5/16 fuel line bottleneck ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Green Machine · 02-23-2005, 01:24 AM

At what point does the 5/16 fuel line become a bottleneck in the system? Many of us have done motor swaps and/or improved the stock engine. The larger stock engines used the 3/8 what about 327? anyone? 350 and big block for sure. But many have the smaller line. Should sending unit be changed too if putting in larger line ? Any thoughts or experience ???

skokie · 02-23-2005, 01:27 AM

I am curious about this as well. My truck came with a 307 and has 5/16 line but when I went to get a fuel pump for it the pump has is 3/8s.

Green Machine · 02-23-2005, 01:52 AM

Don't want to get off subject, but yeah my 307 68's been in the family since 1974 and I've been thru many pumps. I KNOW they used to make one with a 5/16 inlet, but I think my previous pump and the one i put on last year had the 3/8. inlet. Kind of a b!tch to stretch that 5/16 hose on the pump ain't it ??? And I told the parts guy about the difference, but kinda hard to see the diference, and he said there was and this is one you need. This was an AC Delco pump. Maybe the difference he meant was on the outlet cause that's 5/15 also and for sure 3/8 on that side would not work. But I know we talked about the inlet too...

But does the 5/16 matter ??

Fred T · 02-23-2005, 01:55 AM

350 has the 3/8 line. I didn't realize the 307 had 5/16, I thought all V8s had 3/8. You can use the 3/8 pump and you will never know the difference.

Green Machine · 02-23-2005, 02:11 AM

Fred that's right, I think the key may be V8 with 4BBL gets the 3/8. my 68 307 now has the 5/16 outlet with 3/8 inlet and 5/16 back to tank and works ok. Just a pain to fit. I also have a 70 c10 I'm working on that had the 250 6 banger with small line back all the way into the tank . I'm planning a pretty healthy 350 or 383 to replace the temporary 283 we put in there to get her going. I'm wondering if that will starve the motor when I'm in the throttle with bigger engine ?? In A car application some suggest a 1/2 line from rear of car forward to avoid fuel starvation, But since the tank is closer and higher than a car, well what to do ??? I can get the 350 type pump with 3/8 in and out for the new motor but what about back to the tank ??

cableguy0 · 02-23-2005, 02:20 AM

a healthy small block will definately starve badly with a 5/16's line even the stock 3/8's sending unit is restrictive because of how the feed line bends abruptly coming out of the tank

Green Machine · 02-23-2005, 02:39 AM

Soo - It looks like the 5/16 won't cut it. But if I spend 50 bucks on a new sender unit with 3/8 and run a new 3/8 line up front thats still marginal. Could I modify the 5/16 sender for a 3/8 or 1/2 inch or is that to much trouble for what its worth ? How do the higher horsepower guys feed their babies ???

cableguy0 · 02-23-2005, 03:15 AM

changing the sender would be a total pain in the @ss considering a new unit is under a hundrer bucks and you could probably pick up a used unit on here for cheap. im switching to a fuel cell very cell it starts starving for fuel at around 5800rpm even with the holley blue pump and 3/8 line. thats the easiest way i know is to switch to a fuel cell and just run -8 braided line which is roughly 1/2 inch inside diameter

Fred T · 02-23-2005, 05:22 PM

One thing you could do as a step toward an upgrade is to run a new 1/2" steel line from the tank to the pump. If you don't have a double flare tool, use compression fittings on the ends. Put a hose barb on the ends that match the size of hose at the pump and the tank. The short section of smaller hose will slow down the flow some, but not near as bad as the length of 5/16 tubing. Then when you're ready to do the work on the tank, you can plumb it for 1/2".

Sounds like cableguy0 also got into the distance loss in the line when he moved his tank. The longer the run, the more loss you have.

**CPNE** · 02-23-2005, 05:31 PM

Quote:

Originally Posted by Fred T

350 has the 3/8 line. I didn't realize the 307 had 5/16, I thought all V8s had 3/8. You can use the 3/8 pump and you will never know the difference.

4bbl carb = 3/8 line; anything else = 5/16 line

Tx Firefighter · 02-23-2005, 06:03 PM

I ran a stock 454 with an Edelbrock 750 in my 70 model off of the 5/16 original 6 cylinder line and sending unit. No problems with it.

The fuel bowl holds enough fuel to supply then engine for a good bit of spirited driving. If you stay in it long enough though, I'd imagine you could run into starvation issues.

cableguy0 · 02-23-2005, 08:49 PM

i didnt move my tank and with the holley blue there wouldnt be any distance loss to speak of its a 120gph pump the pump is mounted on the frame rail on under the passenger side and the tank is in the stock location. the pressure is just fine but the volume isnt there at 5800 and up it wont feed it. by spring hopefully i will have the fuel cell in the bed and just run my -8 line from the tank to the pump. the pump forward is already -8 split to two -6 lines at the regulator going to the carb

Blazer1970 · 02-23-2005, 11:51 PM

I have seen a few people post on this board who have fixed a fuel starvation problem by swapping to the bigger tank pickup/sending unit.

02-23-2005, 01:24 AM	#1
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	5/16 fuel line bottleneck ? At what point does the 5/16 fuel line become a bottleneck in the system? Many of us have done motor swaps and/or improved the stock engine. The larger stock engines used the 3/8 what about 327? anyone? 350 and big block for sure. But many have the smaller line. Should sending unit be changed too if putting in larger line ? Any thoughts or experience ???

02-23-2005, 01:27 AM	#2
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	I am curious about this as well. My truck came with a 307 and has 5/16 line but when I went to get a fuel pump for it the pump has is 3/8s. __________________ RIP to my son Dylan. 5/17/2002 - 8/18/2018 If you want to know more about rare forms of pediatric cancer or if you want to help fund pediatric cancer research, please check out the website for the non-profit I started. https://slothforpedcancer.org 68 build thread http://67-72chevytrucks.com/vboard/s...d.php?t=223234

02-23-2005, 01:52 AM	#3
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Don't want to get off subject, but yeah my 307 68's been in the family since 1974 and I've been thru many pumps. I KNOW they used to make one with a 5/16 inlet, but I think my previous pump and the one i put on last year had the 3/8. inlet. Kind of a b!tch to stretch that 5/16 hose on the pump ain't it ??? And I told the parts guy about the difference, but kinda hard to see the diference, and he said there was and this is one you need. This was an AC Delco pump. Maybe the difference he meant was on the outlet cause that's 5/15 also and for sure 3/8 on that side would not work. But I know we talked about the inlet too... But does the 5/16 matter ?? Last edited by Green Machine; 02-23-2005 at 01:58 AM.

02-23-2005, 01:55 AM	#4
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	350 has the 3/8 line. I didn't realize the 307 had 5/16, I thought all V8s had 3/8. You can use the 3/8 pump and you will never know the difference. __________________ Fred There is no such thing as too much cam...just not enough engine.

02-23-2005, 02:11 AM	#5
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Fred that's right, I think the key may be V8 with 4BBL gets the 3/8. my 68 307 now has the 5/16 outlet with 3/8 inlet and 5/16 back to tank and works ok. Just a pain to fit. I also have a 70 c10 I'm working on that had the 250 6 banger with small line back all the way into the tank . I'm planning a pretty healthy 350 or 383 to replace the temporary 283 we put in there to get her going. I'm wondering if that will starve the motor when I'm in the throttle with bigger engine ?? In A car application some suggest a 1/2 line from rear of car forward to avoid fuel starvation, But since the tank is closer and higher than a car, well what to do ??? I can get the 350 type pump with 3/8 in and out for the new motor but what about back to the tank ?? Last edited by Green Machine; 02-23-2005 at 02:45 AM.

02-23-2005, 02:20 AM	#6
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	a healthy small block will definately starve badly with a 5/16's line even the stock 3/8's sending unit is restrictive because of how the feed line bends abruptly coming out of the tank __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

02-23-2005, 02:39 AM	#7
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Soo - It looks like the 5/16 won't cut it. But if I spend 50 bucks on a new sender unit with 3/8 and run a new 3/8 line up front thats still marginal. Could I modify the 5/16 sender for a 3/8 or 1/2 inch or is that to much trouble for what its worth ? How do the higher horsepower guys feed their babies ???

02-23-2005, 03:15 AM	#8
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	changing the sender would be a total pain in the @ss considering a new unit is under a hundrer bucks and you could probably pick up a used unit on here for cheap. im switching to a fuel cell very cell it starts starving for fuel at around 5800rpm even with the holley blue pump and 3/8 line. thats the easiest way i know is to switch to a fuel cell and just run -8 braided line which is roughly 1/2 inch inside diameter __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

02-23-2005, 05:22 PM	#9
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	One thing you could do as a step toward an upgrade is to run a new 1/2" steel line from the tank to the pump. If you don't have a double flare tool, use compression fittings on the ends. Put a hose barb on the ends that match the size of hose at the pump and the tank. The short section of smaller hose will slow down the flow some, but not near as bad as the length of 5/16 tubing. Then when you're ready to do the work on the tank, you can plumb it for 1/2". Sounds like cableguy0 also got into the distance loss in the line when he moved his tank. The longer the run, the more loss you have. __________________ Fred There is no such thing as too much cam...just not enough engine.

02-23-2005, 06:03 PM	#11
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	I ran a stock 454 with an Edelbrock 750 in my 70 model off of the 5/16 original 6 cylinder line and sending unit. No problems with it. The fuel bowl holds enough fuel to supply then engine for a good bit of spirited driving. If you stay in it long enough though, I'd imagine you could run into starvation issues. __________________ I'm on the Instagram- @Gearhead_Kevin

02-23-2005, 08:49 PM	#12
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	i didnt move my tank and with the holley blue there wouldnt be any distance loss to speak of its a 120gph pump the pump is mounted on the frame rail on under the passenger side and the tank is in the stock location. the pressure is just fine but the volume isnt there at 5800 and up it wont feed it. by spring hopefully i will have the fuel cell in the bed and just run my -8 line from the tank to the pump. the pump forward is already -8 split to two -6 lines at the regulator going to the carb __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

02-23-2005, 11:51 PM	#13
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	I have seen a few people post on this board who have fixed a fuel starvation problem by swapping to the bigger tank pickup/sending unit. __________________ Tim



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