cranking compression

[randy wilson]

Does high cranking compression slow a car down?

[JOE B]

Maybe.. need alot more info to get a better answer.

[SSDiv6]

Originally Posted by JOE B

Maybe.. need alot more info to get a better answer.

X2
Need specifics about the engine such as type of cylinder head, static compression, cam type, etc...

[Mike Taylor 3601]

depends on why you have high cranking compression? Cam advanced will raise cranking
compression as one example,duration, overlap changes cranking compression,valve lash can change it.
compression works both ways like high spring pressure you have one cyl. compressing have another that just fired and is pushing another piston down. just like on valve springs people claim strong springs use power,but when you are opening one valve another is closing it evens it out. proof of that is turn engine with one valve adjusted it will be all you can do to turn engine each one you set engine gets easier to turn when all are set engine turns easy .
have you raced much this year? I got to go about 4 times set IHRA F/PS record at Mountain Park Pro Am 4th July weekend went 7.997. May go to UMTR race at Owingsville Ky. this weekend maybe Doorslammers at Ohio Valley.
Maybe give more info on what you've got going on might be able to help give me call if need to.
Mike Taylor 3601

[art leong]

Originally Posted by Mike Taylor 3601

depends on why you have high cranking compression? Cam advanced will raise cranking
compression as one example,duration, overlap changes cranking compression,valve lash can change it.
compression works both ways like high spring pressure you have one cyl. compressing have another that just fired and is pushing another piston down. just like on valve springs people claim strong springs use power,but when you are opening one valve another is closing it evens it out. proof of that is turn engine with one valve adjusted it will be all you can do to turn engine each one you set engine gets easier to turn when all are set engine turns easy .
have you raced much this year? I got to go about 4 times set IHRA F/PS record at Mountain Park Pro Am 4th July weekend went 7.997. May go to UMTR race at Owingsville Ky. this weekend maybe Doorslammers at Ohio Valley.
Maybe give more info on what you've got going on might be able to help give me call if need to.
Mike Taylor 3601

Another weird note is that 4 cyl DOHC motors can get awful high and still like it. I run 290 pounds. Got crazy when I found out tried to lower it and ran a lot slower.
Now I just accept it as one of those things I don't understand. Like how they get those ships in the bottles. LOL

[randy wilson]

Thanks guys, here's some details, advanced cam 1 degree, widened valve lash .003, went from 213 to 256 cranking compression, picked up 19 lbs torque, 21 hp with single 4, 51 hp 39 lbs. torque with duels, slowed down a tenth and 3 mph, doesn't make sense to me. The reason we don't go back is we tightened up compression, and that's where everything has to be set. Maybe we just haven't found the sweet spot yet. Will be running at eddyville this weekend in the last modified lbs. per cube, no break-out race this weekend, and we need to have our ducks in a row.

[Robert Simpson]

Originally Posted by randy wilson

Thanks guys, here's some details, advanced cam 1 degree, widened valve lash .003, went from 213 to 256 cranking compression, picked up 19 lbs torque, 21 hp with single 4, 51 hp 39 lbs. torque with duels, slowed down a tenth and 3 mph, doesn't make sense to me. The reason we don't go back is we tightened up compression, and that's where everything has to be set. Maybe we just haven't found the sweet spot yet. Will be running at eddyville this weekend in the last modified lbs. per cube, no break-out race this weekend, and we need to have our ducks in a row.

Compaired to your original combination, did the new power happen at the same spot in the torque curve? We had a similar situation but the combination of the engine on the dyno did not match what the car liked, we had to change the car to fit the new curve of the engine. In our case we had to change low gear and shift points. That is a big change with 1 deg of cam movement. Good luck.

[randy wilson]

Pretty much the same, peak torque at 7900, peak power at 9400. The cam movement was only part of it, tightened clearances for more compression, and different ring package. Actually, it surprised me how much the cylinder pressure went up. Same dyno, same operator.

[randy wilson]

Jeff, i agree, i've never had a motor slow down after a gain on the dyno. We always have ran more speed than ET, not uncommon. Ring seal is 1 percent or less. Last year was at 6 percent. Vac went from 17.89 inches to 20.13. Star vac pump. Don't know all the answers, or the car would be running 5.70, 120 mph. But something is not jiving, and we will see this weekend.
All these are 1/8 mile times.

[Mike Taylor 3601]

Are you just looking at increase at peaks? Look at hp&tq average #s over whole pull if you are'nt ,if you gain @ peaks but averaged #'s are less it will be slower to be faster you have raise average #.
Mike Taylor 3601