4-valve v's 2-valve heads

[TK]

Oh, yeah - forget about piston speed limitations - with a 3.63" stroke & 6" rods + real good slugs you could spin the jigger to 9000rpm.
Wouldn't last long tho.

[Tripper]

why dont we use the ford 390, it came with both 2v and 4v.

[TK]

Bill is a cheating bastard, his sims were based on a 7L donk, not a 6L.
4.125" bore 4" stroke.

So, with a whole litre less my bogan 2V 6L matched his dohc 32 valve 7L

I've got the file working now, I'll do some sims with faster ramp rate in the morning.

[Billzilla]

Oh, yeah - forget about piston speed limitations - with a 3.63" stroke & 6" rods + real good slugs you could spin the jigger to 9000rpm.
Wouldn't last long tho.

Will do, gimme a minute.

Bill is a cheating bastard, his sims were based on a 7L donk, not a 6L.
4.125" bore 4" stroke.

So, with a whole litre less my bogan 2V 6L matched his dohc 32 valve 7L

I've got the file working now, I'll do some sims with faster ramp rate in the morning.

Nah I told you that was for the LS7 engine mate.
I'll attach the two six litre ones I mucked around with here.
test 1 is the small cam one, test 2 is the big cam one.

[Billzilla]

859hp @8600rpm.

[Nero]

grab an F3 cam spec and use that. I's for a 4v engine.

[Sketchy]

And this is why I love performance forums :D

Hats off to you both for being stubborn cranky buggers who know their shit and teaching us all more in the process.

I'd love to be able to add to this thread but my head hurts from everything I've just read in the last half hour

[arcane]

BMW already did that with their throttleless engine.. where the valve lift is used to act as throttle.. i forget which one

Valvetronic. Infinitely-variable valve lift between 0 and 10mm.

[Uncle]

Just to keep things going.
This is my old LS1
242,242ish@110lsa Comp cam,918 springs,78mm T/B.OTR,CHE 4 into 1 headers and duel 3" all the way out and a MAFless tune by the motherfucking king of LSx tunes Dale from CHE.
Other than that it was 100% stock bottem end,stock never been off the ute heads,stock 28lb injectors stock fuel pump ect ect..
The two runs are between stock cam with springs ect in place 2nd run is cam in 2hours later same weather bla bla bla.
This set up ran 244 passes reving to 7,200rpm in 1st and 2nd gear never missing a beat once.
Same cam with FAST 90mm manifold and T/B and 36lb injectors made 401rwhp with no other changes on a back to back test,with Dale and I doing the cam change on the dyno.

Not bad for a 2v LS1..
P.S fucking good thread cunts

[GTSBoy]

All right. Attached is the quick and dirty spreadsheet with the ratios of interest.

What I have done is just calculated the areas associated with the valves and the bores and compared them against each other, and some against the diameters directly.

The inputs are in italics in the top table. You can change them there, to see what changing a valve size does for example. That will change all the tables below as well.

The top table shows the numbers as given by Bill. There is also a line at the bottom for Tony's 2V 6L, but I didn't have a valve diameter. So I guessed 2.3" and coloured it red to make sure people realise it is a guess.

Note we need to get Tony's 6L valve size into it, and hopefully some data for at least one small bore 2V engine of good design/reputation.

The 2nd table is all the same data, but I normalised the valve lift on all of them to the same 0.55" lift.

The 3rd table is the same data with the lift scaled to the bore diameter.

The 4th table is the same data with the lift scaled to the bore area. I did this to remove a significant variable between the various engines presented.

I think two more tables could be made with the lift scaled to valve diameter and valve area, but can't be stuffed. There's too much info here as it is.

I did the various normalisations of the lift to remove a significant variable between the various engines presented by Bill. His 4AFE and the 3SGE have a lot more lift than the other small bore engines. That inflated the curtain area a lot.

Anyway, as it stands, once the first normalisation was done (ie, just fixing lift at 0.55") the standout effect is that the ratio of curtain area to valve area is noticeably lower for the big bore engines than for the small bore engines (the normal ones, the 1UZ and the Suzuki). Compare cells Q27 and Q28 against Q31 and Q32. This shows that for a fixed valve lift, the big bore engines do indeed suffer from less valve than the small bore ones do. Bill's race engines apparently have quite large valves squeezed in, so they stand out as having a lot of curtain area - but we will ignore these for the moment.

By contrast, if you normalise the valve lift to bore diam, then the big bore engines pick up a lot of lift compared to the small bore engines, and the equivalent ratios change over to marginally favour the big bore engines.

If you normalise the valve lift to bore area, then the valve lifts start to get closer to what Bill provided for the big engines (ie they get even more lift) but the small bore engines start to get more ripped off. (ie, generally, if the bore is bigger than the engine I used to normalise against, the engine gains lift, and if it is smaller bored than the engine I normalised against, then it loses lift compared to what Bill gave me).

So all this info is just waiting for Tony's numbers. But working with what we have already (ie my guess) there are some interesting comparisons to be made between the 2V and 4V 6L motors.

1) At 2.3", the 2V has more valve area than the 4V.
2) At 2.3", the 2V has less curtain area than the 4V. A lot less. And a really poor ratio of curtain area to valve area. This is with supplied lift numbers as well - no normalisation.
3) At 2.5", the 2V has a lot more valve area than the 4V.
4) At 2.5", the 2V still has a fair bit less curtain area than the 4V. Still with supplied lift - no normalisation.
5) If you normalise the lift via any of the methods in the lower tables, then the 2V curtain area just plummets. Kinda obvious, because we are giving the 2V the same sort of lift as a 4V.

Play with it as you wish.

cheers

[Billzilla]

Lots of numbers, not sure what to do with them ... ?

So more 2V data will help eh?
I'll bring back some numbers from that Renault 1300 I'm working on tomorrow.

[GTSBoy]

Well you can't graph them, but the idea is to have some numbers to look at any time someone comes up with a point in the discussion stating that X has more Y than Z does. You can see if that is right, and look for trends.

What I was hoping was to see that there was a definite trend in the ratios for 4V heads as the bore size got bigger, and a different trend for 2V heads as the bore size got bigger - the 2V trend would probably be in the same direction, just different slope, indicating a divergence in how the two types respond to increasing bore.

To be really useful, it needs a lot more engines in it. The best thing would be to concentrate either on completely stock engines, or engines which have been worked to take the biggest valves that will fit. The latter is probably a better indication of the limits of each type, but there will be a lot more data available for the OEM sized stuff.

cheers

[TK]

Sorry Bill - it occured to me after I left work that you're not stupid enough to think I wouldn't notice it was a 7L donk.

Back on topic - I was using a 2.1" intake valve.

Bills results kinda prove something else - with more rapid lift rate the only real benefit was at higher rpm.
Which basically says that up to 6500rpm both 2V & 4V engines are injesting the max air they can anyway - so helping breathing is not making any more power coz the damn things just won't swallow more air anyway.

Which also proves that a 2V engine can have enough flow that there is no advantage to 4V untill revs get quite high - ie. outside the usual operating range of a large bore engine.

So it's basically irrelevant that the 4V flows more - no benefit can be gotten from that extra flow.

The only power increases achievable in the given rpm range (up to 6500rpm) would come from better combustion efficiency - something the 2V is definately equal to the 4V in, in some cases superior.

I've learned a bit.

Basically, if you're running a bore size up around 4" you'll see no benefit of a 4V over a 2V untill it's revving past 6500rpm.

Forced induction would be a different story - the ability to shove more air in than the engine can aspirate on it's own would see a benefit from the increased flow of the 4V.

[TK]

Just re-ran my last sim again to look at VE & confirm that there can be no gains from more flow.

At peak torque it's showing 125.4% VE, ie the motor is inhaling 25.4% more air than could physically fit in the cylinder at atmospheric pressure, meaning the pressure in the cylinder with the valve still open is 1.254 bar.
Or the equivalent of a motor running at 100% VE with 3.5psi boost.

That's pretty fucking good ram tuning.

[Billzilla]

All good stuff, Tony.
Had an idea last night, but it'll be hard to implement.

I'll simulate a single cylinder, starting at (say) 100cc's and go up in 100cc increments to about 1,000cc's. That'll cover pretty much everything we'd come across. The single cylinder will eliminate a few variables with exhausts & so on. Do it in both 2V and 4V configurations.
Make the bore/stroke ratio fixed, something like 0.8:1 (first guess) so that with the piston speed is high but liveable. (say 4800 ft/min) This would progressively reduce the rev limit as the pots get bigger as well.
That also reduces a few variables.

Make the valves a fixed ratio of bore size, say the 4V inlets at 35% of bore size and the 2V ones say 48%. Make the exhausts say 85% of the inlets in both cases.

Make the cam(s) also fixed, say 232° @ 0.050" and the lift say 35% the diameter of the inlet valve for the 4V engine and say 45% for the 2V's. Fix the lobes centres at say 107°. We'll have to figure out something with the ramp rates that works for both.

Keep the same compression, say 11:1.

I haven't figured out what to do with the inlet & exhaust lengths and diameters, other than to change the diameters to get the same airspeed velocity for each engine to try to make it as equal as possible at max revs.
Not sure what to do with the lengths of each though ...

Do you think we'll get some useful info out of that?