I've heard of old 1.6 Rabbits doing this and making huge power.
Has anyone here done it? I dug up an interesting bit of information concerning one of my favorite motors that made me think about it.
As well as reading a feature on a Gatebil Audi A4 that does the same thing. (Diesel 5 cylinder bottom end.)
How would this even work without spark plugs?
Sorry... you would swap the head over to a gasoline head. I forgot to mention that part, didn't I? 
In the case of the Rabbit, you take a gas head and slap it on your diesel bottom end. (I'm still researching) In my case, i'd swap my gas bottom end out for a diesel.
EDIT: I was replying to the initial, no-mention-of-non-diesel-head post...
Here's more tantalizing hints that i keep running across.
http://www.speedhunters.com/2012/07/you-know-that-one-audi/
article said: Power comes from a Frankenstein engine using a 2.5L inline five cylinder diesel block and a 20v head from an S2. The block, which costs next to nothing (around $100 US!), was designed by the German car maker to withstand extreme punishment making this not only a cheap bottom end but also and incredibly reliable one. When combined with a head from a vehicle which, during its day, was the top of the range sports car from Audi, you’ve got a pretty potent setup.
Big turbos and a bazillion pounds of boost!
Isn't there a video of a veyron getting smoked by some innocuous looking awd vw that had done this?
A VW 1.6 Diesel bottom end plus a 1.8 JH head nets a 13:1 compression ratio. That is all I remember. There was a local guy building a drag car like this years ago but it never ran very well. It was before E85 was available around here and he was using the CIS system with it.
I have heard of this being done when the Olds 350 V8 Diesel was common.
Here's video of the Audi in the Speedhunter article: http://youtu.be/P46gPRrxf28
On the Olds it was considered necessary.
How fast can you spin an unmodified diesel bottom end? I'm not sure what these particular motors were built for, but I'd wager you'd want more than 4k rpm in your gas frankenmotor...
peter wrote: How fast can you spin an unmodified diesel bottom end? I'm not sure what these particular motors were built for, but I'd wager you'd want more than 4k rpm in your gas frankenmotor...
Small diesels often aren't RPM limited by their bottom ends.
But that's certainly something to wonder about. The R2 diesel (block i'd want) makes peak HP at 4500rpms, which is really only 1700rpms lower than the factory redline of my gas equivalent engine.
At 23:1 compression, i can't imagine the bottom end being less tolerant of abuse than the 7.8:1 gas equivalent.
I gather one of the "hot-ticket recipes" (of dubious quality, I'll give you) for BMW M20s is to use the 524td diesel crank, because it's forged, unlike the e or i engines. I don't recall the relative stroke or other impacts, but I gather it was favored for its strength, so there's one incredibly dubious and unverified piece of info indicating that a diesel crank is good for a gas performance application
Remember that revs put different loads on the rods than compression.
As for E85, it's excellent stuff. You can throw lots of timing at it and make lots of powers. And you'll have to feed the engine lots of fuel. Biggest problem is that the 85 is a maximum percentage, you might have quite a bit less - and thus less octane. On the Miatas, we're using a GM fuel sensor to tell us what the ethanol content is and blending the fuel/ignition maps accordingly.
Keith Tanner wrote: Remember that revs put different loads on the rods than compression. As for E85, it's excellent stuff. You can throw lots of timing at it and make lots of powers. And you'll have to feed the engine lots of fuel. Biggest problem is that the 85 is a maximum percentage, you might have quite a bit less - and thus less octane. On the Miatas, we're using a GM fuel sensor to tell us what the ethanol content is and blending the fuel/ignition maps accordingly.
Haltech has a new FFS that says it reads to 100% ethanol...
http://www.haltech.com/flex-fuel-sensor/
I've never tried to find out how far ours will go, as we don't have E100 here :)
Keith Tanner wrote: I've never tried to find out how far ours will go, as we don't have E100 here :)
If you can get E85 at the pump, you should be able to get E98 from the fuel supplier. I know I can even though they don't supply E85 around here. The bulk oil supplier here carries it back at their facility.
Revwise, your problem will come from the extra weight of the pistons. Fast requires light, and diesel isn't either. The low rev limit of diesels has far more to do with the speed of combustion than it does with bottom end construction.
Your biggest reliability issue will be the VW sign on the grille. (Sorry, I had to. I can't let VW people go without abuse. Its a bit like popping bubblewrap for me.)
You can get that same comp ratio with stock 16v pistons and the 8v head. I dont see any advantage to using the lower displacement duesel bottom.
I may have spoke too soon about the vw displacements. Seems it may be the 1.8 diesel with a 16v gas head.
Either way that's secondary. I'm looking at the R2 mazda diesel. Uses the same block as my F2, possibly/probably the same crank. I'm not real worried about weight since I'm only talking about revving 1000-1500rpms higher anyways.
I need to find details on the diesel head. I feel like the head design is what jacks the compression through the roof, not the pistons. 23:1 pistons with similar head to the f2 would give you large positive deck height and the R2 doesn't have that.
So basically I'm gathering that nobody here has really done this?
In reply to Streetwiseguy:
No worries on the VW crack. I don't own a VW and the thread isnt about a VW.
In reply to Paul_VR6:
Are stock 16v pistons anywhere near as strong as diesel pistons made to withstand 10 more points of compression?
I'm talking boost here. I've had my fill of n/a motors for the moment and a single cam 12v mazda motor would be my last choice for n/a builds.
The more i look into this, it seems that people may be just using the diesel blocks... I need to ask my buddy to elaborate. If it's just the blocks, then there's really no advantage here for me.
Keith alluded to the difference in stresses between revs and compression - Corky Bell's book on turbocharging does an excellent job of describing this. Changing direction very quickly is a bitch!
One of the other things I'd think about is the oil pump - spinning it 33% faster must result in interesting behavior.
(33% based off your 4500rpm + 1500rpm comment earlier, perhaps I misunderstood your goals).
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