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Timing a MG 1500 with modifications
- Thread starter jbuffalo
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RonMacPherson
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One sure way is to use a vacuum gauge. Warm the engine up, a drive around a long block is good. Hook up the vacuum gauge to manifold vacuum, a port below the throttles. Turn the distributor to where the vacuum reading is the highest, then back off 2 degrees.
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RonMacPherson
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Basic auto shop taught back in the 60's followed up by the old Motor's manual tuning guides, remember the old cloth covered ones? AHM factory schooling, VW factory schooling, Porsche factory schooling, all taught the same thing. Gotta remember this was back when they were all carbureted.
Now if you're doubting my advice, please do research on it. You will find info supporting it.
Ideally, the max engine timing efficiency will result in maximum vacuum. I know it works on the early MG A's and B's.
Late rubber bumper B that a friend had was not so receptive, as the cam timing and grind was set for max smog inefficiency. We could turn the distributor pretty much full span and vacuum would barely change and co/hc was also minimally affected. Which should have also had a large change.
If you don't want to use a vacuum gauge, find a gas analyzer and he can help you set the timing(to a degree) by watching the HC change.
Now if you're doubting my advice, please do research on it. You will find info supporting it.
Ideally, the max engine timing efficiency will result in maximum vacuum. I know it works on the early MG A's and B's.
Late rubber bumper B that a friend had was not so receptive, as the cam timing and grind was set for max smog inefficiency. We could turn the distributor pretty much full span and vacuum would barely change and co/hc was also minimally affected. Which should have also had a large change.
If you don't want to use a vacuum gauge, find a gas analyzer and he can help you set the timing(to a degree) by watching the HC change.
jcatnite
Jedi Knight
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A vacuum gauge will get you very close. I often end up a little advanced when I use a vacuum gauge. My 76 seems to be happy at around 14 degrees btc. With a vacuum gauge the best vacuum seems to be around 20 - 22 degrees. I get a lot of spark knock at that point. I recently switched to a 45D setup by Jeff of Advanced Distributors. 14 degrees works great with that dizzy and advance curve.
JC
JC
aeronca65t
Great Pumpkin
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Personally, I ignore timing at idle speed in a car that is used for high performance.
Best bet is to time for max advance and let idle timing spec fall where it may (assuming the car will start and idle OK).
To do this, I guesstimate a max advance based on fuel available. Then I test for spark-knock (or detonation, or pinging or whatever you want to call it) and I adjust timning as needed. A good place to start for most cars is around 30 degrees of max timing advance, generally set at a fairly high rpm.
As it so happens, I have a mildly modified 1500 Spridget with 10:1 compression, Euro-cam specs, 2-1/8" race carb, mild port matching, header, etc.
On street fuel (93 octane RON), I am able to run around 26 to 28 degrees max advance (I set it at 5000 rpm). For race fuel (in my case, Sunoco GT 100 unleaded), the engine can tolerate a max advance of 32 degreees total.
The street Midget above would probably work out well if set for about 26 degrees max advance at 5000 rpm (on premium street fuel).
Obviously, you need a degree wheel or marks on the front timing pulley to measure this. I simply marked the front pulley from 24 to 36 degrees and use a non-adjustable timing light.
Again, this is in response to the needs of a car that is modified for perfomance and assumes the car running at relatively high rpms and hard acceleration.
For street cars, where smooth idling is important, low speed timing may be more important.
I haven't a clue where my timing is at idle speed.
Best bet is to time for max advance and let idle timing spec fall where it may (assuming the car will start and idle OK).
To do this, I guesstimate a max advance based on fuel available. Then I test for spark-knock (or detonation, or pinging or whatever you want to call it) and I adjust timning as needed. A good place to start for most cars is around 30 degrees of max timing advance, generally set at a fairly high rpm.
As it so happens, I have a mildly modified 1500 Spridget with 10:1 compression, Euro-cam specs, 2-1/8" race carb, mild port matching, header, etc.
On street fuel (93 octane RON), I am able to run around 26 to 28 degrees max advance (I set it at 5000 rpm). For race fuel (in my case, Sunoco GT 100 unleaded), the engine can tolerate a max advance of 32 degreees total.
The street Midget above would probably work out well if set for about 26 degrees max advance at 5000 rpm (on premium street fuel).
Obviously, you need a degree wheel or marks on the front timing pulley to measure this. I simply marked the front pulley from 24 to 36 degrees and use a non-adjustable timing light.
Again, this is in response to the needs of a car that is modified for perfomance and assumes the car running at relatively high rpms and hard acceleration.
For street cars, where smooth idling is important, low speed timing may be more important.
I haven't a clue where my timing is at idle speed.
R
RonMacPherson
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backing off is retarding. This is what I used to do using a Clayton(anyone remember them?) chassis dyno.
Ran a 14 car line diagnostic center once upon a time, back in the days of youthful omniscience.
A lot of the cars that would come over my dyno wheels were ones that finding timing information was next to impossible, so good old mechanical engineering application was sometimes necessary.
Anyone ever have to find timing for a "deux chevaux"?
Ran a 14 car line diagnostic center once upon a time, back in the days of youthful omniscience.
A lot of the cars that would come over my dyno wheels were ones that finding timing information was next to impossible, so good old mechanical engineering application was sometimes necessary.
Anyone ever have to find timing for a "deux chevaux"?