacity. I wish Tori would have said what the psi was with vacuum ON because I can adjust to 43 (vac line off) all day. My problem is the Return line creates a lower limit of 40 – 41 psi (vac line on). In other words, the pressure doesn’t drop properly with 18Hg vacuum applied at idle.
 
Restriction in the return line? Or pump puts out too much pressure for the return line to put it back to the tank.
 
You might try a search for the thread on drilling out the return lines. They state the size of the drill for the fitting down at the frame which I think they determined is the culprit. Maybe that would solve your issue without having to run new line.
 
You're right Charlie, the pump pressure is higher than the return line can handle. I proved the culprit is the frame mounted portion, checked it visually for crimps and blew air through it from back to front. Since the fitting end opening is so small, I'm assuming that is the "restriction".

And Pronto, in the post I read about drilling the pipe, a 9/64" bit was used. I measured the i.d. on my pipe and it is 7/64" so I'm not sure if a 1/32" larger opening will solve my problem. As I'm typing this a voice in my head is saying "Try it and see what happens!". :eek:
 
At least it wouldn't cost you anything.
 
you might be surprised what that 1/32 inch larger opening will do....I tried to give you a solution in post #40 with supporting information and another TB member to contact to verify...

consider that saginaw fitting as an orifice plate. basic equation from fluid mechanics for volumetric flowrate calculates that drilling out that fitting from 7/64 to 9/64 results in a 65% INCREASE in the volumetric flowrate through that "restriction."

use the online calculator here to prove the calculation to yourself...ask member @Tori for confirmation and just drill the fitting to 9/64 and see what your result is.

http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm#calc

to simplify the calculations....I used tubing data for 1/4 OD T-304 SS tubing, wall thickness 0.028 yields ID of 0.194
1. return line is 0.25" OD; yes, OE line is galvanized and I used SS for calcs - not a big deal
2. orifice diameter: 7/64 = 0.109375 9/64 = 0.140625
3. density of gasoline = 0.026 lb/in^3
4. flow coefficient = 1
5. whether pressure drop across orifice equals 1 psi or 2 psi or 3 psi, it is negligible and makes no difference in the resulting % increase in volumetric flow rate.

calculations using 7/64 opening...
Ret line flow 7_64 saginaw.png


calculations using 9/64 opening
Ret line flow 9_64 saginaw.png


the increase in volumetric flowrate is 0.695/0.421 = 1.6508 That's a 65.1 % increase for just enlarging that saginaw fitting 1/32"

play around with different pressure drop values, make no difference, there is a gain to drilling out the fitting to 9/64.
 
There you go, get to a drillin'.
 
Anthony, thank you for the flow info and the link to a calculator. This is exactly what I needed to know before I put a drill on the pipe.

OK here's what I learned thanks to Anthony, and please correct me if this is wrong. Drilling the pipe end to 9/64" will increase the flow rate by 65% but although the other post on this subject claimed to use a 9/64" drill bit, he couldn't have because the difference between 7/64" and 9/64" is 0.0312". The tubing wall thickness is only 0.028" (which I verified with ClassicTube who uses oem specs).

However, if I use a 1/8" bit the difference is 0.0156 (1/64”), which leaves a wall thickness of 0.0124 in. I don't know what if any, affect this has on the coupling. But more importantly, comparing Volumetric Flowrates for 1/8" and 7/64" yields a 30% increase. (Still worthwhile.)

And since we're throwing numbers around, my vacuum-off pressure is too high by about 20%. I am now anxious to see if a 30% increase in flow rate corrects my 20% pressure overage. So I'm about to "get to a drillin'".
 
I took some measurements from the new, not yet installed stainless return line from Classic. at that saginaw fitting, I can get a brand new 7/64 bit to twist by hand thru that opening - it's tight. to make that saginaw fitting, the tubing is pressed and drawn. the tit for the o-ring is hour-glassed shaped to retain the oring. I measured approx. 0.187 to 0.190 across multiple diameters top and bottom. the middle, where the oring would sit is about 0.184.

I get your point Dennis about using a 1/8 bit. not everyone has #'d bits so I don't know if any difference would be gained by trying anything larger than 1/8 in your case like #30 or #29, trying to sneak up to the largest opening you can an still have some wall thickness remaining.

which has me thinking that the OE galv. steel lines can vary a little bit (even new lines) depending how much use the tooling has had making those saginaw fittings. were talking 0.015 to get to 9/64 from 1/8, that could be the difference between theory and real world application.

Hopefully the eighth is enough to make a difference for you.
 
I do have number gauge drill bits and intend to start with a #34, then #32, then 1/8. If the tube wall thickness can 'handle it', I'll keep drilling with a #30 and possibly a #29.

It's interesting how the flowrate increases with each larger opening.
#34 = +3%, #32 = +12%, 1/8 = +30%, #30 = +38%, #29 = 54%

So Anthony is the wall thicker at the saginaw fitting? I'm not versed in metallurgy so I don't know what happens when the straight pipe is pressed into a saginaw fitting. After looking at the numbers though, it will have to be thicker than 0.028" to safely use a #29 bit.

I'm just trying not to create a 'point of no return' but let's see what happens. This project has been very educational for me and I thank everyone that took the time to contribute.
 
Maybe if you perforate it you could cut off the fittings and use a swageloc union fitting? You'll have to see what size the hole is in that fitting too.
 
just wiggle an awl in the opening to reopen the hole , said this way back at post #18
 
I've already done that, twice actually. First with a narrow awl then again with one that has a wider taper. It helped but didn't solve the problem. Maybe I don't have enough muscle, or my awl is too short. (Although my wife never complained).;)
 
the restriction is the hourglass of the tit. consider the opening has a slight flare to it, then it necks down slightly where the o-ring sits, then there is the base where the tubing is folded making the retainer for the tubing nut. kind of a non-answer but drawn processes yield thinner while pressed processes yield thicker.

using measurements from the new Classic SS return line...
OD at middle of hourglass tit approx. 0.184 while at the base approx 0.187 to 0.190 - there is a radius shoulder at the base from forming.
7/64 bit just passes thru if twisted by hand 7/64 = 0.109375
math yields a wall thickness of 0.0373 which is slightly thicker than the spec of 0.028 for the straight tubing in my example.

without doing destructive analysis on multiple fittings, I'm not sure how these #'s translate to everyone else's scenarios.

After seeing the replies this morning, I tried experimenting with different scratch awls on the stainless line. with a short taper and pressing and rotating by hand, I achieved the following:
where the opening was 7/64 at best, now a #35 bit will pass thru.
worked the awl some more and got a #34 bit to pass thru.
but that's all that I can get an awl to do in these few minutes. #33 just won't go.

maybe try a tapered hand reamer before a drill bit? 1/8 to 3/8 starts smaller than 7/64. lots of trying, re-assemble and test but just trying to sneak up on a solution.

in other threads, some have noted that expansion via an awl did not work for them. some report that it did. i'll find the links about supply line fitting work. I know that's not the matter here but searching here gives the OOPS result so have to use google search specific to turbobuick.com
 
line sizes to remember....
fuel feed/supply line is 3/8"...............fuel rail feed line is 3/8"
return line from fuel pressure regulator is 5/16 while return line to tank is 1/4"
vapor line is 5/16"

here are the two threads that discuss drilling out the saginaw fittings on the 3/8 FEED line so as to get more fuel to the motor. some are using a double pumper setup while others use a hobs switch set to whatever boost setting to activate the second pump.

https://www.turbobuick.com/threads/an-fitting-fuel-line-adaptors.370348/

https://turbobuick.com/threads/drilling-out-saginaw-fittings.395240/

these two links above are the only ones that specifically reference a size to open up the saginaw fittings on the supply side. the participants in those links above are not concerned about the return line as the OP is here. but those threads do give details about cutting and replacing the saginaw fittings with full port fittings.

others suggest swapping the return line and the vapor line at the tank end as well as at the frame cross member so that the return line is now 5/16. the use of full port fittings to connect the lines at the frame crossmember eliminate the saginaw fitting restriction there.

But I'm interested in the result of drilling out that saginaw fitting on the return line before cutting off that fitting and replacing it or swapping the return and vapor lines.
 
Imagine if GM was really innovative and put AN fittings in the fuel system? So much of the issues with the fuel system would have been reduced.
 
Imagine if GM was really innovative and put AN fittings in the fuel system? So much of the issues with the fuel system would have been reduced.

True, but then again, remember that at the time they were engineering a fuel system to 28lb injectors and maybe 15lbs of boost. What they put together was very capable for what it was originally designed for.
 
since this is becoming a very detailed thread, thought it would be good idea for reference to briefly explain how many of us get to this point of having to address the fuel return line saginaw fitting "restriction."

a bone stock, as delivered by GM, 86-87 LC2 engine had some components and supporting sub-systems that were essentially maxed out at the stock as-delivered performance level of 14 psi boost, controlled by the factory chip.

my bone stock, untouched '87 GN on the dyno ten years ago produced 13.77 psig boost (non-adjustable wastegate) and the factory original fuel pump delivered a max of 51 psig. 14 psig boost plus the Bosch 233 regulator giving 35 psig, vac line off - idle yields needed fuel pressure of 49 psig. the 20 year old stock fuel pump has 2 psig cushion. stock fuel pump was not hot wired, so voltage at pump using factory wiring could be 10 to 12 VDC, with current draw from accessories, lights, cooling fan, etc. that 2 psig cushion may not really exist if the pump actually receives less than 12 VDC due the the factory size wire harness to the rear of the car containing the fuel pump wiring plus the current draw and corresponding voltage drop caused by the other accessories in use.

the factory stock fuel pump max capacity rating was (if I remember correctly) 205 liters per hour (lt/hr) or 54 gal per hour (gal/hr).

the factory stock fuel pump for the '89 TTA was 225 lt/hr or 58 gal/hr as it's stock boost setting was 15 psig. TTA also used the Bosch 237 fpr (44 psig static) over the Bossh 233 fpr (34-37 psig static per service manual, 36psig static per spec)

when someone decided it was time to replace the fuel pump, whether for performance enhancing bolt-ons or just due to age, what became the "standard" stock replacement fuel pump was the Walbro 340M (now F20000169) pump rated at 255 lt/hr or 67 gal/hr. One has to remember that the 1990's up to the mid-2000's was all about bolt-on performance, so 255 lt/hr fuel pump is what the vendors carried as stock replacements. there was no internet 'til later part of the 1990's...finding stock replacement parts relied upon the parts counter dude/fool or phone calls to companies listed in the back of car magazines. You were laughed at if you were keeping you car stock. "Everyone" had at least a performance chip installed.

Several years ago, reformulated gas was intoduced to the market. So this new reformulated gas now uses lower quality hydrocarbon base fuels (lower octane) mixed with ethanol (higher octane) to achieve the pump octane rating today. The factory prom chip has way too much timing at WOT and during power enrichment for today's gas. 24 to 26* advance is possible via the factory chip. Eric Marshall at TurboTweak worked with all the old chip programmers to create today's best chip for the factory ECM. the street chip allows 16-18 psig boost and does that at lesser timing levels of 18* at WOT - excellent for today's pump gas.

So for safety with today's reformulated gas, we change out the factory prom to a TT chip. Recommended baseline static fuel pressure with a TT chip is now 44 psig (vac line off). Now we need a fuel pump to deliver 44 plus the boost level. 44 + 18 = 62 so the 255 lt/hr fuel pumps are a good choice, including the new DW200.

For a fpr, some just get a Bosch 237 or standard motor products PR4, etc. as a non-adjustable solution while some prefer and adjustable fuel pressure regulator like accufab or Kirban's. for many, the 237 will give rock steady performance without variation. some prefer the adjustable so as to be able to fine tune engine performance at top end rpm on the dragstrip.

Now that we have the chip, fuel pump and regulator to meet our performance level for a safe street car, the limitation of that 7/64" opening in that saginaw fitting on the stock fuel return line at the frame cross member presents itself. At idle, the fuel pump output is too great, engine uses a minimum amount of fuel so the unused has to be returned to the tank. For a street car and a stock appearing street car. drilling out the return line saginaw fitting without destroying it should provide the ability to reduce the static fuel pressure at idle to the desired level.

some of us just change the fuel pump to a 255 lt/hr unit while keeping the stock prom chip and the Bosch 233 regulator. In this case, the return line fitting can be an even greater issue getting the static fuel pressure down to the 34-37 psig.

In any case, we add a hot wire kit to our new fuel pump to maintain steady voltage. that only enhances the fuel pump output and high fuel pressure potential problem at idle.

this is turning into a novel, so it's time to stop.
 
Well I'm back from the garage and have good news and bad news. Good news first - I was able to drill the Return line to #28 (0.1405) without destroying the Saginaw fitting. I blew out the line from the rear then hooked everything back up.

Now for the bad news - fuel pressure w/vac off = 43 psi, with vac on = 41. I can't begin to describe my disappointment. I was sure this would finally fix the problem.

I snapped a picture after the drilling for a closer look at the end.
Well I guess it's time to replace the return line.
 

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Well I'm back from the garage and have good news and bad news. Good news first - I was able to drill the Return line to #28 (0.1405) without destroying the Saginaw fitting. I blew out the line from the rear then hooked everything back up.

Now for the bad news - fuel pressure w/vac off = 43 psi, with vac on = 41. I can't begin to describe my disappointment. I was sure this would finally fix the problem.

I snapped a picture after the drilling for a closer look at the end.
Well I guess it's time to replace the return line.
I'm sorry I haven't really been following this thread closely. Just glancing in from time to time.

But years ago, when I had a stock style set-up, I remember we (Cottons Performance and myself) removed the stock fuel return line and used the factory supply line as the new return. Then we added a new supply line.

I think we did this by using a AN adapter fitting down low in the front of the motor to connect the regulator steel line to the supply. Then another couple of fittings and a small piece of braided line to transfer back at the gas tank.

Then we added an entirely new supply line from the tank all the way to the rail. We did away with the pulsator after the pump and cut that little "neck-down" restriction out off the line at the hanger. Used an adapter fitting on the hard line leaving the top of the tank and ran braided line all the way to the rail.

So to put it simple.......the old supply was now the return and so now it was bigger. And then added an even bigger all new supply.
Seemed simple back then. And it worked for me up until a few years later when my combination when completely ballistic.
 
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