rev counter quiestion v8 helpp plz

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johnd444wph
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rev counter quiestion v8 helpp plz

Postby johnd444wph » Sun May 11, 2014 10:50 pm

Putting a v8 chevy 350 in my mark 3 been ttold I can get a speedo cable made up ,but need to know how the rev counter will work as its a 8cylinder insted of 4 , been told about a resister or something ? Thabks

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Re: rev counter quiestion v8 helpp plz

Postby stevemarl » Sun May 11, 2014 11:09 pm

It may be a problem as it works by counting the pulses from the coil, hence the 4 & 6 cyl Tachos are different, and marked so. If you have a 4cyl tacho fitted, a V8 will show double the engine speed. My plug in test meter has to be switched 4,6,8 cyl. Can`t think of a simple way round it tbh.

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Re: rev counter quiestion v8 helpp plz

Postby Terra-Kotta » Mon May 12, 2014 2:09 am

:headscratch: Fit two 4 cylinder ones and you can have a rev counter for each bank :applaud:

Can I bagsy you little pinto please.

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Re: rev counter quiestion v8 helpp plz

Postby stevemarl » Mon May 12, 2014 8:08 am

Terra-Kotta wrote: Fit two 4 cylinder ones and you can have a rev counter for each bank

Now that`s a good idea!!!

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Re: rev counter quiestion v8 helpp plz

Postby Matty2148 » Mon May 12, 2014 9:15 am

I forget the details now, I think it was 2005 when I did my V8 cappa, you can get tacho`s with a potentiometer built in, you can use this as a dial to get the tacho to read good, you will also need to know what your engine is idling at in the first place, I used a snap on timing light for that bit...I`ve found an old thread:
http://www.fordcapriforum.com/forum/viewtopic.php?f=13&t=8357&hilit=pot

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Re: rev counter quiestion v8 helpp plz

Postby pbar » Mon May 12, 2014 9:19 am

stevemarl wrote:
Terra-Kotta wrote: Fit two 4 cylinder ones and you can have a rev counter for each bank

Now that`s a good idea!!!


But just think of the modding being done to accomodate the extra counter!

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Re: rev counter quiestion v8 helpp plz

Postby stevemarl » Mon May 12, 2014 10:32 am

pbar wrote:But just think of the modding being done to accomodate the extra counter!

:xd:

Matty2148 wrote:, you can get tacho`s with a potentiometer built in, you can use this as a dial to get the tacho to read good

As I remember, there is a trimmer pot on the ford one isn`t there? I wonder if there might be enough adjustment on that? In fact, are the 4 & 6 cyl the same - just set up using this?
All you need then is someone with a square wave generator so you can recalibrate.....

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Re: rev counter quiestion v8 helpp plz

Postby Matty2148 » Mon May 12, 2014 10:44 am

stevemarl wrote:
pbar wrote:But just think of the modding being done to accomodate the extra counter!

:xd:

Matty2148 wrote:, you can get tacho`s with a potentiometer built in, you can use this as a dial to get the tacho to read good

As I remember, there is a trimmer pot on the ford one isn`t there? I wonder if there might be enough adjustment on that? In fact, are the 4 & 6 cyl the same - just set up using this?
All you need then is someone with a square wave generator so you can recalibrate.....


Not sure why you`d need anything other than a accurate way of reading the engines current RPM, and a terminal screw driver.
As I say, I used a snap on timing light and got it to idle at 850 rpm, then turned the pot to show 850rpm, then using the timing light I set the engine to 1500rpm checked the tacho then finally 3000rpm and checked the tacho, it was spot on. Its on the late Capris after 85 I think when they became standard fit. I did a whole thread on in someplace after I stuck a RV8 in mine. I think colin (capri turbo) did a write up too.

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Re: rev counter quiestion v8 helpp plz

Postby stevemarl » Mon May 12, 2014 10:46 am

Matty2148 wrote:Not sure why you`d need anything other than a accurate way of reading the engines current RPM, and a terminal screw driver.


No, I was just thinking of a way to calibrate it on the bench that`s all.
So if it can be done with the trimmer, that`s his answer!

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Re: rev counter quiestion v8 helpp plz

Postby Matty2148 » Mon May 12, 2014 11:11 am

stevemarl wrote:
Matty2148 wrote:Not sure why you`d need anything other than a accurate way of reading the engines current RPM, and a terminal screw driver.


No, I was just thinking of a way to calibrate it on the bench that`s all.
So if it can be done with the trimmer, that`s his answer!


Just have to find the right instrument cluster now, I`m pretty certain after 1984 variable ones were standard. (lasers and specials basically)


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