4 mil stroker porting?

[bholmes]

I have read alot about porting and read Grahm Bell's book on porting and the two-stroke tuning handbook by Gordon Jennings. So I have a pretty descent understanding of porting my engine but I am trying to get all the information I can before I cut into my engine. I'm doing a 4mil stroker and using a 2mil base plate and am running 115mil rods. I understand that I'm gaining 2mm at the top and 2mm at the botttom of my stroke, but I'm not really sure what this translates into for me as far as porting. I have yet to do my calculations for porting, but logically speaking my if I run long rod pistons that will take care of my +5mm at the top of the stroke due to the rods, then the +2mm spacer takes care of raising my ports and clearing my head from the piston. But what is unaccounted for is the 2mm at the bottom of my stroke. Would that mean that the only additional porting I would need to do is lower the ports or no? Also I have read that using a blaster piston with my long rod set up will work (http://www.macdizzy.com/1ban.htm) rather than buying long rod banshee pistons. I'm not sure there's much advantage one over the other, but I was just curious a bout experiences and input. Thanks.

[jbooker82]

You run 795 series pistons if your running the standard bores 64mm-66.5mm. If your running cylinders that have been resleeved with big bore sleeves then you run blaster pistons. Blaster pistons are avalable from 66mm to 68mm.

 

 

Just so you know, I have not ever ported nor claim to know exactly what to do. This is just general advice.

 

 

 

Most builders don't port 4mills to run a spacer plate. When you use a plate you gain 0mm at top dead center (like a stock stroke). You gain 4mm at bottom dead center.

 

If you run no spacer plate and a cut head you gain 2mm at tdc, and bdc. That way you can start off by lowering your ports down 2mm. Then figure your current durations out and determine. What you need to do. Just remember that your working with an engine that now has +2mm deck hight.

 

 

To be honest with you I would have some one port the cylinders. You are leaving a good amount of power on the table by doing it your self.

[bholmes]

I see what you're saying about the spacer, I may end up just cutting the heads then... we'll see. I'm pretty confident in my porting abilities, I understand what I read and I just got a good 2 stroke calculator from that website that should help answer alot of my questions. My biggest deal is getting the crank installed and mapping my engine and going from there i think.

[jbooker82]

Knock your self out. There is only one way to learn.

 

Most guys that run a non spacer 4 mill run a cool head. That way they can throw a set of stroker domes in and not have to worry about modding the stock head. Get ahold of david noss at noss machine. He can hook you up with what ever custom dome you need. He is a great guy.

 

 

 

 

 

As for the spacer if you do run one it doesn't leave you with as many options. Say you automatically lower the ports 4mm so the are flush with the piston crown. Then come to find out your transfer ports are to large. Where if you run no spacer, lower the ports 2mm. You have the option to do some work on the top of the port to dial it in with out going over board and making them to large.

[firebanshee]

I see what you're saying about the spacer, I may end up just cutting the heads then... we'll see. I'm pretty confident in my porting abilities, I understand what I read and I just got a good 2 stroke calculator from that website that should help answer alot of my questions. My biggest deal is getting the crank installed and mapping my engine and going from there i think.

I would not run a spacer plate if i were you. You should just run cut domes and lower your ports to the top of your piston at bottom dead center as stated before. I tried a spacer before and they don't work very well and you lose alot of power with a plate that lifts your cylinder up 2 mils. If your cylinders have never been ported before it should run pretty good.But if you are after max power then you should have a pro do it.I have ported my own cylinders and use to have fun trying different things but when i had Redline do a set of cylinders what a HUGE difference.But i still had alot of fun and learned alot playing with my own, have fun.

[AKheathen]

just a little info- the spacer plate is actually 1.5mm, and will tighten up the squish a bit. you need to factor in the spacer thickness and extra gasket. best to assemble it and take the measurements off the degree wheel first, then start cutting..........now, how the builder is going to make the power is more than the port time/area. there is also shapes and angles of each port that will greatly effect it. if you want to do it, go ahead, but i would go in stages, and ditch the spacer plate to run recessed head/domes.

[bholmes]

Thanks for all the great information. I ran some numbers on my ports and could see alot of the issues with the stroker. The stock exhaust port would open at 90degrees and the stroker with base plate would open at 84 deg and with out the base plate would be 90 deg still. The Transfer ports would open at 143 deg stock, 133 with bast plate and 139 w/o base plate. ... so you can see the differences. I spose sticking close to stock would be the best idea. I'm actaully looking for more torque, but i'm sure the stroker will supply that, even if i port it proportionally as stock timing.

[278]

As stated, dont use a base plate. Get a cool head and a set of cut domes. Here's a link to some helpful porting info. porting Brandon at Wildcard gave this info. talking about a 4mil. so it should help. You should call and talk to some of the different builders on HQ here and see if you can pick their brains a little. DOnt get discouraged after this first port job either, its taken good builders many years of research and developement and many sets of ported juggs to be as good as they are. It may take you multiple sets of juggs to get close to your desired performance. Good luck man!

[AKheathen]

.............why does that thread seem so familiar?

[jonny6634]

Just wondering if u think its a bad idea to try and do my own port job i have all the tools just not sure how much to take off

[AKheathen]

you need to read through a few books, and get your pipe specs, pick a few brains, and do the calculations to port a 2 stroke......

[278]

Its not necessarily a bad idea. Its a hard thing to do properly. Porting isn't just removing material it really is an art. You have to understand the mathematics of the motor, do the proper calculations, remove material in the in the right places, shape the ports in the right way, and understand the material you removed or places you reshaped are part of the motors mathematical equation and you have to know how what you do will effect your numbers, also almost any change in motor performance and elevation will effect your air/fuel, which has to be taken into consideration when porting. So a good understanding of how different parts will effect flow and what different pipe set-ups work best for the different port durations are also something you need to have. Its alot of work, but you have to start some where, all good builders did.

[AKheathen]

a little off topic, but would anyone be willing to sell either books, or make copies, lol?

[278]

Here's a link to some basic porting and engine mapping info. that was posted on the HQ a while back MacDizzy

[bholmes]

AKheathen, Depending on what the forums policies are in regards to copywrited materials I have both Grahm Bell and Jennings books in PDF format and a Banshee service manual and owners manual. If you want any of them let me know.