Stroking a 3.5

Wotland · Post by **Wotland** » Wed Jul 30, 2008 4:57 pm

Long stroke is not all. You need to take attention to stroke/rod ratio and the revving capabilities. Generally long rod engine allows to produce more power at high rpm.

There are several advantages with long rod engine :
- Less rod angularity
- Higher wrist pin location
- Helps resist detonation
- A lighter reciprocating assembly
- Reduced piston rock
- Better leverage on the crank for a longer time
- Less ignition timing is required
- Allow slightly more compression to be used before detonation is a problem
- Less average and peak piston velocity
- Peak piston velocity is later in the down stroke
- Less intake runner volume is needed

HairbearTE · Post by **HairbearTE** » Wed Jul 30, 2008 6:22 pm

The tricky bit is actually getting a decent rod ratio from an RV8. Most of the standard pistons that are available have quite a large compression height that makes it more difficult to squeeze in a longer rod. Also given the lack of choice when it comes to std rover rods you end up being faced with the dilema of trying to find a good combo from std parts or splashing out on custom pistons & rods.

chodjinn · Post by **chodjinn** » Wed Jul 30, 2008 6:37 pm

Well that's the thing, I can't afford to splash out on anything special/new at the moment! I was looking into changing the engine for something else, but it would be very expensive and a lot of hassle to get a similar spec to what I have now, even more so with forged bits. I'm slowly collecting RV8 bits as they come up and i can afford it, with the aim of building a decent and very strong bottom end to slot into the car as is. Doing that means i can keep all the other nice bits i have like the ACT plenum and twin turbos etc. Bought a large single turbo on the cheap to play around with things as well, if i can; no harm in trying something without spending a fortune, and if it doesn't work i wont have lost much, and can sell the bits on. In theory

Post by **demo2** » Sat Aug 02, 2008 9:51 am

Yes marki u r rite, the tvr crank has different size journels, good memory u have.

chodjinn · Post by **chodjinn** » Sat Aug 16, 2008 1:58 pm

Er, spoke to V8D and also saw on DJE website that the early 5 litre cranks do indeed have 2.3" mains and 2" big end size; as in standard RV8. So back to the earlier question, in a super strong bottom end build (xbolts, girdle etc), would the 5 litre crank hold up to abuse or not?

Think only the later ones had a wierd size then? Strange as I've not heard of that before anywhere.

Wotland · Post by **Wotland** » Sat Aug 16, 2008 3:34 pm

Olly,
in USA SBB guys continue to use genuine ArmaSteel cast crank (pearlitic malleable iron) without problem. And some engines produce more than 700BHP.

chodjinn · Post by **chodjinn** » Sat Aug 16, 2008 3:56 pm

maybe, but I'm asking about the 5 litre RV8 crank which has a bad reputation for snapping. All I want to know is would one hold up or not and whether its worth it.

Wotland · Post by **Wotland** » Sat Aug 16, 2008 4:35 pm

It's certainly strong enough if SC-Power offers supercharger kit for TVR 500.
http://www.sc-power.co.uk/SC%20Power%20 ... argers.htm

SC500 · Post by **SC500** » Wed Sep 24, 2008 9:31 am

FYI we run our customers cars with 400 at the fly with my car being nearer 420 and that is on the std 5ltr tvr engine.

David SC-Power

chodjinn · Post by **chodjinn** » Wed Sep 24, 2008 10:13 am

Thanks for the reply David. I'm assuming they are dyno prioven figures? Are the cranks you use completely standard 5litre or do you modify them, e.g. radiussed oilways, cross-drilled, nitrided etc??

thanks

ChrisJC · Post by **ChrisJC** » Wed Sep 24, 2008 10:26 am

I seem to recall somebody on the old forum who worked for Land Rover said that they could snap cranks with boring regularity on the 4.2 litre Range Rover LSE engine on the dyno. That crank had the smaller journals. Presumably that's why they went up to the larger journals for the P38 engines..... So what 400BHP would do I don't know. Probably not last for long on a dyno I guess.

Chris.

chodjinn · Post by **chodjinn** » Wed Sep 24, 2008 11:13 am

meh here we go once more, different stories . . . . . I just need to know what would be the best crank to use, that's all!!!

I have considered just offset grinding a 4.6 to give me 4.3 litres.

Post by **Rossco** » Wed Sep 24, 2008 12:51 pm

Not sure if someone has mentioned this but a 4.6 crank wont fit in a 3.5 block even if you do turn the mains down. The couterweights are to big to clear the inside of the block.

The other issue with using offset 4.6 cranks is getting sufficient clearance between the piston skirt and the crank counter-weight. Been there and had real problems.

Strongest stroker crank would be the 300 but as you say that's a whole heap of machining.

Good to remember as well that it's torque which snaps the crank and torque is a function of vehicle weight. So in a heavy car you would stand more chance of busting the crank. In a lightweight you'll light up the rear end first and as soon as the rears are spinning the torque reaction is effectively nil anyway.

Chris is right about the guy who mentioned that he could snap 4.2 cranks on the engine dyno. I've used a 4.2 in a 3.5 block and found it a pretty good combination but not sure it would survive nitrous for long.

You could always go with a 455

SC500 · Post by **SC500** » Wed Sep 24, 2008 1:14 pm

I have no idea on the history of cranks used in various forms of the RV8 (sorry) but I have been running my car now at over 400 for 3 years. The engine was new but a completely std 5ltr TVR RV8 when I fitted the supercharger. If you want some specs then a call to Jason at TVR Power will answer all your q's.
It has done many many hours on the r/r, mapping, developing and checking power figures which is hard on a engine.
I also do lots of track days all over this country and abroad always giving the car maximum abuse. I run Dunlop semi slick tyres so putting the power down when the tyres are hot is not a problem.
We had to design engine mount restraints to stop me tearing the mounts in half, I was getting through a set a month. We now use polyurethane mounts that we make ourselves.
With the std TVR mounts I could tear a brand new one clean in half if I pulled away quick on the high grip tarmac you find at pedestrian crossings.
We are pretty happy the crank could take more but we really are pushing our luck with the T5 gearbox at this power level.
Hope that helps a bit

Wotland · Post by **Wotland** » Wed Sep 24, 2008 1:44 pm

Rossco wrote:Not sure if someone has mentioned this but a 4.6 crank wont fit in a 3.5 block even if you do turn the mains down. The couterweights are to big to clear the inside of the block.

It depends of which 3.5 block is used. Very last 3.5 blocks use same 38A block casting like interim 3.9/4.2 and of course 4.0/4.6 block.

Like last interim blocks, they can be X-bolted.