De-tuning a 3.9 V8

[RPR]

Short Preface:

Surprise, surprise, I have arrived at the conclusion that my 2.25 pertol, even with the beneficial bolt on ACR stuff just isn't enough power, especially with those 36" SS on the portals.

In the Land of "cubic inches are King" I could/should put the SBC 350 in and an NP435 with a 6.68 1st gear. But that is a lot of fabbing and modding and I do not have the time, tools, or facilities here in any event to do anything complex. I have worked out a deal to do the odd bit here and there on the Tonka at my corner mechanic's shop on the weekend, but a repower is outside those parameters so anything I do will be spendy.

For that reason, I am down to two options (covered in previous thread):

A very neat conversion to a GM 2.5 4 cyl (descendant of the Iron Duke) bored out to 3.0 l with a nice flat torque curve that is virtually bolt in, but very spendy, or; Numbers are 127 hp and 178 lbs ft torqu with 160 pretty much off idle.

Rover V8 to Series box.

The Analysis:

Before all the cries of "change to an LT77 or R380 and LT230", remember that these, while not exactly on the same shelf as hen's teeth over here, are much more scarce and expensive and would require much chopping, fabbing, shifting etc. That = money.

On the other hand, most of the components needed for bolting to the Series box are readily available and it's much less faffy.

"But the power" you say. A detuned V8 delivering 130 HP will generate a power to weight ratio of 81 HP per (US) ton - exactly the same as the reported power of my 5.9 L I6 Cummins Turbo Diesel Ram pickup. On torque, a 180 lbs/ft Rover V8 in the Tonka will deliver exactly the same torque per (US) ton (112) as the average petrol V8 would in a similar full-size pick up (350 lbs/ft). I bet that, with conservative use of the skinny pedal and for the conditions I use it in, the Series box will stand up to those numbers. Granted, others wouldn't. My bet, my risk.

Now, ideally, there would be that carbed 8:1 compression 3.5 lying around that nobody wanted because everyone is putting TDI's in their rigs anyway (yes, I would love a Defender 200 TDI - who's got one with all the ancillaries this side of the pond and will sell it to me as cheap as a V8?). But the 3.5 didn't make it over here in numbers (although the Buick ancestor exists), so I'm looking at having to do this with a 3.9.

The Mission:

So - here's the challenge. Would you please give me your recommendations for detuning a 3.9 to @ 130 hp and 180 lbs/ft while delivering the most torque low down as practical - including suggestions for the right cam/cam profile if possible. Fuel economy is not a major consideration b/c my 2.25 doesn't do better than 14 mpg on a good day and despite all the screaming here, $ 2.85 a gallon is not the end of the world. Reliability is a key consideration (in the LR sense of the word admittedly).

Thanks for thoughts on an admittedly odd request.

[geoffbeaumont]

Add water

Seriously, I guess a cheap'n'easy method (albeit hardly the 'proper' way, and l guess lousy for emissions) would be to retard the ignition.

[SOA 93]

Short Preface:

Surprise, surprise, I have arrived at the conclusion that my 2.25 pertol, even with the beneficial bolt on ACR stuff just isn't enough power, especially with those 36" SS on the portals.

In the Land of "cubic inches are King" I could/should put the SBC 350 in and an NP435 with a 6.68 1st gear. But that is a lot of fabbing and modding and I do not have the time, tools, or facilities here in any event to do anything complex. I have worked out a deal to do the odd bit here and there on the Tonka at my corner mechanic's shop on the weekend, but a repower is outside those parameters so anything I do will be spendy.

For that reason, I am down to two options (covered in previous thread):

A very neat conversion to a GM 2.5 4 cyl (descendant of the Iron Duke) bored out to 3.0 l with a nice flat torque curve that is virtually bolt in, but very spendy, or; Numbers are 127 hp and 178 lbs ft torqu with 160 pretty much off idle.

Rover V8 to Series box.

The Analysis:

Before all the cries of "change to an LT77 or R380 and LT230", remember that these, while not exactly on the same shelf as hen's teeth over here, are much more scarce and expensive and would require much chopping, fabbing, shifting etc. That = money.

On the other hand, most of the components needed for bolting to the Series box are readily available and it's much less faffy.

"But the power" you say. A detuned V8 delivering 130 HP will generate a power to weight ratio of 81 HP per (US) ton - exactly the same as the reported power of my 5.9 L I6 Cummins Turbo Diesel Ram pickup. On torque, a 180 lbs/ft Rover V8 in the Tonka will deliver exactly the same torque per (US) ton (112) as the average petrol V8 would in a similar full-size pick up (350 lbs/ft). I bet that, with conservative use of the skinny pedal and for the conditions I use it in, the Series box will stand up to those numbers. Granted, others wouldn't. My bet, my risk.

Now, ideally, there would be that carbed 8:1 compression 3.5 lying around that nobody wanted because everyone is putting TDI's in their rigs anyway (yes, I would love a Defender 200 TDI - who's got one with all the ancillaries this side of the pond and will sell it to me as cheap as a V8?). But the 3.5 didn't make it over here in numbers (although the Buick ancestor exists), so I'm looking at having to do this with a 3.9.

The Mission:

So - here's the challenge. Would you please give me your recommendations for detuning a 3.9 to @ 130 hp and 180 lbs/ft while delivering the most torque low down as practical - including suggestions for the right cam/cam profile if possible. Fuel economy is not a major consideration b/c my 2.25 doesn't do better than 14 mpg on a good day and despite all the screaming here, $ 2.85 a gallon is not the end of the world. Reliability is a key consideration (in the LR sense of the word admittedly).

Thanks for thoughts on an admittedly odd request.

What about a 3rd option!

Supercharge the Landy.

I'm sure all the necessary bits and info are available in the states, and you can still drive the truck around while your sorting/fabricating bits for it, tune in what power you want by changing pullies etc, no exhaust to make, no engine mounts, no adapter plates and reuse the SU ideal for supercharging. Torque increase from Tickover up!

I'm afraid I'd want the SBC 350/ 435 B) , but I can understand your reasoning.

Remember!! If some is good, more is better and too much is just right!!

[Bull Bar Cowboy]

Backing off the timing will destroy the low down grunt, make the engine as flat as a pancake, and make it run hot.

From memory ……. As I don’t have the reference books to hand tonight ……..The early 3.5 in the 110 , before it was fitted in the 90 …… so that must be 83/85 was 114ponies. This was done to make it less powerful than the Classic RR which was selling well at the time for much more money. The RR engine (again carbed 3.5) was 135ponies.

This same 135 bhp engine was later used in the early 90…… because the RR went to 3.5EFI (flapper) which put the power up to 160 ish ponies. The RR engine then went to 3.9EFI (hot wire) which IIRC was something like 180 ponies.

Anyway, to get back on the subject. The early 110 was low comp and I believe the SU carbs were jetted differently (OK different needles). I don’t think there was any difference in the carb cams, however, the 3.5 carb cam I think is still available, so is the 3.5EFI cam (that accounted for about 15bhp over the carbed cam), and the 3.9EFI cam (slightly hotter than the 3.5) is also still available.

To get the toque that you require will need a bit more power than you want. Any 3.9 with a few miles on it will exhibit cam wear, so the power will be down where you want it.

The Mil engines and the Series III stage one IIRC used low compression and carb restrictors in the inlets.

IMHO I think it would be wise to build a standard Hot wire 3.9…… use composite head gaskets to lower the compression by 0.6:1 and drive using the torque as opposed to the power……… without being rude ……….. there IS a variable power pedal.

My 3.5EFI in the truck cab runs a warm / mild cam (not hot cam as I need the low down grunt), very high compression (over 10.5:1) and polished / ported heads. This is just sub 200 ponies…….. but even using the LT77S/10 spline axles/standard diffs, I have not managed to trash anything after 40K miles and it is a joy to use off road by using the just enough torque technique of driving.

What I am really trying to say is build the engine to the minimal spec and use the power sparingly. Its probably best described as like driving a stinkin’ diesel (use the torque) but with instant throttle response.

Ian

[RPR]

SOA -

I want the 350 horses in the SBC, but it's just not feasible.

In fact, I did look into supercharing - pretty seriously. There are problems. One is that supercharging and carburation is as much art as science. Another is I'm already running a 9:1 head, which is a limit on supercharging benefits. The most boost the engine can structurally take and still run on pump gas is probably about 6 - 8 psi absolute boost, which would just about cover the power required to generate it, so it's a wash. I then looked into electrical supercharging and even studied a DIY electrical charger, but the boost claims were dubious and the device even more so.

Ian,

I think your plan makes sense. I thought I had heard that the composite gasket was notorious for blowing, but that should be covered by conservative use of the go-pedal as you note even if this is true. Thanks very much for the advice on cams as well. I may have a line on an 80's twin solex 3.5 which would be the ticket. Thanks.

[Turbocharger]

Slightly OT and no help to your V8 quest, but

6 - 8 psi absolute boost, which would just about cover the power required to generate it, so it's a wash. I then looked into electrical supercharging

Surely electrical power isn't free?

[RPR]

Surely electrical power isn't free?

Sure. It called for mounting a long metalic whip antenna that would both collect charge from lightening strikes and generate/store it from static electricity, using that power to drive the supercharger.

[Turbocharger]

... but only at 88mph, right?

Seriously, could you e-boost when you want the power, and run NA in cruise? I still think that OTS V8 is the best route though, less fabrication and less to go wrong!

[Gremlin]

Get the 3.9, junk the injection and run carbs with stage 1 v8 restrictors, you should be down by 30bhp. Stage 1's had only 90bhp or so.

Grem

[will_warne]

To make you feel better, Fridgefreezer ran a 3.9 in his Series (with a series box) for about 2 years and never broke it. You should be fine....

[Tonk]

or to make u feel worse, i ran a series box on a 2.5 n/a diesel for about 4 years, went through about 10 series gearboxes, different driving style maybe?

thats why when i upped the power with a tdi i went lt77

[Diff]

Richard,

I agree with the earlier posters, that the simplest and most practical option is to convert to 3.9 either with injection or carbs, whichever is easier for you. I wouldn't be too worried about restricting it either, just be sensible. You will get the power you want for less agro than forced induction of you current engine, and you will have the benefit of a little less weight. It may even be more economical too!

I am not sure I agree that supercharging wouldn't be worth it on a 9:1 compression. It is true that you couldn't run much boost, but if you used a small EATON supercharger as fitted to mini cooper s (regularly on ebay over here) you could gain a lot for not much. Besides, if 9:1 is too much, it is an easy job to switch to a standard 8:1 head and sell your ACR one for a profit. A simple draw through system using your current ACR SU carb would solve any carb issues, and you would just need a bypass and valve for overboost and when throttle is shut.

HOWEVER, you will need to use decent octane fuel, and if you don't get the ignition set up right you could wreck the engine. There would be a lot of faffing etc. I looked into this a bit, and have shelved the plans for the time being. Current long term project is to fit a small KKK turbo to my 2.5 9:1 petrol/LPG. In theory it is an easier fit and using a small turbo should give very fast spool up off idle.

The composite gaskets are LESS prone to blowing than the copper type.

Regards,

Diff

[02GF74]

Get the 3.9, junk the injection and run carbs with stage 1 v8 restrictors, you should be down by 30bhp. Stage 1's had only 90bhp or so.

yep; just wot I was gonna say. AFAIK these aqre just discs with holes drilled in them that fit in between the inlet manifold and the carbs; I guess by drilling more/.bigger holes you can fine tune it.

alternatively remove one or 2 ignition leads; to make the egine run smoother put in circuit to shut of every 7th igniton pulse so the non-firing cuylinder changes.

[Gremlin]

alternatively remove one or 2 ignition leads; to make the egine run smoother put in circuit to shut of every 7th igniton pulse so the non-firing cuylinder changes.

Oh good idea, then you get onboard air very easily, just plumb the remaining cylinder to an air tank via the plug hole!

Grem

[TheRecklessEngineer]

To make you feel better, Fridgefreezer ran a 3.9 in his Series (with a series box) for about 2 years and never broke it. You should be fine....

And I ran that same box with an uber-mega tuned 3.5 on the end for another year....and its still going (I have a heavy right foot).

[Bull Bar Cowboy]

IMHO the Series III stage one @ 90bhp was not at all pleasant to drive ……….. it always felt like the engine was gutless & being strangled …………. and that is due to the carb restrictors.

The gasket that has the deserved bad reputation are the tin gaskets …… these are OEM on both the 3.5 & the 3.9. The problem was due the head bolt pattern design rather than the gasket …………pulling down the outer row would cause the inner edge of the head to lift slightly , thus giving rise to combustion gases blowing into the valley ……. this in turn causes a high build up of carp and contaminates the oil ……. the solution has been well documented ……… only use the outer row to fill the holes ……… the outer row was in fact deleted in the 4.6 engines. The aftermarket composite is a much better approach, however, it reduces the compression ratio by 0.6:1 due to the extra thickness (IIRC they are 40 thou when compressed). In your case this would be ideal for the reduction in power that you are looking for.

The Compression of the RV8 is dictated by the piston crown shape (the lower the compression the larger the dish in the piston crown) ……….

IIRC the 3.5 came as standard compression ratios of 8.13:1 (Land rover), 8.5:1 (Rover P6), 9.35:1 (Rover SD1 Auto & RR Classic), 9.75:1 (Rover SD1 Vitesse), and 10.5:1 (Rover P6)

The 3.9 only comes in mainly one flavour of 9.35:1, however there was a low compression version made available to some markets for the RR /Disco (89/92) of 8.13:1 ……. my info tells me these were prefix 37D & 38D engines, but they were still EFI and pushing about 170bhp (173 to be precise). So in theory you should still be able to source LC pistons for the 3.9 (but at what price though ?)

If you go down the 3.5 route, then avoid any of the early P6 engines as these have crankshaft rope seals and the block is the weakest of the line-up. Anything from engine prefix 24D will do fine as this was the later strengthened block (it has extra webs) and was first used at the introduction of RR EFI (around 86). Any of the 3.9 blocks will be OK as they are all of later origin.

The early Carbed engines used the Stromberg 175CD ………. and for many reasons this is not my favourite or preferred piece of kit ………. The later engines used the SU HIF44 …….. IHMO a far superior carb.

I think where you are I would probably be tempted to use as many STANDARD bits as possible ………. So again maybe use a standard 3.9 (I suspect these are readily available)………. for the fuelling you have many options ……… keep the EFI ……… the Hotwire EFI is fine ……… simple and very effective …….. easy to fix on the trail … or use Stroms (not so easy to fix on the trail) …….. or use SU’s …… or if height is a problem use the edelbrock or offenhauser inlet manifolds topped off with a Holly 390 or an Edelbrock 500 performer (bit OTT).

However, as usual there are other options ……… mainly due to the instant availability of muscle engines in the states. Some of these are real sloggers that don’t make too much BHP ………….I would be looking at SBB 300/340/350 or the Ford V8 221/260/281 or the SBC engines. I think the only engine I would avoid is the old buick nailhead. One thing that the yanks were really good at was big & solid V8 engines. Probably best to couple these to a TH300/350/400/440 auto box (again…. plentiful in the states).

The biggest problem with all the yank engines will be weight …….. IIRC all the SBB, SBC, & Fords are heavy cast iron blocks & heads ……… although Alloy race heads are readily available.

Ian

[jules]

Why don't you get someone in the uk to find a two Door RR or 110 v8 which is nice condition would cost around £1000 take it to southampton talk to the vice chirman of the SAD LRC and ask him if he would like to put it on one of his big ars car ships the go from england to the states with all the new Land Rovers he is a charge of.

another £1000

but think of all the spares you would have to sell