Hi im in south africa we race 1/4 scale cats and F1 boats i have a zenoah with a 30.5 cc top end mod and a cy 27 cc mod i would like to buy a mod motor but not quickdraw what motor can i get up to 30 cc that would be fast need help as we have to rely on info as south africa dont have the know how thanks

Big block Zenoah is 29.5cc. Several builders making these. CC Racing makes one...it's called the Monster. This email address is being protected from spambots. You need JavaScript enabled to view it.


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Yes the cc engines are good , how ever I have seen a Gizzmo motors RCMK full mod K30 kill the cc racing monster engine , 3 heats out of 3 , and both were running the same hull , myself I think it all comes down to personal preference , get on the net and find engine builders and ask questions
I have been down that road when I started out and now have just started doing my own work .
So happy boating
Kiwi racer

LOL! Thats some good stuff right there!


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I think Carlo will get a kick out of that one!!

BUT, how long do the RCMK's live? Will that last a full season or will you have to replace the top end a couple of times.

BUT, how long do the RCMK's live? Will that last a full season or will you have to replace the top end a couple of times.[/quote]

The top and bottom live a long time. It's the ignition (primary) that quits.

I have a tip for the 30.5cc kit. That engine uses a 2mm stroked crank, and 30.5cc kits are not created equal by different builders. The problem with the 2mm cranks for the boat racing application is, the transfer port duration gets large enough to lose valuable high RPM and mid range power. If you have a kit where the head was not modified to fit the 2mm crank, you would have had to add a 1mm thick spacer under your cylinder so the piston does not hit the stock head squish band. That makes the transfer duration even worse, and I doubt any boat racer would be happy with it. If you have a kit that has the squish band cut, and the combustion chamber cut larger to lower compression back to normal levels (my kits), you can use a thinner gasket to achieve a .010" (.25mm) squish clearance. This will drop the cylinder more to get the transfers working better, but you are also losing about 2 degrees of exhaust duration. The 2mm cranks with a cylinder and a stock gasket thickness may cause what is called "Free porting", where the piston skirt opens up the bottom of the ex port near TDC. Although we have not found power loss in a piston port engine with a little free porting (with a good pipe doing what it is suppose to do), you can fix that problem by using the RCMK 36mm diameter piston. The RCMK piston is the same weight as the Zen piston, and has .020" longer piston skirts than the zen piston. The Zen ring fits the RCMK piston. The longer intake skirt will decrease the intake duration by about 4 degrees duration, but you can easily fix that by removing .020" (.5mm) from the bottom edge of the intake skirt. Make sure the camphor the skirt edge so it can't catch the intake port, or scrape oil from the intake side of the cylinder.

I have sold a few 30.5cc kits with Daves Discount Motors (DDM) because Dave told me people were asking for them (which was news to me). But I know they are not running as well as boat racers want yet, and I have not built them for about a year. That----is about to change. I and one of my racers are currently testing a properly built 30.5cc kit, and if it runs the way we hope it will run, I should be able to sell them through DDM, possibly with the RCMK piston if needed. It passed my racers "test stand" test with flying colors, and should be hitting the water for the first time this week---weather permitting. Other 30.5cc kits my racer played with recently pulled so hard out of the corners, he was twisting cranks a bit. We hope that problem will be solved by using a 3rd bearing (Sealed Zen bearing out of the G290 engine) to replace the large diameter crank shaft seal, to offer the crank more stability under load. When you get around 6hp or more---2 bearing cases allow the crank to flex quite a bit.

If that is one of my 30.5cc kits you bought, I will upgrade it for you for the tiny cost of $40.00 (all ports and head mods changed), and you should see huge improvement. I recommend using the QD pipes, if you can get one, and the new configuration should pull very hard out of the corners, and waste no time hitting over 18,000 RPM before the next corner.

If you got the kit from DDM a while back, I am pretty sure it is a ESP "race ported" (My championship porting is faster also) 30.5cc PUM kit that uses the stock cylinder gasket. I really did not want to sell them that way for boat racing, but Dave wanted some before I could do more work on them. I did not sell many of them (may be 10 or so), but if you want me to upgrade it, call me by phone, and we will make the arrangements.

Doug @ ESP
(616) 458-8103 (EST Zone)