Timing & Gas Milage

[HO455]

Originally Posted by Rich72C10

Okay, girls are pretty worthless. I figured I'd have my daughter rev up to 35k by moving 500 RPMs at a time. By the time she got to 25k, she bailed and ran back inside and said never to ask her to ever do that again. So I got her mom out there. She could figure out how to keep a real good lock, 15k was the worse for her. When we were down, she said she was freaked out too and her palms were all sweaty - YUCK!

Anyways, it seems to be following the copper/silver advanced chart, with all in around 25k
LOL

I'd be scared too if I had to rev it to 25,000 rpm.
Sounds like you have things going your way now congratulations! The documentation you received with your distributor looks pretty nice.

[Rich72C10]

Originally Posted by geezer#99

If you need to adjust the idle too much with the adjustment screw you could uncover the transition slot and waste fuel because it’s idling on the power circuit. And you might get a slight stumble at first.
Using manifold vac helps sometimes.

Thank you Geezer! I'll keep an eye out for that, right now she seems happy with Ported Carb Vacuum. I mainly wanted to follow their directions for a bit - just incase I need to email them about something - that why I can say I done everything by their instructions ;-)

[HO455]

Originally Posted by Rich72C10

I also got in the mail today the replacement Vacuum Canister from TSP. This thing won't hold vacuum either. I have to keep pumping just to get near 15 - I think it leaks more then the one on my TSP distributor!

The Pertronix I pre-tested to 15hg can it held that for well over a hour. I guess I am glad I went with a new distributor.

With the Pertronix I am getting ~17hg (up from ~15hg) vacuum when the engine is running at idle. So I ganged a good 1~2hg with the new distributor.

I also swear my oil pressure is running to normal levels of my stock gauge - before I'd always seem to be at the 2/3 to near H mark on the oil gauge (especially before warm up). Though I haven't any clue why a new distributor would make a difference with the oil gauge readings. Kind of scares me that the oil gauge reading pattern changed. Though it's not like it is ever reading to the L mark (far left) of the gauge.

The oil pump is driven by the distributor. If there is a lot of play in the teeth and/or in the pump drive shaft the pump can flutter which might be noticeable on your guage.

[Rich72C10]

Hmm, interesting - I suppose that makes sense. This thing from TSP, I guess there is a reason why you can pick them up off eBay for 90 bucks...

[MAC71Cheyenne]

I've been reading along and gaining insight along the way. When it warms up a bit I am going to apply all the tidbits to the pumpkin coach.
As it stands, there is no separate vac fitting on the manifold. Take care of that, check the weights, and make some adjustments and I'm betting I will have better idle, up the gas mileage a hair, and a touch more umph. As it stands the mileage is around 11-12 and idle won't drop below 900 rpm even with idle screw lightly turned to seat. From last drop to seat is 1n1/2 turns and has no effect. Runs down the road at 20 mph just on idle. Not cool on snowy roads....

[Rich72C10]

I am glad my ignorance has helped at least one other person ha! Having a 900 RPM idle would bother me for sure. Though I may likely need to up mine once I start kicking in the A/C when the weather warms up again. I think 650 RPMs will be okay but since I got the truck right before x-mas I haven't really needed to run the A/C.

I just wished it would stop this freezing rain/snow crap. My ~50 mile test drive has way to many bridges on the route. But at least I got the distributor installed - I couldn't take seeing it on my table anymore LOL!

[geezer#99]

Originally Posted by MAC71Cheyenne

I've been reading along and gaining insight along the way. When it warms up a bit I am going to apply all the tidbits to the pumpkin coach.
As it stands, there is no separate vac fitting on the manifold. Take care of that, check the weights, and make some adjustments and I'm betting I will have better idle, up the gas mileage a hair, and a touch more umph. As it stands the mileage is around 11-12 and idle won't drop below 900 rpm even with idle screw lightly turned to seat. From last drop to seat is 1n1/2 turns and has no effect. Runs down the road at 20 mph just on idle. Not cool on snowy roads....

If you can’t get the idle lower than 900 rpm then check primary throttle plates aren’t hanging up in the bore and that they both sit the same.

[MAC71Cheyenne]

Well Rich, if you guys didn't like the freezing rain so much! 😂
Geezer I will check that out to make sure. Everything on this was an unknown. Hasn't been a ride through the park with any of it so far. Edelbrock intake and carb..."universal" plug wires, and omg wiring...
High temp today is 5, wind chill -45, garage with crappy heater is 18.

[BigBird05]

Just a question, What type of dist gear is on the Pertronics Dist. I have read that some gears will eat up a cam gear. I don't remember why tho.

[HO455]

If you have an aftermarket roller cam you need to run a bronze or composite gear. The factory gear on the distributors are hardened and will eat the softer cam gear that comes on an aftermarket roller cam.

[Rich72C10]

Originally Posted by BigBird05

Just a question, What type of dist gear is on the Pertronics Dist. I have read that some gears will eat up a cam gear. I don't remember why tho.

Says: Distributor Gear Material - Steel.

Originally Posted by MAC71Cheyenne

Well Rich, if you guys didn't like the freezing rain so much! ��
Geezer I will check that out to make sure. Everything on this was an unknown. Hasn't been a ride through the park with any of it so far. Edelbrock intake and carb..."universal" plug wires, and omg wiring...
High temp today is 5, wind chill -45, garage with crappy heater is 18.

I guess 29 is a heat wave fo you then ;-)

[Steeveedee]

Originally Posted by Rich72C10

I also got in the mail today the replacement Vacuum Canister from TSP. This thing won't hold vacuum either. I have to keep pumping just to get near 15 - I think it leaks more then the one on my TSP distributor!

The Pertronix I pre-tested to 15hg can it held that for well over a hour. I guess I am glad I went with a new distributor.

With the Pertronix I am getting ~17hg (up from ~15hg) vacuum when the engine is running at idle. So I ganged a good 1~2hg with the new distributor.

I also swear my oil pressure is running to normal levels of my stock gauge - before I'd always seem to be at the 2/3 to near H mark on the oil gauge (especially before warm up). Though I haven't any clue why a new distributor would make a difference with the oil gauge readings. Kind of scares me that the oil gauge reading pattern changed. Though it's not like it is ever reading to the L mark (far left) of the gauge.

Maybe the original (and the replacement) diaphragm had a bleed hole to keep fresh air in there? Yeah, probably not.

[68 P.O.S.]

Originally Posted by Rich72C10

I just wished it would stop this freezing rain/snow crap. My ~50 mile test drive has way to many bridges on the route. But at least I got the distributor installed - I couldn't take seeing it on my table anymore LOL!

Have you gotten some more mileage on it and how's it working out?

[Rich72C10]

Nope - Truck is frozen in the garage - there is a car behind it that is covered in snow & ice in the drive way. I haven't driven anywhere in anything since Saturday.

I don't expect to get her out of the garage until Sunday, at the earliest. Though we might starve by then and the truck will shortly after that be up for auction - ha!

[68 P.O.S.]

Damn, that sucks. We had our bad weather here, but it was only over the weekend. Well, good luck over there and let us know how it goes.

[68 P.O.S.]

Originally Posted by MAC71Cheyenne

I've been reading along and gaining insight along the way. When it warms up a bit I am going to apply all the tidbits to the pumpkin coach.
As it stands, there is no separate vac fitting on the manifold. Take care of that, check the weights, and make some adjustments and I'm betting I will have better idle, up the gas mileage a hair, and a touch more umph. As it stands the mileage is around 11-12 and idle won't drop below 900 rpm even with idle screw lightly turned to seat. From last drop to seat is 1n1/2 turns and has no effect. Runs down the road at 20 mph just on idle. Not cool on snowy roads....

Since you have an Edelbrock carb, there's a few things you have to set up on it first. Not sure why, but Edelbrock doesn't advertise it very well. First thing, Edelbrocks don't like fuel pressure higher than 6psi, or they flood. They recommend a pressure regulator set to 5.5 psi, or their fuel pump. Second, setting the floats to spec is very important because, once again, it can make the carb flood. They're never right out of the box due to shipping and handling. Third, the transition slots need to be squared or it will never run well. Square them, and don't touch the idle speed screw again. Doing this will get rid of your 900 rpm idle. Fourth, you need to buy a calibration kit for your model carb so you can install the step-up springs that work with your manifold vacuum level to further eliminate hesitations and the like. Once the above is completed, get it running and set your total timing to 36 btdc. Then restrict your vacuum advance to around 10 degrees and connect it to manifold vacuum. If you don't connect it to manifold vacuum, the rpms will be lower and you'll have to adjust the idle up, which in turn, screws up the transition slots again. If your idle mixture screws have no effect, you need to open up the carb and clean it out real well. Probably a good time to rebuild it as well if it's old. I hope this helps.

[MAC71Cheyenne]

68POS thanks for all that! Going to have to wait a bit for it to warm up before I can dig into it but I'm sure that all needs done. (Wife said no truck parts in the house)
Don't know the history of the carb, PO installed it and I do know it sat for a while. Got my shopping list made from your posting.

[Rich72C10]

Well finally an update - darn Texas Snow last weekend!

The changes are: New Pertronix Flame-Thrower II, New Flame-Thrower Coil & Wires. 12° initial timing, ~900 RPM idle (Park) and ~640 RPM idle (Drive).

60 Mile test drive, great mixed city and highway (Tx Farm Roads up to 70 MPH).

15 MPG!

I after changing my spark wires for the matching Pertronix Flame-Throwers that actually made a noticeable change in how she preformed. Before I'd get this odd power loss between 1st & 2nd / 2nd & 3rd shifting when just getting up to speed (say on a side street, getting up to 30~35). It wasn't a big drop or did it feel she was bogging down - just an odd blip of power loss. So something was up with those wires for sure. I am glad I decided to listen to Pertronix support and bought their wires to match their distributor!!

[Rich72C10]

16.5 mpg after a 50 mile interstate test drive, kept it at ~65 mph / 2.5k rpms. Though she really wanted to go faster, keeping it steady at 2.5k was not exactly easy.

I expect when I get back my rebuilt Qjet in March or so I might see even more improvement! But I think I am **now** in the right area for my LWB SBC 350/TH350/3.07 rear end?

[HO455]

Good work! Getting above 15 mpg with that combination is excellent. Not many achieve 16.
I never recorded above 15 with my Burban. I got 14.9 before the Gearvendor installation but haven't taken a road trip without a trailer or a couple of engine blocks in the back. Not to mention I got the Gearvendor installed just in time for Covid.
You have made me curious about what mileage the old girl is getting now.

[Rich72C10]

I serious doubt I'll be keeping it at that peak, as I was doing a carefully controlled test driving test. I really did my best to stay at 2.5k. I did no gunning and eased my way through my targeted speeds from start to finish. There was very little surface driving as I am very near the I35 on ramp(s). Traffic was very light too, though I felt like the big rigs were going to blow me off the road, especially when I got into construction areas!

Though one thing after all that highway driving at 2.5k this morning - I had to be really light on the gas pedal. Which is why it was so hard to keep her at 2.5k because of needing to have a feather light touch on the pedal. There are also some good hills on this drive and I only had to give her a wee bit of pedal to stay on speed but if I was not careful I started to push into 70 a few times. So I guess I am doing okay on power now too.

Now back to give'n her some gas -- Zoom Zoom! LOL

PS: Seems like a 'burb would be a lot lower (or me higher) - it has to be heavier than a C10 LWB but perhaps without the bed opening it is better on the wind?

[geezer#99]

Would seem 2500 is the ‘sweet spot’ on your motor.
That’s the spot where the motor becomes perfectly efficient. It’s not needing to work any harder to maintain your speed.
You should be able to hear that spot in your exhaust too. The exhaust should go dead quiet.

You do know Murphy’s law says that your original carb will drop your mileage down to 12 mpg!

[Rich72C10]

You are correct, she purrs like a kitten at ~65.

Gee thanks for that carb comment :p

[HO455]

Originally Posted by Rich72C10

I serious doubt I'll be keeping it at that peak, as I was doing a carefully controlled test driving test. I really did my best to stay at 2.5k. I did no gunning and eased my way through my targeted speeds from start to finish. There was very little surface driving as I am very near the I35 on ramp(s). Traffic was very light too, though I felt like the big rigs were going to blow me off the road, especially when I got into construction areas!

Though one thing after all that highway driving at 2.5k this morning - I had to be really light on the gas pedal. Which is why it was so hard to keep her at 2.5k because of needing to have a feather light touch on the pedal. There are also some good hills on this drive and I only had to give her a wee bit of pedal to stay on speed but if I was not careful I started to push into 70 a few times. So I guess I am doing okay on power now too.

Now back to give'n her some gas -- Zoom Zoom! LOL

PS: Seems like a 'burb would be a lot lower (or me higher) - it has to be heavier than a C10 LWB but perhaps without the bed opening it is better on the wind?

I don't know about the aerodynamic differences but I do know it is definitely heavier. It weighed 4970 at the garbage dump a couple months back, and that was without the back seat .
Two and a half tons of Detroit's finest!

[68 P.O.S.]

Glad to see its running well now. I can imagine the smile on your face, haha!