Re: NORMAL COMPRESSION???
[Re: Labratt]
#841572
10/29/10 05:51 PM
10/29/10 05:51 PM
|
Joined: Nov 2003
Posts: 6,293 Rock Springs
Bob_Coomer
master
|
master
Joined: Nov 2003
Posts: 6,293
Rock Springs
|
There might be, but hard to say when you have large overlap cams bleeding compression out the exh valve. When you test, make sure you run the test the same way. Like warm the engine up, and test with the carb at WOT. Make sure the battery doesnt run down so you have the same cranking power. This can effect the numbers, or if the engine cools etc. Look at each cylinder and they should be with in 5% of all others. I like my race engine in the 225-250 lbs + range. I healthy street engine should approach 200 psi. But many factors come in play here
[color:"red"]65 Hemi Belvedere coming soon [/color] [color:"#00FF00"]557" Indy engine 1.07 60ft 144mph in the 8th 2100 lbs package [/color]
|
|
|
Re: NORMAL COMPRESSION???
[Re: Bob_Coomer]
#841576
10/29/10 07:24 PM
10/29/10 07:24 PM
|
Joined: Jan 2003
Posts: 4,616 Kissimmee Fl.
dusturbd340W5
master
|
master
Joined: Jan 2003
Posts: 4,616
Kissimmee Fl.
|
my 14-1 small block stroker with a solid roller with 267/272 @ 50 only has 190# and the leakdown is less than 3% and it runs 6.32 at 109 in the 1/8 in a car that is 2975 lbs.
70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake
best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4
|
|
|
Re: NORMAL COMPRESSION???
[Re: Bob_Coomer]
#841577
10/29/10 07:25 PM
10/29/10 07:25 PM
|
Joined: Apr 2010
Posts: 1,049 ohio
all spooled up
super stock
|
super stock
Joined: Apr 2010
Posts: 1,049
ohio
|
my small block 230-235 psi cam is solid roller 650 lift duration at .020 in 296 exh 303 @ .050 263 270 in at 106
Last edited by hookd; 10/29/10 08:53 PM.
|
|
|
Re: NORMAL COMPRESSION???
[Re: all spooled up]
#841579
10/29/10 08:58 PM
10/29/10 08:58 PM
|
Joined: Jan 2007
Posts: 3,695 nc
emarine01
master
|
master
Joined: Jan 2007
Posts: 3,695
nc
|
Quote:
my small block 230-235 psi cam is solid roller 650 lift duration at .020 in 296 exh 303 @ .050 263 270 in at 106
Whats the compression ratio?
|
|
|
Re: NORMAL COMPRESSION???
[Re: emarine01]
#841580
10/29/10 09:02 PM
10/29/10 09:02 PM
|
Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
master
|
master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
|
Quote:
Quote:
my small block 230-235 psi cam is solid roller 650 lift duration at .020 in 296 exh 303 @ .050 263 270 in at 106
Whats the compression ratio?
Based on the PSI though, I will guess, 13.5 or more
|
|
|
Re: NORMAL COMPRESSION???
[Re: Thumperdart]
#841581
10/29/10 09:25 PM
10/29/10 09:25 PM
|
Joined: Dec 2007
Posts: 10,542 BROOK PARK, OH
WILD BILL
Senior Member of the Junior Dragster Club
|
Senior Member of the Junior Dragster Club
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
|
Quote:
Guess our junk`s wore out.
No,
Just points to how inaccurate a compression test is at telling you anything.
About the only thing you can learn from one is if you took one and wrote it down when the engine was built and then compared it to when you think you may have a problem.
I prefer a leak down test myself.
|
|
|
Re: NORMAL COMPRESSION???
[Re: Labratt]
#841585
10/30/10 01:37 AM
10/30/10 01:37 AM
|
Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
master
|
master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
|
Thats more like it. On one of your other threads you registered 185 PSI witch I felt was high for your combo. IMO with around 10.25 Comp and that 262* cam your 170-175 PSI is in the normal range for the combo. Maybe even a little high. But, FWIW, the Calulater that Dodgem posted was Happy about by 20# PSI for my Combo. But with your engine specs, it was almost right on. mike
|
|
|
Re: NORMAL COMPRESSION???
[Re: Bob_Coomer]
#841586
10/30/10 10:44 AM
10/30/10 10:44 AM
|
Joined: Oct 2007
Posts: 4,205 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,205
New York
|
large overlap cams bleeding compression
How exactly does this happen?
Boffin Emeritus
|
|
|
Re: NORMAL COMPRESSION???
[Re: polyspheric]
#841587
10/30/10 10:56 AM
10/30/10 10:56 AM
|
Joined: Feb 2005
Posts: 4,309 Prospect, PA
BSB67
master
|
master
Joined: Feb 2005
Posts: 4,309
Prospect, PA
|
Quote:
large overlap cams bleeding compression
How exactly does this happen?
...out the exhaust valve" ???????
|
|
|
Re: NORMAL COMPRESSION???
[Re: Labratt]
#841588
10/30/10 11:07 AM
10/30/10 11:07 AM
|
Joined: Feb 2005
Posts: 4,309 Prospect, PA
BSB67
master
|
master
Joined: Feb 2005
Posts: 4,309
Prospect, PA
|
Quote:
I just checked a couple of cylinders for S&G's! One was 175psi..the other was 173 or so! Didn't know about holding the carb open,though! Thanks fella's! RandyB
If your doing it for S&G, and you like data, pick a cylinder, get a good consistant technique and baseline numbers, then change your intake lash plus 0.004" and minus 0.004". And then of course report back
|
|
|
Re: NORMAL COMPRESSION???
[Re: BSB67]
#841590
10/30/10 12:24 PM
10/30/10 12:24 PM
|
Joined: Oct 2007
Posts: 4,205 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,205
New York
|
...out the exhaust valve" ???????
Which cam is that where the exhaust valve is open during the compression stroke?
Boffin Emeritus
|
|
|
Re: NORMAL COMPRESSION???
[Re: polyspheric]
#841591
10/30/10 12:36 PM
10/30/10 12:36 PM
|
Joined: Feb 2005
Posts: 4,309 Prospect, PA
BSB67
master
|
master
Joined: Feb 2005
Posts: 4,309
Prospect, PA
|
Quote:
...out the exhaust valve" ???????
Which cam is that where the exhaust valve is open during the compression stroke?
I think you failed to understand my post. Obvously none, that's why there are the question marks. I'm quoting the other poster.
|
|
|
Re: NORMAL COMPRESSION???
[Re: BSB67]
#841592
10/30/10 05:09 PM
10/30/10 05:09 PM
|
Joined: Oct 2007
Posts: 4,205 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,205
New York
|
You're right, sorry, yes I understood your comment to mean "Whaaaa?". Was referring to prior comment.
Boffin Emeritus
|
|
|
Re: NORMAL COMPRESSION???
[Re: polyspheric]
#841593
10/30/10 05:24 PM
10/30/10 05:24 PM
|
Joined: Jan 2003
Posts: 4,616 Kissimmee Fl.
dusturbd340W5
master
|
master
Joined: Jan 2003
Posts: 4,616
Kissimmee Fl.
|
But, FWIW, the Calulater that Dodgem posted was Happy about by 20# PSI for my Combo. But with your engine specs, it was almost right on. mike it's not even close for my motor and as stated my leak down is less than 3% so I know it is sealed up well I also know someone that there roundy round motor is well over 600hp and only 165 cranking compression.
70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake
best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4
|
|
|
Re: NORMAL COMPRESSION???
[Re: dusturbd340W5]
#841594
10/30/10 05:34 PM
10/30/10 05:34 PM
|
Joined: Jan 2003
Posts: 17,916 Akron, Ohio
ProSport
I Live Here
|
I Live Here
Joined: Jan 2003
Posts: 17,916
Akron, Ohio
|
I run a big overlap pump gas cam, I get 150 cranking compression. I put one gallon of 110 race gas in the tank when I race but don't need to. I've used lawn mower gas to drive to a local car show before, and still goes 9.80's. If I go E85 this winter, it will get a better cam for performance.
1970 Challenger, all aluminum 528 Hemi, HDK suspension, Tremec 5 speed manual
|
|
|
Re: NORMAL COMPRESSION???
[Re: Labratt]
#841595
10/30/10 05:44 PM
10/30/10 05:44 PM
|
Joined: Apr 2006
Posts: 3,675 Akron, Ohio U.S.A.
roadhazard
master
|
master
Joined: Apr 2006
Posts: 3,675
Akron, Ohio U.S.A.
|
Quote:
BTW...how important is it to have the butterflies partially open,as Hardcore suggests?
LABRATT, I feel it's very important. With the throttle closed can cause a restriction and produce lower than normal cranking compression readings
My personal preferance is to set the carb @ WOT when testing. Usually I'll hold it open with a wire or use the return spring to hold it FWIW.
Don't forget to return the throttle closed before you start the motor again
|
|
|
Re: NORMAL COMPRESSION???
[Re: Dodgem]
#841597
10/30/10 08:52 PM
10/30/10 08:52 PM
|
Joined: Jan 2003
Posts: 4,616 Kissimmee Fl.
dusturbd340W5
master
|
master
Joined: Jan 2003
Posts: 4,616
Kissimmee Fl.
|
yep carb wide open or removed and all 8 plugs removed and a battery charger hokked up and running is how I do it.
70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake
best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4
|
|
|
Re: NORMAL COMPRESSION???
[Re: polyspheric]
#841598
10/30/10 09:05 PM
10/30/10 09:05 PM
|
Joined: Dec 2008
Posts: 1,200 UK
602heavy
pro stock
|
pro stock
Joined: Dec 2008
Posts: 1,200
UK
|
Quote:
large overlap cams bleeding compression
How exactly does this happen?
My thoughts exactly , overlap has no bearing on compression whatsoever.
|
|
|
|
|