Gs 1100 ex porting

[4cyl h2]

Good idea or not. gs1100 e. To back cut the exhaust valves at the bottom of the factory 45? Stock 1100 23mm valves, radiused factory valve seats seated near outer edge of valve if so how much? any advice appreciated!

 

[4cyl h2]

51 looks and no thoughts? Or am I asking for for valuable info??

 

[Nessism]

Sit tight. There are only a few guys around here that know such things.

Personally, I'd leave a reasonable margin for wear. Why not lap or blue the valves to describe the contact face, then back up up to within 1 mm or so of the face? Not sure about the back cut angle.

 

[Guest]

If you search the board you'll find usefull information. In the section tips and tricks there's a topic about flowing 1100's heads. Your questions about back-cutting are answered there too

 

[Guest]

I looked it up for you, think it was in a different part, but hey, here it is

http://www.thegsresources.com/_forum/showthread.php?t=137631

 

[4cyl h2]

Much appreciated got a project going I think will be fun. Just hoping to make it a little better

 

[Guest]

Much appreciated got a project going I think will be fun. Just hoping to make it a little better

What kind of project? I'm currently building a classic superbike racer

 

[4cyl h2]

putting an old conversion cartire chassis back on the dragdtrip will be a ported stock valve 1100 head with a hi dome 1260 piston

 

[Guest]

Dats a small motor for a car tire bike

 

[4cyl h2]

1 of the reasons im looking for all the tips-tricks i can find to use

 

[gearhead13]

28mm 1150 intake valves are bigger and can be found cheap. That and some Neway seat cutters to open up the seats. Thats what I used.

 

[Guest]

Why stock valves? Why not put a set of lighter 28.5/24 stainless valves to give that little motor some power to push that huge tire and rim. I mean if your gonna spend the $$ on porting it why not?

 

[gearhead13]

Why stock valves? Why not put a set of lighter 28.5/24 stainless valves to give that little motor some power to push that huge tire and rim. I mean if your gonna spend the $$ on porting it why not?

It sounded to me like the guy was on a budget, he was asking tips and tricks

 

[headsbikesmopars]

Back cutting the valves is always a good idea when you have the valves out. Use some layout dye on the valve seat area on the valves themselves and lap the valves in. You will see the seat contact area very clearly. Take them to a GOOD head shop and have them (intake and Exhaust) back cut to 37 degrees. What this does is open up more valve area and picks up the flow thru the port earlier in the lift cycle. It gets the moving column of air moving sooner. You will have the same flow at .050 as it was at .100, same at .100 as it was at .150 and so on untill around .300 lift, at this lift value the valve is open enough to where the valve shape isnt a factor . this will creat MUCH torque production and torque is what we want on the street. Expect to pay about $20.00 to $40.00 for this cheap mod. I never charge more than $20. for a set. 37 degrees is what Hemi chambers like , the Kawasaki's will flow better with 35 or 36 degrees as does Honda but The GS's LOVE 37 degrees. Just FYI wedge chambers (auto) like 30 degrees, if you cut these to 37 it will hurt flow. Low lift flow IS what we are after.

Terry

 

[Starion007]

Can you do the back-cutting on a lathe with carbide? or do you need a grinder.
I'll have to chuck up a couple used ones and give it a try.
Thanks Terry that's some really good info.

Mark

 

[posplayr]

Terry knows his stuff, he did my head and it is the best

 

[headsbikesmopars]

I have heard of it being done on a lathe,..I personnly have never tried that. I feel it best to have them back cut on a valve refacing machine. The operator can change the angle in an instant to what you desire. Thay will grind the existing angle off at 37 degrees and bring that cut right up to the top of the 45 seat on the back side of the valve itself. this cut is only about .030 wide, and looks to ' radius ' the backside of the valve. This cheap and easy mod REALLY works and is great for street engines as well as race engines. I perform this on ALL my engines whenever I have the valves out. It is ALL good and there isnt ANY down side to it. More flow is a GOOD thing. I learned a long time ago that a flow bench is an impartial judge and doesnt care to hurt your feelings,... ! My flow bench LOVES it when I back cut the valves, it tells me so.

Terry

 

[4cyl h2]

thanks for the info, thats just what i was looking for, im wondering about the depth or width of this cut, i have seated the valves on the seats near the outer edge of the valve and it seems like if the backcut area was to go up and almost touch the bottom edge of the lapped in area on the valve the 37 degree cut would be very wide ?

 

[headsbikesmopars]

Width really isnt an issue since the back cut doesnt touch anything like the 45 does. On a complete set you will have some wider than others, and it doesnt hurt anything, it is all good. when you move the seat out to the edge of the valve you can make the bowl larger and it is almost like having a slightly larger valve. The bowl should be 88% of the valve diameter. I have gone as large as 93% but those were on Pro Stock heads (auto) that are freshened after ever race. I feel there just isnt enough material under the seat area to support the seat. Bowls at 88% flow very well and is durable enough for daily use.

 

[GregT]

I've done the back cut both ways - lathe and valve refacer.

Valves with a larger stem diameter are easy to do in the lathe as they don't flex or chatter under the tool. Small OD stem valves are best done in the valve refacer IMO. So 8V stuff is fine in the lathe but I'd use a refacer for the 16V valves.