Low HP/cc (comparing to other engines)?

[SundayFlyboy97]

Hi, so I have been thinking about our little 66cc engines and actually how little HP they put out compared to even, say, chainsaw engines (plenty of 62cc chainsaws put out 4-5.5hp).

AFAIK, out 66 cc's put out only about 2 hp.

Don't get me wrong, I am happy with the performance I am getting out of my piped (ktm65 pipe ) 66 cc, the thing screams and pulls my 230lbs like nothing in the hilly area on a 44T sprocket. Actually having hard time to believe it's any less than 5 hp, but without dyno impossible to tell.


But of course me being me, I had some other ideas on how to put in use my other 66cc engine (being an aircraft nerd, I wanted to see how much thrust I can get using a 60 inch propeller and whether it could be used to propel a paramotor...it's a whole another crazy topic).



Soooo...what hp figures are you guys getting (if anyone has actually dynoed their China girl)?

And why is that even comparable in terms of cc's chainsaw engines outperform ours?

In theory 10hp should be pretty doable out of 66cc.

 

[ImpulseRocket]

And why is that even comparable in terms of cc's chainsaw engines outperform ours?

In theory 10hp should be pretty doable out of 66cc.

Many reasons. One, the power varies by manufacturer. The Zeda Firestorm puts out a bit more power than a dirt cheap ebay engine. Better ports and castings.

A big reason is that they are not forced air cooling like a chainsaw or even weedeater. That makes a big difference.

Low compression and conservative port timing figures make for cool running engines that, in theory, will last a long time under heavy use. Think about the old big blocks from the 60's and 70's that barely made 300hp, sometimes much less, on spun up to 4000 or 5000rpm max, and had 8:1 compression. Unimpressive power for their size, but they ran and ran and ran and ran.

 

[GW's Motorized]

The bt80(the kit I have) is supposed to put out 4-5 hp stock. Considering my top end of 40 I'd believe it is 4-5. I've also cut the baffle out of it and put a high flow filter on so it is probably near 5 hp.

 

[ImpulseRocket]

The bt80(the kit I have) is supposed to put out 4-5 hp stock. Considering my top end of 40 I'd believe it is 4-5. I've also cut the baffle out of it and put a high flow filter on so it is probably near 5 hp.

Yeah, but the BT80 and my P85 are both specialty engines and cost 2 to 3 times that of a typical cheapo 66cc. That's why I didn't bring up the Phantom, because it easily makes 5hp in stock form, or possibly a bit more.

 

[GW's Motorized]

Yeah, but the BT80 and my P85 are both specialty engines and cost 2 to 3 times that of a typical cheapo 66cc. That's why I didn't bring up the Phantom, because it easily makes 5hp in stock form, or possibly a bit more.

Yeah, it was quite expensive. It's worth it if you ask me. You pay twice as much for twice the power, and more potential for power down the road.

 

[SundayFlyboy97]

The ktm pipe makes a BIG difference. It starts out a little bit better than stock, and then when it accelerates, I assume hits the sweet spot rpm band it just wants to gooooo lol. Also the throttle response is legendary.


The only thing that seems like a bottleneck is the exhaust flange. The opening on the flange and the subsequent tube are only 22mm in diameter, which is tiny compared to the pipe's inlet diameter.


PS: "the throttle response is legendary"

So is the reaction from pedestrians covering their ears lol ( currently no muffler).

 

[ImpulseRocket]

Yeah, it was quite expensive. It's worth it if you ask me. You pay twice as much for twice the power, and more potential for power down the road.

The appeal to me is mainly the charging system.

 

[GW's Motorized]

The appeal to me is mainly the charging system.

It is very nice having a headlight and tail light wired in

 

[ImpulseRocket]

The ktm pipe makes a BIG difference.

The only thing that seems like a bottleneck is the exhaust flange. The opening on the flange and the subsequent tube are only 22mm in diameter, which is tiny compared to the pipe's inlet diameter.

This is why the more powerful engines on the market, such as his BT80 and my Phantom have much bigger exhaust outlets with different flange styles to accomodate them. The Phantom outlet is 28-29mm in diameter with a 60mm stud spacing. The intake port is actually the biggest restriction on it, which I am sure was done intentionally. Port matching my intake really woke mine up.

 

[GW's Motorized]

This is why the more powerful engines on the market, such as his BT80 and my Phantom have much bigger exhaust outlets with different flange styles to accomodate them. The Phantom outlet is 28-29mm in diameter with a 60mm stud spacing. The intake port is actually the biggest restriction on it, which I am sure was done intentionally. Port matching my intake really woke mine up.

I don't remember the exact size, but the BT80 exhaust port is a few mm larger than the phantom