DJ vs MV on carb and LPG

[itchyfeet]

I have been thinking of converting to DJ or MV when I rebuild.
both 2.1 with the same stroke and cam but DJ has different pistions to give higher compression.

DJ 112 bhp is based on an injection system and 98 RON petrol
MV 95 bhp is based on a injection system and 91 RON petrol

I guess if you were to run a DJ on 91 RON you would not get 112bhp


I'm wondering if you ran both on a standard Pierburg 2e3 and LPG if the difference of 17bhp would be significantly reduced to the point where the condition of the engine would make as much difference.

LPG has a higher RON but I read it has less engery per litre ( lower energy dencity) than 98 RON petrol.

DJ compression 11 to 14 bar
MV compression 10 to 13 bar
Quite an overlap in these, easy for a worn DJ to have less compression than a good MV.


Any thoughts or wisdom on this?

[Jawin89]

Not sure if this helps but I know the kWh per litre of LPG is 7.4 - 91 RON KWh is 9.6 and 98 RON KWh is 10.9.

I knew the LPG conversion rate was low as we use this as comparison to Kerosene at work. I am sure I have read somewhere that higher compression ratio can increase LPG performance and that 98 RON should be used in higher compression ratios to stop pinking.

I may be wrong but Mr Google would have more info

[itchyfeet]

Thanks thats exactly the sort of info that helps.
I guess I could have asked the question...

... is lpg better suited to high compression or low compression engines?

so much to learn....

[Mocki]

I'm only speaking from experience here, but,
I have run a DG , SS and DJ on lpg with the same carb in the same van, and the DJ loves it, no difference in real life power tween petrol and Lpg . Timing was set to 10° so only run SuperDecaffonated liquid gold tho

The DG never had as much power on lpg as petrol, , timing was 7° for best all roundness

The SS was below the DJ on power, but better than the DG , but much smoother on LPG than the DG

In my current van I have a DJ on a DG carb with a blos, and there is apsolutely no difference tween LPG and petrol ( super decaf) in power , at 10° timing

[itchyfeet]

Thanks, is super decaf 98?

[Mocki]

Yeah think so, super unleaded .....

[itchyfeet]

To add something else to the mix, my lpg was always lacking ìn power until I closed the loop, now I have stoich feed it has so much more power, mpg is lower but who cares

[Mocki]

Think that really depends on how you set it up on open loop....
i always had mine set for power rather than mpg anyway, because I was always towing and hauling stuff about
Not such a issue with the blos, it solves it itself by design

[itchyfeet]

Does an SS have same pistons as an MV?

[Mocki]

I'm not sure, but it is a lower output than a DJ .... I used to know, but brain is refusing to send info to fingers!

[itchyfeet]

ss is 9:1 same as mv so I guess same pistons.
dj 10.5:1

still can't understand if a DJ with same measured compression test figures as a MV would perform better?
the ranges are very similar, condition would to me seem more important.

[Jawin89]

Link from your WBX thread by Silverbullet below. Scroll down and it gives specs for the different Pistons.

http://perlindgren.tripod.com/wbx.html" onclick="window.open(this.href);return false;

May help

[DoubleOSeven]

Paul, you are more than welcome to pop round and take my MV on Pierburg carb. out for a spin if you want.


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[itchyfeet]

Paul, you are more than welcome to pop round and take my MV on Pierburg carb. out for a spin if you want.

Thanks Martin,
I'm sure it's faster than my DG, just trying to work out if it's worth hanging out for DJ pistons as they don't come up used often and 400 quid a set new.

[DoubleOSeven]

I wouldn't bother personally. The low end torque and all round improved performance you'll experience compared to the DG will be more than satisfactory. Also, as it's a carb fed rather than injected upgrade, I'd bet the difference to the DJ's would be negligible. We should set up a drag race between MV & DJ perhaps?! No seriously, save your £


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