Fords fron distributor design is superior to chevys rear distributor

To keep this topic out of the other thread where the person was asking for help, I've started this thread to discuss like adults the reasons why the front mounted distributor is superior to the rear mount distributor. It's pretty simple actually. The load of turning the oil pump at the rear as well as actuating the valves puts too much stress on the cam which causes the cam to actually twist. This twisting effects both the valve timing because the valves near the back of the cam will be opening and closing later because of the twist and it also effects ignition timing. You may set you ignition timing at idle or 3,000 rpm's or however you do it but at higher rpm's the timing will be retarded dut to the flex in the camshaft over it's length. Some cam manufacturers actually grind their cams to compensate for this by advancing the lobes towards the back of the cam a certain number of degrees. Don't beleive me? Check here, they actually talk about the rear distributor of the chevy engines being a shortcoming:
http://www.summersbrothersracing.com/distributor drives.htm

 

Interesting! Have they measured the variation that it causes? To play devil's advocate, is the variation large enough to even be noticeable?

 

That is amazing. Who would know that. I am glad that some of you are way better at finding this info.

 

This is something that has been known for many years. Like I said, cam grinders have been known to compensate for it. To answer mercgt73, I'm sure they have all that figured out and they deemed it important enough to develop the part.

 

Flex in a shaft is a terribly easy thing to measure (with the right equipment... probably not in the engine in a garage at home)

And that's not at all an uncommon issue. Hell in most things where you have a driven (or driving) side of a shaft and a non-driven (or driving if the other side is driven) side you have to account for flex and variance between the 2 sides.

Do ford crankshafts have no load on them on the rear end? When you have a load on the shaft at both ends you normally get conflicting flex. Maybe chevy actually has it right by putting everything at the rear.

I understand what they are getting at, but honestly that flex is still going to be present, and your valve timing would still be disparate from your ignition timing. I would think even more so because as you approach the rear the timing variation will be greater, whereas with the rear mount distributor your timing variation would become less as you approached the rear. And if the cam was ground to adjust putting your distributor at the front would cause that adjustment to have nearly the opposite of the intended effect.

I prefer a front mount distributor for much more sensible reasons than this. Rear engine is a pain to work on.

This is the kind of issue that is common to many different types of machines, not just car engines. There are complex mathematical formulas for determining exactly how much a shaft will flex based on expected load and they can be used to determine exact flex at any point in the shaft.



Another edit because it's still not time to clock out yet-

A great text-book example of shaft flex is roller extrusion machines, because typically you only drive one side of the shafts that side will always have a tendency to "pull" harder and flatten out the extruded material more. This flex in the shaft varies depending on factors in the drive mechanism, such as speed, up- and down-system load, shaft thickness and length to name a few. But universally you find some method of compensating for this on the other end or across the shaft. A really good example is machinery used in printing processes. Paper being so thin the slightest variation from flex completely destroys the process or shreds the paper so lots of tricks have to be employed, such as variable thickness shafts, and adjustable thickness shafts. Some fancy roller shafts can even be disassembled to have entire sections taken out to prevent that 1 area from over or under contacting.

Common engineering problem, solutions abound.


TL-DR - I would suggest that this is a non-issue and a red herring from a company to sell unnecessary kits that solve non-real problems.

 

You're over thinking this thing here, forgetting that the rear mounted distributor and oil pump increases the load and thus the amount of flex in the cam shaft.

 

I don't know who it was aimed at in the other thread in closing it, but it's hard to respect someone's opinion when the only argument they give is that you're dead wrong, then run away and hide. This is a forum for discussion, not discussing the issue is contrary to it's purpose.

 

Thats kind of what I was thinking. These engines are archaic push rod motors mainly for street use. I get the idea of the cam twist but I think its irrelevant. Id rather have no dist at all to be truthfull.

 

EXACTLY! But ok, I'll bite. There certainly is some truth to the rear mount shortcoming and it is very well documented through the years. But despite that shortcoming unfortunately Chevy was still kicking many of our Fords asses for quite a few years due to all the factory support and longer list of legendary tuners who coaxed that mill beyond its inherent shortcomings. Smoky Yunick also went into great detail about the cam flex shortcomings that are unfairly being exxagerated here too.. but yet he overcame that issue by simply having custom cams ground for the issue. Don't get me wrong here.. I would rather drive a Ford.. than a Chevy.. but ehre are inherent flaws for both engine platforms without doubt.

Or.. like most do these days(for builds where it even becomes relevant to worry about) simply use a billet solution, larger core and/or roller bearings to move forward and worry about all the other more important points of variation, stress, and failure for any of these old engines.

And for god's sake guys.. do you seriously think that your little itty bitty hydraulic cams and little weak matching springs are severely twisting your cams at the mediocre tractor-like rpm range you're dealing with on a mild'ish street car? Only when you get outwards to the edge of the engines design parameters do you even need to worry about such things. Such as well over 200+ lbs of seat pressures combined with 500+ open's and the rpm that goes along with such pressure requirement.

Oh, I don't know.. maybe worry about more important things such as.. the pushrods, studs(do you need a girdle yet?), valveguides(size and length does matter you know) and springs themselves. Not to mention that it's fairly well known that even aftermarket rocker arm ratio's can vary by small degrees as well. Ever peek inside the valvetrain of a running engine?(I'll let you search for the vid's since I have just enough time to ramble off some various thoughts on the hair splitting going on here)... FAR more flex and varations occur at that juncture than worrying about the cam twist variance between an engine with front mount distributors compared to one with a rear. The pushrods alone turn to speghetti strands with big rpm/spring pressures.

Also consider the effect on timing that running the oil pump off the cam has as well regardless of which end it's driven off of. Spark scatter/cavitation is a very real issue with either design and using a newer gerotor(I run a Titan pump on my Chev and plan on one for my SBF when it eventually goes more towards full tilt) rather than the old spur gear design pump on its own will help far more than worrying about setting lobe timing differently from front to rear. Not to mention that I've degreed well more than 100 cams through the years and have yet to see one that is ground in the manner mentioned above(and yes.. I've often checked more than just #1 lobe timing). And that includes more than a few custom spec cams from the bigger aftermarket manufacturers too. Try calling Crower or Comp Cams to have custom piece done up for a really hot street motor and ask them to vary timing from front to rear to see what they tell you. Do they change that variance based on the spring tension?.. the firing order?.. bearing clearances?.. a happy medium guesstimate to come up with a "better than nothing" spec?

It's also a fact that a cam twists and returns many times over a single rotation(similar to a crankshaft) as it gets loaded/unloaded along its entire length).. .. not anywhere near linear fashion like twisting a towel to wring it out. So, if anything.. the timing would osscilate back and forth depending on many factors and would be tough to test each and every combo to come up with universally accepted variance from one end of the grind to the other.

I'll leave it at that for now and check back for the fireworks display replay later on.

 

I'm with you. The motor in my 03 Mach 1 is great. No dist. is 1 of many reasons its such a great motor.
All thing above have merit but for me the Fords dist. in front is SO much easier to work on. I like things easy. lol

 

wiping the dust off of it so their trailer queen is still shiny?

 

I'm with you groberts. It's splitting hairs and not noticeable for 99.9% of users including myself. This thread was just for some interesting conversation to get your mind thinking of things that you normally don't think about. And yeah some of my engines have 200+ seat and 600+/- open pressure with a solid roller of course. Yup it worries me! LOL And yes I cannot deny that the chevy smallblock kicked the ford smallblocks ass for many years. The reasons??? Cylinder heads, cylinder heads, and cylinder heads. Stock windsor type heads flow like **** and they always have. Thank god for the aftermarket! And yeah I've seen those video's of what happens to valve springs, valves, rockers, studs, etc. at high rpms and all I can say is WOW!

 

Oh and back on the topic of advantage of front/ford versus rear/chevy. Who wants to have to pull the distributor every time you remove the intake manifold, huh?

 

Depends how many times you screw up the install. LOL.

 

I remembered the best reason of all.

When I'm at the car show all those chrome'd up rear engine dizzy's look like a waste of money sitting next to the fords.