compression

[Anonymous-0]

how much do you gain by adding more compression to the motor?

 

[buickanddeere]

Compression is really saying "expansion ratio" on the power stroke.
Torque is combustion chamber pressure. That's from mechanical compression ratio and cam duration.
The cam duration and compression ratio has to be matched to intended engine rpms. Plus factor in about a dozen other variables.

 

[Gearnut]

As a general rule of thumb, you gain 4% for every point you raise the CR --up until the pumping looses overcome any gains.

 

[Anonymous-0]

(quoted from post at 07:17:14 07/31/09)
As a general rule of thumb, you gain 4% for every point you raise the CR --up until the pumping looses overcome any gains.

Might be pumping losses on a single cylinder but multi cylinders the higher the compression the harder the piston drives down the harder the other piston drives up. even if the horsepower flat lines the torque will climb with higher compression ratio also.

 

[Gearnut]

Mr Plankey, you should go hang-out over in automotive engineering forums

http://www.eng-tips.com/threadminder.cfm?pid=71

and see how long you get away with talking mindless crap like that

 

[Anonymous-0]

well i hang out at automotive speed shops. nascar shops actually hook a electric motor to a engine and turn it all through the rpm ranges to see how much horsepower is robbed. naturally aspirated prostock engines run at 16.1 round track engines around 14to 15.1 . I guess youre rebuttal will be that high compression works better in high rpms and not in the low rpms of tractor pulling . the electric motor test proves different though. you can believe everything you test and only half of everything you read.

 

[Anonymous-0]

(quoted from post at 12:54:58 07/31/09) well i hang out at automotive speed shops. nascar shops actually hook a electric motor to a engine and turn it all through the rpm ranges to see how much horsepower is robbed. naturally aspirated prostock engines run at 16.1 round track engines around 14to 15.1 . I guess youre rebuttal will be that high compression works better in high rpms and not in the low rpms of tractor pulling . the electric motor test proves different though. you can believe everything you test and only half of everything you read.

HERES A FORMULA FOR YOU . GET BACK WITH ME WHEN YOU FIGURE OUT WHAT ITS TELLING YOU. E=1-(1/RK-1)

 

[buickanddeere]

The mechanical compression ratio maybe 14,15 or 16 to 1 but...................Those are extreme rpm engines with very long valve duration.
Cylinder pressures are no higher than an 9 to 1 engine cammed with very short duration.

 

[Anonymous-0]

thanks for the info but still not real clear,if i have a high dome piston and shave the head down to almost zero tolerance does this help or hurt my H.p. ?

 

[Dblair]

if it's a farmall with 4.125 bore 12to1 mechanical compression ratio will get you about 80 hp. that's up a bit from 52 drawbar hp stock.

 

[Anonymous-0]

(quoted from post at 14:22:32 07/31/09) The mechanical compression ratio maybe 14,15 or 16 to 1 but...................Those are extreme rpm engines with very long valve duration.
Cylinder pressures are no higher than an 9 to 1 engine cammed with very short duration.

the formula will show that if you have a 8 to 1 original compression ratio and you increase it to 16 to 1 it will be a 18.6 percent increase now it can be more than that if you change the cam. 8 to 1 up to 12.1 is a 11.5 percent inrease and there again cam profile can help the percentage again . everything in our universe has a scientific equation . Its up to the individual whither they find them and use them or not. no matter what type of chat board they choose to lurk around.

 

[Anonymous-0]

you will always have to have piston to valve clearane and that is critical to the net valve lift as to where the valve will strike the piston remember they move in time with one another so you dont need .400 cause you have a net valve lift of .400

 

[Anonymous-0]

a 9.1 naturally aspirated engine has never nor will it ever need 116 plus octane think about what you wrote the dynamic is still higher on a 16to1 than the static is on a 9to1 .

 

[buickanddeere]

The extreme mechanical compression is used to make up for the loss of expansion ratio with long duration cam's required for high rpms.
A short duration cam on a slow 9 to 1 engine opens just prior to BDC on the power stroke. And obtains an expansion ratio of 7-8 times.
On a high rpm long duration cammed 14 to 1 engine with the exhaust valve opening when the piston is only half way down the power stroke. The expansion ratio is still approx 7-8 times.
There are a lot of losses up front compressing that mixture to 250+ psi. That are hard to make up for when the exhaust valve is opening early. So the engine can breath at high rpms.
The gain in power from compression is not linear. Take a 4 to 1 engine to 8 to 1, great power gains. Now take the same engine to 12 or 16 to 1 and the gains are much less to minimal.

 

[james rumph]

ML , you are debating with the "teacher" when it comes to this topic, i know one of these two gentelmen .

Trust me when i say this !

 

[dan m]

in simpler terms. increase in compression will increase horse power at all r.p.ms.

 

[Anonymous-0]

(quoted from post at 04:41:23 08/01/09)
ML , you are debating with the "teacher" when it comes to this topic, i know one of these two gentelmen .

Trust me when i say this !

Teachers know equations there is no rpm in the equation E stands for otto cycle and k is the coefficient of adiaptic expansion of air.

 

[Anonymous-0]

Thankyou dan

 

[Anonymous-0]

thanks agian you guys, i'm trying to decide what to do to get more power out of a stock puller. At this point it does real well but everyone else seems to be adding to their power so i would like to know what step to take next? Do you think a stroker is the answer?

 

[Anonymous-0]

(quoted from post at 16:08:20 08/02/09) thanks agian you guys, i'm trying to decide what to do to get more power out of a stock puller. At this point it does real well but everyone else seems to be adding to their power so i would like to know what step to take next? Do you think a stroker is the answer?

3 ways of making horsepower relatively cheap is stroke bore and compression . no replacement for displacement.

 

[Gearnut]

LMBky , you have come to the right place !

Mr Plankey will guide you. His vast array of sound bites will lead you in the right direction.

 

[Anonymous-0]

(quoted from post at 19:28:46 08/02/09)
LMBky , you have come to the right place !

Mr Plankey will guide you. His vast array of sound bites will lead you in the right direction.

MCQUIOD youve changed youre login.