Exhaust port height / porting question

[TIM LUTZ]

After 11 years running on Klotz I think I’ll do a new top end. It’s just a shame that I have to do it due to a hole in the lower coolant hose causing it to overheat and pushing a head gasket. Anyway, While I have the jugs off might as well to do some porting . I have all the CC specialties equipment and have done a few Blaster cylinders with great results. The plan is to match and clean up the intake and transfers as well as case match the transfers and polished the exhaust. I have read that the Banshee can benefit from raising the exhaust port and not hurting low end. Can anyone suggest an exhaust port to deck dimension that will work well with the mods below and keep the nice wide power band of my DMC 916’s or even better a port map of a good trail/MX port job? Has anyone done the intake to transfer boost port mod? Any input would be great.

 

DMC 916 pipes

Stock carbs 290 mains

Uni filter/ hole in air box lid

Dual stage boysen reeds/ ported cages

4 degree key

Reed spacers between cylinders and reed cages

Edited July 7, 2010 by TIM LUTZ

[SLORYDER]

Assuming you have stock base gaskets that are approx. .025" thick, and your deck has not been milled:

 

Raise the transfers 1mm for a duration of 119-121 and a distance from deck of 43mm

 

Raise the exhaust 1.5mm for a duration of 189-191 and a distance of 28.5mm from deck

 

Widen the exhaust port to 45mm chord assuming 64mm bore. 70% of bore would be a good safe number as long as you don't square up the port too bad.

 

The best way to do this is with a degree wheel. Google printable degree wheel. I would recommend 120/ 188 for a mild port, or 120/ 190 and have you mill .020"-.025" off the head to make up for the loss in power stroke. I would actually recommend shaving the head regardless, and go with the 188 for more bottom end and 190 for more rev-out.

 

I would also recommend raising the intake port roofs to 70mm from deck and lowering them by 2-3mm, and give the bottom of the window a very gererous radius. Narrow the bridge to 5mm.

I would also recommend drilling the auxilliary intakes as well. Best way to do this is by drilling 3 small holes on top of each othervertically and tying them in with your porting tools; there is not a lot of lateral area to play with without going through the side of the case. A lot of builders add these ports; surely it must be backed up with a dyno..

[TIM LUTZ]

Thanks Sloryder. This is some good info. Would you or anyone else by chance have info or a section drawing of the best way to reshape the head on the Shee?

Thanks

[SLORYDER]

Thanks Sloryder. This is some good info. Would you or anyone else by chance have info or a section drawing of the best way to reshape the head on the Shee?

Thanks

 

I would definately not recommend reshaping the head yourself unless you do this for a living.

 

I can tell you that you will gain a few ponies by shaving .020" -.025" off the mating surface, and still run pump gas. Mill .030" to run 50/50 pump fuel and race fuel and more hp as well.

 

Or you can get even better results shipping your head to Mull engineering and having them rechamber it. his handle on here is blowit.

[TIM LUTZ]

Assuming you have stock base gaskets that are approx. .025" thick, and your deck has not been milled:

 

Raise the transfers 1mm for a duration of 119-121 and a distance from deck of 43mm

 

Raise the exhaust 1.5mm for a duration of 189-191 and a distance of 28.5mm from deck

 

Widen the exhaust port to 45mm chord assuming 64mm bore. 70% of bore would be a good safe number as long as you don't square up the port too bad.

 

The best way to do this is with a degree wheel. Google printable degree wheel. I would recommend 120/ 188 for a mild port, or 120/ 190 and have you mill .020"-.025" off the head to make up for the loss in power stroke. I would actually recommend shaving the head regardless, and go with the 188 for more bottom end and 190 for more rev-out.

 

I would also recommend raising the intake port roofs to 70mm from deck and lowering them by 2-3mm, and give the bottom of the window a very gererous radius. Narrow the bridge to 5mm.

I would also recommend drilling the auxilliary intakes as well. Best way to do this is by drilling 3 small holes on top of each othervertically and tying them in with your porting tools; there is not a lot of lateral area to play with without going through the side of the case. A lot of builders add these ports; surely it must be backed up with a dyno..

 

How much bottom end do you think I’ll loose with 120/188 I hate to kill the awesome wide power band I get with the DMC’s Most of my riding is gas lines in West Virginia (fast trail riding) I would like to see a wide, useable 60-65 horse power when I put the bike back together if that is possible with stock carbs. Got the cylinders off last night and although there is not as much room to work as the ports on a blaster cylinder, I think I can do a pretty good job. I’m going to make a drill jig that bolts to the intake so I can get all the boost port holes the same. If anyone else wants to jump in with porting specs please feel free.

Thanks all

[TIM LUTZ]

Also, I don't have any left hand cutters to use with my 1MC handpiece. Do you think this is going to be a problem when I do the transfer ports?

[TIM LUTZ]

Anyone else want to jump in with porting specs or a port map?

Edited July 10, 2010 by TIM LUTZ

[AKheathen]

actually, if you want a port map, you can buy just that. i don't remember who sells it, but there is a stencil kit. now, as for the transfers, you really want a 90degree tool to do the roofs, which are worth cleaning up at the minimum. i would suggest you start off conservative, which you should have no prob. hitting 60-65hp, and readding up on the 2 most important books. a.g.bell first, then jennings. they are both pinned at the top of repairs/mods in the thread "usefull links" you can always go more aggressive in steps.

 

...ok, where to start...

with the 916's and wanting to keep it at your trail ridding, you are propbably not gonna benifit from a huge exhaust just yet. start at the top about 68% of the bore wide, and radius it over 2.5-3mm height from top to the corner raduises. bring the sides down mostly strait, but tapering in slightly for about 10mm, then radus to the bottom, even with where the top of the piston bottoms out. 188-190 is the range you want to be in, with a blow-down of 29.5-31, mabey 32, if you end up needing to do that while you cut for any reason, but i wouldn't really go more, imo. now, that brings us to the transfers, which are really going to give you what you are looking for, as far ass the broad, and mid power. keeping in the 131-126, depending on the exhaust, range, start with the roofs. study them verry well as for shape. you will notice how messy it is, and clean that up first, then see what you have to work with for material. slope them up and to the rear a little more (away from the exhaust) widen the transfers to get in the time/area, or just a bit to reshape them widen just at the rear sde on the tops, and front(exhaust) at the bottoms, and not a huge amount, and more so on the rear transfers, than the front. you are going to need a long bit to open them up a bit, but not a huge amount, agin, just enough to keep up with the new openings, or you will loose velocity. i wouldn't jump into the wormholes, just yet, but that's my opinion. after all, you can always rip the topend back off and cut more into it in stages, for meere cost of the gaskets, no bore/hone/rings needed. now the 5th transfer at the rear of the cyl. keep it steep, and just widen it a bit, and you should be real good there. slo pretty much covered the intake, basically matching to the windows on the pistons, and shaping out the bridge, and opening. you want to slope the top of the intake and get rid of that step down, and keep everything except the exhaust not-polished. slightly rough surfaces keep a thin turbulant layer of air which "lubricates" the flow. make sure to chamfer all the ports nicely, so the rings don't snag, and have fun. and the usuall b.s. measure 2x, cut 1x, anylize what your dooing, plan your work-work your plan, etc....... take this advice at your own liability, i do not gaurantee it to be the best, or great, but i believe it to be efficient, and what you are looking for, plus plenty of room to change things, if you find you want a more aggressive, but less broad powerband, or more top-end oriented, etc. it's ust based on what i have learned from the banshee sites, and other literature. good luck- heath-

[ritchieb]

Hi,

I have a 64.5 x 54 stroke banshee with DMC916 pipes, coolhead, 21cc domes, .030" base gasket with .040"squish. It was ported by a builder to suit the pipes.

Exhaust port opens at 84deg ATDC with an exhaust port scallop of 4deg.

Main exhaust port opens at 88deg ATDC.

Top of exhaust port to deck is 28mm.

Transfer ports open at 122deg ATDC 43.5/44mm to deck.

Blow down 38deg.

I have mapped the cylinders and attached is a tracing of the actual ports.

I didn't like it at first because it's all top end but I learnt how to use the power delivery. Just a flick of the clutch if it falls off the pipe and it explodes into action. I've used it for motor cross, trail and in the dunes.

Hope this helps. Any feedback on this porting would be appreciated.

Thanks!

[TIM LUTZ]

Thanks Akheathem and Ritchieb,

Good info. Yea, I have the 44MC, 8MC and the small 182AMC right angle hand pieced and the hang-up motor from CC. Just never done a Shee before. What I plan to do is map/blueprint my stock porting, bring it into Corel Draw and do all my new port timing/shaping on the computer. Then I'll cut a template on my plotter out of mylar. And yea, I think at this time I'll pass on the boost ports. If I have good results I'll post an .EPS or .PDF for all to see/use.

[mopar1rules]

Hi,

I have a 64.5 x 54 stroke banshee with DMC916 pipes, coolhead, 21cc domes, .030" base gasket with .040"squish. It was ported by a builder to suit the pipes.

Exhaust port opens at 84deg ATDC with an exhaust port scallop of 4deg.

Main exhaust port opens at 88deg ATDC.

Top of exhaust port to deck is 28mm.

Transfer ports open at 122deg ATDC 43.5/44mm to deck.

Blow down 38deg.

I have mapped the cylinders and attached is a tracing of the actual ports.

I didn't like it at first because it's all top end but I learnt how to use the power delivery. Just a flick of the clutch if it falls off the pipe and it explodes into action. I've used it for motor cross, trail and in the dunes.

Hope this helps. Any feedback on this porting would be appreciated.

Thanks!

 

I ran your dimensions on my computer program and don't get 122* of duration for your 43.5mm deck to roof dimension. I get 120* deg instead. For your 28mm from deck to exh port roof dimension, I get 192* deg. So, if I use your exh (192*) and trans (120*) duration figures, I come up w/36* deg. Are you sure you have 38* blow down? Your shee would be super "pipey" and an absolute bear IMO to race motocross with, using them porting specs. I tried some specs that were kinds like yours (188* exh, 117* trans, 35.5 BD) for some motocross and found it to be falling off the pipe all the time. I also noticed in your port map, that you have some "staggered" porting going on.....your boost appears to be opening before the main and second transfers.

[blowit]

I ran your dimensions on my computer program and don't get 122* of duration for your 43.5mm deck to roof dimension. I get 120* deg instead. For your 28mm from deck to exh port roof dimension, I get 192* deg. So, if I use your exh (192*) and trans (120*) duration figures, I come up w/36* deg. Are you sure you have 38* blow down? Your shee would be super "pipey" and an absolute bear IMO to race motocross with, using them porting specs. I tried some specs that were kinds like yours (188* exh, 117* trans, 35.5 BD) for some motocross and found it to be falling off the pipe all the time. I also noticed in your port map, that you have some "staggered" porting going on.....your boost appears to be opening before the main and second transfers.

 

 

Your numbers as well seem a bit high. are you using a 110 rod and 54 stroke from zero deck? I was just trying to figure out how you arrived at your figures or what engine criteria was used.

 

I seem to always seem to find some level of discrepancy between calculated and degree wheel. I don't think we have but that one to bed to determine why..

 

Brandon

[mopar1rules]

Your numbers as well seem a bit high. are you using a 110 rod and 54 stroke from zero deck? I was just trying to figure out how you arrived at your figures or what engine criteria was used.

 

I seem to always seem to find some level of discrepancy between calculated and degree wheel. I don't think we have but that one to bed to determine why..

 

Brandon

 

Brandon, I was using .5mm for deck height. My buddies is .017" w/cometic base gaskets (can't remember the thickness) and mine is like .024-.026", using moose racing base gaskets. Banshee engines are "suppose" to be zero deck motors, but any of us that play around w/these engines knows otherwise.

[blowit]

Brandon, I was using .5mm for deck height. My buddies is .017" w/cometic base gaskets (can't remember the thickness) and mine is like .024-.026", using moose racing base gaskets. Banshee engines are "suppose" to be zero deck motors, but any of us that play around w/these engines knows otherwise.

 

 

Ah, I think it was mentioned as a zero deck motor somewhere in the posts. My bad. That certainly makes more sense now..

 

 

B

[AKheathen]

Are you sure you have 38* blow down? Your shee would be super "pipey" and an absolute bear IMO to race motocross with, using them porting specs. I tried some specs that were kinds like yours (188* exh, 117* trans, 35.5 BD) for some motocross and found it to be falling off the pipe all the time. I also noticed in your port map, that you have some "staggered" porting going on.....your boost appears to be opening before the main and second transfers.

yah, that's exactly why i was suggesting no more than 32, but best closer to 30