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08' big bore kit, what cam if any?

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As the title states I am going to get a big bore kit for my 450 probably a cylinder works kit. I am going to port the head for better flow as well since the new piston is going to move more air, that being said has anybody got any real world experience with trying aftermarket cams with a 488 kit?

I guess you would need to know a few things first....the 450 is my what I will use for any D38 races, so I am all over in the rpms from low in technical sections to near the limiter in the open sections, so that being said I dont want to shift all my power into the upper rpms only, also I might add I weigh only 145 lbs WITH gear, lol (dont let that fool you).

Another thing I need to mention is I just installed the 13.5:1 CR piston and the Big bore kit drops it back down to 12.0:1 near stock, so I may loose a little pop?

BTW the reason I am tearing the motor down in the first place is because my chain tensioner failed breaking both intake valves and cracking the cylinder where the piston skirt tried to go through the cylinder wall and cracked out a section....ugh! So might as well get a big bore, wanted more power anyway, and the Rekluse really mellows out the motor in the technical stuff which helps me with traction..

Anybody have any experience/recommendations with big bore kits vs. cams??

Any help would be appreciated.

Thanks in advance, I searched but didnt find the answer to my questions..

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Well...

A big bore is going to give you more grunt down low, but it's going to sign off early because even if you port the head and put the HotCams stage 3 in it (works best in the big bore engines) it'll still run out of air because the piston is so friggin big you wont be able to fill the cylinder at high RPM with the short stroke and relatively short rod for the CC's associated with it. Its more about piston speed than actual RPM.

The shorter the rod is, the higher the piston speed is lower in the RPM range.

Now with all that said, if you change your ride style a little, Im sure you could adapt to the new power characteristics of the big engine.

The over all power wont be much if any over a standard bore bike, it'll just make more torque in the bottom and mid ranges.

When you lay over dyno sheets on stock bore engines that have had good port jobs with matching cam and intake mods with good pipes, you actually end up with more power through out the entire range and its pretty smooth all the way through from low clear through the redline.

Do a search on Big bores and then do a search on bikes with RHC 187 and head work etc. There are plenty of dyno sheets out there.

MXA did a test on a big bore setup a while back too. After all was said and done they only ended up making 2 hp over stock and the engine fell on is face at about 7500 rpm.

But porting the head yourself and the stage 3 cam and the big bore will probably be cheaper than trying to build a potent OEM bore bike, it'll just run differently.

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oversize valves would be your best bet to move enough air at high rpms to keep making power, with the stage 3 cam or a web cam custom tailored to your engine, a good port job is crucial too

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Well...

A big bore is going to give you more grunt down low, but it's going to sign off early because even if you port the head and put the HotCams stage 3 in it (works best in the big bore engines) it'll still run out of air because the piston is so friggin big you wont be able to fill the cylinder at high RPM with the short stroke and relatively short rod for the CC's associated with it. Its more about piston speed than actual RPM.

The shorter the rod is, the higher the piston speed is lower in the RPM range.

Now with all that said, if you change your ride style a little, Im sure you could adapt to the new power characteristics of the big engine.

The over all power wont be much if any over a standard bore bike, it'll just make more torque in the bottom and mid ranges.

When you lay over dyno sheets on stock bore engines that have had good port jobs with matching cam and intake mods with good pipes, you actually end up with more power through out the entire range and its pretty smooth all the way through from low clear through the redline.

Do a search on Big bores and then do a search on bikes with RHC 187 and head work etc. There are plenty of dyno sheets out there.

MXA did a test on a big bore setup a while back too. After all was said and done they only ended up making 2 hp over stock and the engine fell on is face at about 7500 rpm.

But porting the head yourself and the stage 3 cam and the big bore will probably be cheaper than trying to build a potent OEM bore bike, it'll just run differently.

Yeah I figured it would be a bit of a give and take situation....I wouldnt even think about doing this if my cylinder was salvageable since stock seemed to work pretty well, since I need a cylinder and piston, the BBK is about the same money as stock parts, I like the power of my buddys KTM 505, I noticed it layed down at upper rpms as well, but had more down low so like you said, riding style, live where the power is...I am going to give it a shot and see what happens, thanks for the input Shawn.

oversize valves would be your best bet to move enough air at high rpms to keep making power, with the stage 3 cam or a web cam custom tailored to your engine, a good port job is crucial too

I am probably going to run a stg III hotcams as long as I can use stock springs, and as for oversize valves its not in the budget unfortunately, the porting will have to suffice, I know my older bike that I ported sounds wicked and seems to rev really quick compared to my 08, so I am hoping a good port job should let it breathe a little better, I guess well see.

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Big bore kit ordered, will be here tomorrow, I will start porting the head today should have it done within 3-4 hours depending on how much time I want to spend on it, I am going to make a makeshift flowbench with a pingpong ball and a plexiglass tube, I did that for the 05' and it is a good way to make sure your actually increasing the flow and to match them. Porting isnt just removing material, its about increased flow and the reduction of turbulence.

So after that it is time for cam selection, still waiting on Ron Hamp to return my PM on choices, or I may just go with a stage III like I mentioned, I tried to get a hold of Ron before with no luck on another project so I may just do that since I can find even slightly used stage 3 cams for cheap.

I may just try the stock cam at first to see what the difference between stock and stg III is that way I have a comparison.

I will keep you posted on what happens!

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if you want more power to mid i like hi comp piston and the hotcams 2 stage.

3 stage work good but better on over rev.good on supermoto but for mx i dislike it.

for mx use the 490 is very strong engine,difficult to 100% use and remember the crank rod have less time life.the hp on big bore are the same of 450 only torque increase.you are a light rider i think you dont need it

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Porting is not just about increasing air flow. If you just hog the ports out for maximum air flow, you'll kill velocity - and that's what is important. The engine will scream up high, but will fall on its fast down low if you reduce the velocity too much.

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if you want more power to mid i like hi comp piston and the hotcams 2 stage.

3 stage work good but better on over rev.good on supermoto but for mx i dislike it.

for mx use the 490 is very strong engine,difficult to 100% use and remember the crank rod have less time life.the hp on big bore are the same of 450 only torque increase.you are a light rider i think you dont need it

I dont need it, but I want it. I do a lot of Desert riding where power is King, and I can actually use more power in some instances, also the cost for stock vs. BBK is almost exactly the same, also I thought the crank/rod assembly was only adversely affected by stroking much more than an overbore? Either way it is what it is, I guess we will see if the larger bore is going to work out well or not....

Also the unfortunate thing is I only had 4 or 5 hours on a brand new 13.5:1 piston and now I will have a larger bore, but lower compression, I hope I dont lose any low end torque, I "think" the larger bore should give some of that back, but its all hearsay until I ride it!

All the big bore kits seem to provide a near stock compression ratio...I may look into going higher compression on the next piston if possible, but there has got to be a reason all the kits have lower compression? If not I will up the CR on the next piston ..

Porting is not just about increasing air flow. If you just hog the ports out for maximum air flow, you'll kill velocity - and that's what is important. The engine will scream up high, but will fall on its fast down low if you reduce the velocity too much.

I completely agree, I was just trying to simplify that statement, and did it so much I left out a very important aspect, VELOCITY, better know as air speed...when I port the head I only increase flow a small amount not hog them out till I need to weld up the water ports, lol. There is a lot more going on than just enlarging them, my statements sometimes make me look ignorant by leaving info out, I swear I am not as dumb as I seem sometimes..

Either way I am very curious to see how the bike feels after I get her back on the ground again, I am going to run the stock cam for the 1st ride and see how it goes. Hopefully by then I will have spoken to Ron Hamp to see if he has a cam for my setup that is well rounded. If he gets back to me that is....

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100mm bore, stock ports top end cam

13.5:1, ave tq=31.9, pk HP=59.5, pk tq=39.1 9.47 dynamic compression ratio

12:1... ave tq=31, pk HP=57.6, pk tq=38.1 8.45 dynamic compression ratio

Ported head, stock bore top end cam

14:1, ave tq=31.4, pk HP 61.1, pk tq=37.6 9.81 dynamic compression ratio

13.5, ave tq=31.2, pk HP 60.5, pk tq=37.2, 9.47 dynamic compression ratio

STG 2 will raise the dynamic compression .41 points and increase the TQ a few ft.lbs

For wide open areas you can't beat a stock bore, mild porting and somethinglike a 14/48 combination.

The larger piston upsets the balance of the motor and induces vibration which causes resonant frequencies to play havoc on the motor. The cost is much more in the long run with more frequent crank changes.

Porting with a ping pong ball and a vaccum cleaner? Please take a pic! Would be a kewl experiment. I don't think the ping pong balls will travel the same distance due to the port length in each of the ports.

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100mm bore, stock ports top end cam

13.5:1, ave tq=31.9, pk HP=59.5, pk tq=39.1 9.47 dynamic compression ratio

12:1... ave tq=31, pk HP=57.6, pk tq=38.1 8.45 dynamic compression ratio

Ported head, stock bore top end cam

14:1, ave tq=31.4, pk HP 61.1, pk tq=37.6 9.81 dynamic compression ratio

13.5, ave tq=31.2, pk HP 60.5, pk tq=37.2, 9.47 dynamic compression ratio

STG 2 will raise the dynamic compression .41 points and increase the TQ a few ft.lbs

For wide open areas you can't beat a stock bore, mild porting and somethinglike a 14/48 combination.

The larger piston upsets the balance of the motor and induces vibration which causes resonant frequencies to play havoc on the motor. The cost is much more in the long run with more frequent crank changes.

Porting with a ping pong ball and a vaccum cleaner? Please take a pic! Would be a kewl experiment. I don't think the ping pong balls will travel the same distance due to the port length in each of the ports.

Actually learned this trick in tech school, you cant use it for real world flow numbers, just the ability to see if your actually increasing flow, and you are right on the flow equalization, but I think it would be nice to match them or get them a bit closer than stock if possible, I do a lot of automotive fabrication and tuning, etc...since that is my main job, I like playing with motors..

It seems like max power would be down a bit, but hopefully I will have better power under the curve, sounds good anyway.

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i have a 490 athena on my bike,for desert use??for supermoto i need new cooler sistem.the 490 cylinder have less water around the cylinder.for the crank/rod problem remember the 2002-2003 crf with 490 broke the rod ,maxim at 15-20 hours. the first crankrod are with less flexion.the 490 give more spin on the rod and on bearing.on my cylinder i use woessner 11.2:1 comp piston with dlc on piston pin

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I guess well see how it works out as far as engine life goes, I have my cylinder head done and it should flow very nicely, smoothed all the casting and deshrouded the valve seats. Didnt remove a lot of material just enough to try and improve the flow a bit.

I will be installing a Vapor Trailtech computer as well, this way I can keep an eye on coolant temp and see if there are any issues with increased temperatures...I think I should be fine if I can run my other bike with a 13.5 piston in the tight stuff without overheating as long as I can keep a little speed. I may add a small fan if it becomes an issue...

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I put the motor back together and reshimmed the valves, and went to turn the motor over after installing the new timing chain and notices things didnt look right, as far as it seemed to want to open the intake valves when the piston was at TDC and I lined up the marks on the cam with the cam lobes pointing toward the rear of the motor as I have done dozens of times in the past, I own 3 CRFs...

So the only thing that could have happened is that I lost timing on one or both of the sprockets. Either the cam spun on the flange that bolts the upper sprocket on, or on the bottom end may be out of sync if the key broke, I will check to make sure piston is really at TDC with a long screwdriver, but the lower end feels normal to me, I think it was the cam...I am going to search to see if the cam can spin because I think thats what happened.

Wierd.....

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So my choices are stage III vs. stage II.

I am thinking the stage III is the way to go as recommended by others. I just dont want to lose any low end over my 13.5:1 stock bore setup if possible.

It seems like the stage II will bump the dynamic compression a little bit which should add a little bit of torque over the Stage III but since it is bored to 488cc that should give a little bit down low so it should feel nearly the same as before with more mid and top end? Sounds good anyway, I wish there were dyno sheets with different combinations that I could look at to see the power curve to help me decide between my setup with stage 2 and 3 Hotcams..I really want the bike to be as well rounded as possible and have somewhat linear power..

I hate making these types of choices without knowing what to expect, but it is what it is.

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i can t help you i have tryed 3 stage and 2 stage and i use the stage 2 but i have different piston and valve porting. you must make a try whit the 3 stage and hope.

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Yeah I just ordered a stage III Hotcams so it should show up sometime this week, I will TIG weld it when I receive it for cheap insurance to make sure I wont spin the cam on its flange like I did the stock one..I think it will all work out, I also ordered the hagher capacity radiators since I plan on racing it in District 38 ( A local Desert racing series with 100 mile races) starting in Janury.

I think the new radiators should really help keep things a bit cooler since they hold about 40% more.

I cant wait to ride this thing again, it will be a new animal, and with the rekluse clutch it mellows out any roughness associated with the motor thats why i can get away with all this power and still be a very small rider and make it work for me. Now maybe I can take a tooth or two off the rear sprocket and get a little more top speed out of it, I run a 14-48 currently and could use a bit more top end..I would like to drop down to a 46 or 45 rear if power allows, we will see.

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Oh and another question reguarding pipes, I have the MRD full exhaust setup with the mid-range header pipe, would I benefit by going with the Top-end header instead with the 488 and stage III? Seems as though I would due to the increased flow characteristics of the motor after the mods right?

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Oh and another question reguarding pipes, I have the MRD full exhaust setup with the mid-range header pipe, would I benefit by going with the Top-end header instead with the 488 and stage III? Seems as though I would due to the increased flow characteristics of the motor after the mods right?

Id run the one youve got. The higher end header is more than likely a little bit shorter than the mid range pipe as opposed to being larger in diameter.

The length is usually what they tune the RPM with.

You could call Dave at MRD and ask him though. Its raining here so he's probably in the shop. :bonk:

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So my choices are stage III vs. stage II.

I am thinking the stage III is the way to go as recommended by others. I just dont want to lose any low end over my 13.5:1 stock bore setup if possible.

It seems like the stage II will bump the dynamic compression a little bit which should add a little bit of torque over the Stage III but since it is bored to 488cc that should give a little bit down low so it should feel nearly the same as before with more mid and top end? Sounds good anyway, I wish there were dyno sheets with different combinations that I could look at to see the power curve to help me decide between my setup with stage 2 and 3 Hotcams..I really want the bike to be as well rounded as possible and have somewhat linear power..

I hate making these types of choices without knowing what to expect, but it is what it is.

I can post the curves for you. Do you wan to see the difference between the stg 2 and 3 with BB kit compared to what?

I already posted some numbers to show you in general.

The stage 3 cam loses allot of bottom end and picks up some good power on top. Not the cam for racing a track, unless you are a "gifted" rider (lol),but good for running in open areas.

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I can post the curves for you. Do you wan to see the difference between the stg 2 and 3 with BB kit compared to what?

I already posted some numbers to show you in general.

The stage 3 cam loses allot of bottom end and picks up some good power on top. Not the cam for racing a track, unless you are a "gifted" rider (lol),but good for running in open areas.

Are your tests on the big bore engine?

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