engine mods??

[bschloop]

I am looking at refreshing the top end on my SR185 this winter, since I am starting to lose a little compression, and run hotter than it should. My question is while I'm in there, is there something I could do that would not be ridiculously difficult to increase torque? I thought maybe I could have the head shaved down just the tiniest bit to get a very slightly higher CR than stock, but I don't know if that would help bottom end torque or just at the top end. I saw that renault_megane_dci is opening up his exhaust ports, would this be likely to net me gains? I will definitely be at least cleaning and polishing them up a bit. along with the intake. since that costs nothing and can only make the engine run better. any other suggestions would be good, just keep in mind that I have average mechanical skill, and fairly low budget. I do know a machine shop that does good work, for a fair price. and I could probably afford the head milling, or getting the cylinder bored, or something simple like that.
Thanks,
Ben

[Frank Lee]

I'd bump the CR a bit, get a good 3-angle valve job, and leave the ports alone except maybe for some port matching. If there is a tech college nearby with a machining program they may do it for cost.

[bschloop]

Is there a best way to increase CR? is having the head milled (so long as there's clearance) the way to go? to test for clearance, I was going to take the head gasket out put the head back on, and turn over the engine slowly to see if anything hits.

[2000mc]

Originally Posted by bschloop

I saw that renault_megane_dci is opening up his exhaust ports, would this be likely to net me gains? I will definitely be at least cleaning and polishing them up a bit. along with the intake. since that costs nothing and can only make the engine run better.

I think polishing the exhaust is good, but as I recall you should not polish the intake. I've heard of using offset woodruff keys to advance cam timing, but haven't ever used them myself. Look at the pickup coil or where it attaches to to see if you could advance the ignition timing - this I've done, but I probably wouldn't have if I hadn't had several sources on how much could be advanced and aftermarket stator plates were available for the engine as well.

[bschloop]

Well, specific info and aftermarket parts pretty much don't exist for this bike. I could check if the stator from a TW200 would fit. I don't know that it's worth the hassle tho. How much damage would it do if I screwed up when advancing the ignition?

[renault_megane_dci]

Best bang for your buck as long as torque is concerned is to overbore the engine (not substitute for cubic inches as they say) but it would increase capacity so the FE can suffer.

I polished the piston crown and cylinder head (more reflecting allows for more air expansion) since it is free.

Boosting the CR is especially good from bottom to midrange, no gain up top.

My exhaust port modding turns out to be more a pet project than something useful I am affraid.

Is your bike a two valver ?

You could have the camshaft grinded for more lift instead of more duration.

There was a guy called motoman who epoxied his inlet port for more midrange but it was on a liquid cooled bike, I wouldn't do it on a air cooled engine.

A smaller more free flowing carb can be a good torque booster but you won't find any that small I am affraid (maybe one of the old Kawasaki I4 had 28 or 30 mm pumper carbs) but that sounds like a lot of work as far as tuning is concerned.

A free flowing exhaust can boost FE but it is detrimental to mid-range torque.

[bschloop]

Originally Posted by renault_megane_dci

Best bang for your buck as long as torque is concerned is to overbore the engine (not substitute for cubic inches as they say) but it would increase capacity so the FE can suffer.

I seem to be losing the FE competitions to bikes with lots more displacement than mine, so maybe it would help rather than hurt. For lots more bore I might be able to fit the cylinder and head out of a TW200 into my engine. Apparently they are the same engine. That would add $$ though. I have yet to find a source for overbore piston for this bike. Actually I haven't even found a new piston. I can get rings.

I polished the piston crown and cylinder head (more reflecting allows for more air expansion) since it is free.

This I will likely do. Like you said FREE

[QUOTE]Boosting the CR is especially good from bottom to midrange, no gain up top.[QUOTE]

Perfect that's exactly what I need. I don't use the top end anyway, even at 80mph

Is your bike a two valver ?

You could have the camshaft grinded for more lift instead of more duration.

It is two valves.
I'd worry that I wouldn't be able to get a new one if it didn't work, but maybe I could find a camshaft on ebay and mod it then I could switch back and forth.

A free flowing exhaust can boost FE but it is detrimental to mid-range torque.

Oops, I did a straight through muffler, I guess I'll have to change that back.

[renault_megane_dci]

Originally Posted by bschloop

I seem to be losing the FE competitions to bikes with lots more displacement than mine, so maybe it would help rather than hurt.

I bet you're losing competition to bikes with the hability to pull more mph out of less rpm, be it through a 6th gear or just enough capacity to cough out its lungs at 80mph.
A proper sprocket set is one that allows 75% throttle for half rpm around 80mph.
If it can go for more RPM @ 75% throttle, it is geared too low.

Originally Posted by bschloop

For lots more bore I might be able to fit the cylinder and head out of a TW200 into my engine. Apparently they are the same engine. That would add $$ though. I have yet to find a source for overbore piston for this bike. Actually I haven't even found a new piston. I can get rings.

Perfect that's exactly what I need. I don't use the top end anyway, even at 80mph

It is two valves.
I'd worry that I wouldn't be able to get a new one if it didn't work, but maybe I could find a camshaft on ebay and mod it then I could switch back and forth.


Oops, I did a straight through muffler, I guess I'll have to change that back.

Not necessarily if it is not overdone

[ksa8907]

With the exhaust, longer and smaller manifolds will increase torque, shorter and larger manifolds increase flow capacity I.e. more hp at the top end.

I would definitely shave the head to increase compression, it will increase efficiency and therefore power throughout the rpm range.

Ignition, more energy in means more power out. Get a bigger coil if feasible, search how to retrofit coil-over-plug ignition systems, it pretty simple.

[renault_megane_dci]

I am investigating having my piston and head coated, there is an interesting thread (on a Subaru board) if you Google piston skirt coating homemade.
It can then lead you to techlinecoatings.

My target is to have the engine run cooler and more efficiently.
I have been traumatized by last year's engine failure.