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 Qjet setup for a 400 performance build 
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 25
TDC verified several times from short block stage with a dial indicator and again with a piston stop with heads on. Cam was originally for a 10:1 383 but degreed it per Mike Jones 106ICL instead of 104ICL since the compression got bumped almost a point on this 400. I'm glad I set it at 106.


Sat May 06, 2017 9:24 pm
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 25
I've found the engine wants alot of initial advance and not too much total. 30total is a sweet spot but idle sucks because then I'm only 8-10 initial. Just for kicks I set initial at about 24 and vacuum peaked at 13.5. That initial is not gonna work with the distributor curve I have now where travel is about 22 degrees.


Sat May 20, 2017 7:50 pm
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
Remove the rotor and take a picture of the advance mechanism from about a foot above or so, so the mechanism of the weights, springs and advance cam fills the image, so exactly what you have to work with is easy to see. Is it a GM HEI or a Chinese copy? Are the pins (and bushings if there are any) the weights pivot on in good shape? Do you have any other HEI distributors you can rob advance parts from? If I can see what you have, I might be able to give you some advice. Perhaps some simple tinkering with springs and such will shorten the curve so you can have the initial and total where they need to be. If the weights are steel, solid steel, not the sintered type, they can be heated and bent to shorten the range of the curve.

viewtopic.php?f=21&t=765


Sun May 21, 2017 10:45 pm
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 25
It's a Pertronix Flamethrower HEI. I would assume it's proudly made in China.... It works as described with 20 or so advance movement but running the lightest springs it jumps around a little on idle up to about 1000rpm. Was thinking about just putting the heavier springs in and advance the initial but that would just slow the advance down and move it up in the rpm band right? Right now it's all in at 3000. Looking at the old HEI from the 350, the center plate is a bit damaged from having a weight riding on top of it and they are sintered steel. It's doubtful the Pertronix nor the old HEI have the good heavy GM weights in. I'll take a pic when I have time.

What I think could be the next step, IF the Pertronix weights are also the sintered ones, is to hook the vac advance up again and see how that acts. Initial is now about 8deg and with the vac stop limiter in place that would maybe put it at a "total" initial of 16deg. Vacuum is low at 8deg so it might not kick in that much. Well that's what I'm thinkin.


Mon May 22, 2017 11:46 pm
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 25
I just hooked up the vac advance and it pulls another 8deg initial advance max now on vaccum and it idles, runs and responds nice. Got to close the throttle plates a quarter turn again. I had the little *puff* in the exhaust when slamming the throttle and secondaries open on a low initial(8deg) and throttle plates open 1/2 turn(because initial was so low I had to) but now with ~16deg vac and mech initial there's no puff and no secondary feel it just goes. Seems like I've cheated a little. Part throttle is super nice.


Sat May 27, 2017 5:18 pm
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 25
Came to think of this thread again and help offered. You asked for pics of what I have and I remembered to snap a couple while changing springs last week. Erratic idle timing bugged me and I got the startup ping only on occation. Well I got rid of the copper springs and installed the silver springs from a Moroso 72300 kit.

Image
Image

Idle timing is steady now and mechanical advance all in at ~3500rpm. No startup ping, timing has a nice climb from 1000rpm and I got to close throttle plates yet some more. 700rpm idle. Mech advance is 28, part throttle is 37, initial is still 8 and about 16 with vac. Not gonna push it more than that on 91 octane. I think this is a nice place to be. Now hook up the AFR stuff and really get on top of that carb. It still puffs a little when I slam the throttle, I think the secondaries need adjustment.


Wed Aug 02, 2017 3:31 am
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
The advance parts, weights and cam (football shape), are similar in appearance as other "Advance Curve Kit" pieces. No guarantee this will work for you, but if you turn the football shape cam over, so the larger side from the mounting pin is contacting the weight, the spring posts will have more angular offset which will provide more leverage for the springs to pull the mechanism to retard as the RPM decreases. As it the mechanism is configured now, the spring pins are nearly in a straight line in the full retard position and without angular offset the springs have no leverage to rotate the reluctor pole piece.

The purpose for trying this is to see if the amount of mechanical advance can be reduced so you can have more initial with the same total.

Measure the spring mounting distance on the outside of the pins and measure the inside distance of the spring eyes and use identical springs with identical preload (EG" pin span .700", spring length .685"). If you use springs with large wire diameter, .040" ~ .046" they can be installed with light preload so the advance starts near 1200 RPM but the large wire diameter will provide slow advance, which is what you want with higher initial (18*) because with more initial the timing is already where it would be with weaker springs and less initial which does not idle as well (as more initial).

The large wire diameter springs that come on new MSD distributors (approx. .046" x .280" coil dia.) are good for this when the cam shape and weights are appropriate (do you have any other genuine GM HEI advance parts?). Heavy springs can be installed with light preload for a 1000-1200 start and (with the right cam and weights) will provide a slow creeping curve through the power band of about a degree per 1000 RPM. Most engines like that. I recently had some dyno time on a short-track 383 with Vortec Bowtie Fast Burn heads that distinctly wanted 26* @ 4000 and 30 @ 7000.

It would be nice if you could get to a distributor machine.


Wed Aug 02, 2017 4:01 pm
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 25
More initial would be great and I'll try flipping the center plate this weekend. Now I'm crutching the initial with vac advance, it might very well be positive to a yet higher initial with the same 8deg vac on top of that. Obviously it liked a slower creep and it didn't lose any response or seat of pants power. I'll keep the distributor right where it is now and compare timing degrees pre-flip with post-flip center plate.

This timing tuning does test other parts as well. All this 4000rpm tests with hot engine took its toll on my rebuilt steering box last time. Spat out all the fluid over the pitman arm. This is the last time I buy rebuilt and I'm glad it happened in my driveway and not on the highway.


Fri Aug 04, 2017 8:30 am
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 157
Location: Frostburg, MD
If you need more initial w/o starter bucking issues, you can use a 5 pin HEI module to retard timing 5* while cranking.

Wioth 5th [small] terminal grounded, ign timing will retard 5*. Ground 5th terminal via N-O relay, close relay via 12v solenoid feed [from ign switch].

GM/Delco D1941. I have several of those module if anyone needs one.

Dave


Wed Aug 09, 2017 4:35 pm
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Joined: Tue May 06, 2014 5:34 pm
Posts: 45
I've been thinking about using the 5 pin module for quite a while. Not that I'm experiencing extreme starter bucking, but that would sure help and I'm sure I could add a degree or two to the initial, and that would be beneficial.

Did you mount it using a relay connected to the starter signal ? I'm even thinking about installing an overide switch for extreme cases or the occasional bad gas we encounter sometimes.

I'm pretty sure I've read that during the retarded period, ignition power is not the same, is that true ?

Do you have factory modules or aftermarket ones ? How much would you sell those for ?

Frank.


Fri Aug 11, 2017 7:55 am
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