Aftermarket advance spring kit Mr. Gasket 928G

[Jim V.]

Duke et. al.

I have tested the black and the gold springs included in the Mr. Gasket advance spring kit on my freshly rebuilt 1965 L75. The black is considered their light spring, while the gold is considered their heavy spring. I did not test their supplied silver spring but I expect we can extrapolate between the light and heavy. I had limited time and tools. I had some limitations during the test since I was alone and I had to rely on my dash tachometer. This meant I had to set a rpm and then measure the timing. So...I measured timing at 600 rpm, 1500 rpm , 2000 rpm, and max with the VAC disconnected and with 8* initial advance at idle.

Centrifugal Advance Results..
Black 0,25,25,25,27
Gold 0,16,21,21,26
OE Spec 0,15,--,--,26

Needless to say I am going with the Gold set and will see if detonation is an issue. If so I will try to a less aggressive curve with a set of aftermarket L75/L79 springs (gm 1884095). Are these available anywhere other than LIC's kit? Corvette Specialty Products used to offer them but I believe they may be long-gone.

[Mark #28455]

Re: Aftermarket advance spring kit Mr. Gasket 928G

In the "good old days" I typically found that the aftermarket springs were MUCH lighter than stock. To get the advance curve "all in" at about 3000 RPM usually required one of the "heavier" aftermarket springs and one of the stock springs. If I used both "heavier" aftermarket springs there didn't seem to be enough spring tension to get the initial timing back down above idle, so it was very hard to get a stable idle timing setting.

Mark

[Duke W.]

Re: Aftermarket advance spring kit Mr. Gasket 928G

I don't understand your data. You said you tested at 600, 1500, and 2000, but you have five data points for each spring set.

The OE spec for a '65 300 HP engine is:

0@700 (start)
15@1500
26@4100(maximum)

Can you post the data in this format? Make sure you annotate the "start" and "maximum" points and as many intermediate points as you have.

Also, I'd like to see a data point for the OE springs in the 3000-3500 range.

Duke

[John D.]

Re: Aftermarket advance spring kit Mr. Gasket 928G

Jim, You really are working hard at this project I see but in my humble opinion you should have the distributor spun in a good Sun or Allen Distributor machine. It's highly unlikely the Mr. Gasket kit is any good for your application. At least we haven't found that kit to be correct no matter which color of spring is used. Good luck, JD

[Jim V.]

Re: Aftermarket advance spring kit Mr. Gasket 928G

Yeah...ignore fourth data point. so should have read
Black 0,25,25,27
Gold 0,16,21,26
OE 0,15,--,26

Due to the reasons mentioned earlier these readings are at 600rpm, 1500rpm, 2000rpm, and max. Did not document start. Hope it helps. Duke, did you ever get any Moroso results...?

[Jim V.]

Note the OE is spec not as tested...

My as tested with the OE springs was very strange. I posted those numbers in my earlier thread. Note that for that earlier test my procedure was different...I did not disconnect the VAC and deducted my initial and VAC advance (8+16=24) from my measurement to back into my C.A.

At 600, 1500, 2000, and max rpm my C.A. was:
0,18,21,22.

[Duke W.]

Re: Note the OE is spec not as tested...

So what was the RPM that maximum advance was achieved.

Please present the data in a format that makes it clear what the data says.

Duke

[Jim V.]

Re: Aftermarket advance spring kit Mr. Gasket 928G

Mark I agree, but maybe since this L75 idles at 600 it is not an issue. I am sure with a bumpy cam with an idle above 750 it could be. Despite this car being very original the OE spring curve was very early/aggressive. I measured the OE spring free-length and compared to the parts catalog they seemed a tad long and loose. Can OE L75/L79 springs still be found...? I would like to test with another pair.

[Jim V.]

Re: Note the OE is spec not as tested...

Sorry Duke...I don't have the max rpm. From the engine bay I hand revved the motor to see where the advance maxed out. I had no way of reading the tach from the engine bay.

[Jim V.]

Re: Aftermarket advance spring kit Mr. Gasket 928G

Thanks JD...that of course would be the gold standard.

[Duke W.]

Re: Note the OE is spec not as tested...

Find a helper to run the throttle while you handle the timing light. Use a known accurate test tach if possible and take a reading at the start point, then 1000, 1500,... in 500 RPM increments until it maxes out and record that speed.

I usually do the test twice and look for the same results to ensure the data is accurate.

Duke

[Timothy B.]

Re: Aftermarket advance spring kit Mr. Gasket 928G

My experence with these kits is that the silver springs are the lightest then black/gold. I set a 65 L79 distributor and changed the weight base from #530 to #726 because the slot is a little smaller, then used the silver springs with original weights and mainshaft 0@800 - 6@1000 - 18@1500 - 20@2000 - 22@2500 - 24@3000 - 26@3200 Sorry for the long post but the car seems to run good, the black springs yielded 26@4000 and the gold 26@5000 so the choice was easy. I agree with John about distributor machine testing.

[Duke W.]

Re: Aftermarket advance spring kit Mr. Gasket 928G

That's a pretty good curve, and it should run well with 10-12 initial. The ideal SB total WOT timing would be to get 34 by about 2500 (assuming this is possible without detonation) and then an additional degree per thousand revs to achieve 38@6500.

The early 24 degrees distributors have a fairly linear curve, but the later distributors with over 24 degrees attempt to duplicate the above.

According to Taylor if timing is retarded 3 degrees from optimum the power loss is about one percent, so there is some wiggle room.

Duke