Engine and Transmission Tech

Hi everyone, thanks for letting me join.

I was wondering if you may be able to help me. I have a 4.6 stripped and also a 3.9 small journal too. I have read that by offset grinding the 4.6 crank and using the smaller 3.9 rods its possible to build a 4.8. Trouble is the piston to go with this! I get to the name Ford.. and then the info fizzles out. I've made calls to various people today. I get offers to make them for a load of cash but if I have to I'd rather put the cash into heads to get the C R right, if anything. What I'm really after is a piston I can use or mod to use. Its only going in a van so we wont rev it past 5k.

Steve

I suggest you look at the KB 832, on the Icon webbsite. Forged, app is for 305 sbc. Might massage for your use. Valve reliefs are 23 deg. Good luck. roverman.

Curious why you would spend that kind money on an engine going in a van that won't see more than 5000 rpm?

Thanks Art I will check out that piston tomorrow and let you know how it goes.

Carl, If it was for a lightweight car, I'd probably not bother chasing the 4.8 solution as I'd probably find it both easier and more cost effective to build the same sort of power from a 4.6.

But all the parts so far haven't cost me anything so its no that expensive.....yet. The piston price, could change all that.

Steve

So will that crank machining & treating, rods resized, cylinder boring....gonna add up fast besides pistons. Have fun.

Don't forget, Carl, it's about the chase, and not the catch. If it were just about results, I would probably be building a LS1 instead of twin turbo, big bore, injected RV8.

... and I wouldn't be wasting my time trying how to get a 4" bore with a Buick/Rover. ;)

Ok, Upon a re-read, I believe a 4.6L stroke is 3,322" ? You wish to offset to ? 305 sbc, hypereutectic ? roverman.

May not quite answer your question, but here is a blast from the past about a similar build.

[forum.britishv8.org]

Hi,

you can find pistons in Uk : [www.v8tuner.co.uk]

Cheers.

Another option is a forged piston set from Real Steel UK, see [www.realsteel.co.uk] and part number DW49952.

These are made by Icon. I have a set of these, if you need any measurements just let me know.

Hi, I've read all of the thread and thanks for your collaborative input.

The KB ones are not a lot of piston for quite a lot of money. I'm not sure how long they would last in a van that can weigh in at a couple of tons from time to time.

The V8 Tuner pistons , they only have one set left and they're keeping them back for an in house build.

The realsteel ones, they don't stock as they cant get their stroker cranks any more.

There was another option in the other thread. but my block wont bore past standard as the liners have O rings at the bottom and it would be dumb to rip out new unused liners to fit the 96mm ones for the sake of 200CC.

The original plan was to "recycle" the parts I had and just add the magical Ford Truck piston to the mix.

I'm thinking maybe its easier to accept the destiny and just plod along and build a 9.8:1 4.6. using standard parts?

Steve

It would be way more economical for truck engine.

Today, I'm thinking; I wonder how many other people aves got this far and would like a piston to do that job? What if one could be made to use the 4.0 / 4.6 28cc. Head and provide 9:.8 to 1. IMO the 4.0 / 4.6 cylinder head design is poor but there are two pistons already that already that are working models. if I were to get those back into CAD they could be used as a design base. I know there's a lot to be taken into consideration. but a lot of the critical dimension work will get inherited.

A good friend runs a CNC shop nearby. A couple of others are Design engineers working with CAD and Photogrammetry. Maybe I should build the 4.6 to keep things moving but develop a design for this piston as well?

What do you Guys think ?

Well, speaking as someone who did go the custom piston route, I can say that taken as a fraction of the cost of a conversion the difference between a stock cast piston and a custom forging is not really that great. Correct, it does run into several hundred dollars but amortized over the life of the engine that's pennies per mile. I feel it is a worthwhile investment to be able to work with the piston maker and get exactly what you want with no compromises, and look at it as a one time investment. It is reasonably likely that I will not have to replace this engine.

I went with Venolia because they are an old name in the piston business, had the Buick blanks on hand, and gave me a competitive quote. But up and coming companies like Diamond can probably do better. The quote was a baseline and was IIRC $70 each. By the time we met my specifications we were closer to $100 each including the rings, wrist pins, and pin locks and weight was down in the 500 gram range. So that was something over $700 the set when you could buy off the shelf cast for under $300, a difference of, well let's just say $500 shall we? What could you do in your engine build with an extra $500 that is a better investment? Can't port the heads, need more money. Might manage a better intake if you can find one. Not enough for aftermarket forged rods really, but close and then you need the forged pistons anyway. Can't get a forged crank. Can't get aftermarket heads.

The point I guess is that when it makes sense in the engine build, usually there are not enough builds that are the same or close enough to justify starting from scratch when the piston companies already have most of the design work done. (a piston is not a simple undertaking and certainly is not a simple round cylinder what with skirt flex, unequal expansion, and other considerations) Group buys have been known to happen though, not too long ago the Buick 350 guys had Diamond make them up a run of SBB pistons and I think they got the price down into the $500-600 range or close which is pretty reasonable if you are the guy spec'ing out the piston. For the rest, well who knows?

Jim

Thanks that was interesting to hear you speak from experience on it. i was talking to someone today and it's funny how as you start to do that, things come to mind. (note to ones self - talk more to our dogs, they don't ask defeatist questions and have a great attention span). I already have two Land Rover pistons designed to go in the bore. Sure things need to move about a bit but, to a piston manufacturer this is just everyday business.

So that's it I'll get onto some and report back. Many thanks.

One thing to remember: when you add stroke and use a relatively short rod please make sure that the rod is long enough to clear the crank counterweights with the piston fitted. The piston still has to have enough material underneath the pin to stay together.

I think that TVR used a 4,2 litre piston in their longstroke 5,0 litre engines. Machined both the top and skirt and added valve cutouts to the top. IIRC this rod is shorter than 3,9 kitre rod.

Another thing you get to do with a custom piston is move the piston pin up. As you can see above there is quite a lot of room to do that, it allows you to use a longer rod, and a lighter piston. You can also use a lighter wrist pin. I may have overdone that just a little in my build, using thin wall 3/4" diameter short length tool steel wrist pins and 7" FHF Scat rods (which were inexpensive and used the Buick big end bearing) but the end result was a very light piston and rod package and a rod/stroke ratio over 1.8 without getting into the oil ring land. (340 block so a higher deck as well) Because mine is a blower application the pistons have a thicker crown than they would have been for N/A but still very light. I have a nice squish land around the edge of the piston with just over .040" gap at TDC and a dish that gives a 10.6 compression ratio. No valve cutouts and right at 1/4" valve clearance with .500 lift. (checked with clay)

Jim

Thanks for taking the time to post these things. Just for the chase, it would be nice to either hunt down or have made the piston to work with that original idea of 4.6 offset ground crank and 3.9 small journal rods. I just have to find the quiet time to work on it all a bit more. The piston company were very helpful. Over here John Eales has the rights to Omega pistons so I imagine they have some interesting rover stuff on their books or why else would!JED tie up a deal?

Steve