The V8 Owners Forum -

I know this is an open question, but what would be the best route to convert a 4.6 to a 5.0?

The engine is in a TVR Griffith, originally it was a small journal, non x-bolted engine which has departed this earth (long story.....)

The current engine was built by V8D and is a 4.6, x-bolted, flanged liner block with standard 4.6 rods/pistons and Stage 3 heads. Running a Megasquirt 2 with EDIS8 it made 283bhp after tuning on the RR.

The reason for going to 5.0 is to put the car back to 'standard', i.e. back to a real 'Griffith 500', but without the original TVR 94mm bore and 90mm stroke (I'm not fan of this small journal crank - please don't ask..... )

Is the following a 'good' option, or is there a better route:

1. Have the crank ground to 86.36mm Stroke, 2" big ends.

2. 96mm forged pistons

3. ??? Conrods - not sure on this one?

For the increase in bore, I'm assuming machining and new flanged liners required. Would it be better to sell the existing (94mm) flanged liner block and invest the money in a used block and the machining for 96mm flanged liners?

This is 'next years' winter project, this years is a JE crossover manifold.

Any opinions gladly received....

Hi,

If you offset your 4.6 crank to 3.4 stroke, you can use SBC 5.85" small journal rods with SBC 305 pistons.

If your block has been flanged with Westwood T-liners O.D. 99.1mm you can bore it up 96.5mm.

Cheers

Thank you. Will have to have a chat with Rob at V8D, it's one of their earlier engines, so he may know which flanged liners they used.

As much as I'd like to tackle it myself, I may be better off pulling it out over the winter and taking it over to Rob to do the work.

You're wanting to do this, spend £3.5k+, just to put the engine back to a 5.0? And not any old RV8, a 4.6 with top hats already? Ok.

If you must do this, whatever route you choose, my advice would be to sell the 4.6 short block complete and buy an old 4.6 block that needs liners for peanuts and have V8D turn that into a 5.0.

That way, you can scrape a little money back as a top-hatted 4.6 is about the best you can get for a 'standard' RV8 configuration, there would be plenty of buyers around. Doing all the work to the engine you have means pissing away every penny that has already been spent on it! Mind you, if you are seriously looking at the x-over manifold from JE then I guess you do have money to burn £3k for an inlet is stupid money IMO (I'm assuming that doesn't include a standalone ECU to run it all as you'll be running MS2?).

By the time you've bought that and the engine work you could have just about fitted an LS1

Good luck whatever you choose.

For that budget you could have one of these
http://shop.partsworldperformance.com/l ... e-19244549
including the ECU and wiring kit. . . and it is a GM crate engine so it comes with a warenty.
As a crossover manifold isn't original I am not quite sure why you would put 5 litre rover in the car with one in preferance to this lump .
Best regards
Mike

btwe my reply was in no means a criticism, I was just offering alternative to reworking the current 4.6 that you have ... you never know you might get a grand or so back from the short engine, which isn't to be sniffed at!

God, I'd love an LS motor!

All valid comments, and all well received. I tend to agree on selling the existing 4.6, and going for a 'new' build of a 5.0.

I will be keeping the original inlet in storage, along with all the other original bits that were on the car. When (if) it comes to the time to sell, in theory it could all be put back to original. People are a bit funny about modifications on these cars.

I'm still not fully decided on the x-over manifold, I'm meeting up with a guy who has one fitted at present to see how it drives.

Again, the LS route is an option, but it just doesn't have the same sound - and most people I have talked to who have carried out the conversion have racked up the best part of £10-12k after engine, gearbox, manifolds, etc. etc.

Agreed, the LS1 can spiral a bit in terms of cost, depends how much you do yourself. I know a few TVR guys have done the conversion tho.

Have you looked at ACT products carbon manifolds? They are a work of art and a quality cheaper alternative to the x-over manifold set up, not sure on the performance differences tho. I used to have a twin throttle one, lovely bit of kit and held it's value when I sold it lol.

http://www.actproducts.co.uk/shop/tvr-i ... 75_77.html

they do a lot of TVR stuff.

The current intake I have is from the 500 engine, which was modified by TVR Power to the same type they fitted to their 'Taraka' conversion. Nothing too major, but ported all the way through at 45mm, with trumpets blended to the base and a phenolic thermal spacer between the trumpet base and manifold (which also increases the length of the runners slightly to compensate for the 'loss' of trumpets). The throttle opening is also increased to 71mm and there's no MAF with the MS2.

On the RR we measured around 2-3bhp difference with the intake connected to the pipework filter, against just a pipe connected to the throttle hanging out the side of the car. I'm not sure the ACT system (as wonderful as it looks) would really give me that much benefit.

The idea of the X-Over was to tame the slightly wild cam (M248) that came with the engine. I know I could change this, but it really does make the car car a hoot to drive - and as a weekend toy, I can live with it to a certain extent.

I guess the X-Over manifold would hold it's value pretty well over the years too? Even TB's on their own seem to hold pretty good value.

Result from RR, not sure what causes the 'dip' at 2500rpm?

'New' 4.6 Rolling Road Graph

Not quite TVR 5.0l 340bhp - but then the original 5.0l engine only made 264bhp (with a healthy chunk of torque)...

TVR 5.0 Rolling Road Graph

4,6 litre torque at 260 lbft is quite low, i would have expected an easy 300 lbft.

About the originality, if you don't use a TVR block and small journal crank, any other engine will be equal in terms of originailty, be it a 4,6 or 4,6to5,0 or whatever.

One thing though, i believe you do have some potential in your current engine. You have basically a std short engine wit stg 3 heads. What is your CR ? Your cam needs quite a lot of static compression to work properly. I have not used it but I'd guess somewhere around 11,5:1 ? Now, with 4,6 pistons with big dish you need to skim the heads or block or both to raise the CR even when using steel head gasket.

4,6 litre torque at 260 lbft is quite low, i would have expected an easy 300 lbft.

About the originality, if you don't use a TVR block and small journal crank, any other engine will be equal in terms of originailty, be it a 4,6 or 4,6to5,0 or whatever.

I tend to agree, more over it's the fact the car is called a 'Griffith 500' based on the engine capacity, a 4.6 kind of flies in the face of that. The TVR block wasn't special or original, just a standard small journal block with an engine number stamped by hand.

One thing though, i believe you do have some potential in your current engine. You have basically a std short engine wit stg 3 heads. What is your CR ?

I've 'been told' the heads were skimmed. They are ERC0216 heads, so originally 36cc combustion chambers I think? Am I correct in thinking that there can't have been that much skimmed off the heads as the intake manifold still fits without any problems?

Your cam needs quite a lot of static compression to work properly. I have not used it but I'd guess somewhere around 11,5:1 ? Now, with 4,6 pistons with big dish you need to skim the heads or block or both to raise the CR even when using steel head gasket.

On holiday at the moment, so will carry out a compression test next weekend. Is it possible to get a rough estimate of the CR from the results?

Well, I did some calculations using an online tool at:

http://www.csgnetwork.com/compcalc.html

Pretty handy, and let me put some numbers in which are think are close to the mark. I'm not 100% sure on the deck clearance - I put it in as 1.35mm to get the 'Standard 4.6' figures to a CR close to 9.35. From research I think the standard is closer to 1.01mm.

I estimated that a 1mm skim of the heads would reduce the CC by roughly 7cc, not sure how far off I could be there?

Calcs are here:

http://thumbsnap.com/f/9PO8rHgi

I spoke to V8D a while back, and to be fair this engine was built by them a long time ago, so they don't have any information on it. They did say that they would not normally build 4.6 engines over 10:1, so I think it would be safe to assume that it is probably close to the original 9.35:1.

When I get back home I will spend a bit of time next weekend having a look at it. On my list of 'things to do' I have the following:

1. Test compression on all cylinders (I realise now there is no real way of relating this to CR).

2. Use USB endoscope to inspect inside cylinder (good old ebay) and see if standard 4.6 pistons are used.

3. Check if composite/tin gasket is used (I am pretty sure it's composite).

4. Remove plenum top and use Endoscope to check down inlet tract to see if there is any mismatch to cylinder head.

5. I have to replace a leaky sump gasket, so will be a good opportunity to inspect the bottom end and also to have a look at the pistons/rods/liners.

As for the low torque figure, maybe this is just the wrong cam to have in this engine - maybe I should change it out for a stealth? I has less than 2k miles on it. Either that, or the CR is low and maybe some forced induction may be a wiser investment....... There are a few people out there doing kits which are easily reversible.

jeboa wrote:
I estimated that a 1mm skim of the heads would reduce the CC by roughly 7cc, not sure how far off I could be there?

I was told by V8 Developments that 8 thou off the heads is worth 1cc out of the chambers. I've had loads of heads skimmed now and it does works out to be what they said. The reason that is is not the same as removing metal from the deck is that the chambers do not extend out to the bore walls.

So 7cc from the chambers would be 7X8 which is 56 thou. That is 1.49mm

You could take metal off the block, this would mean less has to come off, also it helps to get rid of the huge chamfer at the top of the bores which is no good at all because at least half of the fire ring on the head gaskets end up just 'floating about' in the chambers and is not compressed.

Assuming that your bore is 94mm then 1.01mm off the deck is 7cc.

You could of course do a combination of removing metal from the decks and the heads.

Really I would not remove any metal until I had measured everything with a burette but that's just me!

Thank you for the reply.

I think what is interesting is how my inlet manifold matches to the engine.

I didn't think about it before, but I retained the inlet manifold from my 5.0l and am using it on this engine. Not sure if that could be causing an issue?

I don't know if V8D would have just machined the heads, or the decks also. Either way, it would be interesting to see how the ports on the inlet match up - I didn't check before (just assuming it would be 'normal'). My mistake I guess.

All things considered, I would say that the CR is less than 9.5:1, so may be a good candidate for a bit of forced induction.

Maybe this (in combination with a different cam) is a wiser investment in the short term....

I believe the decks of the top hat linered blocks need to be machined flat after the liners are fitted. Personally I would only skim the block to make the decks flat, no more. Having said that, I have had my block machined to raise the CR, at that time 4,0 pistons were quite expensive and it was cheaper to machine to block.

My preference is to build the bottom end with proper pistons, suitable dish and compression height so that the piston is close to deck at TDC. Of course one needs to know which heads and gaskets to use so CR can be factored in.

If you machine the block and heads, you might need to machine the intake as well. In the end you will have a bunch of engine specific components that will not fit another engine

But, check first and the make the calculations before having anything machined.

I am running my 4,6 engine at about 10,5:1 with std pistons. Stevieturbo used to run twin turbo engine with Rover pistons. He might have some ideas for your engine as well. Twin turbos on your current engine would be actually cheaper than building a 5,0 engine. with TT you would easily get the TVR quoted HP figure.