Lost My Lope
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
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From: Bishop CA
Lost My Lope
A couple of months ago I had a different cam put in my 75 SB. I previously had a Crower 241 and wasn't happy with the sound and performance. The new cam sounded great, I had people commenting on how great the motor sounded. Performance was improved but not a lot. A couple of weeks ago I installed a aftermarket HEI. It seemed like immediately there was no lope to the cam. My initial was at ten degrees and still is. This might just be a coincidence that I noticed it at about the same time. Could something else be happening besides the HEI to take away the lope. Performance seems about the same as it did right after the cam was installed. Any ideas. Thanks in advance.
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
Likes: 0
From: Bishop CA
a couple of months ago i had a different cam put in my 75 sb. I previously had a crower 241 and wasn't happy with the sound and performance. The new cam sounded great, i had people commenting on how great the motor sounded. Performance was improved but not a lot. A couple of weeks ago i installed a aftermarket hei. It seemed like immediately there was no lope to the cam. My initial was at ten degrees and still is. This might just be a coincidence that i noticed it at about the same time. Could something else be happening besides the hei to take away the lope. Performance seems about the same as it did right after the cam was installed. Any ideas. Thanks in advance.
Le Mans Master
Joined: Apr 2005
Posts: 6,347
Likes: 418
From: Seattle Area WA
If your vaccum advance wasn't working correctly and the timing was retarded it might lope more. What are the specs on the new cam? That lopey sound is all due to the duration, overlap and LSA. Was your vacuum advance can working on the old distributor, is there any difference in advance bewtween the two distributors when the vacuum hose is hooked up?
Last edited by Scott Marzahl; Jul 3, 2011 at 11:18 AM.
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
Likes: 0
From: Bishop CA
If your vaccum advance wasn't working correctly and the timing was retarded it might lope more. What are the specs on the new cam? That lopey sound is all due to the duration, overlap and LSA. Was your vacuum advance can working on the old distributor, is there any difference in advance bewtween the two distributors when the vacuum hose is hooked up?
Le Mans Master
Joined: Apr 2005
Posts: 6,347
Likes: 418
From: Seattle Area WA
That seems like too much timing, 36 by 2,700-3,000 RPM is more common. I would start by removing the vacuum hose and see where your timing is at 3,000 RPM. It should be 36 degrees at 3,000 RPM.
Last edited by Scott Marzahl; Jul 3, 2011 at 12:00 PM.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
i am 100 % sure it is timing related.....look at the springs on the weights and see if they are the same as the new ones.... and hook up vaccum gauge/pump to old vacuum cannister and see how much vacuum it takes to make it move and then do same with the hei unit....if you make the hei unit have the same settinjgs as the points one the lope will come back
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
Likes: 0
From: Bishop CA
i am 100 % sure it is timing related.....look at the springs on the weights and see if they are the same as the new ones.... and hook up vaccum gauge/pump to old vacuum cannister and see how much vacuum it takes to make it move and then do same with the hei unit....if you make the hei unit have the same settinjgs as the points one the lope will come back
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
you really want to duplicate what you had....did you change the port you had the vacuum cannister hooked up to? that would cahnge the lope
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Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
un plug your vacuum cannister and see if it brings your lope back....i wonder like scott was getting at if your old vacuum cannister was shot and not pulling in any vacuum or even worse creating a vacuum leak...try leaving the vacuum line open when you unplug the vacuum cannister and see if the loope comes back....vacuum leaks create lopes
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
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From: Bishop CA
un plug your vacuum cannister and see if it brings your lope back....i wonder like scott was getting at if your old vacuum cannister was shot and not pulling in any vacuum or even worse creating a vacuum leak...try leaving the vacuum line open when you unplug the vacuum cannister and see if the loope comes back....vacuum leaks create lopes
Le Mans Master
Joined: Apr 2005
Posts: 6,347
Likes: 418
From: Seattle Area WA
Verify timing without vacuum at 3,000 to start with, then hook it up and see where it goes at 3,000. This it totally a timing thing. Have you read the Lars timing sticky at the top? By cannister Bob means the vacuum advance can.
Last edited by Scott Marzahl; Jul 3, 2011 at 12:21 PM.
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
Whats wrong with a smoother idle, and might be your new distributor has a multi-spark module in it. I've put together a few motors with bigger cams, and while seperate boxes in my case, found MSD multi-sparks tamed lumpy idles down quite a bit.
Le Mans Master
Joined: Apr 2005
Posts: 6,347
Likes: 418
From: Seattle Area WA
Lets get the actual timing numbers pinned down first and see where he is actually at. Is the 40 degrees at 2,500 RPM with vacuum hooked up or not, is he using full manifold vacuum port for timing or not?
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
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From: Bishop CA
I was wrong its 38 degrees at 2500 with vacuum disconected. Vacuum hose from dist is running into front of edelbrock 650 carb.
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
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From: Bishop CA
There is nothing wrong with a smoother idle if thats what you want, just so happens I just paid $1100 to install a bigger cam with a lope. As far as whether the dist has a multi spark is not known to me, I bought it from a guy at a car show with no info. But it is new.
Le Mans Master
Joined: Apr 2005
Posts: 6,347
Likes: 418
From: Seattle Area WA
That is pretty high, set it at 36 at 3,000 and see how it goes. BTW, what was your total timing reading? Also what is your idle RPM set to? Should be around 900ish RPMs.
Last edited by Scott Marzahl; Jul 3, 2011 at 02:45 PM.
Le Mans Master
Joined: May 2006
Posts: 9,993
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From: League City Tx
Cam going flat.....LOL (hopefully not)..
Me thinks your tune up is just better now since the new dizzy is in....Likely multiple spark smoothing it out...
Sometimes lumpy idles are caused by other things...non-performance things...
I had an old 400 Pontiac with a crane 290H cam that had a decent sound to it, slightly lopy idle but fairly mild.....Well when I hooked up the oem EGR valve, it sounded like I put big ole nasty solid flat tappet in it.....Really lumpy/choppy idle...but it would smooth out at 1600rpms or so and ran fine everywhere else....only at idle was it nasty......Disconnect the hose to the EGR valve and it would smooth back out at idle again... This was obviously not lumpy in a "good" way....,,
Me thinks your tune up is just better now since the new dizzy is in....Likely multiple spark smoothing it out...
Sometimes lumpy idles are caused by other things...non-performance things...
I had an old 400 Pontiac with a crane 290H cam that had a decent sound to it, slightly lopy idle but fairly mild.....Well when I hooked up the oem EGR valve, it sounded like I put big ole nasty solid flat tappet in it.....Really lumpy/choppy idle...but it would smooth out at 1600rpms or so and ran fine everywhere else....only at idle was it nasty......Disconnect the hose to the EGR valve and it would smooth back out at idle again... This was obviously not lumpy in a "good" way....,,
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
Wow, it's all about perspective, ain't it? When I first read the OP's post, I wanted to post saying congrats on getting rid of the screwy idle. But then I read further, and find that he is disappointed that it is gone!! Just play with the idle screws until it idles poorly again, that's all.
Scott
Scott
Thread Starter
Racer
Joined: Oct 2010
Posts: 474
Likes: 0
From: Bishop CA
Wow, it's all about perspective, ain't it? When I first read the OP's post, I wanted to post saying congrats on getting rid of the screwy idle. But then I read further, and find that he is disappointed that it is gone!! Just play with the idle screws until it idles poorly again, that's all.
Scott
Scott