.21 engine question

[Greywolf74]

So I realize this is a newb question but its just one I've never bothered to ask before. Do .21's come in big block and small blocks cuz I've read things here and there that would seem to indicate that but I dont know for sure.

 

[Phins Fan]

Once you get over a .19 you get into bigblocks. I'm not aware of anyone making a .21 smallblock or vice versa on a bigblock .12

 

[Greywolf74]

Oh? I thought .21s were small blocks typically....The OS .21TM is a direct drop in on a MGT 3.0 (or at least thats what I read somewhere) and the MGT 3.0 has a smallblock engine from stock. Or did the post I read saying that have it all wrong?

 

[Phins Fan]

There are bigblocks that can be drop in replacements for smallblock rigs (The OS Tmaxx for instance) but its just a matter of having the proper engine mount that will allow you to line everything up correctly.

 

[mikeyt]

could i use the traxxas trx 2.5 connecting rod in the OFNA .21b 3 port nitro engine. I'm building my own engine and i like the design of that rod. connecting rod is longer than in any other small-block .15 engine. The longer rod decreases the rod angle throughout the entire stroke of the piston, reducing side load on the piston. It adds up to less friction and more power.The edges of the connecting rod are knife-edged, a feature usually found only on expensive, hard-to-get Italian engines. The TRX 2.5 Racing Engine's knife-edged connecting rod slips through the dense fuel air mixture in the crankcase, reducing turbulence and drag. Why? More power of course!

---------- Post added at 11:21 PM ---------- Previous post was at 11:18 PM ----------

I'm going to use the OFNA racing engine case .21b 3 port. everything is going to remain the same except for the connecting rod. can i do this? also the ez start system founf on the traxxis rustler could i put that on another rc car?

---------- Post added at 11:22 PM ---------- Previous post was at 11:21 PM ----------

I'm going to use the OFNA Ultra GTP chassis 4 wheel drive.

 

[Snook Man]

I wouldn’t think the rod will fit and would be a bad idea to use it if it did unless just experiment with a worn engine your willing to take a chance of destroying.

The rod is used in both the 2.5 and 3.3 traxxas engine. When used in the 2.5 engine (.15 size) it holds up decent. When used with the 3.3 engine (.20 size) it has a reputation for splitting down the middle due to the lack of an upper bushing for the piston wrist pin.
Add the little extra power output of a .21 size engine and more stress would be applied to the rod and failure may be more prevalent.
A knife edged con rod will add a few more rpms over a rod that’s not, but the difference alone is not that significant between the 2. I don’t consider the 3.3 rod to be all the knifed edged anyway.
Modifying the stock rod may be the better option as it is a double bushed rod and you know it fits.

 

[2revo1maxx]

A big block is just that, a big block. It has nothing to do with displacement, although you probably won't find one under a .21.

All .21s used to be true big blocks, but since the picco .21 max and os 21tm that's all changed. Those are considered mid blocks. Even the picco .26 and sirio s27 are mid blocks.

 

[mikeyt]

okay i will buy two rods for the .21 and try filing it down a bit if it doesn't work i will have the spair rod. Do you think i could someway connect the ez start system to the OFNA engine?

 

[2revo1maxx]

I would just get the proper parts for it. A knife edged rod isn't going to make much difference, and filing one down is just insane.

 

[mikeyt]

well i could use a hand file instead of like a grinding wheel or something. With the hand file i could take my time and get exactly what i want. Is there any other way i could mod the OFNA .21 enigine? i want a fast car man

 

[mikeyt]

IS there any upgrades i can put on the ofna engine to make it faster i want like an 80 mph car 2spd trans and 4 wheel drive

---------- Post added at 6:18 PM ---------- Previous post was at 6:17 PM ----------

and on road i already have an off road truck

 

[mikeyt]

This is the 1/8 scale glow powered, radio controlled, 4 wheel drive
Ofna Ultra GTP Oval Racing Kit.
what does glow powered mean?

 

[2revo1maxx]

Nitro powered.

 

[avelciario]

IS there any upgrades i can put on the ofna engine to make it faster i want like an 80 mph car 2spd trans and 4 wheel drive

---------- Post added at 6:18 PM ---------- Previous post was at 6:17 PM ----------

and on road i already have an off road truck

Mikeyt- If you want to modify that engine to become faster on top speed you have to adjust the length of your exhaust to a shorter one, cut it little by little. 2nd try to port and polish the sleeve, put a heavier flywheel, good air intake, and bigger cb. and most important good tunning. This one can easily get power on LRP Z21R nitro engine, I have one.

 

[mikeyt]

Alright cool thanks for the info man