250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Yamariv · 03-31-2023, 05:41 PM

Just curious if anyone has actually had any issues with using the smaller 6 cylinder stock 5/16th's fuel lines when upgrading to a SBC 350? My understanding is the 350 or larger engined trucks got the bigger 3/8's fuel lines?

**pjmoreland** · 03-31-2023, 06:59 PM

I've had two trucks that I converted to a 350 and still had the 5/16" line. Both 350s were in the 300HP range, and I didn't have any fuel starvation issues. I ran mechanical fuel pumps in both cases. I'm not saying it's the best way to do it, but in my case it worked.

geezer#99 · 03-31-2023, 07:17 PM

I ran this dual quad up past 120 several times using a stock pump and 5/16 line.
And later a 750 vs Holley up to 7 grand thru 3rd gear.

**Steeveedee** · 03-31-2023, 07:57 PM

OK, it was only a 283, but my '64 Malibu with a 283 got to 120 (indicated on the speedo) with the 5/16" line. I did put a 4GC Rochester and dual exhaust on it.

jumpsoffrock · 03-31-2023, 10:10 PM

Even if you had a big block 1 ton truck fully loaded GVWR, going up a steep incline at full throttle with engine at redline speed, I wonder if you'd need the 3/8 line.

???

**Palf70Step** · 04-01-2023, 08:26 AM

I changed mine to 3/8" because of matching hard line to fuel pump. I didn't have any 5/16 that would go into the V8 fuel pump I had. Don't know if that was something weird on my part or ??? I have done several with friends where they kept 5/16 and ran it for MANY years without issue

72SB · 04-01-2023, 09:07 AM

GM used 5/16 on 6 cyl and 2 brl V8 motors. 3/8 on all 4 brl V8's.

FWIW I had a 2 brl V8 5/16 set up. When I put in a 411 hp motor, I swapped to 3/8" as the 3/8" fuel pumps put out more than a 5/16 fuel pump.

I am not a GM engineer but play one on TV...so I assume GM had their reasons for specking 3/8 fuel line

With that said several people still keep the 5/16 apparently without issue....or at least none they know of.

I got Right Stuff tank to pump pre-bent line

Yamariv · 04-01-2023, 09:24 AM

Thank you very much guys, this is exactly what I needed! So no point in preemptively changing out the lines, thanks!

**special-K** · 04-01-2023, 10:16 AM

You only need to change to 3/8" fuel lines for a BBC 350

**'68OrangeSunshine** · 04-01-2023, 10:27 PM

Quote:

Originally Posted by special-K

You only need to change to 3/8" fuel lines for a BBC 350

On the 350 Big Block, do you have to buy a 396 bare block core and sleeve it down?

**67 twins** · 04-02-2023, 12:06 AM

Quote:

Originally Posted by '68OrangeSunshine

On the 350 Big Block, do you have to buy a 396 bare block core and sleeve it down?

No, no no. It's a destroked crank & special pistons.

**'68OrangeSunshine** · 04-02-2023, 05:06 AM

Quote:

Originally Posted by 67 twins

No, no no. It's a destroked crank & special pistons.

Like That Other Manufacturer's 351 Cleveland?

**special-K** · 04-02-2023, 05:51 AM

I was just joshin'. That's why the LOL emoticon. I find it humorous to be adding SBC when speaking of a 350. Thought I'd give a poke. I guess the 366 would be a good candidate if someone wanted to build a BBC 350, for whatever reason. When I think big block I think go big. I love the idea of playing with displacement in SBCs. Ever seen a 283 crank in a 400 block? Special main bearings required. A whole lotta meat in those bearings! But boy does that mill scream. To the tune of 500 hp!

**Sheepdip** · 04-02-2023, 09:42 AM

This might put your mind at ease

https://help.summitracing.com/app/an...e-do-i-need%3F

Yamariv · 04-02-2023, 01:23 PM

Quote:

Originally Posted by Sheepdip

This might put your mind at ease

https://help.summitracing.com/app/an...e-do-i-need%3F

Nice, thanks!

54blackhornet · 04-02-2023, 02:38 PM

I was taught to not install a filter before a mechanical type fuel pump ?

72SB · 04-02-2023, 03:24 PM

I believe the Summit link noting to put a 100-micron filter between the pump and tank was referring to a Electric fuel pump placed near the fuel tank

Mechanical FP, yeah filter goes between FP and carb

**'68OrangeSunshine** · 04-02-2023, 03:25 PM

Quote:

Originally Posted by special-K

I was just joshin'. That's why the LOL emoticon. I find it humorous to be adding SBC when speaking of a 350. Thought I'd give a poke. I guess the 366 would be a good candidate if someone wanted to build a BBC 350, for whatever reason. When I think big block I think go big. I love the idea of playing with displacement in SBCs. Ever seen a 283 crank in a 400 block? Special main bearings required. A whole lotta meat in those bearings! But boy does that mill scream. To the tune of 500 hp!

Yeah. I knew it was an April Fools gag, I just wanted to see how deep the BS went. FoMoCo did exactly that with the 351 Cleveland. While the 351 Windsor was a regular run-of-the-mill SBF, the Cleveland used a big block and was underbored to use small block components, making a high performance engine.
At least I think that was it. Not really a Ford guy.

**special-K** · 04-03-2023, 08:46 AM

^^^ All I know is Ford making three 351s in the approximately same time period did nothing to help their already confusing parts compatibility issues. Which 351, C, W, or M? Are you sure it's not a 352? I never knew that about the Cleveland. That's how interested in Fords I ever was

**'68OrangeSunshine** · 04-04-2023, 01:01 AM

Quote:

Originally Posted by special-K

^^^ All I know is Ford making three 351s in the approximately same time period did nothing to help their already confusing parts compatibility issues. Which 351, C, W, or M? Are you sure it's not a 352? I never knew that about the Cleveland. That's how interested in Fords I ever was

Not a Ford guy either, but my mechanic is.

03-31-2023, 05:41 PM	#1
Yamariv Registered User Join Date: Oct 2022 Location: Regina, Saskatchewan Posts: 343	250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? Just curious if anyone has actually had any issues with using the smaller 6 cylinder stock 5/16th's fuel lines when upgrading to a SBC 350? My understanding is the 350 or larger engined trucks got the bigger 3/8's fuel lines? __________________ 1971 Chev C10 - 250ci L6 w/3 speed on the floor Upgrades: Power Steering 3 Core Radiator 7 Hole Gauge Cluster Power Brakes (Incoming!!..) 1971 350 (Incoming!!..)

03-31-2023, 06:59 PM	#2
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 6,234	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? I've had two trucks that I converted to a 350 and still had the 5/16" line. Both 350s were in the 300HP range, and I didn't have any fuel starvation issues. I ran mechanical fuel pumps in both cases. I'm not saying it's the best way to do it, but in my case it worked.

03-31-2023, 07:17 PM	#3
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,776	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? I ran this dual quad up past 120 several times using a stock pump and 5/16 line. And later a 750 vs Holley up to 7 grand thru 3rd gear. Attached Images

03-31-2023, 07:57 PM	#4
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,932	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? OK, it was only a 283, but my '64 Malibu with a 283 got to 120 (indicated on the speedo) with the 5/16" line. I did put a 4GC Rochester and dual exhaust on it. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

03-31-2023, 10:10 PM	#5
jumpsoffrock Registered User Join Date: Apr 2014 Location: California Posts: 999	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? Even if you had a big block 1 ton truck fully loaded GVWR, going up a steep incline at full throttle with engine at redline speed, I wonder if you'd need the 3/8 line. ???

04-01-2023, 08:26 AM	#6
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,466	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? I changed mine to 3/8" because of matching hard line to fuel pump. I didn't have any 5/16 that would go into the V8 fuel pump I had. Don't know if that was something weird on my part or ??? I have done several with friends where they kept 5/16 and ran it for MANY years without issue __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

04-01-2023, 09:07 AM	#7
72SB Registered User Join Date: Apr 2022 Location: Moorpark, CA Posts: 775	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? GM used 5/16 on 6 cyl and 2 brl V8 motors. 3/8 on all 4 brl V8's. FWIW I had a 2 brl V8 5/16 set up. When I put in a 411 hp motor, I swapped to 3/8" as the 3/8" fuel pumps put out more than a 5/16 fuel pump. I am not a GM engineer but play one on TV...so I assume GM had their reasons for specking 3/8 fuel line With that said several people still keep the 5/16 apparently without issue....or at least none they know of. I got Right Stuff tank to pump pre-bent line

04-01-2023, 09:24 AM	#8
Yamariv Registered User Join Date: Oct 2022 Location: Regina, Saskatchewan Posts: 343	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? Thank you very much guys, this is exactly what I needed! So no point in preemptively changing out the lines, thanks! __________________ 1971 Chev C10 - 250ci L6 w/3 speed on the floor Upgrades: Power Steering 3 Core Radiator 7 Hole Gauge Cluster Power Brakes (Incoming!!..) 1971 350 (Incoming!!..)

04-01-2023, 10:16 AM	#9
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? You only need to change to 3/8" fuel lines for a BBC 350 __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

04-02-2023, 05:51 AM	#13
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? I was just joshin'. That's why the LOL emoticon. I find it humorous to be adding SBC when speaking of a 350. Thought I'd give a poke. I guess the 366 would be a good candidate if someone wanted to build a BBC 350, for whatever reason. When I think big block I think go big. I love the idea of playing with displacement in SBCs. Ever seen a 283 crank in a 400 block? Special main bearings required. A whole lotta meat in those bearings! But boy does that mill scream. To the tune of 500 hp! __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ Last edited by special-K; 04-02-2023 at 09:52 AM.

04-02-2023, 09:42 AM	#14
Sheepdip Senior Member Join Date: Nov 2018 Location: Waterford California Posts: 2,700	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? This might put your mind at ease https://help.summitracing.com/app/an...e-do-i-need%3F

04-02-2023, 02:38 PM	#16
54blackhornet Registered User Join Date: Jul 2008 Location: Eastern Oregon Posts: 2,416	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? I was taught to not install a filter before a mechanical type fuel pump ? __________________ 71 C-20 07 Magnum RT AWD

04-02-2023, 03:24 PM	#17
72SB Registered User Join Date: Apr 2022 Location: Moorpark, CA Posts: 775	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? I believe the Summit link noting to put a 100-micron filter between the pump and tank was referring to a Electric fuel pump placed near the fuel tank Mechanical FP, yeah filter goes between FP and carb

04-03-2023, 08:46 AM	#19
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 250 6 Cylinder to SBC 350 - Do you really need to change fuel lines to 3/8's? ^^^ All I know is Ford making three 351s in the approximately same time period did nothing to help their already confusing parts compatibility issues. Which 351, C, W, or M? Are you sure it's not a 352? I never knew that about the Cleveland. That's how interested in Fords I ever was __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~



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