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Exhaust VVTi - Is it worth it?

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Protok
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Exhaust VVTi - Is it worth it?

Postby Protok » Tue Jul 22, 2014 1:04 pm

Right Ladies (are there any lady owners?) and Gents, I need some help and possibly advice.

As some know I have a turbocharged Beams in my MR2 though it is the single VVTi redtop variant. Now I was looking at turning it into a dual VVTi (Blacktop Head) but the other day my wife asked what the point in it was and I genuinely couldn't answer other than it’s unique. She went on to suggest that using an adjustable pulley would be an easier and cheaper option than using the VVTi anyway and even then the gains would be about 100rpm less spool time.
Now I know that she’s just trying to get me to make it all a bit cheaper but she had quite good points.

So questions:
1) Does the exhaust VVTi help anything at all? Will it make the turbo spool any faster?
2) Are there any real world advantages to using the Blacktop head? 10hp at 9000rpm wouldn't be worth the time and effort really.
3) Finally, has anyone had any gains from messing around with either of the VVTi on a turbocharged car? In theory the VVTi should help but I have yet to see anything that backs this up.

Thank you in advance as always
Red

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Tosh21
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Re: Exhaust VVTi - Is it worth it?

Postby Tosh21 » Wed Jul 23, 2014 10:12 am

Depends on your turbo etc if you have a small turbo and a well designed manifold you will see very little difference In spool time. If you have a big turbo with high boost and high power (personally) I'd run different cams anyway so no vvti.


Also, I don't think the ge head even fits on a gte? And Youl need a way to control it.


That's my opinion on it anyway

Protok
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Re: Exhaust VVTi - Is it worth it?

Postby Protok » Wed Jul 23, 2014 11:27 am

Turbo is a custom jobbie, mainly a GT28RS with GT-SS wheel and T3 exhaust housing.

I am also using a GE; head will fit directly for the most part, only difference is water outlet. Fits the GTE too as far as I know though the pistons won't be happy when they meet the valves.

I'm using a Link G4 Storm to run it all so getting it working isn't a problem.

I am more looking into whether the exhaust VVTi will actually do anything?


Does anybody know all the differences between the auto and manual cylinder heads?
Mine is basically an auto head without the exhaust VVTi from what I know.
Last edited by Protok on Wed Jul 23, 2014 2:38 pm, edited 1 time in total.

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Tosh21
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Re: Exhaust VVTi - Is it worth it?

Postby Tosh21 » Wed Jul 23, 2014 1:30 pm

Oh sorry I assumed you were running a gte.

This is all I could find about the differences of the head

http://z4.invisionfree.com/lexusaltezza ... opic=14406

Protok
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Re: Exhaust VVTi - Is it worth it?

Postby Protok » Wed Jul 23, 2014 2:40 pm

Another thread which brought me to Catch 22.

I'll never decide at this rate :roll:

Thanks for your help dude. Any other information, please keep it coming then I can maybe figure out where I'm going.

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Re: Exhaust VVTi - Is it worth it?

Postby Soiled » Wed Jul 23, 2014 8:13 pm

Manual and auto heads have different valves and cams. Go manual head for best flow.

I can't say personally about the older gen 3sgtes but the Altezza 3s head is incredible so I can't see why it wouldn't be anything but a good thing aslong as you get the cams/valve springs that are more suited to boost (look at the Toda cam profiles for keeping vvti if you want someone to custom make some, I can vouch for these workingwell.) and as you say make sure the pistons clear the valves etc (reliefs cut into the pistons?)

Most gains are from adjusting the intake vvti but I think just the gains from the head/valve sizes would probably be decent. Unless of course you already have a ported older head in which case maybe not worth it other than just for the fun of getting something different to work.

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Re: Exhaust VVTi - Is it worth it?

Postby tais300 » Thu Jul 31, 2014 5:33 pm

Protok, arent you also using ITB's on you engine? Regardless i spoke with a tuner who has his Masters in engineering and a bachelors in physics and Im building my engine off his advice. You already have a turbo engine so air is forced in. Now with the Altezza head it already has a ton of lift from the factory, close to 11mm. Now with the upgraded Toda cams you get 12mm lift with the intake and 11 with the exhaust while retaining vvti. Most of the 1000+ HP 2JZ engine here in the states run a maximum lift of 11mm. In other words too much lift and you will hurt the engine, the more ideal would be keeping the valve open longer. A turbocharger spools on velocity, not flow. Look at the Porsche with a variable geometry turbos that make 400FTLBS of torque at 2500 rpm. The engineers added restriction to make the flow of the exhaust a higher velocity. If you have an exhaust cam that lifts 12 or 13mm you have a shorter time the valve is open. Also if that lift is on the exhaust, you are wasting useable energy. If the cams lift is high exhaust is closer to being vacuumed out fast than forced out. If the lift is smaller say 11mm, the cam lifts but there is still pressure being forced out of the engine, what the exhaust stroke is supposed to do. Too high of lift can almost make a suction force. On NA engines this is great, get the air in and out as fast as possible but for an engine relying on velocity and a form of back pressure it can hurt the power band. I felt like an idiot when i didn't even think of basic physics before planning on engine build. Now onto why utilizing the VVTI would be worth keeping on the exhaust side. im not familiar with the vvt used on the beams engine. Other vehicles have on/off switching. If the engine management can change the points of which the vvt-i engages then use it! VVTI when tuned properly can be like having two completely different cams. A great tuner would be able to look at dynos, a/f ratios/ dips in the graphs and vvti engagement all at the same time. He's getting payed to test so make him test. You can move a powerband around by moving the engagement points, if the tuner is capable of it. Im paying my tuner to get that right balance. if he just gets target a/f ratios and timing he's not doing the complete job as a tuner. I dont know what everybody else pays but here in the states dyno fees run $140 per hour on average.

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LovingMyAltezza
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Re: Exhaust VVTi - Is it worth it?

Postby LovingMyAltezza » Sun Aug 03, 2014 12:14 pm

Hi, here's my two cents, which may or may not help - I only have two Toyotas, a '98 Rev5 MR2 n/a running the 178bhp I think it is, and my '99 Altezza semi-auto which has 200bhp - I would say that if the BEAMS engine in the Altezza is a VVTI version of what I have in the MR2, well you couldhafooled me - see, the MR2 just GOES with a smooth surge of urgency, no matter where you are in the RPM range, but the Altezza (Oh, and I am SO not criticising it for this) is a Jekyll/Hyde device - below the 4000 RPM kick-in point, it is sm00th and torquey, but also relaxed. It feels quite like the Mercedes 2.6 straight six in the 190E - I know what they feel like, and with a blindfold on I couldn't tell them apart. Not sure why I'd be driving blindfolded, but there ya go. ABOVE 4 grand, it gets busy and hauls for the red-line - now to me, this suits the Altezza perfectly. I often have a few passengers who don't wish to go everywhere at Warp 7 - and if I'm in no particular hurry, I'll pootle along and amaze myself with the efficiency and MPG that this saloon can deliver. By contrast, the MR2 gets caned just about everywhere, save for obeying urban speed limits. I haven't driven an MR2 with the BEAMS engine, but I wouldn't want it to be docile, laid-back and relaxed at ANY point in the tacho dial. And then again, you are using a one-off turbo, which will change everything anyway. I don't know what you have done to lower static compression, how much boost you are using, how happy you are with it off-boost - I would just fear that IF it stays bogged-down till 4grand, that may be too much dead-space for you to feel happy with.
Perhaps merely going through a process of ultimate optimisation of what you have would help you gain a few more pound/feet on the way to a few more BHP? Thermostat, wrapping/zirconium-coating the exhaust manifold, fitting a few more heat shields, installing a Water/Meth-Injection kit if you don't already have one, then taking some mass out of the car and flywheel - again you may already have this covered.

Protok
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Re: Exhaust VVTi - Is it worth it?

Postby Protok » Mon Aug 04, 2014 1:34 pm

I used to own an MR2 with the Gen 2 3SGE.
Then had an MR2 with the Gen 4 3SGE (VVTi) but that was modified with ITBs, exhaust manifold and 0.3mm HG. Never really drove it standard.
That MR2 then got turbocharged with a smallish TDO4 turbo, ITBs and HG still there.

I now own the MR2 Beams Turbo(GT28RS) and Altezza RS200 Automatic.

The old MR2 was decently fast and responsive but you could feel that lack of torque in the low revs, especially on the motorway. It had that sense of urgency as you say.

The N/A Beams MR2 was world's apart, throttle responsiveness was amazing; it just wanted to shoot off and go whenever you even blipped the throttle. On the motorway there was no effort to stay in 5th all the way.

Automatic Altezza is as you described, I kind of wish they fitted a better gearbox to it; takes too long to act really but engine itself is great.

Small Turbo Beams MR2 was great to one extent and horrible to another. Basically it was dumping boost at 1700rpm, full boost at 2400rpm and then it ran out of push at 6700rpm (Effectively making that the rev limit).
It was great, acceleration beat practically everything else on the road but I got fed up of driving what was basically a diesel engine. I ended up wanting a little lag just so I could drive it in traffic without having to hear the turbo spooling.


What I want is something that spools quick but not too quick and has the throttle response of when it was in N/A form. I am asking the impossible in a way but building it myself has meant specifying specific items and needs for it all.

I have spoken with a tuner and he suggests that in turboing, the exhaust VVTi actually does nothing. The intake VVTi aids power at the top end so I think I will just stick with that.

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Re: Exhaust VVTi - Is it worth it?

Postby oaasport » Fri Sep 11, 2015 4:42 am

Bm ringing back from dead, as i think this is a really good topic! I wondered the same thing, is the exhaust vvti worth it? I believe it is as i agree with tais300. Moving the vvti can result in earlier spool but also result in more over all power and torque through the whole range. Id love a fast spooling turo like yours protok, but keeping in the range of the turbo is key. Running out of breath in the top end means sacrificing bottom end, run a bigger a/r housing and possibly slightly bigger turbo. My old nissan 240sx had a gt3071 with a .86 housing. Spooled pretty quick but it pulled all the way to the 7800rpm i had the engine built for at the time. I lost 250rpmain spool and maybe 10hp down low, but gained way more up top where it was needed. My engine builder advised me of a way to seem like less lag was present, lighten the engine rotating assembly. We knife edged the crank, put lighted rods and a super lightweight flywheel and clutch then an aluminum drive shaft. It revved sooo much faster and hit that power band it almost made up the difference for the feel of lag. Just my two cents it only seemed to make up lag by response even though it really didnt


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