Dizzy recurve for 440 MH input

-
mbaird

mbaird

mbaird
Joined
Dec 10, 2005
Messages
9,341
Reaction score
6,555
Location
Boise, Id
My daughter bought a 77 Dodge motorhome with a 440 and I want to recurve the distributor to help with power and temps.

My thinking is around 14 base and 38 total with mechanical. Mechanical starting around 1200 and all in by 2500-2800

Additional Vacuum adv of 14 for 52 total.

Input ?
 
I'm not sure that will be good. You want all the timing in VERY early for a heavy vehicle like that? Hot curves like are for light cars with low gears.......something easy to move. You can try it, but I think you may run into detonation. Give it a try and see. Heck who knows?
 
Sounds like Mopar did their homework. I wouldn't change a thing. Don't crowd the initial or advance it too fast. It will ping all over the planet. Too much total will burn it up. Just my opinion.
 
Hmmm. So I want more advance early or not ?
I have read some old RV forums in which guys had recurved similarly with much success.

But that is why I posted here...
 
Ok. After rereading RRRs post I see you guys are saying the same thing.
So you would leave the curve as the factory created it ? I wouldn’t have thought detonation would be a big issue with 7.8:1 compression .

RustyRatRod said:
I'm not sure that will be good. You want all the timing in VERY early for a heavy vehicle like that? Hot curves like are for light cars with low gears.......something easy to move. You can try it, but I think you may run into detonation. Give it a try and see. Heck who knows?
Click to expand...

toolmanmike said:
Sounds like Mopar did their homework. I wouldn't change a thing. Don't crowd the initial or advance it too fast. It will ping all over the planet. Too much total will burn it up. Just my opinion.
Click to expand...
 
mbaird said:
Ok. After rereading RRRs post I see you guys are saying the same thing.
So you would leave the curve as the factory created it ? I wouldn’t have thought detonation would be a big issue with 7.8:1 compression .
Click to expand...

Pulling that much weight with the advance coming in that quickly, it could be. It's simple to do. You can put it back it it gives you problems. So certainly it's worth trying. Just know that you may end up with detonation. It's one of those things where you're just going to have to try it and see. What size motorhome is it?
 
It just seems to make a lot of noise with no real pull . I understand it’s heavy but not any different than a truck with a trailer behind it . I had a 74 W100 with a 440 and it would haul a car trailer with far more vigor than this thing. I assumed that Ma Mopar had destined it for emissions and killed the torque . When you add in the fact that most of our uphill climbs out here are around 5k-8k ft in elevation it makes for a real dog !
 
mbaird said:
It just seems to make a lot of noise with no real pull . I understand it’s heavy but not any different than a truck with a trailer behind it . I had a 74 W100 with a 440 and it would haul a car trailer with far more vigor than this thing. I assumed that Ma Mopar had destined it for emissions and killed the torque . When you add in the fact that most of our uphill climbs out here are around 5k-8k ft in elevation it makes for a real dog !
Click to expand...

What year model is it? Does it have cats on it?
 
Rear gear makes a huge difference. Tire size messes with that as well. I would imagine there's a compression difference as well between the two. I had a 454 powered tool truck that I freshened the engine in. A Edelbrock intake, Comp rv cam, and some headers. It ran better but really not worth the effort.
 
It’s a 77 or a 78.
My W100 has 3.55s and 31” tires
I assume this has 4.10s and 33inch tall tires so it should be a wash
 
'77 is prob pre-cat for 49-states in truck. '78 too but this is all asumes it still has the factory distributor.

It works something like this for pre-cat cars.
For the CAP and CAS Chrysler retarded the initial timing and used a quicker, long advance so off-idle everything was close to the same as non-CAP.
This was coupled with lean 14.2:1 idle fuel mixtures. The idea was to reduce CO and HC at idle.
Then they played with some different methods to reduce emmissions on deceleration.

In the 70s things changed just about every year, but you may find initial timing is retarded compared to a similar mid 60s non-CAP truck engine.

A mid 70s vehicle, especial a truck, may have a coolant temperature switch to boost timing at idle if the coolant gets hot. These switches allow manifold vacuum to the distributor vacuum advance.

By '77 on truck there might be EGR, but hopefully not the vacume advance delay system.
If it has a timing delay on accel, that would be worth experimenting going without. Came in around '74 for the cars.
EGR feeds in hot O2 so I'd go with the factory timing on an EGR equiped engine.
Make sure its hooked up right. No EGR cold, No EGR at idle hot or cold, No EGR at wide open throttle.

Timing is advanced more with the slower the burn. A heat soaked engine should have pretty good burn. I think thats where RRR and TMM are coming from.
 
No cat on it. I didn’t think to check for an egr or air pump last time I worked on it.
Going camping this week in it so it would be fun to experiment.
 
The best thing I ever did was to install a dash-mounted,dial-back, timing device.
Mine has a range of 15 degrees . If I set the base timing with the knob on the device set centered, then I can add or subtract 7.5 degrees at any time. This timing chunk gets added/subtracted to whatever the D is rolling in.
This allowed me to do hundreds of roll-ons to discover the detonation commencement at any and all rpms and loads.... while driving. I did a few basic pulls and plotted the points on graph paper as, advance versus rpm at WOT. Then I built a curve to connect as many dots as I could. Then I re-centered the device and changed the base timing as was required, and another week of testing. And so on. This is your rolling chassis, real-world, ignition dyno.
Eventually it worked out that the engine needed three curves; one from idle to about 1600, and another from there to 2800 and another above that. Well three curves is not possible but two is. That was a tricky problem to solve but perseverance got it done.
After that, I tuned the vacuum advance system.
I don't recall the buy-in on that device but it paid for itself right away cuz I never melted the engine down. And now, after 100,000 plus miles, it probably helped save me thousands of dollars in fuel savings, cuz the engine always has the appropriate timing. Or at least darn close.
I highly recommend you get one, and an accompanying stand-alone knock sensor, cuz a lot of the time you cannot hear detonation. And long-term mild detonation can break stuff too. And even if it doesn't, detonation always costs power or economy.
It is better/safer to be two or three degrees short of optimum WOT-timing, than even just one degree too much. So you cannot just arbitrarily crank it up to some number your buddy throws out. And just changing the base timing does not solve all points on the timing map....... unless it was perfect to start with, and somebody just retarded it a touch; in which case you would be restoring the timing to it's former perfect state.
The dial-back allows you to determine the perfect WOT timing; you still have to figure out how to make your D meet the need, or if indeed, it actually can meet the need.
Then you still have the Part-Throttle to deal with, and the base timing
 
What I would do before anything is just do some simple lookin around. Distributor advance might be seized up. You can pop the cap and twist the rotor and see. It should twist (I forget which way on a big block) and then spring back into position when released. Make sure it springs back all the way. It might just need some simple repairs.

I mean after all, it's never gonna be a barn burner, but you can make sure everything works as intended. That would be a start, IMO.
 
First thing I will do is plot the current timing curve.
A/J ... I had a Jacobs timing controller at one time but I gave it to a buddy . Maybe I can see if he still has it.
 
mbaird said:
First thing I will do is plot the current timing curve.
A/J ... I had a Jacobs timing controller at one time but I gave it to a buddy . Maybe I can see if he still has it.
Click to expand...
The Jacob's is what I have too. The bonus with that unit is that it has a built in amp that you can trigger with just about anything. I used the Mopar magnetic pick-up. This device has been in continuous use since 2002 or 2004, not sure which exactly, but it totals somewhere about 120,000 miles.

I now use it to optimize my cruise timing and to retard thechitout of it at idle when I want to slow-cruise with a manual trans.
 
mbaird said:
First thing I will do is plot the current timing curve.
A/J ... I had a Jacobs timing controller at one time but I gave it to a buddy . Maybe I can see if he still has it.
Click to expand...

I think that's a good start. See if somethin "ain't workin".
 
I'd recurve it to get more initial on the engine and keep the curve a bit slower than a performance car set up.

Well for 77 it was 8btdc which is not bad. I think 12-14 would be better.
 
You must log in or register to reply here.
-

Back
Top