Revo 2.5 big block upgrade(Engine suggestions?)

[E1ev1n]

I've never really bought a new nitro rc engine, but I would like to upgrade my Revo 2.5 that is on a 3.3 chassis to a big block as the extra power just sounds nice. I know I will need a conversion kit, but what I'm not sure about is the engine I want to choose. Every thread I've found off google about this are all 10+ years old so the information isn't as relevant anymore.

So I'm hoping you guys have some good recommendations, and experiences with some of the nitro rc engines.

 

[XeroMyHero]

I have a few revos now. I just bought the

LRP ZR.32X .32 Spec 4.1 Monster Truck Nitro Engine​

from here:
https://www.amainhobbies.com/lrp-zr.32x-.32-spec-4.1-monster-truck-nitro-engine-lrp32826/p1391509

Features:

• Big Block size - You cannot replace displacement with anything… but even more displacement!
• CoolDownMax cylinder head provides improved cooling through updated cooling fin arrangement
• Fits all major .21 engine mounts
• 7 + 1 Ports
• Extra reinforced connecting rod
• XTEC T6 engine housing
• XTEC PowerCarb4 thermal protected 15S-3 needle Carburetor
• 9.0, 8.5 and 7.5mm venturi inserts included (9.0mm installed)

It states it will fit all major .21 engine mounts. I have an OS .21 on one of my revos with the easy start and it is a great motor. So the 3.3 mount will work with the OS .21, I did mock the engine into one I was changing the clutch out in and it seemed to fit just fine. Not sure if the easy start will work on it thought, might have to go to a pull start. But for me if the easy start don't mount to it I will just make a plate adaptor to get it to work. I paid just over $300 for the OS engine and the LRP is just over $200. I know it has a longer shaft on it for the clutch system you may have to move the trans back some and drill some holes to do that. Not sure myself yet, I am working on a revo speed run unit now that I have a post going on how I am setting it up. The LRP is for a future project. I will post that project when I start on it.

Let us know if you get it and how it works out. I am interested in know what you did to put a big block in as I will be doing the same myself this summer or fall.

 

[Maximum_Quake_Pro.com]

Put a losi 3.4 in it.

F#$K a 3.3

 

[olds97_lss]

I have a few revos now. I just bought the

LRP ZR.32X .32 Spec 4.1 Monster Truck Nitro Engine​

from here:
https://www.amainhobbies.com/lrp-zr.32x-.32-spec-4.1-monster-truck-nitro-engine-lrp32826/p1391509

Features:

• Big Block size - You cannot replace displacement with anything… but even more displacement!
• CoolDownMax cylinder head provides improved cooling through updated cooling fin arrangement
• Fits all major .21 engine mounts
• 7 + 1 Ports
• Extra reinforced connecting rod
• XTEC T6 engine housing
• XTEC PowerCarb4 thermal protected 15S-3 needle Carburetor
• 9.0, 8.5 and 7.5mm venturi inserts included (9.0mm installed)

It states it will fit all major .21 engine mounts. I have an OS .21 on one of my revos with the easy start and it is a great motor. So the 3.3 mount will work with the OS .21, I did mock the engine into one I was changing the clutch out in and it seemed to fit just fine. Not sure if the easy start will work on it thought, might have to go to a pull start. But for me if the easy start don't mount to it I will just make a plate adaptor to get it to work. I paid just over $300 for the OS engine and the LRP is just over $200. I know it has a longer shaft on it for the clutch system you may have to move the trans back some and drill some holes to do that. Not sure myself yet, I am working on a revo speed run unit now that I have a post going on how I am setting it up. The LRP is for a future project. I will post that project when I start on it.

Let us know if you get it and how it works out. I am interested in know what you did to put a big block in as I will be doing the same myself this summer or fall.

Not sure what "OS 21" you have, but there is one that fits in the stock mount, the 21TM. Their others will not as the block is considerably wider. The 21TM is built as a drop in for 1/10th use.

Finding a big block conversion these days can be difficult. Traxxas offered one, but it only worked with specific engines with roto start or tiger drive or a special bump box as other engines would hit the rear arm. The old New Era "leaner" mount is hard to find, but it would fit any standard .21 sized big block engine in a revo as it raised the engine up high enough to not come into contact with the arm. Then you had to figure out how to get a pipe to work with it.

The easiest is the 21TM, it comes with a manifold to work with the stock pipe, but would suggest getting the single chamber traxxas resonator pipe at least for it so it can breath a bit better. Or the THS pipe if you can find one.

I have 2 nitro revo's. One with the OS 21TM and the old THS "torque" pipe as well. One with an LRP28 Spec 3, a new era leaner mount, a cobbled up THS big block revo header and THS big block revo pipe. I did have an old OS21RG (standard 21 big block) in that before as well as an XTM 24.7 (another cheap RTR big block).

Both setups required RRP steel gears in the transmission or they would just grenade. The 21TM would work ok, but the small pins that hold the plastic gears on the shafts inside the trans would rip out, then the gears would eat themselves. After having the trans apart 3 times, I got the RRP steel set for that one too.

My LRP28 revo:

I cut a couple fins off the top of the engine so it wouldn't contact the ground. With a couple fins removed, it sat lower than the raised roll bar and "wing".

I also usually don't use wings... just a HDPE block with rounded corners to act more as a slide/tall bumper that doesn't dig into the ground as much as a wing.

My 21TM revo still has a wing:

I don't really drive either truck anymore. But I'd never get out of them what they are worth to me, so I just let them sit and run them once in a while. They are the only nitro's I have left.

 

[XeroMyHero]

Yea I have the O.S. .21 TM on mine.
I don't have it in my revo crawler yet. I have Summit locker diffs I want to put in as well. need to modify the chassis a bit to get them to work. going to be a project for next month. Right now I am working on my revo 3.3 speed runner.

Speed runner link: https://www.rctalk.com/forum/thread...-it-to-go-goal-is-80-mph.133814/#post-1328952