best money spent to give the 20v more ballls

[kaibeecee]

well if you're smart about it you'd make a more responsive motor without VVT, especially on a ST as the VVT is actuated by oil pressure not the 'infinite' style of the BT. its not either entirely on or off.

If i was doing a 20v, i'd delete VVT and just get larger lift cams with a less extreme duration, a bit more timing and tune more precisely in the top end.

it'd be way more drivable but still pretty punchy up high.

[slydar]

im guessing green = vvt working, red vvt enabled.

interesting to see, but i dont know if its a really fair comparison. simply disabling the vvt isnt a real world scenario.. really. if you disable vvt, i would expect you would be using adjustable cam gears. in which case you would hopefully be dialing your cams in.. and it probably wouldnt end up in the stock position.

either way, the only thing i can add is that ive driven one black top powered car with tighe 288s and my own 16v car with wade 277 and neither of these cars was really any trouble to drive.. dont be scared to go for some decent sized cams is all im saying. i would never buy cams of less than 272 duration i dont think. they work but theres just no reason to go smaller.

[Frak]

They are both activated by oil pressure, they are both on/off.

I have vehicles powered by both, have tested both and they are definately on/off........can we put this to rest once and for all!

BT use tps as an input as well as rpm which may give the impression of being variable, the timing is still changed 30deg(crankshaft) one way or the other(ie advanced/retarded in one hit....no inbetween, a BT CANNOT advance or retard the cam somewhere between 0-30deg crankshaft and hold it there, the cam phaser is not designed to do it)

It only takes a certain amount of oil pressure to COMPLETELY move the cam in the phaser, this pressure is below that of what the oil pressure regulator is set to. Which means that every time oil is ducted into the phaser via the vvt solenoid, the camshaft moves COMPLETELY, if the oil pressure was VERY low, then this will affect the cams operation......but with oil pressure that low, I'd say your engine was fucked anyway.

[Frak]

I go thru how vvt operates and how it affects engine volumetric efficiency during my night time dyno/tuning classes.

[Anthony]

Eddie: no prob, give me a call and we can organise it.

Frak:

[Frak]

Just had a read, must of missed it before. nice

[ae86hachiroku]

Yep, go large. I'm on 304 duration and if it were a daily with a less aggressive suspension/chassis setup it'd still be fine to drive around.

Just to add, and no offence intended, by why do you want it to rev to 10,000 for? It's fairly pointless. At around 8500-8800 a 4AG is starting to almost peak out, and any gains above it are miniscule, to be able to rev to 10k you're spending a shit load of money for very very diminishing returns, better off just having fun going to 9000rpm or so and save yourself troubles and money. Especially if your thinking of taking it for some dori action occasionaly, sitting sideways at 10,000rpm is simply empty revving, torque peaked out long ago at around 7500ish, in simple english your not really going to be going forward anymore, kinda just sitting there and baking the tyre.

If your intent at 10krpm though, I'd definately looked at all forged internals, it's a lot of work as being able to rev that high also means a engine that is capable for a lot of power. 304 or 288 duration camshafts, forged crank (Jun, Toda, Tomei etc?), forged rods and pistons, the works. It'll easily cost you over $10,000 as there will be plenty of headwork involved, including a decent set of extractors too.

[Sam-Q]

frak: Silly me I think I asked about the rod weight in the other thread. 467 is pretty decent, I assume the bolts where in that at the time. The spool rods are even lighter at 459g which is considererably lighter than even the blacktop rods. However I will be quick to say that I have no idea what the real world effects of this would be.

lucifer d: there is no reason why the exhuast cant be changed to a larger duration and keep VVT. For many people I am sure a 272/280 combo would work pretty well.

FAST EDDIE: just a perk of the engine, however I will be doing work in the future to even it out. I know 20v engines love to not follow theory in this area but my intake resonance is at 6000RPM and my exhuast secondary resonance at 5000. This might explain the big surge that then evens out. I want to have this peak at just past 7000 instead and my next port of call is some shorter trumpets.

Its interesting that you comment that you have lost power with forged pistons, the reason I was thinking of is only vaid for non forced induction engines though. With either 4age to achieve higher comp with the pistons the crowns are made to be quite high in a wedge shape and particulally in the case of the 20v I think it somewhat increases the surface area of the combustion area and forces combustion in two. Earlier yamaha engines had a real problem with this as their middle intake valve was placed in a raised secion of the chamber so the effect was more pronounced again. I also dont see a point seeing I have never seen a non boost related piston failure from normal use and the pistons on the market dont even seem to be lighter??. So I say use the 0.8 TRD gasket and shave the head. Some people argue that it changes the cam timing, and it does but I worked out it only changes 1degree in retard for a full 1mm shaved off the head. Well this is from my rusty memory of a while back.

Jonny: yes well noted, I do believe one is set to have the VVT to turn on and then off at the ideal time and the other graph is on the oppersite setting. Not a tottaly fair comparasin but it does show the real gains under 6000.

slydar: your right it isnt tottaly fair but I personally think even with the cams dialed in there still would be a very large loss of mid range power. I hear that there isnt much to be gained with the stock cams in terms of adjustment but I cant personally vouch for this yet so I am open to correction.

I tottaly agree with you on not buying anything less than 272 degrees. There isnt big gains from the stock 250 to 270s and no power loss anywhere, this I know as a fact so it seems real silly to go through the high cost and all the hastle to have something inbetween.

I have a simple thery in cam choice, let me know what you think, I believe everyone should chose one of these options and nothing inbetween:

stock with vvt

270/270 with VVT (or 272s same shit) or 270/280 with VVT

280/280 or greater without VVT and adjustable gears all round.

so its basicly you leave it alone, have a nice power upgrade without the compramise or go all out with the low end comparamise that it comes with.


Anthony: nice article I didnt know the blacktop was still considered VVTi, where did you find out about that? your right it has caused a few shitfights in the forums over it.

ae86hachiroku: got a dyno graph for that engine? I would love to have a look at the shape of the power and torque curves.



This is turning out to be a really interesting thread

[FAST EDDIE]

So how much we shaving off the head? Just as an outline. And what does everyone else reccommend with the cams 272 toda?

[cracker]

bigger cams eddie

304 in

288 ex

10mm lift or more

4 into 1 extractors 2.5 inch exhaust

20 th off head 0.5 gaskit no vvt

well balanced motor, good head work black top quads

dry sump?