breathing and cylinder heads for a 5L

ppyvabw · Post by **ppyvabw** » Mon Dec 15, 2008 2:23 pm

I am going to be putting the real steel 5L stroker conversion in a 3.9.

I'm just thinking about corresponding mods to my cylinder heads. I want to do the porting work myself tbh because I won't be able to afford the stroker kit and the heads

Idealy I'd like the Merlin heads or the Wildcat heads

Because it's the 3.9 bore, large valves are shrouded by the cylinder walls. I was going to put the stage 2 valves in which don't need the seats changing before I decided to go to 5 Litres. Should I go to the expense of even bigger valves with a 5L despite the shrouding problem?

I'm using larger trumpets anyway on the manifold. Im currently making a custom trumpet base, so I will port the manifold correspondingly etc..I will also be making a twin plenum jobba somehow.

What other things do I need to consider when modding heads for a large capacity conversion? Just lots and lots of porting and polishing work? I know really head modding is a specialist job but I don't have the dosh in my budget to do both the 5l conversion and the heads.

kiwicar · Post by **kiwicar** » Mon Dec 15, 2008 3:13 pm

hate to say this, but you will get more power and better drivability for your money if you forget the 5 litre kit and spend the money on either of the sets of heads you mention, a 5 l kit on any rover ported head casting will have a narrower power band. Also it will be less reliable than a 3.9 with decent heads.
Mike

bones · Post by **bones** » Mon Dec 15, 2008 4:08 pm

ive had 1.630" inlet and 1.400 exhaust valves fitted and it didnt need the seats changing, mine were just re-cut and a 3 angle cut in.

rich

ppyvabw · Post by **ppyvabw** » Mon Dec 15, 2008 4:15 pm

kiwicar wrote:hate to say this, but you will get more power and better drivability for your money if you forget the 5 litre kit and spend the money on either of the sets of heads you mention, a 5 l kit on any rover ported head casting will have a narrower power band. Also it will be less reliable than a 3.9 with decent heads.
Mike

~Cries~ I want the five Litres, it's good pub ammo

Maybe I'll get a mortgage and get the heads too. I'm under the impression the wildcat ones are better? Do the standard rover inlet manifolds fit them? I know they fit the Merlin ones.

chodjinn · Post by **chodjinn** » Mon Dec 15, 2008 4:43 pm

widlcat ahve their own manifolds. If you're gonna spend that amount of money on heads it'd just be rude to put a standard manifold on lol.

HairbearTE · Post by **HairbearTE** » Mon Dec 15, 2008 6:53 pm

I don't know if RS Merlin are back in stock yet but if the are you should definately go that way. Wildcat heads will cost you a lot in associated parts whilst the Merlins accept standard rocker gear and inlet manifolds. The Valve size issue is a problem. You only need to take a look at the valve sizes on a built U.S. small block ford or chevy of 5 litres to realise we're banging our heads against the wall here. I recently saw an RV8 advertised on ebay with a big mechanical cam and stage 4 heads that was proudly claimed to have made peak horsepower at 5200 rpm! That tells you all you need to know about feeding 5 litres through a pair of rover heads..

ppyvabw · Post by **ppyvabw** » Mon Dec 15, 2008 7:54 pm

Maybe I'll go with the 5 lite conversion and put some dustbin lids in for valves on standard rover heads, do some porting myself and run the engine like that for a while and save up for some nice shiny merlin heads and sell the others to cover part of the cost.

kiwicar · Post by **kiwicar** » Tue Dec 16, 2008 11:49 am

If you want 5 litres (for braging rights in the pub) but have an engine that will make real usable power and do it for far less money, build a ford 302 with ally heads, It will probably weigh only 20lb more. Or the old Lsx 5.3 litre chestnut...
Mike

CastleMGBV8 · Post by **CastleMGBV8** » Tue Dec 16, 2008 1:31 pm

And have you worked out what a 5.0L engine with all the right bits to make it work will cost you. What sort of budget you looking at?

Don't forget that even if you buy a stroker kit there a re-bore, block machining for crank clearance, decking to get the compression heights correct and the whole thing will need re-balancing so add anther £225 if heavy metal is required, it all adds up, I know because I've just done it and the engine went quite a bit over budget.

If youv'e got funds now there are a couple of intersting engines on e-bay at the moment, one 5.0 and a well built tophatted 4.6 that look like they might go cheap just before xmas.

Kevin.

chodjinn · Post by **chodjinn** » Tue Dec 16, 2008 1:40 pm

Well the "TVR" 5litre is already at £1500 surprise surprise, prob go for more than that. I wouldn't touch it.

The 4.6 is far better value for money given it's almost a turnkey engine bar the ancillaries and it's been top-hat linered, and it's only £300 more . . .

ppyvabw · Post by **ppyvabw** » Tue Dec 16, 2008 2:35 pm

What's the maximum valve lift I can have with the Merlin heads using standard 3.9 hc cast pistons but with a bit machined off the heads and block to get the compression up a bit more? The valves are less inclined aren't they so you can get more lift? If, as kiwicar suggests i'll get more power with the 3.9 on proper heads, I may do that.

My whole reasoning for going to 5 litres is I want to get the compression up and run lots of cam for the novelty value and I wanted some nice forged pistons. By the time I have bought forged pistons, appropriate rods im paying over a grand anyway so I may aswell get the kit for 1600.

Boosted LS1 · Post by **Boosted LS1** » Tue Dec 16, 2008 4:21 pm

You could fit one or two turbo's onto a relatively standard rover and still see off a 5.0 engine in the power and torque stakes. You still get to keep those bragging rights.

poo slinger · Post by **poo slinger** » Tue Dec 16, 2008 4:53 pm

or if u want pub ammo get some of those 5.0 badges for your rocker covers.