Cylinder heads

Please forgive the possibly stupid question, but a friend has asked & I didn't know the answer.

She has a Disco auto 3.9 and has bu*****d the head gasket. She asks if the old Rover 3.5 cylinder heads would fit her 3.9 just in case one of the heads is cracked. She has a couple of heads laying around from an old SD1 in one of her many garages. Happily she is a complete petrol head and doesn't mind getting down and dirty.:faint2::faint2:

I doubt that they will fit, but thought I would pose the question.

Thanks all.

Sd1 heads are basically the same as 3.9 heads and will fit

Philip0603 said:

Please forgive the possibly stupid question, but a friend has asked & I didn't know the answer.

She has a Disco auto 3.9 and has bu*****d the head gasket. She asks if the old Rover 3.5 cylinder heads would fit her 3.9 just in case one of the heads is cracked. She has a couple of heads laying around from an old SD1 in one of her many garages. Happily she is a complete petrol head and doesn't mind getting down and dirty.:faint2::faint2:

I doubt that they will fit, but thought I would pose the question.

Thanks all.

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She doesn't mind getting down and dirty eh? no wonder your willing to help her out. My kinda girl!

Depends what model of SD1 they came from.
Carb and Injection RV8 heads are different.
Injection heads have a small relief milled into the inlet to clear the nose of the injectors. If these are not present then it is possible to DIY without the expense of sending out to a machine shop.

The heads would need stripping down, valves numbering etc so they all go back in the right places and the castings cleaned propperly in either a parts washer or a petrol bath if you're a cheap skate in order to prevent any swarf entering the engine when it's put back together.

Interesting! I have a 10A engine with i assume its original heads fitted with an EFi manifold!

I think it was originally a carb engine...?!

In fact just checked my old heads and just checked a pic from the build on my new heads and NOPE they dont have the small relief!

Didnt notice any trouble tbh and 700 miles later its all fine...

Mr Noisy said:

Interesting! I have a 10A engine with i assume its original heads fitted with an EFi manifold!

I think it was originally a carb engine...?!

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10A engine would be an ex SD1 lump from between '76 and '86.
If they are the original heads the cylinder head casting numbers will be ERC 0216. When EFi was introduced the casting number of the heads remained the same as they started with the same blank but the machining process differed. Heads were now fitted with flowed Valves with a 30° backcut and had waisted stems on the inlet side and the afore mentioned relief was milled in for the injector noses on each port.
As the SD1 was going out of production the Rangerover was going over to EFi. So, effectively, everything with a V8 was being sent out with heads effectively set up to "vitesse" spec and that includes early 3.9 V8's, but then it starts getting a bit complicated between 93 and 94 when they finally switched over to 10 bolt heads.

In a nutshell, if the head casting number is ERC0216 it's an SD1 style head and you won't be able to tell if it's carb or efi spec without whipping off the inlet manifold.

I've poached this photograph from the interweb of before and after porting, but the left hand image serves as a useful reference to see the injector nose reliefs on an unmodified head.

all heads and manifolds vary slightly but you will get an interrupted spray at valve ,i normally cut with die grinder but a dremel would do

Well yeah I checked my pics and I definitely don't have machined ports. Bit of a bugger if I'm going to get interrupted spray pattern, do you guys think its a big worry?

What do you recommend I do??

get rid and put a set of merlin F85s on lol

Helpful answer there thank you!

Checked my old heads and they have only a tiny amount machined, much less than in the pics provided!

Do the heads in question retain the standard port size or have they been enlarged?

My heads are very very much standard and unported/matched...!

must be why you are getting ****e throttle response

Did you use a tin or composite valley gasket?
What do your plug readings tell you?
Is your fuel consumption on par with your expectations?

Composite, not had the plugs out yet, and on a 270 green laning trip recently she did an average of 10.6 to the gallon. Same as the old engine did really.

Engine ran very nicely over the while weekend, just that jerkiness and hesitation/lack of throttle modulation that annoyed me...

As above though, my original heads really do have the tiniest amount of machining, can't see it making any difference!!

Mr Noisy said:

Composite, not had the plugs out yet, and on a 270 green laning trip recently she did an average of 10.6 to the gallon. Same as the old engine did really.

Engine ran very nicely over the while weekend, just that jerkiness and hesitation/lack of throttle modulation that annoyed me...

As above though, my original heads really do have the tiniest amount of machining, can't see it making any difference!!

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Unless the old engine was a real clapped out old smoker, similar fuel consumption is a certainly a positive thing.
You mentioned that you have a small relief ground into the heads and also a comp gasket.
Comp gaskets are considerably thicker than the tin equivalent so it may well be the case that between these two factors you've actually generated just enough clearance for the injector snouts anyway? Although I would suspect that the spray pattern will likely have been affected at least to some degree.
RE: hesitation issues, that would actually suggest a weak mixture issue. Often that is the result of a split pipe but you could also be looking at AFM or too much advance.
Another option would be a noisy track on the throttle potentiometer. It is essential that it gives a smooth output from one extreme to the other and a high resistance spot on the track may well cause all sorts of weird and wonderful effects. It may even be the fuel pump or regulator.
Start off with a visual inspection of the pipes and then spraying a dusting of carb cleaner, WD40 or easy start around when it's at idle to see if the RPM changes.
Presumably you've already done the usual voltage / resistance checks and exhausted those possibilities?
Regrettably, my intimate knowledge of RV8 EFi systems is sketchy at best being a member of the "flat earth society" (carb enthusiast) - although now Nicola has added the 3.9EFi Disco to our fleet I'm having to do quite a lot of catch up reading!

Hello

Thank you again for this help.

The old engine was a 24D done 124000, worn cam and poor compressions, no oil consumption or head gasket worries. It actually ran very well but was certainly down on power.

I used to get much worse jerkiness on that engine until I discovered the AFM was set far too lean.

Having fitted the new engine, I actually set it up with an exhaust gas analyser so the mixture is known good. I regularly check all the EFi components with a multimeter and all are known good.

Everything has been apart and checked during the build anyway, the only known fault is play in the distributor.

My situation is on the 24D motor I had tin valley gasket and very small ground reliefs, I now have composite gasket and no ground reliefs.

Fuel consumption is similar, if not same tbh, the engine just burns all the fuel now! If I hold the engine at around 2500 rpm the exhaust is rather sweet smelling, where on the old motor it used to smell toxic.

I assume it is injecting the same amount and therefore using the same amount though.

This engine of course makes considerably more power so I spend a lot more time with the foot flat to the floor, which I think spoilt my consumption this time as I would normally expect 12.5 mpg. PLUS this time we did North Wales, not much motorway for me but definitely lots of A roads which are bad for economy!!

Either way I'm now moving on and starting to fit Megasquirt this week so that will get rid of any possible faults with the old EFi system.

If it does turn out to be a big problem with the heads then I will most likely fit 4.6 heads I think, assuming they are ok to go on?? Failing that then there's a set of stage 1 3.5 heads on eBay at the moment

Thanks again, Sam

So I read on the Mez website that as I expected I can do the head mod in situ, with rags and a vacuum cleaner. This won't be much trouble but its work I don't want if I don't need!

Is the best course of action to pull the injectors out and look in the hole for obstruction?

Or just take the opportunity to fit improved heads?

Do 4.6 heads have the cutout for an EFi manifold though?????

Would have been so easy when the engine was out

Cheers!