Exhaust port: How much to raise it for iceracing?

johnnytheswede · Post by **johnnytheswede** » October 29th, 2011, 1:09 am

hello guys! Johnny from sweden here. I have a 500 of course=). My bika has a regular portjob done to the intake side and the transition ports. I also have a Coolhead, PWK 41,5mm, ProCircuit exhaust and Power reeds. As i only use it for the street in the summer and for iceracing in the winter i would like to have some more topend power, and i noticed that the exhaust port is at standard height, but ported wider. How much would be a good level of raising it with my enginespec and how i use it to smooth out the powercurve? I have read some about it and was thinking of around 3mm. I know it,s difficult to recommend as you haven,t seen the jug, but it, s a regular porting otherwise. It,s just rebored to 89,50mm and a new Wiseco will be installed.

Johnny

Cholo · Post by **Cholo** » October 30th, 2011, 4:25 am

Hi Johnny. I´m Francisco from Spain

.Eric Gorr recommended in his book raise the exhaust port 2mm and keep the transfer in stock height for a mild porting. I´m not a expert in the CR500 but I ported mine and I can tell my experience. Recently, I have rebuilt my engine:

-90mm and new Vertex piston.
-190/126 porting (+4mm in exhaust, +2mm in transfers), widening the exhaust port, grinding the exhaust port flangle, ...
-V-Force 2 reed cage.
-41mm PWK by Sudco.
-´86 cylinder head cutted to attain 2mm squish height.

Before I rebuild the engine I have a ProCircuit. When I tuned the engine, it lost some low end but the mid-range and top was better. But I felt the engine wants to pull harder in top-end and the PC don´t allowed it.

Two weeks ago I bought the CPI pipe and the change in power delivery was radical. You can read my review in http://www.bannedcr500riders.com/board/ ... hp?t=12014

I think that the PC doesn´t work properly with aggressive porting. If you need maintain the PC I wouldn´t go so far as I went with 190/126. If you really want mid to top end, I think that the CPI pipe and aggressive porting is the best option.

johnnytheswede · Post by **johnnytheswede** » October 30th, 2011, 1:47 pm

Hello Fransisco! Thank you very much for your very detailed reply. It is very helpful. I have just ported my exhaust and raised it 3mm, and i am about to raise my transfer ports 1,5mm, so i will not be too far from your values i guess. I also use a PWK 41,5mm with a JD kit, power reeds and coolhead with 1,4mm squish and 66CC dome.

It,s very intresting what you say about the pipe! What did you have to pay for it, and what silencer fit? Do you think i would gain much with that pipe too? The 500 has so much bottom power anyway i think. Where do i get that pipe?

Regards

Johnny

Gmbond · Post by **Gmbond** » October 30th, 2011, 3:30 pm

Back when I was ice racing in Canada a few years ago. We often had "soft" ice and it was a 1/4 mile oval with fairly tight corners.

We found that too much power would result in excessive wheel spin when exiting the corners and because of this I was often able to pull on the 500s while on my basically stock 1997 CR250. And because of how tight the track was the higher power didn't get the long straightaway advantage to catch up and pass.

How long are your tracks, and how good (hard and solid) is the ice??

Cholo · Post by **Cholo** » October 30th, 2011, 6:17 pm

The pipe cost me 307 euros, with shipping. You can buy it in http://www.cpiracing.com/store/index.ph ... t&catId=10. Roostius_Maximus did some testing with this exhaust comparing to the old FMF Fatty (some people says that it´s better than ProCircuit) and he found an improvement of 6 hp in maximum power. You can see the dyno graphics in

http://www.bannedcr500riders.com/board/ ... i&start=25

The 500 has some bottom power, but I can tell you that after the porting and the CPI pipe the losses is bottom are very noticeable. Comparing my bike now versus the bike with stock porting and stock exhaust, I think that the low end is 1/3 than stock. In the same way the gain in mid, but especially in top end is massive. Now the bike can pull very hard at high rpm. With stock porting and stock exhaust, the top end of my CR500 was softer than my tuned YZ250

johnnytheswede · Post by **johnnytheswede** » October 31st, 2011, 1:55 am

Gmbond wrote:Back when I was ice racing in Canada a few years ago. We often had "soft" ice and it was a 1/4 mile oval with fairly tight corners.

We found that too much power would result in excessive wheel spin when exiting the corners and because of this I was often able to pull on the 500s while on my basically stock 1997 CR250. And because of how tight the track was the higher power didn't get the long straightaway advantage to catch up and pass.

How long are your tracks, and how good (hard and solid) is the ice??

Hello! The ice we run on is lakes, and it varies in hardness, but it,s no saltwater. On a stock 500 we reach around 140-145km/hour on the straights. We use 14/42 gearing. We also run on the sea when it allows us to. Much softer ice to ride on, but very forgiving.
I also use my bike for the road in summertime and then i can use more power=)! I will try the PC pipe first, but maybe get a CPI also to use if i want to.

Johnny

johnnytheswede · Post by **johnnytheswede** » October 31st, 2011, 3:04 am

Cholo wrote:The pipe cost me 307 euros, with shipping. You can buy it in http://www.cpiracing.com/store/index.ph ... t&catId=10. Roostius_Maximus did some testing with this exhaust comparing to the old FMF Fatty (some people says that it´s better than ProCircuit) and he found an improvement of 6 hp in maximum power. You can see the dyno graphics in

http://www.bannedcr500riders.com/board/ ... i&start=25

The 500 has some bottom power, but I can tell you that after the porting and the CPI pipe the losses is bottom are very noticeable. Comparing my bike now versus the bike with stock porting and stock exhaust, I think that the low end is 1/3 than stock. In the same way the gain in mid, but especially in top end is massive. Now the bike can pull very hard at high rpm. With stock porting and stock exhaust, the top end of my CR500 was softer than my tuned YZ250

Ok, it sounds like a peaky pipe, but maybe i could try it out. I guess my slightly milder porting evens out the powercurve slightly, and i still use standard ignition. How much do you rev your bike, francisco? Any powerfigures? Maybe they can make the pipe slightly less peaky for my application?

Johnny

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » October 31st, 2011, 5:48 am

the cpi is not the way to go if you're trying to roll smoothly into the power

johnnytheswede · Post by **johnnytheswede** » October 31st, 2011, 8:20 am

Roostius_Maximus wrote:the cpi is not the way to go if you're trying to roll smoothly into the power

Hello Roostius. I understand that it gives a hit on higher revs, but was thinking that it maybe would be smoother on powerdilivery out of corners where i use lower revs, but maybe it,s better to use a more moderate pipe.

Johnny

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » October 31st, 2011, 8:25 am

my biggest complaint about the cpi is the way it delivers power

Cholo · Post by **Cholo** » October 31st, 2011, 9:06 am

The low end with this exhaust is very smooth, but the transition to the mid-range it´s very unpredictable, like a elephant kicking your ass

. It gives to the bike a pure '2 stroke behaviour', you can know with exactitude the rpm in which the exhaust and engine are in resonance. It´s very peaky and funny at the same time, but I wouldn´t make a race in a curved track with this exhaust.

100hp honda · Post by **100hp honda** » October 31st, 2011, 8:32 pm

first thing i noticed when i ported mine with cpi it dont like big tranny gaps. 1-3 works good but youll want to add the 89-92 4/5 gears. if you never see the high gears then you should be fine. get the gearing figured out and youll rock and roll. dont worry if your in the 14/52 range. even 13 front should work well. the extra rpm will compensate for the drop in gear.

johnnytheswede · Post by **johnnytheswede** » November 1st, 2011, 1:30 am

Thank you guys for all good info. After some thinking i will start with my PC-pipe and maybe shorten it a bit later about 2 inches. I talked to a tuner here and he said : Try the PC pipe first as it will give you a easy controllable bike, and if you want more top end shorten it to about 115cm tuning length. I tried to measure the PC pipe tuning length and came to about 120-121cm. I guess there will be power enough for my ridingskills=). How much power can my bike deliver? Any ideas anyone?
Spec: 3mm raised exhaust, slightly widened.
1,5mm transfers
66cc Coolhead
41,5mm PWK
PC exhaust
89,5mm bore with Wiseco
Power reeds

100hp honda · Post by **100hp honda** » November 2nd, 2011, 6:41 pm

you happen to know what 3mm exh and 1,5 trans eqauls in degrees rotation ?

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » November 2nd, 2011, 7:43 pm

http://www.torqsoft.net/piston-position.html

100hp honda · Post by **100hp honda** » November 2nd, 2011, 9:31 pm

what i ment is how long the ports are open in degrees after he raised them per EG instructions. i use degree wheel so that measuring crap is foreign language to me

johnnytheswede · Post by **johnnytheswede** » November 3rd, 2011, 1:33 am

100hp honda wrote:what i ment is how long the ports are open in degrees after he raised them per EG instructions. i use degree wheel so that measuring crap is foreign language to me

Hello! After what i have read that would give 186-187 deggrees on exhaust port and 125 degrees on transfers. maybe not the Exact numbers, but very close. I don,y think i will notice a degree in any direction anyway=). Now i,m just after a pipe to pull it to around 7500 rpm which i think is good enough

Johnny

100hp honda · Post by **100hp honda** » November 3rd, 2011, 9:45 am

them numbers sound wrong. aint that close to what a stock jug is ? cpi will work alot better if your ports are higher. did this on mine and thought it worked pretty good first time out. was pretty simple. basically if i recall it was just 197 exh/ 130 main trans and 128 rear trans and flatten the roofs to approx 10* if i remember then added 2 base gasket to raise everything alittle more. theres few more things i want to do over the winter if i get time. maybe add epoxy etc. http://www.bannedcr500riders.com/board/ ... 231#128231

johnnytheswede · Post by **johnnytheswede** » November 3rd, 2011, 9:59 am

100hp honda wrote:them numbers sound wrong. aint that close to what a stock jug is ? cpi will work alot better if your ports are higher.

Hi again. No, a stock jug is 180 exhaust and 122 transfers if i remember right.
Here is the values from fransisco who wrote earlier in this thread, and his porting is slightly more radical than mine.I don,t think i will use the CPI pipe, because i think it will make the bike too abrupt on powerdelivery for the ice, and my porting isn,t that radical anyway. have you tried a DEP pipe?

Hi Johnny. I´m Francisco from Spain .Eric Gorr recommended in his book raise the exhaust port 2mm and keep the transfer in stock height for a mild porting. I´m not a expert in the CR500 but I ported mine and I can tell my experience. Recently, I have rebuilt my engine:

-90mm and new Vertex piston.
-190/126 porting (+4mm in exhaust, +2mm in transfers), widening the exhaust port, grinding the exhaust port flangle, ...

Johnny

100hp honda · Post by **100hp honda** » November 3rd, 2011, 10:01 am

ok been long time since i seen stock jug. i could be wrong. numbers sounded odd but maybe not

johnnytheswede · Post by **johnnytheswede** » November 3rd, 2011, 2:07 pm

100hp honda wrote:ok been long time since i seen stock jug. i could be wrong. numbers sounded odd but maybe not

Ok, you have a more radical portjob than me for sure=). How do you use your bike, and what poweroutput do you have? Do you run the CPI pipe now?

Johnny

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » November 3rd, 2011, 2:24 pm

what is your port height? can u measure it from the top of the cylinder down til the port opens?

johnnytheswede · Post by **johnnytheswede** » November 3rd, 2011, 4:05 pm

[quote="Roostius_Maximus"]what is your port height? can u measure it from the top of the cylinder down til the port opens?[/quote

Yes, it,s 43,5 millimeters!

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » November 3rd, 2011, 5:00 pm

so your exhaust port timing is likely 184.4 to 185.1 depending on base gasket
stock cylinder is around 178

i'll check my book tonight and get back to you if i'm doing this wrong

100hp honda · Post by **100hp honda** » November 3rd, 2011, 8:37 pm

johnnytheswede wrote:
100hp honda wrote:ok been long time since i seen stock jug. i could be wrong. numbers sounded odd but maybe not
Ok, you have a more radical portjob than me for sure=). How do you use your bike, and what poweroutput do you have? Do you run the CPI pipe now?

Johnny

personally i like the cpi. only rode 2 times and scorched the cylinder. probly wont be running again until spring time. these vids is cpi with fmf muffler

[youtube]http://www.youtube.com/watch?v=i43mft2qObU][/youtube]

BannedCR500Riders.com

Exhaust port: How much to raise it for iceracing?

Exhaust port: How much to raise it for iceracing?