jkulhanek

Got bored the other night, and found a site detailing engine modifications,

So I cranked out the ol' Dremel and files and had a go myself.

Engine is a brand new O.S. .12 CV-X

The pictures show :

Crankshaft: Knife edged and flared (not visible) induction port, "turbo fluted" induction tube.

Conrod: Knife edged and polished

Piston: Skirt trimmed so as not to obstruct the sleeve ports when piston is at BDC

Sleeve: Enlarged transfer tunnels, smoothened port window edge, port windows themselves are standard size.

Carb: "Step" in carb barrell lightly polished to match venturi and throat, note venturi was NOT enlarged.

As this is my first porting job, I am not expecting much, perhaps a broken conrod but I doubt i will see much gain...

Feel free to post comments, tips and suggestions .

Jimmmaaa

what site did you get that from??

enjoymentboy

Looks VERY nice. I too would like to see this site you found. I've done these same mods to a few of my CV's with great success. I have not done any work on the pistons though and I have only worked the con rod to a simple knife edge, but all in all pretty much the same. I have doen a few other things that I found to help. I cut a taper on the leading edge of the counterweight to act as a scoop to force any air fuel away fromt he front of the engine and out to the back. It "seems" to have helped out on pickup. I also cut small grooves in the head right around the edge wehre it meets the top of the piston and the inside of the sleeve (hope that's clear). I made the grooves (about 2mm wide and 2mm deep) directly over where the transfer ports direct the air\fuel charge into the cylinder. Thsi helps fullel the charge directly to the plug. It really seems to help wake up the bottom end. I did a simple test with this on 2 CV 12's. Both unmodded. Brought them both up to temp with a stock head and ran them (one offroad on onroad) and did a beaseline. Brought them back and did a quick headswap and ran them again. Definitely better snap off the line and noticeably smoother acceleration. I had some witnesses who ran them each way and they all greed there was an improvement. Each mod has a little effect but when they're all combined it really wakes this mill up. I have not changed the timing of the crankshaft at all.

Polishing up the intake of the carb helps as well. If you have a 10E I like to also open up the bottom end where the screw holes are. Make the entire run round and get out the extra material where the screws would grab. This only works though if you use a cinch bolt. I then fill in the holes with JB weld and sand and smooth it all out. I don't like to polish the tailend of the carb though to help keep the fuel mixed with the air as it enters the crankshaft. I leave it where it is with 220X paper.

I have one that is 7 years old, had the sleeve pinched twice, on only the second rod an pin, and bearings replaced once and has all these mods. It is still going strong after over 15 gallons. I've had it in an ST, and on-road and a boat and it has never let me down. I will continue to run it until I can either no longer get parts or it simply disintegrates.

If you can post that link I'm sure many people woulf make good use of it.

Enjoymentboy

enjoymentboy

I should have asked this before...did you do any work to the crankcase? There are some gains to be had by cleaning up the inside of the crankcase and helping the fuel\air flow through to the transfer ports. There is quite a bit of material in the way at the bottom of the cylinder right over the bearing. It can be removed adn smoothed out to aid int he flow. Basically get rid of any hard corners and polish it up. I have also found that the ports on the sleeve don't match up perfectly with the cylinder so if you can match them you will get better air\fuel flow into the sleeve.

Enjoymentboy

Frost_

My Feedback: (1)

I hope you made the changes (listed above) at the advice of some article that was privy to how this change in intake timing/duration would make power. If you don't have info for the SPECIFIC engine and understand why this is done, leave it alone. You can cause real problems making blind stock removal in this area.

jkulhanek

I'm not quite that stupid, I did some research, and a fellow did this mod to a CV and had successful results, it DOES NOT change the timing in any way the port is not widened, just knife edged.

The website is www.affordablenitrotech.com, and in grindstone there are a few articles on porting, unfortunately rcpics.net has disabled remote linking, so pics are almost non existent now.

BTW thanks a heap enjoymentboy, I did notice some "flashing" in the block where the bottom of the sleeve is, but was worried that I might increase the volume of the crankcase, therefore lowering primary compression....I think piston skirting would do more than removing these flashings, but every little bit helps I guess...Perhaps next time I open her up I'll remove the bearings and grind and polish it up a bit more....how thick is the crankcase at that place??

enjoymentboy

That's a nice site. Thanks for the link. If anyone has a problem getting it to work there is a comma at the end of the posted link that shouldn't be there. Try this instead. www.affordablenitrotech.com

I don't like to knife edge the crankshaft intake. Most people will tell you that it doesn't change the intake timign but my experience tells me that's not the case. I have tried this on some junked cranks and compared them before and after with a degree wheel and a stock crankcase. I found that in general (and this is only a generality not a given) that doing this opens the timing about 2° - 3°. Not much but it will affect the engine operation. Maybe good. Maybe bad but there was a change. I confirmed this was NOT due to removign any material from the outer edge by putting red marker on the edges of the intake port and grinfing and sanding until they were nice and sharpe with some of the red still just sowing. The over all opening size was not changed but the hole was made bigger as the walls were thinned. I hope that was clear.

Think of it this way you have a hole that is 10mm wide with each wall being 2mm thick giving a total width of 14mm. If you thin the edges on each side by 1mm you now have a 14mm overall width but the hole is now 12mm wide with means that each side will open 1mm sooner.

Enjoymentboy

jkulhanek

Yep thats exactly how I did it, did not go past the edge where the window starts on the crank...


I also knife edged the top rear edge of the crank port, in the hope it improves flow slightly.

If the engine doesn't run, I'll just buy a new crank, I'm used to destroying stuff from mods, but at least I learn!

enjoymentboy

That's pretty much the best way to learn I figure. Bugger something up and have to fix it yourself. I found out about the timing change on a 12 CV I got off ebay march last year. The guy I got it from trimmed the threads for a GT and cut them too short. Never even started it up and he pretty much junked it. There were only 3-4 threads left on the crank. I got it for $15. A bargain if ever I found one. I pulled the crank and swapped it with the engine I was running at the time. I put the degree wheel it on and baselined the intake timing. Don't ask me what it was, I didn't write it down but I "think" it had a duration of something like 43° or something to that effect. I carved out a turbo scoop on the back and put a scoop on the leading edge of the counterweight. I put it on my test bench and fired it up. Since it ran I figured I could at least try it in my ST. I use a pilot shaft adaptor and there were just enough threads left to use it. There was a noticable improvement in both low end and top speed. It seemed to be about the same grunt at WOT but it sounded like it was reving much higher and it did pull to full faster.

I figured I had nothing to lose so I decided to work the inside of the crank. Pulled it out and bored it out by 1mm and knife edged the leading and trailing edges of the intake. After putting the degree wheel back on it had a total duration about 3° longer and started about 1° sooner. It ran fine though. I just didn't like the idea of buggering with the intake timing when I had no idea of how it would affect it. Luckily it didn't hurt and it still runs today. I honestly can't say if there was any noticeable benifit to doing that though. I've done all the same mods to other CV\CZ cranks without touching the intake and they all run just as well.

The best mods that I have found for this engine are to clear the inside of the crankcase to ease the flow, to port and polish the sleeve ports (don't touch the chrome) and to cut a scoop on the leading edge of the crankshaft. I still do the rod and the turbo scoop bt they don't seem to make as big of a difference. At least to my eye.

Enjoymentboy

C3Racing

My Feedback: (1)

How would those mods compare to a .12 cv-r?

jkulhanek

CV-R's have much bigger sleeve ports.

I have heard of modified CV's keeping a similar pace with Novarossi's, Sirio's and other expensive engines.

I wonder if i can run a CV-R sleeve in the CV.......what a sleeper!!!

jkulhanek

Oh btw, I tried these mods on a GX15, but since the sleeve is such a weird design, and the carb is a single needle jobby, who knows what results I will see....

jkulhanek

Sorry for the triple post,

enjoymentboy, is there any way you can enlarge the ports on the sleeve? I'm sure I could make a jig and do it myself, but i'm worried about the chrome/nickel plating flaking off around the port edges...

enjoymentboy

Myself I do not like to go into the plating. From what I have been told by a number of people it is not as bad to cut into the nickle as it would be for the chrome as the chrome is much harder and would tend to flake off easier once it's been cut. Can't verify that though.

I haveseen some mods on different engines where the builder has cut right into the chrome and enlarged or widened the ports. Still not ready to do that myself. One builder told me that he uses a fine diamond burr on low speed to open the ports and then he used diamond files to ease the edge with a very small chamfer. Again I can't confirm how this works as I don't have the guts to do it.

Theoretically if you had 2 similarly constructed engines and one was a high end one you could clone the prting onto the lower end mill and get the same performance as the other. Never tried it though. I'm of the mind that it's bette to make the most of what you have and keep it working than to kill what was working fine. IF you have a p\s that is almost done it might not be a bad idea to try to work the ports a little wider. If you do kill the sleeve it won't hurt too bad that way.

I have a Rex 12 that I have thought about copying the timing and ports onto a CV and I do have a few of these lying around with some spare parts so it may make for a good project even if it doesn't work out the way I hope. I also wonder if the materials used in the CV's are able to take the stresses of running that much harder. Doublign the hp to over 1hp might not sound like much but if the engine is only engineered for a max of .75hp than you could be in for soem interesting trouble.

Enjoymentboy

jkulhanek

I am not sure what the genuine BHP rating on the CV's is, but O.S. tend to 'undershoot' the mark quite a bit, perhaps the CV is already a .75 HP engine, so increasing it to 1hp is less of a step than from 0.5-0.75...

I'm thinking that If I decide to go down the port modifying track (I have dozens of diamond burrs, but haven't ever seen diamond files, where could I get some?), I think I'll swap to a kyosho GX15CR conrod, it's about another MM thicker, yet the same length, same big/little end hole sizes from memory.

For the time being I'll just leave it as is, I have no idea if my mods have worked, or how the engine goes, still waiting on some engine mounts...

I ported the heck out of the stock GX15 engine e few days ago, which will be getting a run in today, so wish me luck!

ThunderbirdJunkie

My Feedback: (3)

let's do it!

ofnaliebregts

Question, Ive been recently pondering on doing relitively the same thing to my Ofna force .26, The only arrangement im worried about is knifing the connecting rod and making it subsidily weaker. Im worried if I even take off a slight bit of material even from polishing that I will ruin it! As for the .26 has quite a bit more displacement the pressure the piston must make on the con rod must be extreme. HELP!

SManMTB

Making a knife edge rod woon't give you much, work on the ports instead. More gain with less effort.
Making changes to the rod/crank/piston will change the balance of the engine. Unless you go through with it and balance everything afterwards I'd say just concentrate on the other parts first.

jkulhanek

Guys,

I recently pulled the engine (O.S. CV) down for some MORE work, but didn't get pics as I was too eager to let her rip again!

What I did:

- Cut a scoop on the leading edge of the counter weight to stir/agitate the fuel, like on expensive engines.

- Widened both transfer ports and kept the same port angles.

- This one was experimental, the boost port on these motors is operated via a window in the piston. To me it looked pretty pointless and restrictive, so instead I removed material from the boost port to the bottom of the sleeve to create a small transfer tunnel from the crankcase straight to the boost port like a normal transfer port tunnel, effectively increasing the flow by 200% on the boost port.

-Finally, the I rounded off the top edge of the exhaust port to smoothen the exit.

The results?? I ran a tank through it and went inside, pinched myself hard, rubbed my eyes, went back out for another go....NEVER IN MY WILDEST DREAMS WOULD I IMAGINE SUCH A HUGE DIFFERENCE. I still have trouble believing it, little Red Head now has some seriously freakish performance.

Not only that, the sound has dramatically changed...the engine revs harder than ever, and the power has increased ALL through the rev range, from lowend to topend it is crazy!!! I'm quite confident that this little beaty would be able to knock a TR off it's perch...

My only gripe is higher running temps, but with the Hyper head in the mail due in the next few days it should be running a bit cooler.

Other than that, everybody pray for my conrod lol.

Here are some pics of what I actually did.

Left is the boost port mod and right is the crank mod, note these aren't my engine parts.

SManMTB

That's what I did to the OS. Hard to say how much difference it did since I haven'r run it for some time but the bottom end was awesome.

jkulhanek

This O.S. still has quite a bit more in it, I could make the ports larger again, do more crank and carb work, clean up the crankcase, change the compression. But IMO I don't know it it would hold up, and as it is now, it has loads of power and I really don't need any more...

Porting is an addictive drug...

scottywilkes

man you sure did some porting

scottywilkes

so hows the kyosho GX go

jkulhanek

The plan with the gx was to sit it running at WOT till it popped, but it head such a bad leak in the rear start shaft bushing, it woulndt run, so i hit it with a hammer .

I now use the piston and rod as a keyring...

EtnieSk8r3000

anyone no where i can get info on doing this to a hyper 8 port.thx