The V8 Owners Forum -

Here is a question that I have been thinking about for a while, I nearly bought a 4.6 ford modular engine the other day, so obviously I am thinking about upgrading, I have also looked at the 4.0 Lexus engine too, far to expensive to tune!!!!,So I am again looking at upgrading possibly to a 4.6 RV8, again just speculating, There are things that are a bit stange with the 4.6 in relation to performance spec,
Rod ratio seems to be all wrong, and far too short considering the rods are longer on the 4.0 than the 4.6, the rod angularity must be extreme,
I would be loking for something 6.2-6.4" long 4.6 being 5.9" and the 4.0 being 6.1, this is all guesswork at the moment
The idea of mine is to use a light slipper type piston with a short crown and pin height, by using a longer rod, the piston accelleration is slowed at the top and bottom of the stroke, with the extra time spent at the top of the compression stroke being benificial to performance, plus the piston weight drops too at the expense of rod weight. bit does 10mm of rod weigh as much as 10mm of piston
Pistons, I have seen some 94,, Honda bike pistons that may just work, and Honda 2.0Vtec pistons may work too, especially as my mate prepared a Honda touring car for the BTTC and has a pile of pistons in his workshop waiting for the price of ally to rise, some tasty rods too!! Ford 4.6 modular pistons, BMW X8 pistons, and Bmw Bike pistons may work as well,
any more thoughts on the reciprocating assembly,?????

Ian,

The best Piston I can find to allow a rod length you are suggesting is a Keith Black Chevy 305 Item for a bore size of 3,736" + clearance requirement. The gudgeon pin size is Chevy at .927" and they have a 10cc dish which will raise compression.

These are forged with a compression height of 1.131" and are $396.00 which even at the current exchange rate is not too bad.

Taking a rover V8 deck height of 8.96" the throw of a 4.6 crank, half stroke = 1.614" this will leave approx 6.215" for the rod which I think is the maximum you can achieve subject to final measurement as deck heights can vary.

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Kevin.

Longer rod increases the dwell time of the piston when it's at TDC and this will make more power. Also it improves the leverage the piston exerts on the crank journal and this also increases power.
But it is not so simple... you need also to reason in term air flow during all stroke cycles (intake, compression, power and exhaust), the way how mixture is ignited, and relation with different piston speeds between short and long rod during stroke.
So camshaft figures may need to be modified according this. For exemple if the exhaust port has good turbulance control then you may run a shorter rod which allows you to use more exhaust lobe which reduces pumping losses on the exhaust stroke.

I would think i would run stupid compression again, especially as I run over 14.1 static at the moment, I was never impressed with the flame travel witness marks on the cylinder head, if you can keep compression up there for a moment longer it would probably help with combustion, even more if I used pop-ups, and give plenty of attention to the exhaust area,
Obviously the cam would need to be looked at, but I have a good cam grinder who is capable of working out what I need
How big can you safely go on a 4.6 overbore, this would help with the valve shrouding that the heads suffer from, I realise most of the problem of valve shrouding is caused by the valves being not centeralised in the bore, hence the mods Vizzard made to move the heads to position the valves better in the bore, but that if far too much work.

Most aftermarket LS rods are 6.125"

Might be worth contacting Scat or similar with dimensions you want...and let them see if they have anything cheap.

As for the Lexus...stick a blower on it. The standard bottom ends are good for around 800bhp or so apparently
I'd call that cheap to tune.

or for a very cheap engine...dont overlook the 4.8 or 5.3 LS alloy block variants. Smaller cc...but a huge wealth of aftermarket parts, and cheap to buy.

Steve, did I see a 9.3 1/4mile earlier this year??????

Not from my car lol....

Hi Ian
Have you considered ex nascar rods? 6.25 is the top end of rod length used but you see a few sets each year of 6.2 and 6.25 rods, and for what they are they are cheep!
I presume you are planning very high CR to help with the poor rover head exhaust flow, good plan but if you leave the piston at TDC too long and with too much ignition advance you will get very high peak cylinder pressure and detonation.
Have you considered twin plugging a set of heads if you are going to use the combination of high CR and long piston dwell? It would let you use much less ignition timing, while letting you get all the mixture burnt but with peak cylinder pressure coming when the piston has started moving again.
Still not going to go 302 ford?
Best regards
Mike

Twin Pluging, I know Dave Walker had some improvements with a Twin Plug head with a Pinto, Dunno how I would cope with 16 leads,
8 is normally enough for me, woulld have thought its nigh on impossible to get 2 plugs in the heads without major reworking,, I really do think the way to make power with the Rover is Compression, run it on 99/100Ron fuel it seems to cope with 14.1 without any det, and Im running LOTS f ignition
Im still undecided what to do engine wise, there are a lot of choices, SBF is a real option, but I have a lot of money invested the my RV8, and having to change over to the ford would be a big outlay, especially as Rv8 in any form dont seem to be worth a lot, so there is not much starter cash to get it in and running, Its all the things like custom exhaust manifolds etc, To fit the Ford, or any other engine would take a year or so, as the car is virtually built around the Rover,
I would like to keep my injection, and downdraft manifolds for a SBF seem to be expensive, and with the price of the Dollar being poo at the moment,

I thought you had nitros fitted, or are you after pure engine power, Scat do 6.125 rods, h-beam with a 2" journal, rich

Dont see why I cant run a 4.6 with gas too??, just been talking to a offroader around the corner from me, he has a long stroke crank, cant remember if its a Offset ground 4.6 or a Steel crank, Im guessing its a steel one as he thinks its 5.0, Things are moving at a pace

Sorry i should of put about using with a high compression engine. but i suppose that depends on the amount of gas used, rich. This is the person i e-mailed at scat about the 6.125 rods, MHajimomen@scatenterprises.com,

Whats the rev limit on a stock 4.6??

fookin hell mate give us a fookin chance will ya

What about these, the journal size is 2.20, so its not a huge 0.050 regrind


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