Topic: Building for torque? Hopefully not a stupid question

[BobbyR]

I deleted it so it does not grenade this thread.

[kos]

Right now, I am not worried about idle, but if it will shake the thing apart??? I should have it up and running by Christmas. I'll post some pics on a new thread I am starting about this Trackmaster Dirt Track racer project.

Pic of cam included.

KOS

[Sam Green Racing]

Wow Sam, thats GREAT info! Thanks! Nice smooth rising torque curves from 3500. If I read it correctly CBenF1 had a whopping torque spike about 4500, what would cause that? 

wheelspin perhaps

[Bill/BentON Racing]

Hmmm. I dont suppose you have the cam card from the RC315? Curious about lift and duration. Dynoman has a 360 lift, 250 at .050 duration one they recommend for F engines. I would like to stay away from heavy springs due to the wear that can result from them. Hondaman also mentions in his book using adjustable cam gears and advancing as much as 10 degrees to lower the torque band, not sure how far an F motor will go, but the theory sounds logical. Also using 4-4 megaphone exhausts with longer head pipes to try to lower the torque band. In *theory* should work.

RC315: Lift .365",Duration 310,Lobe centers 104. I used these cams more than once...really wake one up along w/836 etc.I've got a Megacycle 125/75 but no chance to use it yet.But will pick up the SAMAUTO CB750A on Sat. in Valdosta! ,Bill

[754]

 In My 836cc with the Webers and  a light rider, with a 130 Avon Venom, if you came of idele in first, then backed off and nailed it, the tire would spin.. throttle only..

 I think that was 19/54 gearing.. should be close to 17/48.

[vnz00]

Hi Guys, this one has prompted me to come out of the woodwork  . 

Im building a similar spec 836 engine but with CR29's and a Webcam 41 cam for an F2 (as per Buzz's recommendation) with springs.

I have cleaned up the intake ports in my head and taken away any sharp edges, smoothed the short turn and will de-shroud etc to help low lift flow.  I have made sure I didnt open the ports up any more than necessary to keep what low speed velocity the existing ports had.

I recently read that Mark Rieck has worked with 'D-Shaped Ports' previously and am wondering if this might help in this case.  This involves filling the lower part of the intake port with weld/epoxy to decrease x-sect are and increase the velocity in the ports.  Essentially this creates a flat floor in the intake port, and takes away the 'dead area' of the intake port which reduces velocity.  More reading available on the Mototune website however Motoman only details this for multivalve heads.

Mark, if you read this, can you comment as to how you used it and the possible results please?

Also, Hondaman recommended matching the combustion chamber shape to the new bore shape by grinding away the shoulder when the larger bore job is done.  This will promote better combustion too.

I hope this adds some value to the thread.  Im very curious to hear Mark's observations.

Regards,
Steven.

[Retro Rocket]

Intake manifold length and header length also play a part in all of this.....

Mick

[stever]

VNZ00, exactly! D shaped ports dramatically increase velocity by removing the "dead spot" on the port floor (at least in car engines). The area of highest velocity is along the roof of the port. I really believe that some thoughtful porting and modifications can overcome the pulse type carbs and square engine designs lack of low speed velocity. How is your shrouding in the F2? I talked to Mike and he says its not as bad as the K heads. I havent cracked mine open just yet but will shortly. Steve

[vnz00]

hi Steve, I havent had the cylinder bored yet - not far off though as I will have my last parts shipment coming from dynoman next week

Hondaman was deshrouding his F2 head when I emailed him, and he sent me some pics which I promised I would post.  There is not a lot of F2 Head posts out there that I can find with any porting pics and results posted as to improvements.  So I emailed him directly.

Ill get started on my build thread in a week or so and will get the hondaman pics/info on the F2 up here as well.  I hope that Mark gets back to us on the D Shaped ports.  I dont suppose you have tried it personally on a 2 valve head?  I worked out the curtain areas between 1 34mm and 2 25mm valves and it is quite significant how much more there is with 2 smaller intake valves.  I think this would have an effect on the finished x-sect area.

I was just trying the 'suckit and see' method.  If epoxy is used, it can always be ground out later.

Regards, Steven.

[stever]

Steve, Mike and I only spoke briefly on the floor raising. I have ported a pile of car heads but these dang cb's seem so finicky I think I'll just have Mike do the whole thing. I do kno wthat it's very easy to booger up an epoxy job. Cant wait to see your thread. Also, what angles are you using for teh valves? Hondaman says a 30 degree will up the flow 18% but then also recommends a 40-45-60 intake and a 26-45-60 for exhaust. Steve

[754]

I should mention, I run an unequal length turbo header that goes to a long primary tube then a baffled megaphone. The shortest header pipe is only around a foot long, and the primaries are small diameter, smaller than most exhaust.

 Keep in mind stock pipes are double wall, even smaller than they appear, most headers have incresed diameter. I am thinking this will help at upper rpm's but might be at a cost of reduced lower end response.

 Just keep it in mind, if building for torque, smaller pipe smay help.

[Retro Rocket]

I should mention, I run an unequal length turbo header that goes to a long primary tube then a baffled megaphone. The shortest header pipe is only around a foot long, and the primaries are small diameter, smaller than most exhaust.

 Keep in mind stock pipes are double wall, even smaller than they appear, most headers have incresed diameter. I am thinking this will help at upper rpm's but might be at a cost of reduced lower end response.

 Just keep it in mind, if building for torque, smaller pipe smay help.

I think that shorter header pipes has a similar effect Frank, look at most super bike pipes {designed for high revs} and they are all long, drag cars and bikes that need torque usually have shorter pipe set ups....

Mick

[MCRider]

I should mention, I run an unequal length turbo header that goes to a long primary tube then a baffled megaphone. The shortest header pipe is only around a foot long, and the primaries are small diameter, smaller than most exhaust.

 Keep in mind stock pipes are double wall, even smaller than they appear, most headers have incresed diameter. I am thinking this will help at upper rpm's but might be at a cost of reduced lower end response.

 Just keep it in mind, if building for torque, smaller pipe smay help.

I think that shorter header pipes has a similar effect Frank, look at most super bike pipes {designed for high revs} and they are all long, drag cars and bikes that need torque usually have shorter pipe set ups....

Mick

This article indicates just the opposite:
http://www.hotbikeweb.com/tech/0805_hbkp_exhaust_systems/header_pipes.html
which is what I'd always heard. Longer pipe for torque.  But deeper in the article it mentions anything can happen and I think bottom line its a case by case scenario looking at the overall set up.  But the pipe should definitely not be neglected in the search for low end torque in an engine not designed to do that (in line fours)

[voxonda]

To my knowledge longer primary's for torque and the shorter for topend, but.......................also depends on where the carb sits in the intake. In order to improve the torque curve used to lengthen the stacks.

[Retro Rocket]

I should mention, I run an unequal length turbo header that goes to a long primary tube then a baffled megaphone. The shortest header pipe is only around a foot long, and the primaries are small diameter, smaller than most exhaust.

 Keep in mind stock pipes are double wall, even smaller than they appear, most headers have incresed diameter. I am thinking this will help at upper rpm's but might be at a cost of reduced lower end response.

 Just keep it in mind, if building for torque, smaller pipe smay help.

I think that shorter header pipes has a similar effect Frank, look at most super bike pipes {designed for high revs} and they are all long, drag cars and bikes that need torque usually have shorter pipe set ups....

Mick

This article indicates just the opposite:
http://www.hotbikeweb.com/tech/0805_hbkp_exhaust_systems/header_pipes.html
which is what I'd always heard. Longer pipe for torque.  But deeper in the article it mentions anything can happen and I think bottom line its a case by case scenario looking at the overall set up.  But the pipe should definitely not be neglected in the search for low end torque in an engine not designed to do that (in line fours)

Thats why i said "i think" , I was referring to the header length but its been a while since i have been around race bikes and theories change with time but my point was that these should also be taken into account when chasing optimum performance, the manifold length has a similar effect as i mentioned earlier, again i am not too sure if longer is good for torque or revs.

Mick

[Retro Rocket]

To my knowledge longer primary's for torque and the shorter for topend, but.......................also depends on where the carb sits in the intake. In order to improve the torque curve used to lengthen the stacks.

Thanks Rob, this is what i was talking about...

Mick

[mlinder]

Advance cam timing, keep intake ports small for high velocity, less overlap on the cam, and use carbs/filters/box/etc to again, keep intake velocity up. Increase CR, have good backpressure on the exhaust, go as big as possible.

[Old Scrambler]

Great stuff guys...........I'm tuned in and will apply to my current build project.........a Triumph Cub........but the next project is a CB750 for torque.

[mlinder]

I forgot to ad increase intake runner length. There's math for it, but can't remember what it is. Ad an inch to the carb-to-head boots, increase low end power and response. Again, as long as it's small enough to keep intake velocity up.