Wrong Harmonic balancer?
Thread Starter
POSSE ZR-1 Driver
Joined: Feb 2002
Posts: 3,980
Likes: 138
From: Groton CT
Wrong Harmonic balancer?
When I built the motor for my car a few years ago, I turned the NOM 327/300 into a 327/365.
The car has not had as much power as I thought it should have, so I put it on a chassis dyno a few months ago and could only get 190 rwhp out of it.
In the last couple of weeks, I've been putting a lot of effort into getting it to run better, including a complete distributor rebuild with a correct main shaft.
I've always had the initial timing set at 10* btdc. Last weekend I started bumping the timing up a few degrees at a time and taking a test drive.
What I have ended up with so far is 15* initial, all in (about 40*, vacuum can disconnected) at 2800 rpm. The car is much more "peppy". Feels like it could still use more timing.
Since these numbers don't seem to make much sense, I'm thinking I have the correct timing cover, but have the the wrong 8" balancer (newer than '69 style). When the weather clears, I'm going to try about 20* initial. If I don't get any detonation, then I'll pull the #1 plug and see where TDC really is.
Thoughts?
The car has not had as much power as I thought it should have, so I put it on a chassis dyno a few months ago and could only get 190 rwhp out of it.
In the last couple of weeks, I've been putting a lot of effort into getting it to run better, including a complete distributor rebuild with a correct main shaft.
I've always had the initial timing set at 10* btdc. Last weekend I started bumping the timing up a few degrees at a time and taking a test drive.
What I have ended up with so far is 15* initial, all in (about 40*, vacuum can disconnected) at 2800 rpm. The car is much more "peppy". Feels like it could still use more timing.
Since these numbers don't seem to make much sense, I'm thinking I have the correct timing cover, but have the the wrong 8" balancer (newer than '69 style). When the weather clears, I'm going to try about 20* initial. If I don't get any detonation, then I'll pull the #1 plug and see where TDC really is.
Thoughts?
Thread Starter
POSSE ZR-1 Driver
Joined: Feb 2002
Posts: 3,980
Likes: 138
From: Groton CT
Race Director
Joined: Oct 2005
Posts: 12,468
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From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
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Find TDC and check it vs the balancer mark.
They make a tool for this that you insert in the #1 spark plug hole, you take out all the other plugs and rotate the motor by hand, fore and back and mark the two stop points in the balancer, exactly halfway in between is TDC. That should correspond to the mark on the balancer.
You do have 11:1 comp pistons for that cam, right? Are you sure the cam is indexed correctly? A dial indicator on #1 intake vs the cam card will tell you that.
Doug
They make a tool for this that you insert in the #1 spark plug hole, you take out all the other plugs and rotate the motor by hand, fore and back and mark the two stop points in the balancer, exactly halfway in between is TDC. That should correspond to the mark on the balancer.
You do have 11:1 comp pistons for that cam, right? Are you sure the cam is indexed correctly? A dial indicator on #1 intake vs the cam card will tell you that.
Doug
Instructor
Joined: Dec 2006
Posts: 211
Likes: 2
From: peshastin wa.
You answered your own question, physically find TDC of #1, check markers. In the past I have taken degree tape and put on the hormonic THAN with a punch permanatly mark TDC, 5 deg., 10 deg., and so on. The tape will eventually "fly off".
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
When I built the motor for my car a few years ago, I turned the NOM 327/300 into a 327/365.
The car has not had as much power as I thought it should have, so I put it on a chassis dyno a few months ago and could only get 190 rwhp out of it.
In the last couple of weeks, I've been putting a lot of effort into getting it to run better, including a complete distributor rebuild with a correct main shaft.
I've always had the initial timing set at 10* btdc. Last weekend I started bumping the timing up a few degrees at a time and taking a test drive.
What I have ended up with so far is 15* initial, all in (about 40*, vacuum can disconnected) at 2800 rpm. The car is much more "peppy". Feels like it could still use more timing.
Since these numbers don't seem to make much sense, I'm thinking I have the correct timing cover, but have the the wrong 8" balancer (newer than '69 style). When the weather clears, I'm going to try about 20* initial. If I don't get any detonation, then I'll pull the #1 plug and see where TDC really is.
Thoughts?
The car has not had as much power as I thought it should have, so I put it on a chassis dyno a few months ago and could only get 190 rwhp out of it.
In the last couple of weeks, I've been putting a lot of effort into getting it to run better, including a complete distributor rebuild with a correct main shaft.
I've always had the initial timing set at 10* btdc. Last weekend I started bumping the timing up a few degrees at a time and taking a test drive.
What I have ended up with so far is 15* initial, all in (about 40*, vacuum can disconnected) at 2800 rpm. The car is much more "peppy". Feels like it could still use more timing.
Since these numbers don't seem to make much sense, I'm thinking I have the correct timing cover, but have the the wrong 8" balancer (newer than '69 style). When the weather clears, I'm going to try about 20* initial. If I don't get any detonation, then I'll pull the #1 plug and see where TDC really is.
Thoughts?
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,925
From: Washington Michigan
The correct balancer for a Corvette application has the timing index line on the inertia ring directly in line with the keyway slot in the hub; passenger car balancers changed in 1969 by moving the index line 10* counter-clockwise from the keyway slot (and their timing cover tabs also moved the same amount). Photo below is a Camaro 8" balancer, but it shows the location of both marks. 
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Racer
Joined: Apr 2008
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From: PASADENA CALIFORNIA
What pistons do you have?
If you are running a 30-30 cam with Flat top Pistons, your engine will run very flat. Adding more timimg will help a little but that is just masking the problem of not enough compression.
Chris, CWPASADENA
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
The correct balancer for a Corvette application has the timing index line on the inertia ring directly in line with the keyway slot in the hub; passenger car balancers changed in 1969 by moving the index line 10* counter-clockwise from the keyway slot (and their timing cover tabs also moved the same amount). Photo below is a Camaro 8" balancer, but it shows the location of both marks.
Page 38 of the Chevy Power book, Seventh Edition, 2/94, says that the pre-69 balancers had the TDC mark 2 degrees advanced (CCW from the keyway), and that later balancers moved the TDC mark 10 degrees advanced (CCW) from the keyway. So, which is correct for pre-69 alignment - 2 deg CCW or in line with the keyway? Is this an error in the Chevy Power book?
Thanks
Thread Starter
POSSE ZR-1 Driver
Joined: Feb 2002
Posts: 3,980
Likes: 138
From: Groton CT
Not 11:1, but a calculated 10.65:1. Also running the 70 LT-1 cam instead of the 30-30.
Melting Slicks
Joined: Jul 2004
Posts: 2,864
Likes: 195
From: Maryland
The stock ignition curve for 327-365 is the most aggressive curve that GM specified.
Start @ 800 RPM
15* @ 1600 RPM
24* @ 2300 RPM
You could probably bring your curve in faster w. detonation the limiting factor. Start w. an initial timing of 12* and bump higher till you run into knocking. This will increase your low end torque. Use a B 28 VAC for good idle and control of excess EGT. Also use HD points ( BWD 112 hp) and a non emissions rotor & cap.
Start @ 800 RPM
15* @ 1600 RPM
24* @ 2300 RPM
You could probably bring your curve in faster w. detonation the limiting factor. Start w. an initial timing of 12* and bump higher till you run into knocking. This will increase your low end torque. Use a B 28 VAC for good idle and control of excess EGT. Also use HD points ( BWD 112 hp) and a non emissions rotor & cap.
Last edited by Donald #31176; Oct 4, 2009 at 10:48 AM.
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,925
From: Washington Michigan
Question for John...
Page 38 of the Chevy Power book, Seventh Edition, 2/94, says that the pre-69 balancers had the TDC mark 2 degrees advanced (CCW from the keyway), and that later balancers moved the TDC mark 10 degrees advanced (CCW) from the keyway. So, which is correct for pre-69 alignment - 2 deg CCW or in line with the keyway? Is this an error in the Chevy Power book?
Thanks
Page 38 of the Chevy Power book, Seventh Edition, 2/94, says that the pre-69 balancers had the TDC mark 2 degrees advanced (CCW from the keyway), and that later balancers moved the TDC mark 10 degrees advanced (CCW) from the keyway. So, which is correct for pre-69 alignment - 2 deg CCW or in line with the keyway? Is this an error in the Chevy Power book?
Thanks
