Let's talk about VVT...

[ericjon262]

as we all know the Gen 4 motors have VCT, but what about adapting them to VVT?

the dodge viper uses this technology to boost top end performance, this got me thinking, why can't we make this work on a 3900? I made a theoretical motor in Desktop dyno (I know I know...) and was able to stay within 10% of peak torque over a 3500 RPM spread(3200-6700) by adjusting the advance and retard of the intake and exhaust, along with adjusting the LSA. The cam was fairly aggressive, but not a monster either .573/.565 224/214 @.050. peak hp gain @7500 RPMs was almost 75 hp. and low torque gained 40 ftlbs just by adjusting valve events, not changes to lift or duration!

I see this as a very possible thing! it won't be cheap, and right now, it's only bench racing, but this could have scary potential!

here is the "dynograph" of the above mentioned 3500 desktop dyno:


the hangups:

who would be willing to grind the cams for the engine?

where do we get a phaser that will fit under the timing cover, and allow adjustment of both cams independently?

How do we control it? stand alone ECM?

what are your thoughts?

-262

[TurboGTU]

Almost looks like you have to cut the cam phaser right down the middle making it like stacked phasers for one to run the inner and the other the outer. I dont think a aftermarket cam company is willing to make one for us. Personally I find it easyer to run the 3.6 dohc. Or making the tdc 3.4 heads and belt system work using adjustable cams. Granted the tdc is not adjustable driving it but you can adjust them on the fly for racing or eco driving

[caffeine]

Even if you could find someone to make the cams, the cost not only for the cam but for a way to run them would be really high. You could probably buy a 3.6/trans for less and be starting with about the same power.

[3400-95-Modified]

I think right now we are lucky that someone will grind a roller replacement cam for us, nevermind something that fancy.

[Purple pit]

Agreed. We are damn lucky.

[Guest]

This could be used to control it: http://www.diyautotune.com/catalog/v...led-p-459.html

The mechanics of controlling each part of the cam could be interesting though. Possibly adapt the mechanical control directly from the Dodge V10?

[ericjon262]

This could be used to control it: http://www.diyautotune.com/catalog/v...led-p-459.html

The mechanics of controlling each part of the cam could be interesting though. Possibly adapt the mechanical control directly from the Dodge V10?

I was thinking about that, I'll need to get dimensions off of one, and tooth count on the sprocket. the only concern I see is that to get the full benefit, you have to vary the intake and exhaust, and IIRC, the viper only varies the exhaust.



a phaser like this would be perfect, a second set of vanes could be fitted into the windows in between the windows that already have vanes.

one of the thoughts I had for management would have been a High feature PCM, as it supports independent VVT factory, but it also comes with quite a bit of baggage...

[robertisaar]

from a control standpoint, with the 3500/3900, you would need to somehow create two cam sensor signals, one for each cam half.... otherwise you wouldn't have closed loop control of where the cams are positioned.

this is actually the largest issue i'm having with controlling the normal 3500/3900 cam actuator using an OBD1 PCM... the 16149396 PCM's board layout will support the extra hardware needed to decode the cam signal to determine it's position, but it's not present in a factory PCM... it's something that has to be soldered in on your own.

[ericjon262]

from a control standpoint, with the 3500/3900, you would need to somehow create two cam sensor signals, one for each cam half.... otherwise you wouldn't have closed loop control of where the cams are positioned.

this is actually the largest issue i'm having with controlling the normal 3500/3900 cam actuator using an OBD1 PCM... the 16149396 PCM's board layout will support the extra hardware needed to decode the cam signal to determine it's position, but it's not present in a factory PCM... it's something that has to be soldered in on your own.

I thought about this, and I was thinking about having the second sensor mount to the timing cover. I really need to start getting parts together and taking measurements...

[caffeine]

Why would you go this route over a DOHC motor with VVT?

[ericjon262]

Why would you go this route over a DOHC motor with VVT?

Why not? Less moving parts, more transmission options, easier packaging, and of coarse, because I can!

[caffeine]

Are there any GM transverse transmissions with the metric bellhousing that can handle more than 500 hp anyway? You might be able to find a Honda or Misubishi transmission to build but then there's more fabrication to make it work. There just doesn't seem to be many options for upgrading GM manual transaxles (but there are for other brands). At that amount of horsepower you'd be looking at strengthening many more components as well.

It just doesn't seem practical when a DOHC engine will probably last longer with high revs and no doubt have better flowing heads, plus all the modern DOHC V6s have VVT now. I believe the 3.6 has a 7000 rpm redline stock.

People have done 3.4 TDC turbo engines in Fieros before so its not like it wouldn't fit. I would bet the 3.6 is actually a bit smaller physically because it was designed to be a DOHC motor from the ground up.

Also, I don't know where the 2.8T manifolds place the turbo, but they might be an easy place to start for building a turbo 3.6.

You're already looking at standalone or custom engine management for a VVT 3.9 so that's clearly not an issue.

If I were you I'd focus on finishing the 3.5 and then decide if you actually want more power.

[ericjon262]

If I were you I'd focus on finishing the 3.5 and then decide if you actually want more power.

this is all just bench racing for now, Right now, I'm waiting on parts to finish my build.

[caffeine]

Interestingly enough, I was just reading about Magnus dogbox transaxles where they suggest to support the engine with a minimum of 3 solid mounts in a transverse application to reduce stress on the transmission case. Support the transmission mainly with the bellhousing bolts and one side mount for support.

Definitely a good idea no matter what transaxle you use in a high hp application.

Some Honda racers have found it necessary to weld additional bracing to the transmission case itself since high torque loads cause the stock case to flex.

[ericjon262]

Interestingly enough, I was just reading about Magnus dogbox transaxles where they suggest to support the engine with a minimum of 3 solid mounts in a transverse application to reduce stress on the transmission case. Support the transmission mainly with the bellhousing bolts and one side mount for support.

Definitely a good idea no matter what transaxle you use in a high hp application.

FWIW, justinbart on PFF is deep in the 11's on a F23 (same trans I'm using.)