Exhaust holes in crossmember How big ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

72MARIO · 11-29-2002, 11:59 AM

How big do I need to make the holes through the crossmember . I think that I want to use 3" tubes but my dad said he thinks thats way too big . Basically how much room should I have around the tubes is 1/2" enough? Thanks !!

guitarman · 11-29-2002, 12:09 PM

Unless you have a huge BB you're going to hurt your performance by going to 3" pipes. They look real cool but don't give enough back pressure for any low end torque. I'd put 2 1/4" to the back and then put 3" tips.

crazy longhorn · 11-29-2002, 12:19 PM

I would say 1" bigger on the hole vs pipe size(1/2" all the way around) should work. I agree with pipe sizing.....3" is way too big for a sb. 2 1/4" pipe should be fine to about 350hp or so, & 2 1/2" should handle to about 450-460 hp.......

SCOTI · 11-29-2002, 12:50 PM

I put 5" holes in mine w/3" exhaust.

dubie · 11-29-2002, 01:14 PM

what would you cut the holes with? plasma cutter? torch set? I am thinking about doing the same thing for my 2" exhaust

lost wages · 11-29-2002, 02:06 PM

when we did 1971 stepsides we used a sawzall, kinda rought but i filled the gaps in with the mig. I gotta plasma cutter now so if you have access to one that would be the way to go.

72MARIO · 11-29-2002, 03:26 PM

I am going to buy hole saw drill bit thats why I want to know what size of hole to cut . I have alreeady painted my frame so this way it shouldnt wreck too much paint.

crazy longhorn · 11-29-2002, 04:32 PM

If you are plannin a hopped 377 incher, I would go 2 1/2" on the pipe, & figure about 3 3/4 to 4" on the hole......thats way plenty, as that exhaust doesnt move that much back there.......crazy longhorn

Slammed67 · 11-29-2002, 08:53 PM

I think your exhaust shop man would greatly appreciate as much clearance as possible when he pipes it up. I'd go 2-1/2" pipe with at least a 4" hole. That'd give ya 3/4" all around.

Low67C10 · 11-30-2002, 12:16 AM

I did mine through the frame rail rather than the crossmember but I used 4" pipe and plan on using 2.5" exhaust tubing. After boxing the frame and welding in the 4" pipe, I stuck some spare 2.5" tubing through the hole and it seemed to have plenty of room. I cut the pipe at a 45 degree, used a plasma to cut the holes and a mig to weld it all together.

guitarman · 11-30-2002, 10:13 AM

Low67C10,
Where did you put the hole in the frame? Please describe more.

Low67C10 · 01-21-2003, 07:51 PM

The tubes are welded in right in front of the trans crossmember. It actually ended up bieng real simple, basically the tubes pass through the framerails at a 45 degree angle and are welded where they pass through the frame rail and the boxing plate. Ill take a pic and post it as soon as I can.

polevault1977 · 01-22-2003, 12:07 AM

I went with 4.5" inserts. I agree, I think the exhaust shop would appreciate as much room as possible. There is plenty of room, so why not? Just my 2 cents worth. Danny

72MARIO · 01-22-2003, 12:20 AM

I gota 4 1/4 " hole saw blade a few weeks ago so that is what size I went with . Is that pic current or how far along are you now? Thanks for the help.

soala70 · 01-22-2003, 01:06 AM

I have the same type of crossmember as this one what do you do weld it up? And what size exhaust do you all recommend for a mild 402 bb build up about 400hp?

lost wages · 01-22-2003, 02:03 AM

1971 stepside has that same crossmember and we put the pipe up to it and traced around it and after we cut out the circle just fill whats left with weld, there wont be much to fill. after doing his i wish i would have done mine, i still might, just hate to try to blend in the paint.

polevault1977 · 01-22-2003, 06:38 PM

72MARIO,

I think the how far along are you question was for me, I guess. I am basically finished with the frame except gastank. I will be putting in a warmed over 350 w/ vortec heads this spring and 700r4 tranny. I'm starting to redo my cab presently. I have a long road in front of me. Danny

PS What stage are you at? I love pics.

polevault1977 · 01-22-2003, 06:41 PM

soala70,

Nice lookin' frame you got ther'!!!

Danny

**1971Stepside** · 01-22-2003, 06:44 PM

here is what mine ended up looking like....we used a 4" piece of pipe cut at 1/2" thick.

**1971Stepside** · 01-22-2003, 06:46 PM

of the exhaust holes...

VDOG · 01-22-2003, 06:59 PM

The holes you guys are talking about, is that nesscesary for airbags or something like that? Im curious cause im getting my exhaust done in a few weeks.

**1971Stepside** · 01-22-2003, 07:03 PM

VDOG, it is just a real nice way to tuck your exhaust up in the frame on lowered trucks to keep it from hitting the ground. If you are not lowered or barely dropped you would not need to do that.

Polevault, that blue frame belongs to Lost wages

VDOG · 01-22-2003, 07:18 PM

Thanks 71stepside!

I do plan on lowering, but not that much. Might bag the front only for that nose scraping look.

Reumster · 01-22-2003, 08:00 PM

What did you all do with your e-brake cable? It looks like you all welded in the slots for them??

72MARIO · 01-22-2003, 08:09 PM

I dont think 71 Stepside is using the E brake.

11-29-2002, 11:59 AM	#1
72MARIO Registered User Join Date: Nov 2000 Location: Huntsville Ontario Canada Posts: 4,051	Exhaust holes in crossmember How big ? How big do I need to make the holes through the crossmember . I think that I want to use 3" tubes but my dad said he thinks thats way too big . Basically how much room should I have around the tubes is 1/2" enough? Thanks !! __________________ 1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD

11-29-2002, 12:09 PM	#2
guitarman Do it well or don't do it Join Date: Apr 2002 Location: Georgia Posts: 457	Unless you have a huge BB you're going to hurt your performance by going to 3" pipes. They look real cool but don't give enough back pressure for any low end torque. I'd put 2 1/4" to the back and then put 3" tips. __________________ Try to be the person your dog thinks you are. Excellent paint and body site: http://www.autobody101.com/ Visit my Web Site http://home.attbi.com/~agfosteriii

11-29-2002, 12:19 PM	#3
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	I would say 1" bigger on the hole vs pipe size(1/2" all the way around) should work. I agree with pipe sizing.....3" is way too big for a sb. 2 1/4" pipe should be fine to about 350hp or so, & 2 1/2" should handle to about 450-460 hp....... __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

11-29-2002, 12:50 PM	#4
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,080	I put 5" holes in mine w/3" exhaust. __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

11-29-2002, 01:14 PM	#5
dubie Registered User Join Date: May 2000 Location: Flin Flon, Manitoba, Canada Posts: 8,853	what would you cut the holes with? plasma cutter? torch set? I am thinking about doing the same thing for my 2" exhaust __________________ My name's Tim and I'm a truckaholic My 56 Chevy shop truck build http://67-72chevytrucks.com/vboard/s...d.php?t=562795

11-29-2002, 02:06 PM	#6
lost wages Registered User Join Date: Apr 2001 Location: jefferson city, mo Posts: 1,364	when we did 1971 stepsides we used a sawzall, kinda rought but i filled the gaps in with the mig. I gotta plasma cutter now so if you have access to one that would be the way to go.

11-29-2002, 03:26 PM	#7
72MARIO Registered User Join Date: Nov 2000 Location: Huntsville Ontario Canada Posts: 4,051	I am going to buy hole saw drill bit thats why I want to know what size of hole to cut . I have alreeady painted my frame so this way it shouldnt wreck too much paint. __________________ 1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD

11-29-2002, 04:32 PM	#8
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	If you are plannin a hopped 377 incher, I would go 2 1/2" on the pipe, & figure about 3 3/4 to 4" on the hole......thats way plenty, as that exhaust doesnt move that much back there.......crazy longhorn __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

11-29-2002, 08:53 PM	#9
Slammed67 Progress = 0% Join Date: Nov 2001 Location: Kansas City, MO Posts: 2,108	I think your exhaust shop man would greatly appreciate as much clearance as possible when he pipes it up. I'd go 2-1/2" pipe with at least a 4" hole. That'd give ya 3/4" all around. __________________ Jason - '67 GMC swb \| '57 Bel-Air 4dr hardtop \| '56 210 4dr Wagon \| 2000 GMC Sierra

11-30-2002, 12:16 AM	#10
Low67C10 Registered User Join Date: May 2002 Location: Southern California Posts: 66	I did mine through the frame rail rather than the crossmember but I used 4" pipe and plan on using 2.5" exhaust tubing. After boxing the frame and welding in the 4" pipe, I stuck some spare 2.5" tubing through the hole and it seemed to have plenty of room. I cut the pipe at a 45 degree, used a plasma to cut the holes and a mig to weld it all together. __________________ No, Its not a 454

11-30-2002, 10:13 AM	#11
guitarman Do it well or don't do it Join Date: Apr 2002 Location: Georgia Posts: 457	Low67C10, Where did you put the hole in the frame? Please describe more. __________________ Try to be the person your dog thinks you are. Excellent paint and body site: http://www.autobody101.com/ Visit my Web Site http://home.attbi.com/~agfosteriii

01-21-2003, 07:51 PM	#12
Low67C10 Registered User Join Date: May 2002 Location: Southern California Posts: 66	The tubes are welded in right in front of the trans crossmember. It actually ended up bieng real simple, basically the tubes pass through the framerails at a 45 degree angle and are welded where they pass through the frame rail and the boxing plate. Ill take a pic and post it as soon as I can. __________________ No, Its not a 454

01-22-2003, 12:07 AM	#13
polevault1977 Pick'n up the pieces! Join Date: Sep 2002 Location: Marietta, Oklahoma Posts: 198	I went with 4.5" inserts. I agree, I think the exhaust shop would appreciate as much room as possible. There is plenty of room, so why not? Just my 2 cents worth. Danny Attached Images

01-22-2003, 12:20 AM	#14
72MARIO Registered User Join Date: Nov 2000 Location: Huntsville Ontario Canada Posts: 4,051	I gota 4 1/4 " hole saw blade a few weeks ago so that is what size I went with . Is that pic current or how far along are you now? Thanks for the help. __________________ 1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD

01-22-2003, 01:06 AM	#15
soala70 Registered User Join Date: Mar 2002 Location: geneva al usa Posts: 343	I have the same type of crossmember as this one what do you do weld it up? And what size exhaust do you all recommend for a mild 402 bb build up about 400hp? Attached Images __________________ bogey5



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01-22-2003, 02:03 AM	#16
lost wages Registered User Join Date: Apr 2001 Location: jefferson city, mo Posts: 1,364	1971 stepside has that same crossmember and we put the pipe up to it and traced around it and after we cut out the circle just fill whats left with weld, there wont be much to fill. after doing his i wish i would have done mine, i still might, just hate to try to blend in the paint.

01-22-2003, 06:38 PM	#17
polevault1977 Pick'n up the pieces! Join Date: Sep 2002 Location: Marietta, Oklahoma Posts: 198	72MARIO, I think the how far along are you question was for me, I guess. I am basically finished with the frame except gastank. I will be putting in a warmed over 350 w/ vortec heads this spring and 700r4 tranny. I'm starting to redo my cab presently. I have a long road in front of me. Danny PS What stage are you at? I love pics.

01-22-2003, 06:41 PM	#18
polevault1977 Pick'n up the pieces! Join Date: Sep 2002 Location: Marietta, Oklahoma Posts: 198	soala70, Nice lookin' frame you got ther'!!! Danny

01-22-2003, 06:44 PM	#19
1971Stepside Almost Satisfied Join Date: Mar 2002 Location: Springfield, MO Posts: 2,932	pic of mine here is what mine ended up looking like....we used a 4" piece of pipe cut at 1/2" thick. Attached Images __________________ 1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3200 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Finally back on the road in 2021. "I can't complain, but sometimes I still do. Life's been good to me so far."

01-22-2003, 06:46 PM	#20
1971Stepside Almost Satisfied Join Date: Mar 2002 Location: Springfield, MO Posts: 2,932	another shot of the exhaust holes... Attached Images __________________ 1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3200 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Finally back on the road in 2021. "I can't complain, but sometimes I still do. Life's been good to me so far."

01-22-2003, 06:59 PM	#21
VDOG Grand PooBaa Member Join Date: Jan 2001 Location: LA, CA Posts: 5,302	The holes you guys are talking about, is that nesscesary for airbags or something like that? Im curious cause im getting my exhaust done in a few weeks.

01-22-2003, 07:03 PM	#22
1971Stepside Almost Satisfied Join Date: Mar 2002 Location: Springfield, MO Posts: 2,932	VDOG, it is just a real nice way to tuck your exhaust up in the frame on lowered trucks to keep it from hitting the ground. If you are not lowered or barely dropped you would not need to do that. Polevault, that blue frame belongs to Lost wages __________________ 1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3200 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Finally back on the road in 2021. "I can't complain, but sometimes I still do. Life's been good to me so far."

01-22-2003, 07:18 PM	#23
VDOG Grand PooBaa Member Join Date: Jan 2001 Location: LA, CA Posts: 5,302	Thanks 71stepside! I do plan on lowering, but not that much. Might bag the front only for that nose scraping look.

01-22-2003, 08:00 PM	#24
Reumster L.E.D. Freak Join Date: Jan 2002 Location: Polson MT Posts: 1,358	What did you all do with your e-brake cable? It looks like you all welded in the slots for them?? __________________ Specializing in Custom L.E.D. inserts. http://www.ccled.com/ Contact me @ blazer2wd1972@hotmail.com (406)675-8082 or Joel @ jmcwaters@eps-corp.net 1972 2wd Blazer, 350/700R4/3:73 posi, err & Custom L.E.D. inserts! LOL

01-22-2003, 08:09 PM	#25
72MARIO Registered User Join Date: Nov 2000 Location: Huntsville Ontario Canada Posts: 4,051	I dont think 71 Stepside is using the E brake. __________________ 1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD

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