Recurving timing with distributor kit for performance and mileage

[JerryP]

It would probably be fairly easy to modify a stock HEI distributor with a limiting screw to be able to set the amount of vacuum advance using the original vacuum can. Problem solved without spending time or money but for the price of an aftermarket adjustable advance unit I would go that route. So you are doing the same as Jim, we eagerly await your results. I am going to do this to mine if I get time, A lot going on right now so I may or may not get it done.

So if we were to remove all the smog stuff, on say an 89 chevy 454 Winnebago Chieftain, we would need, or it would simplest to get a new HEI distributor, and adjustable vacuum can, with a setup of  "8-10deg initial, 33-36deg initial+mechanical, with 8-12deg manifold vacuum advance".

Honestly, it has been so many years since I played with ignition, I might as well be new to it. I was always good at twisting it around until I got the right sound

[tmsnyder]

That's what I have, a 1989 454 in a P-30.  I would keep the HEI distributor, they deliver good spark, and you can leave it in place, don't pull it.   Just recurve it with a $15 mechanical advance kit and a $25 adjustable vacuum advance.  You won't even have to pull the distributor.  Open the doghouse and the distributor is literally right there almost at floor level.  Sit down, disconnect the the plug wires from the right bank of cylinders at the cap, disconnect the connector on the cap that goes to the distributor base, and lay the cap over on the left side of the engine. Don't remove the odd number cylinder wires from the cap.  Remove the rotor.  Then remove the old mechanical advance (2 springs, 2 weights and the center piece) and put the new kit in.  Remove the vacuum advance and put the new one in.  (clean and lightly lube as appropriate as you go)  Reverse to reassemble. 


With the vacuum advance disconnected and the vacuum hose plugged, set the timing to 8-10 degrees.  Reconnect the vacuum advance to manifold vacuum NOT ported vacuum.


$40 later and 20 minutes of work and you have a good healthy HEI spark and well timed ignition. 


If it kicks back on your starter and is hard to start, then you would want to back off the initial timing. It should be fine at 8 deg BTDC though.

If you hear pinging at partial throttle partial load, then you can adjust down the vacuum advance by inserting a 3/32 allen wrench into the vacuum nipple on the advance can, and turn counterclockwise one or two turns to reduce the amount of vacuum advance applied by the can. 

So if we were to remove all the smog stuff, on say an 89 chevy 454 Winnebago Chieftain, we would need, or it would simplest to get a new HEI distributor, and adjustable vacuum can, with a setup of  "8-10deg initial, 33-36deg initial+mechanical, with 8-12deg manifold vacuum advance".

Honestly, it has been so many years since I played with ignition, I might as well be new to it. I was always good at twisting it around until I got the right sound

[tmsnyder]

I'll keep an ear open for it.


That's the nice thing about the $25 adjustable vacuum advance, if you hear pinging under partial throttle, the vacuum advance can be dialed back with an allen wrench through the nipple of the vacuum canister without changing the initial timing or the WOT timing. 

Ok, sounds good but just so you know this was all discussed five years ago. I can tell you right now that 46 degrees ain't gonna cut it on today's gas unless you are running premium and that sort of negates any gains. But you are on the right path and I am curious to see how it works out for you. One of our current members also wrote up an article not long ago on using a distributor from a ZZ4 I think, crate motor, which has close to the needed curve in it.

Here is the article from back then.

http://forums.motorhomemagazine.com/Index.cfm/fuseaction/thread/tid/25062446/gotomsg/25077917.cfm

[Rickf1985]

Have you actually DONE this to your RV motor and run it on the road yet?
I am not saying this will not work, it worked for the guy that originally wrote the article but that was back when gas was much better quality. If it still works then let us know.

[tmsnyder]

This is a new to me RV, just got it in the driveway about a month ago.  Have not had it on the road yet, just been working on it.  Mechanically this thing was a mess, I'm going through everything and I keep finding things that need repair. Among other things, all new belts and hoses, eliminated the dual SMOG pumps, eliminated the SMOG distributor curve, plugs, cap, wires, rotor, thermostat, exhaust donuts, temperature gauge, and a bunch of other stuff related to keeping water out.  It will go under its own power soon and will report back asap, might be taking it on a trip in July so I can get the mpg. 

It's on blocks right now but it does run a heck of a lot better now then when I drove it in the driveway. Just starting it, idling, tabbing the throttle, ... it's definitely running better than before.  Can't wait to drive it.

[Oz]

This is a new to me RV, just got it in the driveway about a month ago.  Have not had it on the road yet,

When you do, then let us know if the information you posted from the article actually works for you.

[tmsnyder]

Small warning to anyone recurving their distributor, swapping out the stock smog-design mechanical advance put the initial timing off the timing pointer at about 20 degrees BTDC. Be prepared to set the timing right after installing the new mechanical advance.

After setting the initial time to 9 degrees BTDC I drove it around the block (a few miles) last night.  It seems to run quite well but then again I don't have a baseline to compare it to. 

Anyone have any 0-60 numbers to compare against?

Vacuum was 18-20 inHg at idle, 8-10 cruising around, 2-3 at WOT.

No pinging so I may add some more initial timing and a turn or two on the vacuum advance to add some timing there as well.

I have an issue with my tag axle that needs attention before I can run it for a decent distance to get an mpg number, but that will be coming soon!

[Rickf1985]

0-60 numbers?!!! Are you building a racing RV? I don't know about you but I do not want to be replacing my transmission on a regular basis. You really have got to stop thinking this is a Camaro. 0 to 60 means nothing in an RV because first off we do not flat foot it from a stop and second just about every RV weighs a different amount. You went around the block, you need to get out on the highway and go for 50 or 60 miles at speed in varying conditions to get any real feel for how it is acting. You did not even get up to temperature so it is not going to ping. I am not trying to be critical here but if you know so much about setting up the timing on an engine then you should also know how to test it. It is going to take a months worth of running and mileage checking over at least four or five tanks of gas before you will know what you have.

[Oz]

0 - 60.  Yes, half an hour.   :)rotflmao

The search for more power is typically to produce better acceleration when needed at highway speeds and less reduction in speed when going uphill, so I don't expect you'll get that baseline to compare with...

... unless we decide to hold the first annual CWVRV drag race... 

[tmsnyder]

Ok, maybe not 0-60, but how about 0-30? LOL


It was up to temperature    210F and steady.  Gave it some more timing yesterday and it responded even better, put some more miles on it in stop and go and also straight roads.  Wide open throttle from the stoplights and partial throttle loping along at 50mph.  Not too shabby acceleration for 11-12k lbs.


It's certainly not a Camaro, but it is a Chevy big block V8 making both torque and horsepower.  Horsepower is what moves it up a hill at a reasonable rate, and also what takes it from 0-60 mph while merging onto a highway.  With poor timing, it won't do either of those things as well.


A TH400 should have no problem behind a low compression, smog year 454.  They were designed for pre-smog big blocks that actually made some decent power that TH350 transmissions couldn't handle.  There should be no problem unless it has other issues and those should be addressed if they exist, not compensated for by de-tuning the engine.  Are you suggesting we pull a couple spark plug wires when a U-joint starts to squeak?    Not me, I'd rather have it break or blow up while I'm close to home, before I load my family in and head out on vacation.


Anyway, I'm going to keep working on this and will post results.  It's certainly nothing ground breaking, just setting basic timing on a chevy.

[tmsnyder]

Maiden voyage was this weekend, went from Buffalo NY to Centre Hall PA for a bluegrass festival, so I finally have some results for the 30 minute, $40, DIY distributor re-curve.  I set the timing by adding timing until the engine, when hot, would kick back against the starter and begin to start hard.  I backed it off a little from that point and tightened it down.  I didn't measure the initial timing yet, sorry but it's on my long list of things to do.  To give you an idea of my situation, the day before we left I had removed everything from the roof, scrubbed it clean, installed 3 Fantastic Fans, and sealed all the penetrations and seams with a gallon of 2 part EDPM rubber roof, I was kind of up against a hard departure deadline and the timing check wasn't high on the list .

We drove over to Batavia NY on Rt 5 and took 390 to 86 to 15 in order to meet up with family along the way.  Much of the trip was through the northern hills of the Alleghany Mountains, it was very hilly and and we spent a lot of time at WOT. Even saw a couple runaway truck ramps on downslopes which required low gear decents, so you know it was hilly.  After the festival, we headed back over hill and dale again and filled up along the way, got 7.2 mpg on that tank for ~360 miles.  A bit disappointing but again it was very hilly for that tank. 

More hill and dale as the GPS took us cross-lots for about 100 miles using more WOT, then picked up I-81 north of Binghamton and then I-90 at Syracuse to Buffalo.  So it was about 200 miles of I-81 and I-90 which was _much_ easier driving than the first ~100 miles of hill and dale. Even the hills around Cortland to Syracuse were flat compared to the other stuff we drove through on that tank.  On that tank for 200 miles of relatively easy road and ~100 miles of hill and dale, we got 8.7 mpg.  I did 60-65 mph on the highway driving into a 9 mph headwind for the 150 miles from Syracuse to Buffalo.

In the flats and gentle hills of I-81 and I-90, the mileage would have easily been in the mid 9's.  If I assume 7.2 mpg for that first 100 miles of hills and remove that from the equation, I get 9.7 mpg, so I think 9.5 mpg is a conservative estimate of what it got on the interstate.

In case anyone was wondering, I did check the odometer against the road markers on I-90.  Over a 100.0 mile stretch (mile marker 292.0 to 392.0), the odometer read 99.7 miles.  I can live with a 0.3% error, it's close enough I didn't adjust the mpg calculations for it.

I started the trip and ended the trip on the exact same pump with the RV sitting in the exact same position.  So the fill was consistent at the start and end.

For gas I ran 87 octane, 10% ethanol GARBAGE gas the whole time.  Listened for pinging all along the way, there was none.

Anyway, I'm going to keep working on this and will post results.  It's certainly nothing ground breaking, just setting basic timing on a chevy.

[Getoutdigin]

It was said earlier you can re-curve the distributor without removing it from the engine. That may be true but I read recently that a cause of the distributors sluggish operation could be from build up between the distributor housing and the shaft. I read its best to pull the distributor, drive out the roll pin remove the gear and separate the shaft from housing and clean. Measure the shaft up and down end play and buy a shim kit to reduce this to between .005" and .010" if more then that. I'd stay closer to .010". These are some of the areas I'll be checking as soon as I can get to it. That will be soon.

Love these threads, Thanks and keep it coming.

[Rickf1985]

If you are going to go that far it would be better to go the new distributor route through Performance Distributor already dialed in, new gear and backlash set, new module, cap, rotor, high performance coil, adjustable vacuum advance. Drop it in and go.

[tmsnyder]

Distributors can't get sluggish, they are gear driven off the camshaft.  The timing advance parts might need cleaning and lubricating or replacement but that can be done from the top without pulling the distributor. The endplay isn't relevant b/c the gear is pulling the distributor shaft down onto the shims continuously, so the shaft is not going to bounce up and down and change the timing, it can't happen.  It's a great design.  The gear might eventually wear out but very unlikely, you'll wipe the lobes off the camshaft long before needing a distributor gear.

It was said earlier you can re-curve the distributor without removing it from the engine. That may be true but I read recently that a cause of the distributors sluggish operation could be from build up between the distributor housing and the shaft. I read its best to pull the distributor, drive out the roll pin remove the gear and separate the shaft from housing and clean. Measure the shaft up and down end play and buy a shim kit to reduce this to between .005" and .010" if more then that. I'd stay closer to .010". These are some of the areas I'll be checking as soon as I can get to it. That will be soon.

Love these threads, Thanks and keep it coming.

[tmsnyder]

I ran this several hundred miles to a couple camp outs last summer, had adjusted timing by ear and by paying attention to how easy or hard it started when hot.   Set it last summer and ran it, heard no pinging even with the cheapest gas and got the mpg numbers above, only had a few fillups but the results were around 8.


Finally got around to checking the timing to see where I had it set, and it was 13* btdc.  I reset it to 12* btdc and will run it that way for a while.  This is with the recurved distributor as described below.  Hope this is helpful to someone considering the change, it definitely woke up my 454 and should cut down on the exhaust manifold temperatures.

[cook elandan]

tm, did you do any adjustment to the carb with the mixture screws. it is not running to lean or rich at idle with your curve and timing setting.  I am in the middle of pulling the A.I.R. off. because of power steering pump leak and issue with hydrobooster. 
Thanks,

[tmsnyder]

I didn't touch the carb yet, it's a fairly new Edelbrock 1406 and those are set up for fuel efficiency.

[Rickf1985]

A 1406?! That is a 600 CFM carb, the 1411 is the normal carb for a 454 in a motor home. I would think you would be into it pretty hard in hills and such.

[tmsnyder]

Bought it that way, found the box and receipt in a cupboard.  Definitely into the throttle even on straight-aways.  On hills it's WOT   Rick, I'm taking your advise, a new Edelbrock 1411 is on the way.