cranking compression

randy wilson · 09-07-2010, 06:29 AM

Does high cranking compression slow a car down?

JOE B · 09-07-2010, 09:35 PM

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

SSDiv6 · 09-08-2010, 11:22 AM

Quote:

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 · 09-08-2010, 07:23 PM

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 · 09-08-2010, 09:34 PM

Quote:

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 · 09-09-2010, 06:31 AM

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.

Mart Jeltema · 09-09-2010, 02:06 PM

Mike Taylor is correct. If the average is better, then look at the jetting. When my Brake Specific # looked good on the dyno and didn't perform on the race track thats where I head. I have found on a car with a hood scoop needed to increase the jet size. On my single carb 750 I had to increase the jets 3-4 #'s.

randy wilson · 09-09-2010, 12:33 PM

We are up 3 sizes since dyno. It was real slow before that.

Jeff Lee · 09-09-2010, 08:17 PM

Quote:

Originally Posted by randy wilson

We are up 3 sizes since dyno. It was real slow before that.

Then keep going bigger until it slows

junior barns · 09-09-2010, 09:40 PM

what happens when you have no scoop and not much hood to carb clearance?

09-07-2010, 06:29 AM	#1
randy wilson Senior Member Join Date: Jan 2007 Location: N/A Posts: 882 Likes: 0 Liked 22 Times in 22 Posts	cranking compression Does high cranking compression slow a car down? __________________ don,t have one

09-07-2010, 09:35 PM	#2
JOE B Junior Member Join Date: Dec 2006 Location: n.j. Posts: 55 Likes: 0 Liked 0 Times in 0 Posts	Re: cranking compression Maybe.. need alot more info to get a better answer.

09-08-2010, 07:23 PM	#4
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,371 Likes: 352 Liked 306 Times in 103 Posts	Re: cranking compression 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

09-09-2010, 06:31 AM	#6
randy wilson Senior Member Join Date: Jan 2007 Location: N/A Posts: 882 Likes: 0 Liked 22 Times in 22 Posts	Re: cranking compression 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. __________________ don,t have one

09-09-2010, 02:06 PM	#7
Mart Jeltema Junior Member Join Date: Feb 2007 Posts: 37 Likes: 0 Liked 10 Times in 2 Posts	Re: cranking compression Mike Taylor is correct. If the average is better, then look at the jetting. When my Brake Specific # looked good on the dyno and didn't perform on the race track thats where I head. I have found on a car with a hood scoop needed to increase the jet size. On my single carb 750 I had to increase the jets 3-4 #'s.

09-09-2010, 12:33 PM	#8
randy wilson Senior Member Join Date: Jan 2007 Location: N/A Posts: 882 Likes: 0 Liked 22 Times in 22 Posts	Re: cranking compression We are up 3 sizes since dyno. It was real slow before that. __________________ don,t have one

09-09-2010, 09:40 PM	#10
junior barns Senior Member Join Date: Jun 2006 Posts: 541 Likes: 11 Liked 20 Times in 14 Posts	Re: cranking compression what happens when you have no scoop and not much hood to carb clearance?