Thread: 4lt V8 and 4.6lt V8 differance

The stroke in the two engines is as follows 4.6 = 82mm
4.0 = 71mm

If you are able you could remove a spark plug and measure the stroke.

Garry

Originally Posted by walker

Here is a good site with all the V8 engine numbers.

Rover V8 Engine Numbers

Originally Posted by Collins

Same here, have a 55D engine number, 4.0L low compression, not listed.
Not a very comprehensive listing

I have been trying to determine whether my D2 4.0 engine is Hi comp or low comp. No VIN but engine number is 55D03758A - due to the block being skimmed the comp ratio stamped on the engine number pad has been removed. I have been searching the engine number vs comp ratio lists online and finding numbers for 4.0 RRs but not D2s. As part of that search I came across this old thread that I had previously contributed too.

So on the basis of the above quotes can I definitely assume the engine I have is low comp??


Thanks

Garry

The depth of the dish in the pistons should be a give away.

Sent from my K4000_PRO using AULRO mobile app

was there such a beast as a low comp 4L thor??
the dish on the 4.6 is bigger, but compression due to the stroke remains the same as the 4L
none of the 3.9 engine parts transfer,
apparently you can buy low comp pistons,, (which I would guess would be the 4.6 ones)
and transferring the 4l pistons to the 4.6 will give you higher comp

Originally Posted by loanrangie

The depth of the dish in the pistons should be a give away.

Sent from my K4000_PRO using AULRO mobile app

Yes but hard to measure when the engine is still assembled.

Originally Posted by Pedro_The_Swift

was there such a beast as a low comp 4L thor??
the dish on the 4.6 is bigger, but compression due to the stroke remains the same as the 4L
none of the 3.9 engine parts transfer,
apparently you can buy low comp pistons,, (which I would guess would be the 4.6 ones)
and transferring the 4l pistons to the 4.6 will give you higher comp

Thanks - understand all that but Collins above indicated his 4.0 was Low comp and his engine number starts with 55D so just seeking confirmation.

Cheers

garry

do a compression test , this will tell you the ratio and the state of the engine

55D = South Africa. ?

Originally Posted by discorevy

do a compression test , this will tell you the ratio and the state of the engine

Thanks - but I asked the question relevant to the engine number for a particular reason, mainly that the engine is assembled but not in the vehicle so not running. Not wanting to proceed until I resolve this.

Most RV8 engine number lists have just about every RV8 listed but not 4.0V8s in D2s.

Cheers

Garry