grosbc

Has anyone done a comparison of the .18 VX, SH, and OS engines on the same model. I've read that the OS has more power than the SH which is better than the VX, but has anyone done speed comparisons of the three on the same model?

My Volcano with the VX 18 would run 31 with the stock gearbox and now runs a max of 38.5 with the direct drive setup on 20% nitro. That's with my gps taped to the truck, so it's accurate speeds.

grosbc

Surprised no one has ran these engines on the same car or truck to compare. Thinking of changing my VX engine, but wanted a feel for how much the SH or OS would add in power and speed.

el_tonto

Well probably nobody has done all three, and if they have then probably not in the exact car. A lot of people have compared the SH and the VX, since I understand both can be had through the engine exchange program, and a few people have upgraded from one of those engines to the OS.18 CVR (or is it CVRX?).

I've only ever run the VX engine, but my understanding is same as you - that the SH is a step up and that the OS would be a step up again. How big is a step? I dunno, but the VX responds well to a better tuned pipe, so that's a cheap improvement. Perhaps put a better pipe on, run it slightly lean for some more power, and if you blow it up get the SH for half price using the Redcat engine exchange program.

IMHO outright top end is not a good metric for checking engine performance though. I tune my engines to rocket through the midrange since that's where I drive. A sweet running max-rpm might give pretty poor punch off the line, and vice-versa (especially if you'd rather just drive than take the time tuning)

grosbc

Yeah, I just figured top end is the easiest to compare. I was thinking of switching since I couldn't keep my VX tuned. It would get hot and then have a hard time starting after several WOT runs and if you tuned it rich enough to stay cool, it would run like crud until it got hot enough to lean it out. Think I found the problem though. I sealed up everything and it still would run hot. Did a leak test on it yesterday and found the bolt that tightens the carburator to the block leaking. I sealed that and now have no leaks. Ran it today and it never got too hot and would start right up after some hard runs.

So I'll stick with the VX for a while, but am still curious how much difference there are in the 2 or 3 engine choices.

el_tonto

Hmm my VX has a wobbly carb and doesn't perform well until it's warmed up. Maybe I should check the carb mount too...

Easiest comparison is draw three lines on the road. Basically a startline, a "60ft" line and a "1/4 mile" line. (in practice maybe 10-15ft and 100ft???). Set up a video recorder a record a couple of passes. Play it on your computer and count the frames. Divide by 30fps and that gives you a 'launch' time and a '1/4 mile' time. A video you can play at your leisure is so much better than trying to handle a stop-watch on the day. More accurate too. Of course you have to set the camera up where it can see a span of 100+ ft which might be a bit awkward.

Maybe we should start up a "standard" test? I believe the RC drag guys use 132ft as their 1/4 mile. I don't know if they bother with a short-distance line to gauge the launch though.

grosbc

To test for air leaks, I removed the fuel line into the carb and put another piece of fuel tubing on the carb that I could blow into. Get a spray bottle with soapy water and spray down the engine. Remove the air filter and put your finger over the air intake hole while blowing into the carb fuel inlet. You'll see the soap bubble up anywhere there is an air leak. On mine the only leak after I had sealed everything else was that carb mount bolt on the opposite side of where the nut is. Tightening it didn't help. I tried removing it and putting sealant inside the hole, but all the sealant got removed when I reinserted the bolt. I ended up just putting blobs of sealant over both ends of the bolt and that worked. Make sure its clean first so the sealant will stick.

I only ran a few tank fulls after the fix but it looks like it's working better than before. I refuled a few times and several WOT passes and after stopping it, I still had good compression and it restarted back easily. Before the fix after a couple tank fulls of running WOT passes, I would barely have any compression. I knew it was getting too hot, but richening the carb didn't do much unless I had it too rich so I'd lose performance.