low end problems with head?

[damann33]

Alright, a while ago I purchased a head from akunar with the 28/24 valves and with port work. Now will I have any problems using this head with the stock cylinder, piston? I know I would have to probably go up on my pilot jet and maybe richen my midrange a bit, but would it not idle properlly or run good? The reason why I ask is because I remember reading somewhere that someone used a bigger valve head with his stock piston/cylinder and people were saying that it lowers your compression and that you should run a bigger domed piston or gain compression in another matter. I wont buy the 57mm cylinder or akunar piston for my lifan 140cc if the head will work properly with the stock piston/cylinder, thanks

 

[themountain]

why should that lower the compression, if its the same head ?? How much cc got the new head??...same as before??
Only restricting thing I could think of now is the exhaust....do you got a big bore exhaust??

 

[damann33]

I dont know if that happens im just asking to see if it really does effect anything. The head is a 140cc lifan head ported/polished and has 28/24 valves. This will replace the stock head

 

[themountain]

...and? stockhead was??

 

[damann33]

stock is just a 27/23 valve head

 

[themountain]

stock is just a 27/23 valve head

JEZ...I know...but what head?? Lifan140 or Jialing or what??

 

[tubes380]

its off a 140cc said in the first post, bolt it on mate i think youll find itll work a treat and if it doesnt the only thing you would have lost is a bit of time and a head gasket

 

[Cactus Jack]

He's gotten the loss of compression idea from reading where people fit a Lifan BVH to a Jialing GPX ...... The Jialing head has a smaller chamber and valves which gives higher compression with the stock piston .

Obviously fitting a ported Lifan 140 BVH with bigger valves to a Lifan 140 won't cause any compression loss whatsoever ..... but having to deepen the valve pockets to suit a race cam will ....... and a race cam with greater duration and overlap WILL lower the bottom end dynamic compression ...... lowering the torque as well ...... that's why a higher compression piston works to boost power everywhere ...... the problem is that Akunar pistons are made for some other type of engine and sit down the bore ..... creating a potential detonation spot in the quench area ....

He'd have been better off buying a ported Lifan 120 BVH which gives higher compression than a 140 head ....... to use with the stock 140 piston ...... that way the quench area would be a lot tighter .....

 

[themountain]

He's gotten the loss of compression idea from reading where people fit a Lifan BVH to a Jialing GPX ...... .

yop..thats what I was thinking too....that happens when you read too much

 

[mcanix]

There wont be much of a gain with std cylinder anyway as big valve heads work better with bore over 57mm. would have been just as much gain by porting original head and fitting a cam to that.

 

[damann33]

doesnt matter, I only paid 50 bucks more for the valves and the machine work. Here it would be a 100 dollar machine job, then I would have had to buy the valves.

 

[Mack]

in the head volume itself you will gain slightly over the stock head because Akunar uses flat head valves over the stock dished ones, but, as cactus mentioned, there are other variables in play once you fit the pistons akunar has for this engine and change cams. The 140 is a tricky engine to mod up correctly, mostly because there is no piston made specifically to suit and the odd cylinder height and head shape. If you modify to get the piston up you end up with the cam chain in between too long and too short with one link removed. To do it properly you have to deck the cylinder so the piston is flush or protruding then have the piston machined for the squish area and the head machined to remove the factory bevel and get the head even lower so you can then also remove one link from the cam chain and get the compression you need to run big cams...as I have said before there is not what I would consider a decent 'bolt on' kit for this motor.

 

[themountain]

Theoretically, thats true, but I used a 57mm piston from OORacing and the above mentioned properties are the same as the original....alone raising the displacment will logically encrease the compression ratio...so up till now, sixth month pass, there is no issue with the engine, without major work made!!

 

[damann33]

I think I got it all worked out right now, I just bought the head and hc piston from akunar and am buying the cylinder from tbolt. Now akunar is providing me with gaskets to raise the shorted alloy cylinder up to the stock cylinder height. The piston deck height is smaller then stock but the piton itself will sit about 1.2mm down the cylinder. The dome on the piston I am getting isnt that big, about 4mm in height, but I am prepared to notch the pistons with proper clearences. Overall I will have a bit more compression running the 57mm piston and cylinder.

 

[Mack]

Theoretically, thats true, but I used a 57mm piston from OORacing and the above mentioned properties are the same as the original....alone raising the displacment will logically encrease the compression ratio...so up till now, sixth month pass, there is no issue with the engine, without major work made!!

No not in theory. Note i said to do it properly...and I mean also with a big cam which damann33 has a reasonably big cam. If you just bore the stock cylinder and use one of those pistons will work of course, but if you want to run the engine with optimised compression for the fuel you will be using you will strike the above mentioned problems.

 

[themountain]

mmm...Iam running the AHP racecam with it...??

 

[themountain]

I think I got it all worked out right now, I just bought the head and hc piston from akunar and am buying the cylinder from tbolt. Now akunar is providing me with gaskets to raise the shorted alloy cylinder up to the stock cylinder height. The piston deck height is smaller then stock but the piton itself will sit about 1.2mm down the cylinder. The dome on the piston I am getting isnt that big, about 4mm in height, but I am prepared to notch the pistons with proper clearences. Overall I will have a bit more compression running the 57mm piston and cylinder.

yop, I think so too...if you had the new bigger piston flush to your head ,you would raise the compression to 10 :1 if the shape would be exactly the same...now with the piston sitting a bit inside ,but with his dome it will be more or less the same....depends on the form of the dome, claro!!
If you don´t have clearence issues with the valves , the engine will be quite right
Keep us posted!!

 

[Cactus Jack]

I think I got it all worked out right now, I just bought the head and hc piston from akunar and am buying the cylinder from tbolt.

How much did Akunar want for a cylinder , piston , pin , and ring kit ? (complete with shipping)

 

[Cactus Jack]

mmm...Iam running the AHP racecam with it...??

It's not as big as what Damann will be running ....... it's a pity they don't give out the duration specs ...... I've got a similar cam (probably the exact same) and it has .257 thou lift as well and runs NTN bearings (sold to me as a Sachs Madass Cam ) Compression will be more critical with the TBW0300 ......

It's strange how they sell a smaller cam for the 140 which has a longer stroke and would work better with a bigger cam ...... it's quite well known that a cam acts smaller in a larger displacement engine than it does in a smaller engine ........

Anyhow , it's all good ...... we'll get to see how it all pans out when Damann gets his engine up and running ....

AHP Race Cam for Lifan 140cc Engine
[ENG58] $59.00
Our AHP race cam is good for up to 1-2hp alone on the dyno (depending on your tune!) The lift on this cam is 257, stock is 224. This cam also has a much better duration ! Utilizes stock dual HD springs. This cam is for the Chinese engines that do not use a Honda type Camshaft.

TB Race Cam for Race Head/Lifan BVH
[TBW0300] $59.00
This camshaft is for the Race Head and Lifan BIG VALVE HEAD only.
Aggressive lift and duration without sacrificing low end torque. Uses NTN bearings. Specs: .275" intake valve lift and 230 degrees of duration @ .050", 275" exhaust valve lift and 230 degrees of duration @ .050"

The big squish ring is a safety margin against detonation at the sacrifice of compression (and performance) .... it allows the flame to reach everywhere ........ but when you start tightening things up to optimise performance (as Mack is stating) the squish gap becomes more critical ......... it's purpose is to force all gas and fuel out from the edges of the piston towards the flame front (create turbulence and thoroughly atomise the fuel in the chamber) for a cleaner , faster , and more efficient burn ........

 

[Mack]

I dunno bout some of these figures I will check them exactly tomorrow. I just mocked up a 57mm piston from akunar in a motor this arvy. I used an alloy barrel with a 2mm spacer and .5 gaskets either side of it. This still brings the deck up short of stock but the piston is at least 1.8 in the hole. The dome is very slight and doesn't start till 5mm in from the edge of the piston and there are valve pockets in the dome as well. So in a stock cylinder height this situation is even worse. You couldn't be making more compression than stock just from the quick look I had at it...but could be wrong, won't know till I measure everything.