Gas scale help

[Ben Ballard]

Need some advice from the gas scale guys. Ordered a gas scale/winston eagle kit from ML. Great guy to do business with, by the way. Any how I'm looking at engine options and need help. Thinking about a rcmk 30 rear exaust. Anybody have any input on pro/cons? I want to try and stay with the rear exaust to avoid cutting up the cowl or will a side exaust fit under it? Any info will be greatly appreciated as always!

 

[Tim Strange]

I have been running a stock RCMK 30RZ...it's been a very reliable motor for me. Although it has plenty of power, it is lacking in the RPM department. I'd suggest going with a mod motor.

A couple of things to consider: 1) Availability...Gizmo has some spare parts for the RCMK's, is not carrying the line anymore. Not sure if anyone else has stocked them yet.

2) The aluminum RCMK rear header is nice because you can position it at just about any angle you may need. Downside is that using the aluminum header with a steel pipe can cause some corrosion and ruin the header...or get bent when clamping the pipe down. I modified a regular water cooled flange to match the RCMK exhaust port (which was easy). However you will need to find a Rear Exhaust header of the correct degree bend for your application...good luck with that.

If you do go with a Rear Exhaust engine, I would suggest making provisions to use a side exhaust. Namely making sure the header flange will fit under the cowl or deck. Zippkits does sell a 90 degree drop header which may help.

Harvey may chime in since he has a T6 Bud.

 

[Ben Ballard]

Thanks Tim, I was also curious about the engine mounts. I see some rcmk engines that mount on two rails much like a nitro engine. The new cmb gas engine also uses this same style. Other rcmk engines mount on the zen style mounts. Is one better than the other or is it just preference?

 

[Tim Strange]

I would be interested on feedback on the other style mounts you are talking about also. They look like they may be easier to install/remove the engine on a boat with a tight engine well.

I only have experience with the Gizmo/CC style mounts. Be aware that the RCMK RZ uses a different front mount than the Zenoah.

 

[Ron Olson]

OK, maybe I can be of some help here as I had 2 RCMK Evo R-254's. I only ran one and swapped the other recently and ran that one in a Zippkits 'rigger.

Problems with the 265 RE engines was piston wear. I didn't own mine long enough ot have any problems but kept 3 extra's for just in case.

If it has the rail mounts the isolators are a PITA to mount. Get the Zippkits islolators as they go right on and don't have the problem with the stock ones. You will have to cut off part of the threads on 2 of them.

Joe also sells a water-cooled exhaust flange if you don't like RCMK's, just a regular one that's used on SE engines. Joe used to sell straight and angled headers for the RE's also. If he doesn't have them try Vince at Gas RC Products.

Here's a shot of the setup before the boat was done.

 

[larcor69]

Phil and others have the 8255 boats, the side exhaust fit under the top skin, with a little modding of the engine well sides, I would consider a zenoah 29.5 full mod engine most likely the best for now, or maybe the new tiger king?

 

[SayMikey]

Phil and others have the 8255 boats, the side exhaust fit under the top skin, with a little modding of the engine well sides, I would consider a zenoah 29.5 full mod engine most likely the best for now, or maybe the new tiger king?

Yup and a wrap to center header. It all comes down to tub width,figure that out and then ask for measurements.

 

[Ben Ballard]

Thanks to all you guys for your input! I am really open to any engine combo that will fit. Once again I am not looking for a "record breaker" just a good running boat that looks as it should. I love how a scale hydro looks on the water more than I am concerned about top speed.., that being said a hydroplane needs to perform as it should to look right on the water. I know that the boat Hull i ordered is more than capable of performing. What I need to do is build upon what I have. The zen engines are impressive... And have a good backing with parts and tech help. What are the other gas guys doing? Will a zen with a 180 header fit under this CoweI? i am trying to retain a scale looking boat... If I just wanted a gas hydro I would have ordered a whiplash and been done with it. Not to take away from blazer marine, they have some **** fast boats! I'm just looking for a more scale approach.

 

[Ron Olson]

I'm surprised that Mike said to use a WTC header as you really can't get most of them short enough to be effective. If it was a one-piece WTC then those are a different story.

 

[Samuel Hagan JR]

You won't need a record breaker motor but your gonna need a lot of HP to get that thing moving.

 

[jeffaustin]

i also have been running a mod rcmk 30 rz, i gps my 7931 hull and top speed was 64.8, had to send motor back after trying another prop because of bending the crank because of water ingestion. i am now in the process of building another gas scale, i am now making hull so i can run a side exhaust engine or rear exhauust incase parts for the rcmk get scarce. i really do like the rcmk but i also think they need a larger prop because the dont turn the rpms like some modded zens.

 

[Ron Olson]

Jeff, kind of the opposite with RCMK's as I talked to Mike Ross about this. The RCMK's need to rev so I was told to prop down on them.

 

[lohring]

An article on my experiences with the current gas scale two lap record holder are described in Scaling Up. You won't believe how strong things need to be on these heavy boats when they start running 12 second laps. I ended up reinforcing the sponson bottoms as well as the turn fin and its mount twice.

The latest engine was a Brian Buaas modified 30 mm stroke 36 mm bore Zenoah with a 55 mm long rod. We also ran a more conventional 29 cc modified Zenoah last year. Both used a 1" header Beast pipe with an enlarged stinger. I think the best off the shelf engine currently available would be the Quickdraw 29 cc Pioneer. A member of my club is using one in his build. I second the comments on the ML Boatworks frame kits. They really fit well and help the build process.

Lohring Miller

 

[jeffaustin]

Ron that is good to know...............Tim and i were the first around here to try the 30 rz, still trying to find best prop pipe combo, i am using the victory pipe per gizmos recommendation,steel pipe is heavy,am going to try some different pipes and such,

 

[Marty Shallenberger]

Need some advice from the gas scale guys. Ordered a gas scale/winston eagle kit from ML. Great guy to do business with, by the way. Any how I'm looking at engine options and need help. Thinking about a rcmk 30 rear exaust. Anybody have any input on pro/cons? I want to try and stay with the rear exaust to avoid cutting up the cowl or will a side exaust fit under it? Any info will be greatly appreciated as always!

Hi Ben After building many Gas Scale Hydros most with rear exhaust RCMK R-254 engines I have come to the conclusion that if I can make a side exhaust engine work that is how I build now. Main reasons are the RCMK electronics are marginal , side exhaust engines are easier to get and I bend more cranks with front carburetor engines. I have been using ceramic coated Hot Pipes on my rear exhaust setups with a 5 degree header and they work well with the 26cc engines. You can take a look at my R-254 Budweiser build on the WWW.PNWTA.ORG website in the photos page or watch this U tube video



Marty

 

[harvknox]

Ben, you will have a lot of fun with gas scale, but you had better have a strong back. These suckers are big and can get heavy. As Tim noted, I have a T-6 gas scale made from Mike's kit. I have a Gizmo modded K-30 in my boat. Unless your cowl is wider than the T-6, you will not have room for a side exhaust. Marty took his rear exhaust down and thru the transom. Mine goes up and exits thru the turbine tube. If you go with a K-30 and the RMCK ball joint header, check for water leaks at maximum deflection. I do not have the best prop yet, and my speed is improving, engine has plenty of torque. You will need all the power you can get for performance. When you look at Mike's kit, remember that he scaled up his 1/8 scale kit. The frames and all parts are 20% further apart. You may want to consider some reinforcing. I used a combination of 1/16 and 3/32 sheeting. The 3/32 is 5 ply and the 1/16 is 3 ply. It's amazing the increase in strength without going to 1/8. I suggest you have your cowl before building the boat to insure it all fits together. All the Evansville boats last year were the 8255 hull except my T-6.Installations such as a side exhaust are different on the modern day turbine boats, so check it out.I'll be glad to share any info I have.

Harvey

 

[Ron Olson]

The ignition system is weak on the RCMK's but you have to gap down on the plugs to .016" to make them last otherwise you'll fry the secondary coil.

The stock pull-start isn't going to last so you might as well replace it now with some kind of EZ starter. The Zenoah or Zippkits have been good for me, the one from Gizmo fell apart.

I got a SE RCMK 30cc that I dropped in my Rampage mono for next season modded by Suicidal, dyno'ed at 7 HP so it may be too much for that hull. That puppy is tough to turn over with an EZ start so it has a belt at the ready in case I need it and a 24-volt hand-held starter.

 

[Ben Ballard]

Thanks everyone for the info! I have a lot of decisions to make... I am thinking of using the accutech thunder boat hardware on this boat as well... Any one have input on that? I also looked at the blazer marine turn fin? Not sure if a hook fin like the whiplash uses or the straight blade from accutech is the way to go? My plan is to have all the parts I need to complete this build before I start... This will be my first build from start to finish and hoping that having all the hardware when I start will help keep me from a screwup being able to have the part in hand to see how it will fit before I epoxy it together.

 

[jeffaustin]

the extended flat bottom strut from speedmaster is a nice scale looking strut. Harvey has a fantastic looking turn fin on his Bud....... if it was me i would try to get a side exhaust engine to work by building a deep belly pan to get pipe under deck even if you are planning on using a rear exhaust engine. hopefully i will have my new gas scale done in early spring,i plan on trying at least 3 different engines and pipe combos

modded rcmk 30rz

modded 29.5 SS

gzr racing zen 30

maybe modded tiger king

 

[harvknox]

The Accu-Tech strut is scale looking and similar to that used on a number of modern turbine boats. I don't know if the Winston Eagle used one. I have one on my T-6,and it looks like the real one except its swooping curve on the rear of my strut is not streamlined. It has a square edge. Jeff noted that you can get a flat bottom Speedmaster strut, which can give a little rear end lift, which you will probably need. The Accu-Tech strut is only available with a round bottom.

I agree with Jeff concerning a side exhaust engine, plus it gives you a lot of engine choices. However, I measured the top of the exhaust header in relation to the deck height on my T-6.The top of the header is 1 1/16 above the surface of the deck. The K-30 is just high enough above the tub bottom to just get a starter belt on and off a speedmaster starter pulley and collet. If I were to build a belly pan on my boat it would extend lower than the sponson. I don't think I've got room for a short radius turn down then 90 degree header. Your deck may be higher which could give you clearance. I don't think you would want your boat to look like a Pro Boat Zen powered T-6.

Jeff, thanks for the complement on the turn fin. That fin was custom made, and is one of a kind. It is very close to scale, is a straight fin, mounted at 17 degrees and holds a 23 lb. boat on a tight turn with little skid. Ben I believe your boat will work with either a straight or hooked turn fin. You may have to experiment a bit.

Harvey