The Stovebolt Site Forums The Shop Area Engine Shop What About Ignition Systems!

Hi Guys, When I started my truck I planned to go with an all original restoration. Well, I abandoned that for performance quickly, but not before buying a new distributor and coil. Since I already invested in them, I intend to use them. Are their any points available for a 250 that will handle a few more rpm than the stock ones. My engine will peak at around 4500, so I wonder if I even need to worry about this issue.
You Input is always Apreciated,
Bob

The stock points will probably bounce by then, but if you convert to a dual point system you can get around it. You can also add an extra spring.

I got a dual point conversion kit for my 261 for $10 from ebay. Mallory makes one, too. The points used in that kit have much stiffer springs. The points on my motorcycle are good upwards of 9000 rpm, so it can be done.

If you are really worried about it you can drop an HEI system right into your engine.

Some speed shops or parts stores or patricks prolly stock a "high rpm points set" that won't bounce. Has an extra stiff spring & heavier points arm and rubbing block. The points in my 235 used to go into defib about 3000 RPM. Played hell with the tach.

A lot of folks seem to like the Pertronix HEI conversion, I haven't used one. I prefer the factory HEI, as it is easier to recurve the advance. You'll have to change the wire to the coil for 12 volts. May want to change the coil to a performance coil. Standard use to make a really cool looking, about 4-5 inches in diameter and finned. My 2 cents.

Larry
68 C20 327 daily driver
63 C20 292 Camper truck
65 C10 ? Custom Cab AC,PB,PS,$flasher

I would have to vote for the HEI. I just bought 3 along with a MSD 6A box kit(coil, etc.) online. Don't even waste you time with a Pertronix setup. I currently have one, and it's not that great. It's better than points, but I think an HEI will be much better. I can go further into that if you want, but I'll leave it be for right now.

What's the reason for running a points set? I know you bought a new dizzy, but I don't see the point in buying expensive points sets that will keep burning up. Just my thoughts. I would also have to say a dual point setup would be bettern for higher rpms. Twice the adjustments, but better. Hope this helps. John

Here's my point about points! --- I already bought the distributor and coil , so I have all new stuff and I don't relish the thought of sticking it on a shelf and spending more money. We are only talking about 4500 rpm. That is about half of what my motorcycle turns on breaker points. There must be some points out there that are better than stock. Points are retro and retro is COOL!!!

I got points in my modified 261 engine,revs up fine to 4500 maxium, no misfire.Guys used to run small blocks to 6000+ rpm on single points no problem .I'm using NOS GM points gapped at .016 ,the distributer is recurved and has no play in the cam or shaft. I had a GM HEI on the engine a few years back,no difference in performance between the HEI and the points on my engine.
These vintage engines were designed around points ignition systems, the addition of an electronic system is no guarantee of better performance unless your stock distributer is worn.A clean sparkplug needs around 5000 volts to fire,an HEI with the potential of 40k volts won't offer any more volts. If the sparkplug needs 5000 volts to fire,that all the HEI will produce when the plug fires.High out put ignitions became necessary to fire plugs in in leanburn emissions engines in the 70's. Notice today, many new vehicles have skinny plug wires again? The latest engine designs don't require super high plug voltages.
Since most distributers are old and worn, an HEI or an electronic conversion is a good idea. Or if you're running a radical cam on the street,an HEI firing wide gap plugs may smooth it out some
Has any one tried out a multispark unit on these old 6's, like MSD or Crane?

What do you do when you "recurve" a distributor, and why do this?

Bob

Modern distributors have two advances, not included are computers. The vacumm advance which most everyone recognizes by the diaphragm pod on the side of the dizzy with the vacumm line attached. A centrifugal advance which usually consists of a set of springs and weights. In the case of your distributor the mechanism is under the point plate. The factory HEI has the centrifugal advance under the rotor. In any case the vacuum at max holds the distributor advanced per a degree of advance set by the diaphragm. When you open the throttle and the vacuum goes to to minimum the centrifugal advance takes over. The centrifugal then advances the distributor at a rate determined by the springs and weights. To recurve the distributor is to change that rate. Why recurve, better performance.

Larry
68 C20 327 daily driver
63 C20 292 Camper truck
65 C10 ? Custom Cab AC,PB,PS,$flasher

Here's an old dirt-track trick from the point-ignition days. Take the spring off a discarded set of points, and fit it inside the spring on the new points you're installing. It stiffens the spring, and adds about 500 rpm or more before the points start floating. Use a SMALL quantity of disk brake wheel bearing grease on the cam/rubbing block area of the distributor, or you'll wear out the rubbing block in a hurry. I've also got a racetrack trick to get an extra 1,000 RPM or more from an HEI distributor, if anybody's interested in going really fast with that setup.
Jerry

Hotrod, I'm curious, don't know that I would use it, but sounds interesting. How do you get another 1000 out of the HEI?

Larry
68 C20 327 daily driver
63 C20 292 Camper truck
65 C10 ? Custom Cab AC,PB,PS,$flasher

Thought I'd get a rise out of that one!

The reluctor on the HEI has 6 triangular projections that align with the similar-shaped pole shoes on the pickup coil. When these align, an AC voltage is induced into the pickup coil, which triggers the ignition module. At speeds above normal cruise, enough voltage is developed to interfere with the pickup coil's ability to set up for the next firing impulse, causing spark scatter. On the roundtrack V-8's, when we're required to run a stock-appearing distributor, I grind off every other point on the reluctor, leaving 4 instead of 8 projections. It still aligns 8 times, and fires all the cylinders because the ones on the pickup coil aren't altered. It works the same way on a 6, except 3 instead of 4 points are removed. This reduces the induced voltage, and allows 1,000 RPM or more to be gained before spark scatter occurs. A stock V-8 HEI starts to spark-scatter at about 6,000 RPM, and with the mod, it will go to nearly 8,000. Since we run the roundtrack engines about 6,500 or more, I can out-wind the guys with the unmodified distributors. On competition-only engines, we also disable the vacuum advance, and bolt the advance plate solidly to the distributor housing to eliminate plate wobble at high RPM. Since the 6-cylinder HEI is almost identical to the V-8, it works for them, too. We also reduce the centrifugal advance about 10 degrees, and advance the initial timing the same amount to increase acceleration without over-advancing. A good distributor tester is essential to set up the advance curve properly for best performance.
Jerry

The centrifugal then advances the distributor at a rate determined by the springs and weights. To recurve the distributor is to change that rate.
How do you accomplish this, and how do you know how much change to make. This sounds like a retro kind of thing to do, and it is very interesting, so speak to me Daddyo, speak to me!
Bob

Ignition timing is changed according to speed (centrifugal advance), or engine load, (vacuum advance). An "advance curve" is a graph, plotted with speed on the horizontal axis, and degrees of advance on the vertical axis. It's designed into the engine when it's built, by engineers with a lot more equipment and expertise than the average tinkerer has at his disposal. Unless you're well-versed in engine modification, and have a dynamometer and/or a distributor tester to check your results, LEAVE IT ALONE!

For high performance, or running a truck fully loaded all the time, etc., it's possible to tailor the advance for your specific situation. For everyday driving, just make sure everything is working right, not worn, and let the factory-designed advance system work the way it's intended to!
Jerry

Fleetside,

So, have you figured out from the advice above how to recurve a distributor?

Also, with all the impressive answers above, do you have an answer that is useful to someone who is interested in staying as original as possible with a 250 engine (and who wants to make use of an already purchased, original-style distributor)?

Has anyone led you to believe that you will have problems with points?

Just wondering.

My uneducated guess is that you will be just fine with new points and condenser.

Curmudgeon

Hotrod, Thanks for the info good stuff, do you mind if I quote it on another board should the occassion arrive. I'm not sure I agree entirely with your last post, but point WELL taken.

TSP, good points

Fleetside, with the stock distributor Hotrod has the right approach. It should probably be done on a distributor machine. There is another option and it would take some research. That distributor was used from 1963 till 1974 when the HEI replaced it. During that time there a lot changes made for emission control. See if you can find some Delco or factory info as to what springs were available. By the time you have the info hopefully you will have your motor further along and you can ask some more questions. When you advance a motor that tends to lean it out. You lean a motor out to far and serious damage can be done.

Larry
68 C20 327 daily driver
63 C20 292 Camper truck
65 C10 ? Custom Cab AC,PB,PS,$flasher

Larry, there's no big secret to the stuff I do on the race track, just a lot of things I've learned to increase the performance of a stock-appearing unit. BTW, the 4-lobe reluctor in the V-8 distributor was something Pontiac did in the early days of the HEI distributor on their "Daytona" package used by NASCAR racers in the early 1970's. I found out about it in an ignition system seminar at a GM training center in Memphis, TN a few years ago when we were discussing performance modifications. Feel free to pass it along!
Jerry

Curmudgeon,
The only thing that was helpful in this entire thread is the idea about doubling up the spring. I'll do that if I find that they are floating. My Dad, a 55 year vet of inline engines, says the stock points will handle 5500 easy!
Bob

With a stock inline 6 cyl. engine the stroke is long enough that it's built for torque not R.P.M. The new parts you bought are just fine as you wouldn't have any horsepower over 4500 R.P.M. anyway.

Hey Wrench ! Ya might wanna back up and read the thread. My engine will not be stock, and with the right cam and carb combo you can make a 250 turn a whole lot more than 4500!
Bob

Fleet, follow Hot Rod Lincoln's advice if you're gonna spin up that 6.
I don't have a distributer machine, but I degreed the damper, that along with a timing light and a handful of distributer spring and some trial and error got my distributer curved best for my situation.A dial in advance style timing light will work if you have no additional degree marks on the damper.But you have to be careful, dentonation at full load can turn pistons into scrap pretty fast.Old engines like 235/261's only need 34 degrees total cranshaft advance for maximum power, the newer 6's maybe 36 total.I'm running 34 degrees total advance in the 261, all in by 3000 rpm, the vacuum advance limited to half it's original travel.This requires 92 octance fuel to eliminate pinging with an actual compression ratio of 9-1. These older engines including the 230-292's are more sensative to octane requirements than newer fast burn head designs with electronic engine management.My 261 is never run over 4500 rpm so the single points are ok in my case.
As always, your driving style,fuel, gearing and engine modifications will determine timing requirements and ignition type.

Tony -- Do you know any particular distributors which would have stiffer springs? Am I right to think that the higher I'm gonna spin the engine, the later I want full advance?
Bob

Fleet, the RPM where you reach total advance is going to depend on your cam profile, compression ratio, and a few other factors. The only sure way to determine it is with a dyno, where you can monitor torque and horsepower at different RPM's. Where are you located? I've got the dyno setup in Nashville to give that one a wring-out, if you're anywhere near me. It mounts on a bellhousing, with a standard Chevy clutch, so it's a pretty simple setup. I've had engines of over 700 HP on it so far. Nothing beats a good dyno and a 4-gas exhaust analyzer to get the max performance out of an engine!
Jerry

I would love to have a dynometer, but for me, my dyno is the truck's tach and a back road course measured out between two power poles,lol.I like doing it the way the hot rodders did 50 years ago, trial and error, it's fun and keeps ya busy on a relatively low budget.These old 235/261's are just fun to tune, not to be taken too seriously.I've learned a few things on the old 6's from experimetation with a variety of engine modifications.
Fleetside, ya have a lot questions, Jerry has way more general engine tuning knowledge than me, so listen to him.And get a few books on general engine tuning,Leo Santucci's manual on modifing 230-292 Chevy 6's is a good place to start.Generally, what works on a V-8, will work on the L series 6 that you have, more cam, more compression, more carb, better exhaust etc, just have to know what's best for you.Go easy, a lumpy high RPM 6 in a heavy truck won't be fun in a daily driver.

Tony, thanks for the compliments!
I've been out of the 6-cylinder tuning business for a while, especially the old stovebolt engines. Most of the engines I play with now are short-stroke, high-revving V-8's, and they take a little different type of modifications to perform well. The stovebolt engine's big advantage is low end torque. A little higher valve lift, without getting radical on cam duration is the way to go on a low-revving engine. Within reason, higher compression helps, too. We don't want to get into the premium-fuel range, especially with gas prices going through the roof, so about 9:1 compression is a practical limit for a street engine. It might require mid-grade gas, but that's only about a dime a gallon higher, at least in the mid-south area.

Here's a trick I've used in the past,and it seems to work well. If I restrict the centrifugal spark advance 5 or 6 degrees, and increase the initial spark timing by the same amount, low-end torque is helped, without getting the total advance too high. It's done by welding up the slot where the centrifugal weights travel and checking advance on a distributor tester, or with a delay-flash timing light. Someone mentioned a total advance figure of 34 degrees, which seems about right. Smallblock V-8's work best with about 37 degrees max advance, but they're maxing out at 7,000 RPM or a bit more. That's a full-power advance, with no vacuum added, I assume. Vacuum advance is a fuel-economy measure, and goes away when full throttle is used. It will add from 8 to 15 degrees of advance at light-throttle cruise, depending on engine design.

Too much advance is worse than not enough, IMHO. When my Dad was tuning the family dirt-track car 50 years ago (a flathead F*rd), he did some chassis dyno testing in a trucking company shop, one of our sponsors. The car was run at full throttle, and the timing was advanced until the max HP was reached, then the timing was advanced 1 degree more, and the power drop recorded. Back to max HP, and timing was reduced one degree at a time. It took 5 degrees of spark retard to get the same power loss as 1 degree too much timing! Food for thought!
Jerry

HotRod -- thanks for the offer but I'm on the west coast; Northwestern Oregon; kind of a long drive for a tinkerin' session!

Tony -- I still want to know where do I get heavier distributor springs. That is something I would love to play with just for the sake of playing.
Bob

My brother lives in Beaverton, Oregon, and he brought his son's Chrysler 383 engine back to Nashville to build it and dyno-tune it. It's still here, after we discovered he had made a mistake figuring the compression ratio. In about another year, there will be a 16-year-old brand new driver on the streets of Beaverton with a 400-HP mustard-yellow Roadrunner! Duck and cover! (Actually, he's very responsible, and they're only going to hotrod it on the drag strip!)

For an assortment of advance springs, try your local wrecking yard. Since mechanical-advance distributots are at least 20 years out of date, they'll probably have a bunch of them around, with little or no chance for a sale. If they don't give them to you, the price should be low. No real preference about brand name or model, most advance springs are very similar.
Jerry