4-valve v's 2-valve heads

[TK]

Not really, there are too many differences between the engine types to be able to use a single baseline for them.
Eg. the 2V will need a bigger cam, but will swallow it with no detriment - so using the same cam for both will leave the 2V at a disadvantage.
2V will also tolerate more comp due to increased quench area over a 4V.

I think we could spend days trying to analyse exactly what is happening in both styles of engine, but for practical purposes it don't really matter - what is important is getting as much air into the cylinder, regardless of bore size, as possible.

It would be nice to see if there is a correlation between bore size & the effectiveness of a 4V design - but I just don't think I could be bothered, could take fucking ages to get any data that means anything & you're still limited by the practical reality of what is actually available for XX engine.

[Billzilla]

Fair enough.
If I get the time I might have a go at it anyway - it might be interesting.

[Billzilla]

Tony, when/if you get a chance can you please weigh a typical V8 head.
With the valves in place, rockers, etc.
I want to make a more accurate estimate as to how much more a 4V head would weigh.

[GTSBoy]

Other 2V small engine data?

[Billzilla]

Other 2V small engine data?

I forgot to measure the Renault engine but the 3K we used to run was a 3.11" bore, 1 x 1.53" inlet valve that I think lifted around 0.480" ..... really not sure it was a long time ago.

[TK]

Tony, when/if you get a chance can you please weigh a typical V8 head.
With the valves in place, rockers, etc.
I want to make a more accurate estimate as to how much more a 4V head would weigh.

I'd be happy too, but I don't have any scales that would do it, I should be able to find a weight on a typical SBC ally head tho.

TK was right and I was wrong

LOL, I guess you do have a sense of humour Bill.

[Billzilla]

Well, I'm still not entirely convinced ....

I'm simming a five litre Supercar V8, and so far getting a fair bit more grunt than I know they have.

[Cplus]

"know" they have?

how do you know??

[Billzilla]

Because I know some of the people in some of the teams, and one of them has told me exactly how much power they make - on the condition that I don't tell anyone the figures.
So far with the 4V version I'm about 45hp and 35ft-lbs better.

[RA45GTCelica]

valves

tk does valve angles as in the head of the valve have much to do with flow
like tulip inlets, versus penny on a stick as in titatium valve std .
also different sizes as well 34,5 35 mm and 35,5 and last 36mm

[Billzilla]

Here's that odd head I was talking about a few pages ago.

It's called a dual-swirl, and what they've done is basically dig another inlet port down between the cam and sparkplug hole so there's two inlet runners feeding the pair of inlet valves. So each cylinder has two sets of throttles going to it. Each throttle on this engine uses a slide throttle.

Some of the text that went with the article said:
- Highest recorded power output: 289hp. Best driveability attained with 286hp. (Highest output from a conventional 1600cc Cosworth BDD 258hp)
- Driveable rev range: more than 7500rpm. Bdd only 3,000rpm.
- Best torque 158 ft-lbs from 1.6 litres.
- Achieved 180hp/litre only using 10,500 rpm.

I'd love to build one, but it looks like a bastard of a job.

[curmudgeon]

This has been an extremely interesting thread. I'm wondering though, if the trend to 4 valves for production engines has little to do with flow and horsepower, and more to do with durability? I mean small, stock engines with 6500+ redlines are quite common now, and of course with bikes it's much higher. With smaller, lighter valves these speeds are achieved with quite moderate spring pressures, and the engines have quite a long lifespan. I can imagine 2 valve engines being able to make similar power but to make them as reliably trouble free with the spring pressures needed for these speeds would be difficult.

[Billzilla]

I agree - Even though it seems like a big, slow-revving engine that uses a savage cam can match a 4V engine, I'd still use a 4V given the choice.
More simple, less stress, more reliability.

[Ben Wilson]

Bear in mind that there are ways to get more pushrod like cam profiles in direct acting DOHC engines. As well as the finger followers mentioned earlier, you can run domed buckets like BMW did on the M5 a few years ago.

[TK]

The limitations on the stupidcar donks mean they can't run the best heads - no canted valve/twisted wedge style heads, no offset guides etc - so a 4V probably would show an inprovement.
Different story if you built an 'unrestriced' donk for the same fuel & same capacity & rev limit.