4.6 and 3.9 standard pistons are the same????

mgbv8 · Post by **mgbv8** » Mon May 12, 2008 8:38 pm

Thats right isnt it? They are both 94mm but have a different stroke to get the 3.9 up to 4.6 dont they?

I'm hjaving trouble finding a set os stock 4.6 pistons at a reasonable price.
Rimmers want 68 quid a piston??

davemgb · Post by **davemgb** » Mon May 12, 2008 8:43 pm

I think you will find that the 4.6 piston has the gudgion pin nearer the crown and offset to one side compared with the 3.9 or 4.0 piston.

Dave

mgbv8 · Post by **mgbv8** » Mon May 12, 2008 8:44 pm

Thanks Dave

RoverP6B · Post by **RoverP6B** » Mon May 12, 2008 10:02 pm

The 4.6 also has larger gudgeon pins,...24.00mm diameter as opposed to the 3.9 which are 22.2mm.

Only the 4.0 and 4.6 have pistons which have the same size gudgeon pins, but their design are also distinct from each other.

You will need to use 4.6 litre pistons in a 4.6.

Ron.

CastleMGBV8 · Post by **CastleMGBV8** » Mon May 12, 2008 10:03 pm

Perry,

the 4.0 & 4.6 pistons are completely different to the 3.9 ones and have a larger gudgeon pin of .966 and compression height of 35.8mm as opposed to the 3.9 which has a gudgeon pin of .874 and compression height of 38.02mm plus an offset on the gudgeon of 0.6mm.

Real steel has 4.6 +20 pistons for£133.92 for a set of 8 but that would mean a rebore and I guess not what you want to do.

You give them a ring to see if they have any standard size ones or try LandRover agents, I think they are Hepworth manufacture so why not give them a ring direct.

If you want a bit more compression you could use 4.0 pistons, I don't know the bowl volume so cannot give you the actual compression ratio, I have heard 10.8/1 mentioned before but that does sound a little high to me, if you speak to Hepworth you ask them what the actual volume of the piston bowl is and we can work it out.

I think V8 Tuner has 4.6 pistons so you could try them as well.

Kevin.

TVRleigh · Post by **TVRleigh** » Thu May 22, 2008 11:09 am

CastleMGBV8 wrote:Perry,

the 4.0 & 4.6 pistons are completely different to the 3.9 ones and have a larger gudgeon pin of .966 and compression height of 35.8mm as opposed to the 3.9 which has a gudgeon pin of .874 and compression height of 38.02mm plus an offset on the gudgeon of 0.6mm.

Real steel has 4.6 +20 pistons for£133.92 for a set of 8 but that would mean a rebore and I guess not what you want to do.

You give them a ring to see if they have any standard size ones or try LandRover agents, I think they are Hepworth manufacture so why not give them a ring direct.

If you want a bit more compression you could use 4.0 pistons, I don't know the bowl volume so cannot give you the actual compression ratio, I have heard 10.8/1 mentioned before but that does sound a little high to me, if you speak to Hepworth you ask them what the actual volume of the piston bowl is and we can work it out.

I think V8 Tuner has 4.6 pistons so you could try them as well.

Kevin.

could you skim the 4.0 piston to give 10/1 not sure how much you would need to take off. but the 4.0 piston have quite a big bowl.

Also 4.0 pistons are lighter than 4.6 ones.

mgbv8 · Post by **mgbv8** » Thu May 22, 2008 6:47 pm

I've been told by Sean at V8 Devs that the 4.0 low comp pistons will be ok in my 4.6 engine. I hope so, because I've just ordered a set???

CastleMGBV8 · Post by **CastleMGBV8** » Thu May 22, 2008 9:22 pm

Perry,

Just a thought and I hope I'm wrong, but if the 4.0 pistons are lighter as suggested by Leigh won't the engine require re-balancing?

I've just got my internals for the 4.35 engine back from Real Steel and it needed quite a bit of heavy metal to balance it with the chevy rods and pistons. Engine should be going together in the next few days at long last.

Worth checking the piston weights to be on the safe side.

Kevin.

TVRleigh · Post by **TVRleigh** » Fri May 23, 2008 10:39 am

Any Engine that's going to be pushed should get balanced.

for the price £200-£300 it just not worth not doing it.

russell_ram · Post by **russell_ram** » Fri May 23, 2008 11:00 am

"I've been told by Sean at V8 Devs that the 4.0 low comp pistons will be ok in my 4.6 engine"

I'm failing to understand why you would want to use 4.0 Low Comps in a 4.6 motor ? ?

Using 4.0 9.35s gives you a free CR increase compared to 4.6 pistons when used with a 4.6 crank. I haven't done the sums but surely 4.0 Low comps will end up being almost the same as 4.6HCs?

Why not take the free performance upgrade from increased CR? I have been running my 4.6 at 10.5CR with a 100 shot for 8 years with no issues at all.

Russ

Just done a quick sum and I calc an LC 4.0 piston bowl at 33cc cf a std 4.6 at 32cc. So you should end up exactly where started CR wise, just about.

mgbv8 · Post by **mgbv8** » Fri May 23, 2008 3:23 pm

Russ
Maybe thats why he said they would be ok. So I end up about where I should do?? I think its down to the OE suppliers running short on stock.
I hope they are ok mind. I dont want another tear down too soon.

All this talk of minor differences in the 4.0 vs 4.6 pistons has me a little worried I must say. I'll call V8D again on Tuesday to confirm they will be right for my engine. It was built by V8D in the first place.

Kev
The egnine has been balanced, and I will weigh the pistons as usual. I have the correct scales. I wouldnt have thought the pistons being lighter would matter. Would it? If I make sure the pistons are all the same weight, give or take a gram, I will be ok wont I???

Perry

CastleMGBV8 · Post by **CastleMGBV8** » Fri May 23, 2008 4:09 pm

Perry,

I'm no expert in the black art of balancing a V8, but if the pistons are lighter then I would have thought that you would need to lighten the counterweights on the 4.6 crank to match. Mine was the opposite heavier rods and pistons so weight was added to the counterweights.

I have tried to source accurate information regarding the various pistons for the RV8 to include the chamber volumes and weights, so far without success, if anyone has this information it would be useful to post it on the board and made a sticky so it is available to others for future reference.

Kevin

Wotland · Post by **Wotland** » Fri May 23, 2008 5:16 pm

Hello,
In my datas base I have :
- 9.35 4.6 pistons : 22,29cc top dish
- 9:35 4.0 pistons : 13,23cc top dish
Same comp height of 35,9mm

TVRleigh · Post by **TVRleigh** » Tue May 27, 2008 11:30 am

Std 4.0 X-bolted block weights
pistons are 458-462g (no pin or rings)
Rods are 592-596g (with bolts but without sheels.)

I did not weigh the gudgin pins

Hope this helps.

mgbv8 · Post by **mgbv8** » Tue May 27, 2008 5:10 pm

OH!! Shitty tits!!!!

I forgot to bloody ring them today because I got stuffed up with work crap...

Another day down the flippin' pan.