P38 4.6 Engine upgrade

[pesho_range]

Hello all, looking for advice on 4.6 GEMS engine upgrade options. I am in the middle of rebuilding the engine in my P38 and want to do some upgrades along the way, my main goal is to get a lot of torque out of it, high rpm performance doesn't really mattar that much. The upgrades that i will do for sure are top hat liners, mild head work(stage 1), THOR bosch injectors, ecu remap, De-cat. So with this in mind, here is where i need help:

1 - I want to increase the stroke of the engine to 3.5" to get it to 5l, as this will be the best way to get more torque. I am looking at real steels kit for this, but it does comes with forged conrods and pistons, which i don't really need, considering that i am not going for high power or rpms(Will keep the stock P38 rev limiter) - are there any cheaper options for getting this much stroke out of a 4.6?

2 - Camshaft options - I am quite happy with the stock engines power range and don't really want to change this, also looking at heads flow charts, it looks i wont gain meaningful flow with slight increase of valve lift on stage 1 heads and mild cam(up to .450" lift), so is there an actual gain to be made with cam upgrades for my goals?

3 - Currently i have a GEMS engine and i am thinking of installing the THOR manifold on it(I know i will have extra work to fuel line and regulator, TPS, coolant passages, etc) as in theory it should increasy low end torque and somewhat limit higher rpm power. Will this still remain true if i increase engine stroke to get capacity to 5l, or i will just choke my engine at higher rpms, without gaining that much low down grunt?

4 - What is the highest comp ratio that i can run while still being able to use 95 octane fuel without isses - 9.8:1-10:1?

Best regards,

Petar Pelovski

[paul c]

In my opinion changing to the Thor intake is going to be the easiest and cheapest way to increase your torque. If you really have to increase the stroke you need to research rods and pistons that would be suitable and either purchase a custom crank or have yours offset ground.

[minorv8]

One comment regarding the stroking the engine. If you increase the stroke you also need another set of rods/pistons. You can´t use the std ones. One option is to use small block Chevy rods and stroker pistons with short compression height.

I don´t know if Real Steel still has complete kits available. Last time I checked the did not have anything available.

I built a stoker engine based on 4.6 engine. The crank is a TVR stroker crank of unknown origin, cast item with 91,5 mm stroke. Con rod journal size is 2.000". Pistons are +20 forged, made by ICON and bought from Real Steel. For some weird reason TVR cranks have narrower con rod journals which means that neither Rover or Chevy rods fits without mods. I also had a TVR 5-litre bottom end with small mains journal size and that also had narrow con rod journals.

I had a lot of obstacles with the build, mainly because the components being bought during a span of 10 years from various sources. I did expect to run into problems but I was surprised a couple of times when there was more problems than expected. I had access to a lathe and could modify the rods and pistons by myself. Nevertheless, there were several mockup builds to verify the next issues If you really want to take the stroker route I really recommend that you get a complete, PROVEN package from a same reliable source.

[SuperV8]

Hello all, looking for advice on 4.6 GEMS engine upgrade options. I am in the middle of rebuilding the engine in my P38 and want to do some upgrades along the way, my main goal is to get a lot of torque out of it, high rpm performance doesn't really mattar that much. The upgrades that i will do for sure are top hat liners, mild head work(stage 1), THOR bosch injectors, ecu remap, De-cat. So with this in mind, here is where i need help:

1 - I want to increase the stroke of the engine to 3.5" to get it to 5l, as this will be the best way to get more torque. I am looking at real steels kit for this, but it does comes with forged conrods and pistons, which i don't really need, considering that i am not going for high power or rpms(Will keep the stock P38 rev limiter) - are there any cheaper options for getting this much stroke out of a 4.6?

2 - Camshaft options - I am quite happy with the stock engines power range and don't really want to change this, also looking at heads flow charts, it looks i wont gain meaningful flow with slight increase of valve lift on stage 1 heads and mild cam(up to .450" lift), so is there an actual gain to be made with cam upgrades for my goals?

3 - Currently i have a GEMS engine and i am thinking of installing the THOR manifold on it(I know i will have extra work to fuel line and regulator, TPS, coolant passages, etc) as in theory it should increasy low end torque and somewhat limit higher rpm power. Will this still remain true if i increase engine stroke to get capacity to 5l, or i will just choke my engine at higher rpms, without gaining that much low down grunt?

4 - What is the highest comp ratio that i can run while still being able to use 95 octane fuel without isses - 9.8:1-10:1?

Best regards,

Petar Pelovski

Bolt on a couple of Turbos or a supercharger will be cheapest option per £ for loads more torque.
Couple of simple cast log exhaust manifolds, some cheap ebay turbos for low boost <10psi will give a massive difference.
Or an second hand Eaton from a Merc or Jag, but this would need custom intake manifold and custom pulley arrangement.

[stevieturbo]

add boost...it really is the best option to add torque.

[GDCobra]

Bolt on a couple of Turbos or a supercharger will be cheapest option per £ for loads more torque.
Couple of simple cast log exhaust manifolds, some cheap ebay turbos for low boost <10psi will give a massive difference.
Or an second hand Eaton from a Merc or Jag, but this would need custom intake manifold and custom pulley arrangement.

add boost...it really is the best option to add torque.

Got to agree with both of those. I'd either go the forced induction route or just start with a better engine than the Rover/Buick, although my needs may be different.

[pesho_range]

Thanks everyone for replies. I contacted real steel and it turned out that indeed they no longer have stroker kits - actually nobody at the moment sells such kits at anything close to a reasonable price. I found some chevy/ford parts that can be used together with a crank regorund, but seems like a bit too much work for realistically an extra 30-40nm and this p38 has been a project for a bit too long now, so i want to get it done and enjoy it. I think that i will renew everything, do some headwork, install thor manifold and injectors, get the ecu chipped by tornado and get the comp ratio to 9.8:1. If this does not feel strong enough, i will have to consider the force induction route.

I did initially set out on engine swap way for this project and purchased an mercedes m113 v8 with 5g tronic, but the m113 is a bit too wide and in order to clear the brake pump it needs to sit a lot to the right (my p38 is LHD) and to the front in the engine bay, to the point where any belt/timing work will requre me to remove atleast the water radiator and there was no place for a colling fan also.

With the m113 being one of the more compact OHC v8 engines out there, i think it is safe to say, that the p38 was built around an pushrod v8 and making it accept a OHC v8 engine will reqire a lot of cutting and fabricating, that i am not willing to do and sadly LS(or other good pushrod v8's) engines are quite a rare sight around eastern Europe

[stevieturbo]

Back to earlier posts then, I would say absolutely there are gains to be had from a cam swap.

With a lack of engine size, lack of boost, then you need to do traditional tuning. Which is simply improving airflow.

A bit of mild porting and cleanup of the ports, and especially valve seat area will help. If torque is your goal, no need to go mad with the heads

Camshaft will definitely help.

And usual exhaust etc

[pesho_range]

Which cam would you recomend then? Kent's H180 seems like a good fit for my purpose.

[stevieturbo]

Which cam would you recomend then? Kent's H180 seems like a good fit for my purpose.

I'd advise contacting a specialist and discussing your requirements and goals.

The likes of V8 Developments etc who will have extensive testing

https://www.v8developments.co.uk/camshaft.htm