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Old 05-29-2018, 02:52 AM
stollz's Avatar
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Join Date: May 2018
Posts: 3
starting engines

Hi everyone,

New here, but have been reading for a long time.

Very enthusiast people here, with a lot of knowledge.

I've been a mercedes and BMW fan for a long time and gattered a lot parts threw the years.

In my basement under my garage i got several engines laying around.

all mercedes V8. 450, 420, 500, 6.9.

10 years ago i bought a complete 6.9 engine plus gearbox and wanted to put it in one of my SEC's.

It was a 80K mile engine from a totaled car.

It never happened, and the car is gone.

Last year, I really wanted to start the engine and made me a HEI ignition for it.

Didnt connect the fuel system, just poured some gas and paint thinner in the manifold and got it running for a couple of seconds.

Then I tried it in my 560 sec. Disconnected the EZL, and made a connection from the Hei tachsignal to the benz-tachwire. The car was running, but the HEI tachsignal is a very spiky and noisy one, and needs to be converted to a perfect square wave.
My MS1 lost it's mind and was resetting. The rev counter was all over the place. The car was not drivable at all.

Just out of curiosity, i'm going to make a square-wave converter. I want to know if it will run OK on a HEI ignition.
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Old 05-29-2018, 11:28 AM
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Join Date: Feb 2011
Location: Modesto CA
Posts: 2,748
Originally Posted by stollz View Post
I want to know if it will run OK on a HEI ignition.

CAN the engine run on the HEI? You seem to have already answered in the affirmative.

SHOULD it be done? A rather different question.

The OEM ignition system of the 560 engine is a design 12 years newer than the HEI and is crank timed. Has your analysis and comparison of the two systems revealed something superior about the 1974 system? Something that has escaped the notice of many others?

At this point your achievement seems to be in creating aluminum chips.
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Old 05-29-2018, 11:55 PM
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Join Date: Jan 2012
Posts: 7,162
Given GM HEI parts are on the shelf at any auto parts in the US / Canada / Mexico I'd say that is an advantage. A generic 4 pin HEI module is 13 USD and a higher end one $ 22, a cap is $ 15 , rotor $ 8 . A complete 100% new distributor ready to have plug wires snapped onto is $ 75

Frank, please post the costs of the above using MB parts.

Some makers ( Like Fiat and some British makes ) actually used a 4 pin GM HEI module hidden in a box so using HEI on something else isn't new.

Stollz, Frank tends to make a big fuss when someone wants to deviate from what came from the MB mother ship so take that into account when you read his postings.

Have a look at the MSD brand of aftermarket ignition systems, they should have a tach filter. Also look at the DUI brand ( Davis Unified Ignition )

Given it is highly likely someone has run a MS on a GM HEI car, there has to be info on the internet to solve the problem. Have you tried a MS message board? When you have solved this, please post the results.

To make full use of their potential, be sure to run a 12 gauge wire for power all the way back to the ignition switch and to battery. HEI has a large initial current draw and will be limited if the wire is too small. This also might be a reason you are having fuel / tach issues if you are running the MS from the same wire.
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Old 05-31-2018, 09:18 AM
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Join Date: Jul 2013
Posts: 87
Might be a ground issue.

I have a toyota truck, with a ford v8, using an early electronic (duraspark 2) distributor and a remote mounted hei module on a heat sink.

You sure your getting tach signal from the coil negative?
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Old 06-05-2018, 01:53 AM
stollz's Avatar
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Join Date: May 2018
Posts: 3
To get your mercedes electrics working right, it needs a perfect square wave.

I used the tach output of the HEI distributor.

Purpose of the Hei is only for starting engines i have laying around, or I come across.
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