DJ to MV pistons

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DJ to MV pistons

Postby trundletruc » 09 Feb 2018, 09:40

I am about to get my DJ engine reconditioned/rebuilt and have been wondering if having MV pistons put in it, thereby lowering the compression ratio would be better economically as I could use 95RON petrol. We travel all over Europe and 98RON petrol is not always available.
I will be running the engine on a carburettor and I know you can retard the ignition on the DJ to allow the use of 95RON.

When running on 95RON petrol Is it better just to retard the ignition on the straight DJ in terms of power, fuel consumption and longevity of the engine?
Or put in MV pistons in terms of power fuel consumption and longevity?

If anyone has ideas about this or there is anyone who has already done this can you let us know what the result has been, please.
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Re: DJ to MV pistons

Postby itchyfeet » 09 Feb 2018, 10:11

You can run a DJ on 95 no problem, just set ignition to 5 degrees.

IMO ypu are not going to gain any efficiency, they are all poor, how ypu drive it makes a bigger difference.

If you do want to swap I have a set of MV :D
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Re: DJ to MV pistons

Postby 123-jn » 10 Feb 2018, 16:38

There is probably not alot in it unless you run the fuel injection. I went for DJ because I run on gas which is perfect for the high compression. It runs ok On petrol even timed at 8-10 degrees but I use the 98 ron petrol. I have run it on 95 and it didn't ping. My spare engine I am just building will be an MV which I expect will be very close in performance on petrol with perhaps a bit of loss on gas.
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Re: DJ to MV pistons

Postby silverbullet » 10 Feb 2018, 17:42

If the engine has later heads or AMC's, the DJ pistons barely give it 10:1 static compression ratio anyway, due to the larger cc chamber.
The MV is closer to 8.7:1 iirc
Search for my past post with pics to explain.
Modern fuel is not the same as sold in 1987 and much more detonation resistant, even shopping cars have SCR of over 10:1 for efficiency.

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Re: DJ to MV pistons

Postby silverbullet » 10 Feb 2018, 17:45

viewtopic.php?t=149884

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