4.0 P38 vs 4.6 P38

marko10010 · Post by **marko10010** » Sun Nov 28, 2010 12:25 pm

Hi I have heard people say that the 4.0 is a much stronger and more 'thrashable' engine than the 4.6. Is this true or can anyone shed any light on this? Thanks

CastleMGBV8 · Post by **CastleMGBV8** » Sun Nov 28, 2010 1:14 pm

Basically untrue, the 4.0 engine has a shorter stroke so will rev more freely but not untill you fit flowed heads and a fast road cam.

Both 4.0 and 4.6 have 4 bolt cross bolted mains.

The 4.6 blocks were supposed to be assembled from better quality blocks ie a bit more metal behind the liners due to casting variations and they picked the better ones for the 4.6.

The 4.6 subject to bore wall thickness is a pretty tough old lump and will take a fair amount of abuse.

Perry MGBV8 pumps 250+ shots of nitrous through his for 400+ BHP.

Kevin.

ChrisJC · Post by **ChrisJC** » Sun Nov 28, 2010 1:42 pm

Also bear in mind that the 4.6 P38's had 4-pin diffs and the 4HP24 transmission instead of the 4HP22 (the 4HP24 is stronger).

If you 'trash' a P38, you will find that the vehicle doesn't respond well!, OK in a straight line, but ragging it around is an interesting experience.

Chris.

kiwicar · Post by **kiwicar** » Sun Nov 28, 2010 7:54 pm

If you want to build an engine that spends alot of time at wide open throttle and at high revs in a lighter car then I would base it around a 3.9 and a bottom end brace with studs unless you can find one of the very rare 3.9 cross bolted blocks. the larger journals in the 4.0 and 4.6 blocks cause more friction and hence sap power and I believe allow more flexing around the bottom of the cylinders than the 3.9 block. If it is for a range Rover comp safari or similar heavy car then go for the 4.6 but still brace the block as I think the block is too flexable for the stiffer crank and use an auto box with a manual valve body and higher stall converter as this will save the engine from shock loading.
Best regards
Mike

mgbv8 · Post by **mgbv8** » Sun Nov 28, 2010 8:45 pm

marko10010 wrote:Hi I have heard people say that the 4.0 is a much stronger and more 'thrashable' engine than the 4.6. Is this true or can anyone shed any light on this? Thanks

What are you looking to do with this engine??

marko10010 · Post by **marko10010** » Sun Nov 28, 2010 9:42 pm

Thanks to everyone for their input.

mgbv8 wrote:
marko10010 wrote:Hi I have heard people say that the 4.0 is a much stronger and more 'thrashable' engine than the 4.6. Is this true or can anyone shed any light on this? Thanks
What are you looking to do with this engine??

I have two ongoing projects. I have a Dutton B+ that im currently fitting a 3.5 p6 engine that i had into. Its only a temporary thing to get me on the track and have a bit of fun until next winter. It has undergone quite a bit of work. Im 6'6 so the back axle had to be moved back which in turn lengthened the trailing arms. its going to be eventually used for historic racing.
My other project is a Scimitar se5a. I have it stripped and am "slowly" doing a body off restoration. I am hoping to put a 5.0 v8 from a tvr into it (I think). It will be left stripped and used as a fun classic fast road/track car. I need to eventually run the dutton on carbs to keep it period but i was thinking of maybe using the 4.0 or 4.6 for it

kiwicar · Post by **kiwicar** » Mon Nov 29, 2010 8:08 am

Have you thought of putting a ford 302 in the scimiter, would be cheeper than a 4.6 for the same or more power and the engine would be alot more fun being far more willing to rev.
As for the dutton the a decent 3.9 with a mechanical cam, ballanced bottom end, brace optional and merlin heads would suit that very well. The 4.6 will tend to leave you spinning wheels in low gears and still leave you with limited revs even with aftermarket heads. you would be better off spending your money on the aftermarket heads rather than top hat liners that add no power but are needed in these blocks because of dropping liners, the 3.9 block is cheeper to start off with and with ARP studs will strong enough with such a light car.
Best regards
Mike

marko10010 · Post by **marko10010** » Mon Nov 29, 2010 11:12 pm

I haven't thought much about the for or really any alternative to the rover as the scimitar is a relatively light car and i would like to keep it as light as possible. The rover seems to be the cheapest and most readily available. The one other benefit is the guys in the historic race scene here in N.Ireland tend to run with rover v8s I hear and I have a local man who does some work with them.

kiwicar · Post by **kiwicar** » Tue Nov 30, 2010 6:23 am

Hi
The 302 ford for any given output will be far less stressed than the rover, up to about 350bhp it has no issues and can run a standard bottom end. It will weigh 50 to 75 lb more than a 4.6 rover at most but it is just so much easier to get the power, a good set of heads, 4 barrel intake and a set of headers with a suitable cam and you are there.
Best regards
Mike

CastleMGBV8 · Post by **CastleMGBV8** » Tue Nov 30, 2010 1:37 pm

marko10010 wrote:I haven't thought much about the for or really any alternative to the rover as the scimitar is a relatively light car and i would like to keep it as light as possible. The rover seems to be the cheapest and most readily available. The one other benefit is the guys in the historic race scene here in N.Ireland tend to run with rover v8s I hear and I have a local man who does some work with them.

I presume you mean Jim, JRV8 nice guy and very helpful.

http://www.jrv8.co.uk/

Kevin

marko10010 · Post by **marko10010** » Tue Nov 30, 2010 8:27 pm

Its food for thought Mike. What sort of money realistically are you talking for the 302? What sort of gearbox would u marry up to it?

No Kevin I have heard of him but this guy is less specific than him.
Cheers Mark

kiwicar · Post by **kiwicar** » Wed Dec 01, 2010 6:51 am

This is very much a " how long is a piece of string" question however
base engine for rebuild would be between £400 and £600 for a lump for rebuild
A basic rebuild kit, pistons bearings timing chain about £200 in the states so about £350 with postage Vat and duty
http://cgi.ebay.com/ebaymotors/1991-95- ... ccessories
machining the same as a rover
a set of procomp ally heads about £550 to your door
a performance cam about £270
lifters £80-£120
add a good carb and inlet you would be looking at about 320-350 bhp depending on cam.
best regards
Mike

kiwicar · Post by **kiwicar** » Fri Dec 03, 2010 11:59 am

Hi
There is a 2 valve ford mod engine on eurodragster at the moment, with auto box for £600, this has got to be worth a look at for your Scimiter.
Best regards
Mike

Eliot · Post by **Eliot** » Fri Dec 03, 2010 6:16 pm

there's a lexus engine on here for £350

marko10010 · Post by **marko10010** » Fri Dec 03, 2010 7:09 pm

Is that the same engine that comes in the mg zt v8?
How do you rate those engines? What manual gearbox works well with that?

kiwicar wrote:Hi
There is a 2 valve ford mod engine on eurodragster at the moment, with auto box for £600, this has got to be worth a look at for your Scimiter.
Best regards
Mike

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4.0 P38 vs 4.6 P38

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