Thread: #*?#@ Distributor

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I have ordered a SBC HO to install in my 51 Chebby pickup. I have been told that if I don't modify the firewall I won't be able to use the distributor GM sends with the engine. What is the option here. What distributor is small enough to miss the firewall.
I want to keep the firewall stock to be able to add air soon.

If I'm not mistaken you might just have to replace the distributor cap to a smaller diameter. Unless it is an HEI .

I believe you can buy smaller diameter HEI caps also.

Mallory unilite is the smallest.

Yep, if a small distributor will get you there, a Unilite is very compact. Is a small distributor enough, or is there still going to be firewall in the way?


Don

I'm not a big fan of optical triggers ( unilite ), they are deadly accurate, but can be unreliable. MSD has some magnetic pickup billit distributors that you could fire with a GM HEI modual ( isolated in some way ) or a Chrysler ignition box, that could work very well. Hall effect triggers, are good to, but there only advantage, is they send a digital signal, rather than an A/C sign wave.

IMO there is nothing unreliable about optical triggers. They have been around for a very long time. I had a Unilite back in the 70's and worked flawlessly. We use optical triggers for a variety of far more critical things than ignition circuits with 6 nines reliability. I might also point out that optical triggers are used routinely in high noise environments (like ignition systems) to achieve such high reliability.

The Hall efect itself is not digital in nature, that comes from Analog to Digital conversion of the generated voltage signal which is typically an impulse, square wave, or sinusoidal in nature. Most all ABS and speedometers are now using such signals and they too are extremely reliable.

Embrace the technology, it works, don't be scared of it.

Kitz

Yeah, I agree. The unilite in my truck has performed flawlessly for about 4 or 5 years, and I have done no maintainance to it........no cap, rotor, or wires. I just drove it last week after it sat for about 8 months, and it fired up on the 2nd revolution and ran like a top.

I like 'em.


Don

Definition of hot rodding: If it don't fit, make it - or buy something else . . .

I like Unilites also. Ran one in my GTO for years, and it was flawless.

I've got a Unitlite in my Toter, been there for over 100,000 miles and never missed a beat... Not like the truck ever gets abused or anything.... Reliability has never been an issue with it.... I've had more MSD's that I had to send in for warranty work then I've ever had Mallory's. Well, come to think of it I've never had to send a Mallory unit back.... But I've sent 3 MSD boxes and 1 distributor back. This was a number of years ago, I believe there quality control has gotten better since, haven't heard of near as many of them being bad the last few years....

Originally Posted by kitz

IMO there is nothing unreliable about optical triggers. They have been around for a very long time. I had a Unilite back in the 70's and worked flawlessly. We use optical triggers for a variety of far more critical things than ignition circuits with 6 nines reliability. I might also point out that optical triggers are used routinely in high noise environments (like ignition systems) to achieve such high reliability.

The Hall efect itself is not digital in nature, that comes from Analog to Digital conversion of the generated voltage signal which is typically an impulse, square wave, or sinusoidal in nature. Most all ABS and speedometers are now using such signals and they too are extremely reliable.

Embrace the technology, it works, don't be scared of it.

Kitz

actully, the Hall effect, has 2 have a refrence voltage going to it, the shudders and crystal, inturupts the signal compleatly. so it's on off, bianary, square wave, digital signal. it's not digital itself, but that's the signal it sends. these are getting widely used, because a computer can read the digital output signal, where as, with a magnetic pickup, an A/D converter would need to be used, old Chrysler ign box's used a couple diodes, for an A/D converter. I'd take a hall effect, over a magnetic pickup, any day, because they are so accurate ( this is why there used as ckp's ), for a distributor, you might only need 8 shudders ( 8cyl ) but, add in 180 shudders, put the sensor on the crankshaft, and you got 100% crankshaft position.

actully, the Hall effect, has 2 have a refrence voltage going to it, the shudders and crystal, inturupts the signal compleatly. so it's on off, bianary, square wave, digital signal. it's not digital itself, but that's the signal it sends. these are getting widely used, because a computer can read the digital output signal, where as, with a magnetic pickup, an A/D converter would need to be used, old Chrysler ign box's used a couple diodes, for an A/D converter. I'd take a hall effect, over a magnetic pickup, any day, because they are so accurate ( this is why there used as ckp's ), for a distributor, you might only need 8 shudders ( 8cyl ) but, add in 180 shudders, put the sensor on the crankshaft, and you got 100% crankshaft position.
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Took the words right outta my mouth.


Don

I've been using a Unilite for as long as I can remamber the only problems I have ever incountered were if you hook them up wrong. cost about $64.00.
I haven't done it but a friend of mine did he was in a hurry and didn't read ALL the instructions.

I've got a 350 in my '51 Chevy pickup and there is no way a stock HEI will clear the firewall. I went with an MSD distributor and a separate ignition box. There's still not a lot of room, but it works....

You said yo haven't installed the engine yet.......Set it up, so that it will clear the firewall with an HEI........Then anything will fit.