bobtailrangie · Jan 29, 2015

Hi guys

Getting rid of my tired 3.5 carb engine + have to decide between the 3.9 non serp engine + the 4.0 gems p38 engine

Either engine ill be running on megasquirt
I know the gems is a 3.9 too but is there any reason i should go for 1 over the other?

Cheers
James

marccleave · Jan 29, 2015

Just to throw another one at you. You can also get an intermediate 3.9L

It was the gap between the v belt 3.9 and the 4.0. It still uses hotwire injection and a distributor but has a serpentine belt and crank driven oil pump. Has provision for cross bolting but not actually used IIRC. So all the joys of the later 4.0 with the earlier outside bits on it. IIRC.

eightinavee · Jan 29, 2015

Both are poor compared to the 3.5 if you are looking at long term use - unless you go for stepped liners and a bigger sump/decent oil cooler.

jamesmartin · Jan 29, 2015

marccleave said:
Just to throw another one at you. You can also get an intermediate 3.9L

It was the gap between the v belt 3.9 and the 4.0. It uses hotwire injection and has a distributor but has a serpentine belt and crank driven oil pump. Has provision for cross bolting but not actually used IIRC. So all the joys of the later 4.0 with the earlier outside bits on it. IIRC.

the v belt 3.9s use hotwire too, the greatest innovation of the serpentine belt was the water pump that fed booth banks more equally than previous v belt which favoured the rh bank

marccleave · Jan 29, 2015

jamesmartin said:
the v belt 3.9s use hotwire too, the greatest innovation of the serpentine belt was the water pump that fed booth banks more equally than previous v belt which favoured the rh bank

I know the v belt 3.9 used hotwire.

Never meant to imply that the v belt didn't use hotwire injection. Edited my post to clarify.

mussy · Jan 29, 2015

I have only had the 3.5 in a Stage 1 109--I loved that engine ,carbs and all--it was almost indestructible. I once left the car in a greek olive field for 2 years--went back --had it up and running in two days and drove it back to london .
I also have the 39L---it has raised a few mechanics eyebrows over the years as they do not seem to be common. Mine is a july '96 and has done 83k seamlessly.I have replaced the serpentine twice ,not because it was apparently necessary but because it seemed a good idea. Some 'standard' coil/distributor leads can be slightly short, but once you know what you've got there are no real problems.As usual ,change the oil every 3/5000!
My inclination would be to go for the P38 as my 'P38 mates' tell me its the best thing about that car!

Go well

bobtailrangie · Jan 29, 2015

Yes i know about the serp 3.9 however they are fairly expensive + do not come up too often

Id be happy to do an entire refresh on my engine but would be going efi regardless + will be megasquirted so id need to notch out the inlet ports for the injectors

When i look at the cost of a refresh compared a decent mileage 4.0 gems/3.9 v engine it makes me wonder what to do

blackvoguebeauty · Jan 30, 2015

bobtailrangie said:
id need to notch out the inlet ports for the injectors

Or get a 3.9 inlet manifold off eblag...

marccleave · Jan 30, 2015

blackvoguebeauty said:
Or get a 3.9 inlet manifold off eblag...

The notch that bobtailrangie is talking about is on the inlet ports of the cylinder heads. If you look at a set of early cylinder heads from a carburettor engine and then a later EFI engine then you can see the little cut out on the inlet port. This was added to clear a decent path for the injector spray.

cooltide · Jan 30, 2015

I'd be a bit paranoid about liner slippage on a 4.0 unless a Mitchell cotts block or tophat. Having said that, if I did decide on a crossbolted block, it would be a 4.6

blackvoguebeauty · Jan 30, 2015

marccleave said:
The notch that bobtailrangie is talking about is on the inlet ports of the cylinder heads. If you look at a set of early cylinder heads from a carburettor engine and then a later EFI engine then you can see the little cut out on the inlet port. This was added to clear a decent path for the injector spray.

Sorry, of course, early heads. A 3.9 inlet with fuel rail and injectors would be ideal to use with megasquirt though, if he takes that route.

jamesmartin · Jan 30, 2015

cooltide said:
I'd be a bit paranoid about liner slippage on a 4.0 unless a Mitchell cotts block or tophat. Having said that, if I did decide on a crossbolted block, it would be a 4.6

4.0 and 4.6 are the same block and 3.9 uses the same liners and are as equally prone to cracking,4 and 4.6 have larger crank journals

cooltide · Jan 30, 2015

jamesmartin said:
4.0 and 4.6 are the same block and 3.9 uses the same liners and are as equally prone to cracking,4 and 4.6 have larger crank journals

I realise that but i've never had a problem with 3.9 and pushed them pretty hard. I have heard reports of them failing. Land rover didn't seem to get fully up to speed with building **** v8s till they started casting crossbolted blocks and using gems. Hence my paranoia but this is just my opinion.

bobtailrangie · Jan 30, 2015

I was liking the gens v8 as its neater not having a distributor + i liked the serp belt for nice big altetnators for winching as v belt cant handle as much but i could compensate slightly by having bigger batteries

Thi.king about it i dont like the idea of liner risk especially as its guaranteed to be getting pretty warm at points being in an off roader so i think ill be going for a complete 3.9 with inlet etc, run the inlet on the engine i wont be using while i rebuild the other then swap over when ready

jamesmartin · Jan 30, 2015

bobtailrangie said:
I was liking the gens v8 as its neater not having a distributor + i liked the serp belt for nice big altetnators for winching as v belt cant handle as much but i could compensate slightly by having bigger batteries

Thi.king about it i dont like the idea of liner risk especially as its guaranteed to be getting pretty warm at points being in an off roader so i think ill be going for a complete 3.9 with inlet etc, run the inlet on the engine i wont be using while i rebuild the other then swap over when ready

3.9 runs the same liner risk ,hence lr redesigning water pump ,but it wasnt a complete answer

marccleave · Jan 30, 2015

bobtailrangie said:
I was liking the gens v8 as its neater not having a distributor + i liked the serp belt for nice big altetnators for winching as v belt cant handle as much but i could compensate slightly by having bigger batteries

Thi.king about it i dont like the idea of liner risk especially as its guaranteed to be getting pretty warm at points being in an off roader so i think ill be going for a complete 3.9 with inlet etc, run the inlet on the engine i wont be using while i rebuild the other then swap over when ready

In that case a 4.0 with top hat liners sounds like the answer. Get a 4.0, rebuild it with top hat liners (or find one thats already been done!) and drop it in with megasquirt. Is that not an option for you?

jamesmartin · Jan 30, 2015

cooltide said:
I realise that but i've never had a problem with 3.9 and pushed them pretty hard. I have heard reports of them failing. Land rover didn't seem to get fully up to speed with building **** v8s till they started casting crossbolted blocks and using gems. Hence my paranoia but this is just my opinion.

like the later v8s some dont, some did straight away it was a big issue back in the 90s, we used to strip the warranty returns to ascertain the failure

bobtailrangie · Jan 30, 2015

I must say i have heard of occasions where it has happened on the 3.9 but nowhere near as much as the 4.0/4.6

As nice an idea is building a top hat linered block its not an amount im prepared to spend when i could just run a fresh built 3.5 engine, for the sake of the bit of power difference i cant warrant the extra spend on top hat liners

jamesmartin · Jan 30, 2015

bobtailrangie said:
I must say i have heard of occasions where it has happened on the 3.9 but nowhere near as much as the 4.0/4.6

As nice an idea is building a top hat linered block its not an amount im prepared to spend when i could just run a fresh built 3.5 engine, for the sake of the bit of power difference i cant warrant the extra spend on top hat liners

they are more recent and more abundant, 3.5 is bullet proof

cooltide · Jan 30, 2015

3.5 is the safest. Then you just need to arp the heads and add nitrous to make up the defecit

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