Time for More Horsepower

[Don Coatney]

Dave;

As I am away from home I dont have my books with me so this is from my failing memory. The vacuum advance curve for my engine is around 2 degrees advance at 2 inches of mercury and full in 9 degrees of advance at 15 inches of mercury. I do not recall the mechanical advance curve but I believe it to be around 20-25 degrees for a total of 35-40 degrees at wide open throttle.

Goverened industrial engines that run at a set speed range would not gain anything by using a vacuum advance. Race cars that run either wide open throttle or fully closed throttle would gain nothing with a vacuum advance as the mechanical curve in both of these applications will give maxium HP.

The economy benefit in vehicles that use a vacuum advance comes at something less than full throttle when the timing can be retarded without a loss of power and the power can be restored with a push on the accelerator.

Large truck engines need full power all the time so they do not need a vacuum advance.

If I did not have a working vacuum advance on my engine my total advance would only be 25-30 degrees. With the vacuum advance added I now have 35-40 degrees. That is where the added horse power comes from.

[greg g]

For checking the timing with a vacuum gauge, connect the gauge to the windshiel wiper port in the intake manifold. With the engine up to running temp,and at proper idle rpm, loosen and rotate the dist. till the highest steady guage reading is attained. If you want you can check the setting with a timing light. Then lock it down. should be good to go.

[Charles Furman]

Thank you. Now I get it.

[grey beard]

Don,

My B1B shop manual says vacuum and centrifugal are each worth 20 degrees advance at 2500 rpm - or a total of forty, PLUS any initial advance cranked in by setting timing with a vacuum gauge or power timing by ear, listening for preignition.

Somewhere I learned that all lOtto cycle internal engines have a limit to the total amount of advance they can tolerate - without regard to marque or combustion chamber configuration. Like you, my memory ain't what it once was - not that it ever was very sterling - but I believe that total number is somewhere around 45 crankshaft degrees of advance. Beyond that number, negative issues arise that do not bode well for engine health.

I used to call on a shop where the owner was a super stock tractor puller, in Ohio. He ran three Ford 429's with forged crankshafts tied together with roller chains and three GM superchargers. He made full pulls in NINE seconds, so things would happen pretty fast. Several times he seized pistons just from a miniscule fuel leak that would lean out one engine just a tad too much. His goal was a total of 45 degrees advance at about 2000 rpm, and he crossed the finish line at 10,000 rpm.

Somehow I doubt that our L6's will be happy with any more total advance than that number, but who'se to say, these days.

[woodscavenger]

Reg, you're killing me! I just threw up in my mouth!!!

[Don Coatney]

Dave;

I just dug out my book and here is what it says for my 1953 Desoto engine with a IAT-4102 distributor.

Mechanical advance starts 1 degree @ 450 RPM's

Full advance 10 degrees @ 1425 RPM's

Vacuum advance starts 1 degree @ 6 inches mercury

Full advance 9 degrees @ 15 inches mercury

Plymouth 46-48 with a IGS-4207-1 distributor.

Mechanical advance starts 3 degrees @ 400 RPM's

Full advance 9 degrees @ 1300 RPM's

Vacuum advance starts 2 degrees @ 6.75 inches mercury

Full advance 10 degrees @ 14 inches mercury

This is way different from your truck information. The numbers I posted are directly from a 1953 edition of Motor's Manual.

[Reg Evans]

Reg, you're killing me! I just threw up in my mouth!!!

I'm sorry Woodscavenger.

Hey....don't wast it though.

Crack an egg and make an omlet.

OK...I'll quit now

[48Dodger]

Those are interesting advance numbers. First time I've seen those. What was the standard Octane rating in 1953 ? How close are everyone's rpm readings on today's gas? Just curious.

48D

[Don Coatney]

A few weeks ago, as I was leaving the Friday night cruse in here in the Boro, I got in a race with a Hemi powered 56 Desoto while I was heading home on the interstate.

Here is the Desoto I raced. He was at the Friday night crusein here in the Boro tonight.

Also a couple more cars that were there tonight of interest. A nice Olds.

A couple of Bakers.

[grey beard]

Don,

Those low value advance numbers you are showing from Motors Manual are just right - except that they are distributor degrees. As such, when we install that critter into an engine, the engine sees - and we measure with our greedy little timing lights - crankshaft degrees.

Since the crank turns twice as fast as the distributor, we will see a total of TWICE the advance amount you are quoting. If you think about this, it makes perfect sense. Ford - like Motors Manual - always quoted distributor degrees when showing advance curve specs, for the reason that most of these curves were set on a distributor test bench. For this reason we deal in and quote distributor degrees of advance, because that is what we deal with and set and adjust on a test bench.

If you and I had one of those nifty Sun test benches, we could take your specs and use them directly, and they'd be right spot on the money. The specs I mentoned are not from Motors but from MoPar, and are total crankshaft degrees of advance.

When I had my truck nose off and the crank pulley out, I marked off the four quarters of the pulley from the TDC mark. Then with those four 90 degree markings, I measured the center of them with a tape measure and marked off a 45 degree mark. Each of these were painted white for visibility. Now when I use my timing light, at 2500 rpm I expect to be able to see that 45 degree advance mark peaking out of the lower left corner of things. It's certainly not as neat as a Sun test bench, just my quick-and-dirty down-home way of making sure I still have both vacuum and centrifugal advance at that specified speed.

Give it a try. Works for me.

[Don Coatney]

Don,

Those low value advance numbers you are showing from Motors Manual are just right - except that they are distributor degrees.

That splains it. Thanks.

[james curl]

A far as power needed for the hills, the overall ratio with the tire diameter may be below the peak torque curve and be too tall a gear ratio. On my 235 cu in I/6 in my 55 chevy pick up with overdrive which is the equivelent to a 2.73:1 rear end and 235 75 R 15 tires the engine is running less than 2000 rpms at 70. Any hill rerquires wide open throttle just to try and maintain speed where as out of overdrive with the 3.9:1 rear gear and 3400 rpms it pulls the hills at 70 mph with ease.

[grey beard]

Back several years when I was teaching dealer service school for the Ford Division, I remember an old engineer trying to explain to us that the logic behind the really tall final drive ratios was to get the throttle plate wide open on pulls. Did this save on fuel, we asked. Yup, he replied. You make up the difference in economy because when the throttle's wide open, there's less drag on the piston domes from manifold vacuum - which is gonna' be nigh onto zero at WOT. Always seemed to me like you could overdo a good thing by making the final ratio too tall.Don't understand everything I know about that.

Having said all that, I wish my 4:10 Pilothouse was a 3:54 - badly enough that when I find one, I'll swap it out. Anybody know what a 1948 Windsor is liiely to have inside the banjo housing? Got one'a them on the string as we speak - I write - whatever. It's in a tough spot to get under it to eyeball the top of the housing for the ratio mariings.

[1937 Dodge]

I just picked up a '48 Windsor rear end off a fluid drive that had the 3.54 rear axle ratio. Fortunately, the ratio was printed on the housing. It cleaned up real well and all I did was put in a new pinion seal. I plan on swapping it out for the 3.9 that came with my '37 MC later this summer. My MC manual actually shows that a 3:54 rear axle was offered in 1937 on the MC. I am running the stock 16" 6.00 tires.

Right now my 3.9 is mated to a T-5 out of a Chevy S-10 (NWC) with a mechanical speedometer output. The gear ratios are 3.76, 2.18, 1.42, 1.0 and .72

The truck has been retired from hauling heavy loads and the extra horsepower from the modified 265 block should help me start off in first gear and keep from lugging in 5th on most roads. Worst case is I'd shift down to 4th.

I may be getting another 3.54 third member/rear axle out of a '48 Windsor if anyone is interested.

[Don Coatney]

I just picked up a '48 Windsor rear end off a fluid drive that had the 3.54 rear axle ratio. Fortunately, the ratio was printed on the housing. It cleaned up real well and all I did was put in a new pinion seal. I plan on swapping it out for the 3.9 that came with my '37 MC later this summer. My MC manual actually shows that a 3:54 rear axle was offered in 1937 on the MC. I am running the stock 16" 6.00 tires.

Right now my 3.9 is mated to a T-5 out of a Chevy S-10 (NWC) with a mechanical speedometer output. The gear ratios are 3.76, 2.18, 1.42, 1.0 and .72

The truck has been retired from hauling heavy loads and the extra horsepower from the modified 265 block should help me start off in first gear and keep from lugging in 5th on most roads. Worst case is I'd shift down to 4th.

I may be getting another 3.54 third member/rear axle out of a '48 Windsor if anyone is interested.

How does the T-5 perform with the 3.9/1 differential? Have you made any long trips?

[Merle Coggins]

I think a 3.54 is overkill. I have a 3.73 diff in my truck, and with the nearly stock 218 CID engine it works well. It'll do 75MPH down the freeway if I want it to, and it still has decent power for the hills around here. (except for when my points were out of adjustment) I'd be afraid that a 3.54 may be a little much for the hills in Pennsyltucky, where Dave lives. Although if that's what readily available, then give it a try since it's only my opinion with no hard facts.

Merle

[1937 Dodge]

I agree with Merle that a 3.54 is not for every truck especially for those with overdrive and stock engines. As has been mentioned before on this site, several factors have to be taken into account when making these decisions such as engine size/power, what the vehicle is going to primarily be used for, tire size, and transmission gearing. Too often folks go out and buy a transmission like a t-5 or throw in a different axle ratio without running the numbers and end up disappointed with the results.

Some of us are natural "tweakers" who like to run the numbers on a spreadsheat and try and come up with thier own personal "ideal" set up.

[Young Ed]

I've been thinking about this somewhat as I prepare for an eventual T5 flathead powered truck. What do people think is a good ratio? Unknown at this time if I'll be using the stock rearend or swapping in a newer one

[1937 Dodge]

Good questions Don.

I have been following your driving comments with your transmission and it sounds like you are quite pleased with your gearing. I like your modern rear end set up as it gives you an emergency brake.

All local driving (Cleveland area) at this time since I put in the T-5. I am not real pleased with first gear. I run out too soon for my taste. Percentage difference from first to second to third etc seems to be ok. Got the same input from friends who have driven it.

The engine pulls real strong so I can lug in lower gears. I will be doing a 450+ mile round trip to MI in Aug with the 3.9. And will get a better feel for cruisng with the 3.9 at that time. Another good trip would be to PA to visit my daughter, lots of nice hills in her area.

Going to try and strap on a tempory tach for the trip to MI to see if my calculations pan out on the road. Also will take a GPS to check speedometer readings vs. actual speed.

I have been driving the truck with the original 3 speed and 3.9 rear end for over 46 years. It was my daily driver when I worked in a lumber yard as a kid. Used to get her up to 60-65 on the freeways in Detroit and the engine was really straining. She felt more comfortable at 50.

We are still playing with the numbers and may swap the transmission to a t-5 WC with slightly different gear ratios later on.

Seems like part of the fun is playing with the variables as long as we keep the over all cost down.

[Don Coatney]

The pictures of your engine were a big motivator when I built my engine. I would have liked to find a 265CI engine but I scored a good deal on my 251 and went that route. What carburetors are you now running?

The first gear in my NWC T-5 is also a bit low but I can live with it. I have heard tell it is possible to swap the tail stock between a WC and NWC so you can get the better ratios and better shifter location.

Not sure what your truck weighs but the final gearing in my car with a 3.55/1 differential and 27" tires is great for highway driving. 70 MPH at around 2200 RPM's.

I drove my car to Detroit last summer and had a great time. I hope you enjoy your trip.

Here are some old pictures of your engine. Can you post some new ones?

[woodscavenger]

Those pics make up for Reg's indiscretion.

[1937 Dodge]

Thanks for sharing the moldy oldie photos of my truck engine. You are correct on the T-5 tranny part swaps. You can mix and match the WC with NWC and keep the WC gear ratios and gear improvements and still use the NWC tail housing and keep the NWC gear shift location up toward the front. The NWC will add a little more height to the floor but nothing serious. You will also need to change the splines on the the NWC front of the driveshaft to (I think) a 26 spline slip joint.

Here's one that would be fun to try on a 251 or 265 for intake. 3 Harley Davidson carbs!

I have heard of 3 SU carbs also being used.