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Cams? pistons? lets talk engines!

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I've been off the mighty DR for quite some time actually, it hasn't been registered for a while and i've put most of my time into cheaper little pit bikes. One broken collarbone later and a lack of transport has made me think maybe I should get back on the mighty DR, but actually put some new things onto it and get it feeling like a fresh experience.

 

I've currently got about $1800 worth of stuff in mind on the procycle website. Of that, the 2 things i'd like to talk about are cams and pistons. 

 

I'd like to change the engine characteristics a bit. I've always felt it had more than enough power offroad, you just can't use it all unless its a wide open section, even then you get more wheelspin than you can lay down. But it never had enough power onroad. The one thing it could do with is extra snap and response. So i'll be getting the TM40 kit that should help with that situation.

On my order I have the 190 cam, but I havn't seen anyone get just the cam and stick with the stock piston? My bike has 45,000km on it and doesn't show even the tinniest bit of smoke. Engine is very tight, no noises, no rattles, feels very solid. I'd like for it to feel a bit peakier, but i'm worried that just getting a cam is a waste of money since this is only a 7800rpm limitted bike. Or that it may be more hassle than its worth? (i've heard of people having clearance issues, even bending valves, though with a hi-comp piston as well)

Has anyone tried just a cam and stock piston? The general consensus seems to be piston, THEN cam. Or both

 

The next question would then be, if a high comp piston and cam are good. What about vs the 790 kit? because they are about the same price (minus the cam on the latter)

I'm still not sure 'how' one gets the 790 kit in. Is the stock cylinder sleeved and simply replaced? or do you need to take it to be bored way out, then press the sleeve in? does the sleeve need to be bored/honed to match the piston and rings it comes with?

Labor here is quite expensive and depending on how much work, could significantly increase the final cost. I'm handy but I don't have the tools to hone or bore a cylinder 

 

And finally, given that the bike does have 45,000k's is it viable wacking a 790 into it?

Edited by qwerty1234

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I have the h/c piston and 223 cam, fcr39mx from mxrob and Erion racing gsxr1000 can. Yhe bike has more power everywhere and lots more over rev. If you send your cam to web, they'll hard weld and regrind it for you for around 250. Also my bike is set up as a tard and the over rev ability suits my riding style.

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Can't send my cam there as i'm in Australia. Be about the same price to just buy one

Still need to know how the 790 compares. May be best to contact procycle directly

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i've been reading a lot and information is still very vague. There is extremely little real world information on people riding the 790. Build threads yes, but riding? it's almost as if they built it, got on, tickled the throttle and cut a hole in the earth which they fell in to, never to be heard from again.

 

And i've found a grand total of zero comparisons between the 790, and a hicomp + cam. I won't do 790 + cam cause its just ridiculously expensive

 

I'm still confused as to what to do. I have 3 overall options really. I can do up the engine, do up the suspension (which I know is the better move but not as 'fun') or do nothing and get a 2nd hand RMX250 or such for the same price. Which I can register for road use but again i'm not sure what to do since I know the DR is infinitely better onroad but the RMX would be better offroad. Too many idea's not enough money...

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I went with the 190 cam and the HC piston. Yes, i had to clay the valve pockets in the piston and make sure there was enough clearance. I initially had slight interferance as my factory timing marks leave the cam a bit retarded. Now running a slight amount of advance with no issues, I wish adjustable cam gears were available for this motor. I also have the TM-40 pumper carb and the FMF Power Bomb head pipe with a homemade mid pipe and a Yosh RS-3 can.  The bike rocks, plenty of power and pulls hard all the way to the limiter.

 

 

I did not go with the 790 kit as like Qwerty has stated ... lots of build threads, but very little about the longevity of the build.  I also prefer the plated aluminum bore vs the steel liner as i have had thumpers with steel liners develop piston slap after about 10k miles.

 

Just my opinion and experience and as always YMMV.

 

CHeers.

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I think i'm not going to bother at this stage. I'd like to know what sort of difference they make individually, and that I have no found information on

Even procycle doesn't know, they developed the 190 cam to work with either the HC piston or 790.

 

But they did mention the cam probably won't make any difference to power, it'll be more willing to rev but thats about it. Thing is I want some real world impressions

Is the 790 like a slow revving bulldozer?

HC + Cam an overall increase but snappy engine? but snappy compared to what? a bulldozer? It is a low revving heavy engine after all... I have seen some engines transformed dramatically but my gut feeling tells me the DR engine will never feel 'snappy', just more snappy compared to a stock DR650, but nothing even close to like say a Husaberg 550/650

 

It seems difficult to get a solid grasp on what does what.

I'm concerned if I went with a HC piston + 190, I would feel like I didn't go far enough and should have got the 790

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