B pipe manifold diameter

Speedfreak

Speedfreak

Location
So. IL
Can you just chuck that thing up and bore it to 48 or 50 mm or should you port it with a grinder to 48 or 50mm?

I was looking at my pipe the other day and thought that was really wierd that if you put bigger carbs on there to make more power but the pipe diameter is the same then it is hard to get the extra air out. I have dual 48mm carbs and a single 42mm manifold... somehow that didn't add up. I know you need back presure but not a bananna in the tail pipe kind of pressure.
 
Speedfreak

Speedfreak

Location
So. IL
yamasaki said:
you know.. i wonder if the bpipe just was never designed for the cc's we're running through them these days? maybe at the inception 42mm was wide enough until FP realized there were limits that a std big-bore would exceed?
Click to expand...

I think that is where NEW aftermarket companys step up and come out with something new which proves to be better. But almost all of the aftermarket is focused on at the moment is light weight.
I have only been really into this sport for about 5 years and I feel it follows a trend everybody jumps on the bandwagon and off it goes. And we wait for it to come back around...
 
Frosty

Frosty

New York Crew
Location
Western New York
Speedfreak said:
Can you just chuck that thing up and bore it to 48 or 50 mm or should you port it with a grinder to 48 or 50mm?

I was looking at my pipe the other day and thought that was really wierd that if you put bigger carbs on there to make more power but the pipe diameter is the same then it is hard to get the extra air out. I have dual 48mm carbs and a single 42mm manifold... somehow that didn't add up. I know you need back presure but not a bananna in the tail pipe kind of pressure.
Click to expand...

I know a few people that have opened them up with a dremmel. I was going to do mine, but I have enough other work already... I let the pro do it for me :biggrin:
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
I have a size chart that I use for adjusting to match cc's of the motor, Pump and race gas. Back when I ran the Bud tour in 94-95 with Kawasaki stroker modified MRD fuel injected XI-R's, I used a special exhaust manifold and a 'B' headpipe from a Yamaha (kaws ran 'A' headpipe) and we had them bored out BIG 58X52 to keep them from buring the pistons because we had ******** KV's and MSD's ignitions back them!
 
Speedfreak

Speedfreak

Location
So. IL
SUPERTUNE said:
I have a size chart that I use for adjusting to match cc's of the motor, Pump and race gas. Back when I ran the Bud tour in 94-95 with Kawasaki stroker modified MRD fuel injected XI-R's, I used a special exhaust manifold and a 'B' headpipe from a Yamaha (kaws ran 'A' headpipe) and we had them bored out BIG 58X52 to keep them from buring the pistons because we had ******** KV's and MSD's ignitions back them!
Click to expand...

I knew that if you replied it would be somethign like that. If I get up the nerve to distroy this one I will try it but I will more than likely send it to you
 
Speedfreak

Speedfreak

Location
So. IL
Ok heres the pictures I had a 42mm manifold and headpipe the older model I decided to give it a shot. I was told by the motor builder that I needed a 49mm opening.

I started out by making the gasket opening 49mm and aligning it to the manifold. I marked it so that it could be lined up at the exact same spot for reference later. I also marked the headpipe and with a scribe and the 49mm gasket as a guide I marked the manifold and headpipe. Which makes the line under 49mm so I knew not to go outside the line. (hard for me to do)

I used a remer to take the majority of the material out then worked the area with a flap disk to smooth it down. I then smoothed everything with a.... well ... I don't know what it is called. I cut a grove in a piece of 1/4 inch stainless rod and slid sandpaper in the slot then used it as a sanding drum on a stick kinda thingy... That works great for polishing.

I made sure that the flow of the pipe was not upset by making just the opening larger. The opening flows smoothly into the original pipe.

I also took the little stamp off of the manifold and cut 49 in the manifold so that I would remember it is opened up to 49mm and if I ever sell it it will always be there.

Total was only about 2.5 hours. Well worth the extra horsepower that it will produce.
 

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cookerq62

cookerq62

Life's Been Good
Location
Upper Bucks, PA
How did you guys go about widening the manifold and head pipe and keeping the manifolds lined up?? Does anyone sell the bigger gaskets? Mine is at 44mm. How far can I go before i break into the water jacket?
 
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Crab

Crab

thanks darin...noswad!
Location
Seattle
My new A style headpipe was about 47mm, I used the gasket they sent me and used it to scribe the exhaust manifold. It opened up easy with a 1 inch rotary sanding disc.:Banane01:
 
RiverRat

RiverRat

.......
Location
Louisville, Ky
Here are a few more pics to add to this thread. I had Paul at LPW take my manifold and head pipe out to 48mm. You can see the difference it makes by seeing a normal FP manifold and the on I had clearenced.
 

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Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
Uh yeah, those are a bad production run. I'll take them off your hands for testing.
 
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