2nd gen 3s TVIS delete power band timing/fueling

abeans

Member
My car had the tvis deleted currently on stock tuning. Plan to add aftermarket ECU soon.

My delema, is the current driveability or lack there of on this engines power band below 3k rpm, it's terrible, very slow and laggy

I see later 3sgte generations have no tvis and slightly narrower cylinder head intake design, likely to compensate for lack of tvis.

So my question becomes, if I ECU and tune this engine as is with no tvis, throw timing and fuel at it below 3k rpm... How lively can I make the engine? Can I be happy with the results? Anyone doing this on a 2nd gen engine with ct26/27/20? Looks like the Gr. A engines ran no tvis either, but that's probably not a fair comparison
 

underscore

Well-known member
A few guys have swapped to a 3rd gen ECU/sensors/injectors on a 2nd gen engine, maybe look into those threads a bit. If I remember right, when I drove Coreys car many, many years ago it had the TVIS deleted and the 205 EMS swap on an otherwise mostly stock 185 and it drove great.
 

grip-addict

Active member
Underscore is right as far as "easiest/most straightforward" path is concerned. As long as you can easily find those parts, that outta work.

My question to you would be, whats the real goal ? Is it just driveability ? Or more driveability AND more power ? The latter (ems) means a lot of control, but also a lot of cash (to do it right).
 

abeans

Member
So I already have a megasquirt pnp2 ready to go. I don't want to go through the trouble or tuning it as is if it's not going to make much different in terms of low rpm power speed.

Cars purpose? That is a good question. Goal is rallycross so getting some throttle response/wide power band is key. I'm not looking for any record breaking HP attempts here, one of the reasons I went with ct27

I'm not sure what these cars are supposed to feel like, I've seen 2 in my life and owned them both. Lol. I drove a turbo sw20 and it was much more lively. This thing is a dog.
 

grip-addict

Active member
You probably do have something wrong with the car then. I wouldn't call the car "peppy" but it should definitely move pretty good.
If you actually want to be competitive, there are some advantages to be had when running an ems. You're right about timing being important, but you can have even more flexibility and gain further advantage with an ems. What I mean by that is, you can tune in some mild ignition retard in the lower parts of the map to spool the turbo up even faster. Not as far as a rolling 2 step (but that's definitely an option...) but a bit less timing to move the flame front partially into the exhaust manifold/turbo.
Then after you hit your boost target, normal timing.

I'm not sure what the optimal strategy would be for when to transition from normal to retard timing, but it'd definitely be fun to play around with.

Some unsolicited advice: don't install an ems if you don't like to tinker. It never ends.
 

abeans

Member
haha i know what im in for if i go stand alone. But, still trying to make sure all the bugs are sorted out on this thing as stock as possible before i go chasing my tail trying to fix something that isn't there, or trying to fix something that isn't actually "wrong" on the standalone.

Here is a quick clip of acceleration, you can really see AND hear it come to life in the upper power band, and its gutlessness down low. I did the timing belt and timing of distributor my self, its all solid. I don't think the car is broke or has something wrong other than the TVIS being gone.

https://www.youtube.com/watch?v=LksPR15oSmE

I feel like if people add the 3rd gen Injectors/ecu to a st185 and have good results, that answers my question... My fear was the 2nd gen cylinder head intake are just too massive to deal with being treated as a single runner, unless i had some giant turbo, which is no fun at all for my needs.
 

RedCelicaTRD

Moderator
I removed my TVIS a long time ago and the loss of torque bothered me so much I put it back in. I have an AEM EMS and I don't think you'll be able to tune the loss of low end out. The intake ports being so large drops the velocity too much at low RPMs. No real way to get around it. Do I think you can tune it to be around 80% of what it was? Probably. In the end you're kinda screwed by the design.
 

abeans

Member
Curse this previous owner. I dunno what to do.

If it was easier to access i just might do it, but its not.
 

grip-addict

Active member
so I'm just kinda shooting from the hip here, but it could actually be a timing issue after all and the megasquirt/tune could fix it: It's possible that your factory ECU is pulling timing.

Hear me out - the amount of timing you need is based on how much o2 is in the cylinder. It's all about controlling where maximum cylinder pressure occurs. So every motor needs way more timing in the lower rpm's since there's less o2 in each cylinder as it's going to take longer for the fuel charge to burn. And here in your engine, you're sending more air than normal to each cylinder in those lower load areas since those TVIS butterflies aren't blocking off ports. A modern ECU would be able to work around that, especially with a MAP sensor. I'm not sure about how a 90's AFM-based ECU would though...

Honestly, there's no way to know 100% since Mr. Toyota didn't see it fit to give us easy access to what the ECU is actually doing. But I think this is certainly in the realm of possible...

Feel free to discuss/dis(agree). I haven't had a theory-crafting post on this forum in a long time, so I'm due :)
 

abeans

Member
I've got one from the car I parted. I really don't want to pull the intake with the engine in the car. :doh:
 

abeans

Member
Well i was going to start swapping the lower intake today, and my friend suggested i test the vacuum actuator. Good thing i did, thing leaks like a Siv. :bangshead:

Put a used one on order.
 

abeans

Member
Have a hand pump I use for fluids. Diagram has obvious tears when pressure is applied. Can video if Interested
 

abeans

Member
Swapped in a working lower intake went for a drive today. It is way easier than I expected to remove and install.

The driveability is still pretty mediocre at best improvement. :(

Some other issues going on. Exhaust can backfire sometimes. Random surging, which comes and goes seemed like it went away with unplugged the idle air control and plugging back in seemed to clear it...

It's like building a car from scratch using 30 year old parts :eek:wned:
 

Gert

Active member
Back in the days, I made an comparisation between T-vis open or close. My car is equipped with an Autronic.

Tvisverg.gif


As you can see, keeping the T-vis is helping low torque a lot.
Yellow line is T-vis closed all the time.
Purple is open all the time.
Blue is close and open.

In acceleration time during wot:

Tvistijd.gif


Blue = closed.
Purple = open
Yellow = closed and open.

For me reason to keep the T-vis.

Down side is, that years later, due to mechanic T-vis malfunction, the butterflies destroyed my head and turbo.... sigh.
 
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