Exhaust fitment and interchangability

[Hammered]

I know similar questions have been asked in the past and after skimming all 11 pages about "exhaust", I still dont have a clear answer. I know I read that the 850s will fit the 750s. And I see systems listed as GS750/1000/1100 as fitments on the Fleabay. And after measuring the exhaust ports, I know that the 1980 750 I have and the 1983 650G are different. My main question is about exhaust options for my 1980 GS750 LX build.

Will the fact that my 750 is a 16 vavle matter in fitment with, lets say another 750 thats an 8 valve? And if they fit, are the listing grouping the 750s 1000s and 1100s correct in all being interchangable? Will the 850 swap out? I ask becasue the junkyard rescue Im now building off of had a decent header but the cross over and Y connections were trash. Years of rot have done them in. Ive found a MAC that is a 4 into 2 without crossover pipe for relatively cheap, but its for an 850. Cheap or not, Im not looking to spend if I dont have to. Hope this isnt one of those sore subjects that get everyone dander up. And if it is, think of it this way, least Im looking to put and exhaust on my Chopper.

[TheCafeKid]

AFAIK ANY of the GS headers will fit ANY of the GSs...750-1100... and i am pretty sure the 550s and 650s will fit too (at least the INTAKE spacing is for sure the same) The only REAL problem is where the rear mount ends up....

[Hammered]

AFAIK ANY of the GS headers will fit ANY of the GSs...750-1100... and i am pretty sure the 550s and 650s will fit too (at least the INTAKE spacing is for sure the same) The only REAL problem is where the rear mount ends up....

Excellent. The rear mount isnt a big deal since Ill be removing the mufflers to be able to craft the mods for slipons.

[reddirtrider]

The flange spacing is not the same on all 750's and 1100's, neither are the exhaust port diameters. In other words, they aren't all the same.

[Hammered]

The flange spacing is not the same on all 750's and 1100's, neither are the exhaust port diameters. In other words, they aren't all the same.

Ahh. So this leads me back to the questions at hand. SO am I to understand the only 750s to 1100s that are same number valves will interchange?

[reddirtrider]

Ahh. So this leads me back to the questions at hand. SO am I to understand the only 750s to 1100s that are same number valves will interchange?

Nope. The 4 valve 750 and the 4 valve 1100 I have sitting at my disposal have different flange spacing and different diameter exhaust ports. They are not interchangable in any way.

I do believe the flange spacing is the same on a 2 valve 750 and 4 valve 1100, but the exhaust diameters are different. It would be nice to have a table to categorize them all.

[Hammered]

Nope. The 4 valve 750 and the 4 valve 1100 I have sitting at my disposal have different flange spacing and different diameter exhaust ports. They are not interchangable in any way.

I do believe the flange spacing is the same on a 2 valve 750 and 4 valve 1100, but the exhaust diameters are different. It would be nice to have a table to categorize them all.

No doubt. Theres a crap load (yup thats a legal form of measurement) of listing on the Fleabay with 750s 1000s and 1100s all listed as interchangable. Well I guess thats why I come here, to get the straight poop.



Like how I put two, count um two, caca references in one post? OH come on, you know it made you giggle just a little inside when you realized it

[Tom MLC]

I have on hand a 8-valve GS750 motor, a 16-valve GS750 motor, and an 8-valve GS1000 motor. And of course my runner, a 16-valve GS1100. If it means anything to you, I can measure the head spacing on each of these. I can't help with the other models. Perhaps someone else will be kind enough to do so.

[TheCafeKid]

The flange spacing is not the same on all 750's and 1100's, neither are the exhaust port diameters. In other words, they aren't all the same.

I think the flange part you are right on...but ive read on here too many times guys grinding them down and slapping them on a late model 750 to believe the head ports are that much different in spacing...I have a couple to look at outside.. I will take a look...

[reddirtrider]

I think the flange part you are right on...but ive read on here too many times guys grinding them down and slapping them on a late model 750 to believe the head ports are that much different in spacing...I have a couple to look at outside.. I will take a look...

Not exhaust port spacing, exhaust port diameter.

[reddirtrider]

Here's more info, limited as it is.

I BELIEVE (not certain of ALL years) that the exhaust port spacing is the same on all of the below.

The 2 valve 750 and 4 valve 750 have the same exhaust port diameters, but different flange spacing.

The 2 valve 750 and the 4 valve 1100 have different exhaust port diamters, but the same flange spacing.

The 4 valve 750 and the 4 vlave 1100 have different exhaust port diameters and different flange spacing.

Since they all have the same exhaust port spacing, it's possible to modify each to fit the other depending on how much work you want to do and what fab skills you have.

I'm currently modifying a Yoshi 2 valve 750 header to fit a 4 valve 750. I posted a thread on this a while back and I'll update it when I get it done.

[posplayr]

I have a bunch of different headers (to many to mentioned 4:2, 4:1, 4:2:1 for 16V motors GS750/1100 and GSXR 1100 (let me count then 1,2,3......,8 16V exhausts)

From what I know V&H (not only some ebay resellers) list the same header to fit 80-83 GS1100E and the 80-81 GS750E including the rear hanger.I also know that Tom MCL has a 1100ED 4:2 installed on his 1100EX That means that:

the flange bolt spacing have to be the same.
the center to center port spacing has to be the same
the ID of the port has to be close.

Having said that the actual down tube diameter of the GS750 is narrower than the GS1100. The actual OD of the exhaust for GS750/GS1100's are different but they are close enough to fit.


Things are a little more complicated with the GS/GSXR conversions, but 80GS1000 has adapted the same pipes from second gen to GS1000's which I also have on my GS1100 so the port spacing for teh GS1000 must also be teh same as GS1100.

[Hammered]

Cool. This is getting somewhere now. Now if I only had the skills to start a speadsheet.

On that note. Ill measure my 80 750LX and the 83 650G for port center to center and Dia. If we can get enough info pulled together, maybe this would be good for a sticky. I know its stuff Ive thought about, but didnt ask because it wasnt a front runner in the project Im doing.

[posplayr]

80 750LX and the 83 650G

I dont know much about these except I'm guessing that the 80 750LX is 16V.


I just put a 83 GS1100ED black OEM pipe into a 80 GS750E motor; It fit easily. The ID of the GS750E port is only about 0.050" smaller. The OEM pipe on GS750EX (80/81) is about 1.5" v.s. the GS1100ED stock pipe which is 1.6". The collars are larger by a similar amount but they all fit. Not saying it might now be better to use GS750 exhaust gaskets on GS750 headers but the pipes fit into the ports.

I have converted a 1150 pipe to fit an 1100. Everything on 16V motors will likely fit at the port for GS motors.

The 4 valve 750 and the 4 valve 1100 have different exhaust port diameters and different flange spacing.

Red I don't know where you get this unless you are referring to the 83-86 750 motor as it doesn't apply to the 80-82 16V GS750's I just put an OEM 81 GS750X flange onto teh GS1100ED flange and head to confirm.

[reddirtrider]

I just measured the 83 GS750ES exhaust ports (again) and they're 42mm. I also measured the 80 GS1100E exhaust ports and they come in at 46mm. This was done with a micrometer.

I measured the OD of the exhaust pipes for the 83 GS750ES and they came in at 42 mm also (stock pipes). I don't have the stock 1100 pipes anymore, so I can only speculate at to their diameter at the port.

The flanges are different on both of these bikes.

There are significant differences.

I was assuming (that's why I said I BELIEVE) that all 4 valve 750 have the same exhaust diameter, just as the assumption was that all 4 valve 1100's have the same exhaust diameter. That assumption is probably wrong. I guess that's why it would be nice to have a spreadsheet of this information. It's helter skelter.