newbie question about the 4.0 and 4.6

TVRleigh · Post by **TVRleigh** » Fri Sep 07, 2007 11:01 am

Could somone tell me what the differance is between the 4.0 and 4.6 x-bolted engines.

I think the main differance is the crank and pistons.

Are the pistons different of just the Rods.

Thanks
Leigh

russell_ram · Post by **russell_ram** » Fri Sep 07, 2007 11:27 am

Leigh,

Cranks are different - 4.6 obviously has longer stroke.

Rods are different - 4.0 ones are longer to make the pistons reach the top of the bores/deck because the stroke of a 4.0 is shorter.

Pistons are different but ONLY the size of the dish/bowl. The 4.0s have smaller bowl to make up the difference in CR caused by the difference in stroke. either will fit with either set of matched crank/rods and give you higher than std CR for NA performance engines or lower than std CR for blown motors. Will all need reblancing in those cases though.

Russ

TVRleigh · Post by **TVRleigh** » Fri Sep 07, 2007 12:13 pm

Thank you for the info.

One related question whare are higher compression the 4.6 or the 4.0 as I would like a bit more compression that 9.35:1

and have the option to buy some 4.6 pistons.

I need to keep the engine a 4ltr. also only need about 210-220 BHP, but it will be used in a race car.

Thanks
Leigh

Antonyj · Post by **Antonyj** » Mon Sep 10, 2007 7:21 pm

The 4.0 pistons have a shallower bowl than the 4.6.
Therefore they offer the higher compression ratio when fitted to a 4.6 motor.

If you have to keep at 4.0 then I would stick with 4.0 pistons.

minorv8 · Post by **minorv8** » Wed Sep 12, 2007 7:36 am

If you want higher comp in a 4,0 litre engine you could fit the steel head gaskets instead of the std composite gaskets. You will gain roughly 0,6 extra points in CR. The other option is to machine the block or heads.

ihatesissycars · Post by **ihatesissycars** » Wed Sep 12, 2007 8:34 am

I have a 4.0 crank, rods and pistons for sale if you're interested?

adamnreeves · Post by **adamnreeves** » Tue Sep 18, 2007 1:55 pm

minorv8 wrote:If you want higher comp in a 4,0 litre engine you could fit the steel head gaskets instead of the std composite gaskets. You will gain roughly 0,6 extra points in CR. The other option is to machine the block or heads.

If standard cam is fitted then clearance maybe fine but if you have a performance/higher lift cam then will need to check the valve to piston crown clearance or use pocketed pistons.

mgbv8 · Post by **mgbv8** » Tue Sep 18, 2007 7:02 pm

Adam
By pocketed you do mean pistons with valve cutouts dont you?
I've just finished my 4.6 crossbolted build. She has cutouts in the pistons. I'm using comp head gaskets and a Blower cam. It has the same lift (almost) as the Typhoon cam @ 0.494" This should be ok shouldnt it?

adamnreeves · Post by **adamnreeves** » Tue Sep 18, 2007 9:32 pm

Yes that's what I mean. I would have thought this would be okay. I am running a 4.6 with compo gaskets, standard pistons and a piper 285 which is 0.477" lift and I have no cut-outs. Looking back at my records I found that the inlet valve to piston clearance minimum was at 6-8 ATDC was 0.080". Exhaust valve clearance was 0.116" at 16-10 BTDC.

Inlet clearance minmum allowed is 0.080"
Exhaust clearance minimum allowed is 0.100" (owing to more expansion due to hotter gases).

Oh and the other thing the cam advertised lift is not always attained. I checked one of my lobes on the cam and at best it would achieve 0.476" okay pretty close but when I checked the lift when installed and the rockers setup I found that the maximum lift dropped to 0.470"

mgbv8 wrote:Adam
By pocketed you do mean pistons with valve cutouts dont you?
I've just finished my 4.6 crossbolted build. She has cutouts in the pistons. I'm using comp head gaskets and a Blower cam. It has the same lift (almost) as the Typhoon cam @ 0.494" This should be ok shouldnt it?