Get the most power out of a Stage 1 3.5L V8

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Get the most power out of a Stage 1 3.5L V8

Post by Rikard »

Hi I am new to this forum and sorry for a long first post...
Just wanted to hear your thoughts on the 3.5L power/torque raising possibilities
I got a ´85 110 County (pre Defender) since its age it is very much the same as the Stage 1 as it got a army 3.5L V8 and LT95 box and transfercase
But with discs in front and a few other modernities like roll down windows... (I use to own a `83 Army 109)
This truck I have turned into a overland vehicle with all amenities needed for -off the grid adventure-  :D

The engine it got is unfortunately a 10G serial number block which means its a Stage 1 V8 8.13:1cr from `82
As far as I know its all original but recently rebuilt;  Cam, heads, pistons, rings etc should all have been replaced with new original but I cant be 100% sure as I never spoken to the guy who did the job, so what was replaced and what was not is just a guess...

So its pretty weak to start with as being the army engine with 91 bhp, but without the air restrictors could be at 135 bhp, there are lots of different sayings about this so I do not know for sure
Raising the cr is impossible as well unless I put new pistons in, but for that rebuild cost I could easily drop a 3.9L in instead...
Engine itself was newly rebuilt for a 109 project (that got crashed) by some purist who replaced all with original same parts instead of taking the opportunity to put better gear in
I bought it for 600 bucks and put my inlet manifolds and Strömberg carbs on it, but I did not know that it was so weak, if I had known I would not have bought it :(

When I bought this truck it had a another stage 1 V8 in it, literally the same weak army engine
I did some experiments with that one and best effect I got was from a Pertronix Ignitor 2 unit that made it rev like a madman
I got no rev meter but it would not surprise me if it hit 7000-7500 rpm, it was craaaaaazy
It went really well with that setup
One day on the beach it started piss out oil through the dipstick, LOTS of oil
So I think the maniac revving bent/damaged a hydraulic tappet for the pushrods so the pressure went bypass down into the crankcase and out through the dipstick
Instead of rebuilding the old motor I bought the truck with I replaced it with this 10G block without knowing it was just as weak

So I am technically back at square 1 again and trying to figure out a way to gain few ponies and torque...
The exhaust is designed by meself and its a combo of 3.9L grinded out double piped cast iron manifolds and downpipes with full 3 inch pipe all the way out, it sounds  -r e a l l y-  good but could actually lose some power I am told
Got a MSD Street Fire ignition box but made no difference from the original electronic ignition except it runs more even/smoother and starts very easy
I never put the Ignitor 2 on this engine
The 2 snorkels actually helps slightly at motorway speeds, it helps to keep speed up when going up hills, this difference is minimal though
I got an EFI in me basement and think it would be the way to go but its above my knowledge to install myself and the guys I've spoken to to do it for me wants 3 grand for the installation, can't justify that...
The Edelbrock/Weber path would be lovely but can't afford it and justify it for wife would be even harder... and some people on this forum seems to think it would make no difference anyway?

I do not know if its any idea to rebuild the 35 years old Strömbergs and to what difference that would make either?
The adjustment in the dashpots makes no difference then the idling rpm, the only thing I notice difference from is changing the ignition timing, other then that it seems to make no difference whatever I try

Truck is very heavy with all the camping gear, internal double bed, fridge/freezer, watertank, stoves, cooking gear, gigantic pullout drawer system, etc etc
Weighs in on 2450kg...
But we can stay off the grid for two weeks if needed :)
First we run out of is beer, then wine, then water... :D
Two inch lift and 35 inch rubber does not help with power ratio or fuel consumption either, I know, but it looks cool :D  and keeps rev down on motorway heaps
Got a Eaton Detroit locker in the back as well
It also handles surprisingly well, got harder coils in the front and very beefy shocks all around, sits nice on 100 kph if the road is flat
But going uphill it's really bad... get down to 65kph some steep hills and that is not nice when everybody behind you is coming at a 100...
Soooo, any ideas guys???
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Re: Get the most power out of a Stage 1 3.5L V8

Post by map1275 »

Still not sure what you're comparing with to say your 109v8 is so bad.

Presumably you have a NZDF 109V8 (or engine from one)? Therefore a 101V8 24 volt arrangement with a NZDF ignition conversion.

Low compression means you can utilise low grade fuel. None of the Rover V8s have thumping torque unless severely played with at which point they are difficult to drive and generally useless for off road.
EFI from a Range-Rover will give you the smoothest, response and drivability. But you will have trouble fitting the plenum under the bonnet. SD1 EFI will fit but you lose a lot of potential with the shorter plenum. A very straightforward swap and DIY achievable as long as you look and think and refer to the manual and donor vehicle. Only an abortion if you don't.
Very few of the U.S. type carb arrangements have anything to do with performance, save for being a bucket with a hole to poor in petrol. Absolutely none have a linkage kit available to adapt to your installation.
A Leyland Australia 4.4 might be a reasonable compromise for more torque, for similar mass. Plus you can buy manifold adaptors or use the original if you insist on the fixed venturi carb arrangement.
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Re: Get the most power out of a Stage 1 3.5L V8

Post by Rikard »

Cheers for you reply
No I am not saying it so bad
I am saying for the weight of my truck the engine is too weak, thought I was clear about that? if not; sorry

I already told you what it is, its a 10G serial engine from 1982, a Stage 1 3.5L V8
And no, its not 24 volt, its 12 (even that I got 3 batteries and solar panels with 240 AH worth of AUX power)
Why would it have to be from a 101?

Its just too weak for 2.5 tonne, stick a cube of water on the tray of a Stage 1 and you see...

I know and the reason for the low compression was that in a possible war situ, you never know what fuel grad you will find...

Hhmmm, I like the torque off road, thats why V8´s are used and not 25PSI turbo hosed 1.5L straight 4´s ;)

I got the EFI from a 3.9L Disco and there is plenty of space for the plenum under the bonnet of the Defender so no worries there, almost can fit two of them there I say :)
But I am not confident I can do it, the mapping of the ECU 14CUX, to use oxygen sensors or not, run cats or not etc etc

There are several readymade kits for installing the Weber for example (its Italian by the way) made so you do not need a single more bolt or wire to hook it up, like this one: ... -706-p.asp
or: ... 8-3-5.html
But to spend that amount of money for something I do not know how it will perform would be silly even the seller claim "up to 20 hp gain"

A P76 4.4L V8 would been fantastic, but I chose the wrong replacement engine to start with and are unfortunately stuck with it and trying to get another reasonably 20-30 ponies out of it, thats really all I need

Anybody else got any ideas?
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Re: Get the most power out of a Stage 1 3.5L V8

Post by disco2hse »

Phew. OK. That was a long read. Remind me not to shout you beers for a story :lol:

First things first. Welcome aboard.

So, long story short - you want some ideas about how to increase output power and probably performance. I am not clear what kind of demon machine you are after. If you want raw power, then get a more powerful donk. The old Buick block has limitations and is basically inefficient.

Pertronix II is great. Been running it on mine for more than 10 years. Yes, it has a long curve and yes, you need to moderate your foot pressure. I'm not surprised you blew the other engine. From the research I've done on the engine, these were not designed to rev past 5500rpm.

Yes, the engine needs back pressure. Any four stroke does. Have you considered extractors?

The NZDF engine has low compression pistons (cupped) and standard duty cam shafts. Other than that, it is a standard engine running a Mallory dizzy and coil, with an electronic module for the distributor with rev limiter. The 24V input is lowered to 12V for the spark.

I'm with Map. I now have SUs and wish I'd stayed with strommies for fuel consumption vs power output. Big bucket carbs have not shown me any improvement in performance, only the generation of testosterone.

Mine is a 3.9 block. I regularly cruise 100km/hr and tops out at ~140km/hr. Up a hill, I will often get 110-120km/hr even with a trailer. That is 3000-3500rpm-ish. It will happily drag 3 tonnes of trailer for four hours on the trot. To reduce the pain in my pocket, I try to drive at 90-95km/hr but it creeps up if I'm not careful.

So, having said all that. I guess it is a balance of air/fuel and output. You may want to run an MSD HEI system that you can program to achieve the performance gains you are after. I know/knew of one in Manurewa where had that in a 109 SW and it ran like a top. ... ade%20Kits

There are alternative cams you can buy for higher performance. Just be aware that the 3.5 is a lazy engine that lasts when it is not being thrashed. But you probably learned that already ;)

A Crower cam exchange is a cheap upgrade: for example

You could also have the heads milled to increase compression, but YMMV.

The other issue is the tyres you are running. Those look like very large diameter tyres and that will suck more power than anything else. Smaller diameter tyres will allow much more power to hit the road. I run 750R16s.

Finally, are your LT95 hi-range ratios standard or was it "upgraded" to Rangie Classic ratios? If so, then you lose more power there too.

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
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Re: Get the most power out of a Stage 1 3.5L V8

Post by firemanshort »

I think it has been covered but I will pile on with similar guidance. The Rover 3.5 will only grunt so hard. I think I have seen internet stories of "race prepared" 3.5 V8's getting near the 200hp range but I do not think that is a very practical approach to an off road machine. I think you should be happy with modest upgrades, power around the 150hp range, and not flog the guts out of the 3.5 for any more.

That said, the old adage of "no replacement for displacement" always rings true. You can easily swap in a 3.9, 4.2 or 4.6 in the same space the 3.5 occupied. You pair any of those motors with the Edelbrock (or similar) 4 barrel carb or better still a Holley Sniper efi setup and you will see a big jump in performance. You can top it off with a high performance (HEI) distributor to get the absolute most out of spark. If you do all of that you will have a much lighter wallet and could expect reliable power to be north of the 200hp range.
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Re: Get the most power out of a Stage 1 3.5L V8

Post by disco2hse »

Yup, and since my wallet is filled with helium, I stick with what I have :lol:

1983 ex-army FFR 109 Stage 1
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Re: Get the most power out of a Stage 1 3.5L V8

Post by udo1-ton »

the best way to get power ist to make a exchange to 4.2 or 4.6l. You only need a torque camshaft (Viper Hurricane...) with distributor drive. All the other stuff can be used from the 3.5l. You will reach minimum 200-210bhp. I cannot recommend Edelbrock or Holley Carbs, too complicated and thirsty. The best way is the SU with the BGC or BAK needle inside and important: the big air cleaner box.
The second step is fitting a set of 1.113 gears to the transfer box. You get 2300-2400 1/min at 100km/h or 63m/h. The fuel consumption is 5l less per 100Km. Top speed, I don't know. I was not brave enough to go further than 100m/h
It is much faster than a TD5 Defender and makes a lot of fun :D
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