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mknz wrote:Does TVIS not increase low range torque? Is this lost by doing that mod in return for more high end torque?
Yes increasing low end torque is what the TVIS is for. My understanding is that if you install ITB's you loose a bit of low end torque in favor of top end power and quicker overall throttle response.
The induction noise you get from ITB's makes up for the loss of torque I'd say.
I think TVIS is a pretty cool feature especially considering its from the 80's.
Personally though, I've always been into those high strung NA engines. I like the idea of ITB's on a rev happy engine like the 4AGE in a light car. I don't mind having to rev it.
I'm going to keep all the parts though since I want any mod's I do to the car to be reversible.
Yeah the CRX is still my daily, it doesn't have ITB's but has the original dual carb setup, which also sounds pretty good on full throttle:
Well, yeah, but there is more to it than just torque outputs. Having a long intake runner promotes low end torque because the air gains momentum as it's drawn into the cylinder, and this momentum fills the cylinder better and makes more torque. But when the rpms are high, long runners start to become a restriction because they can't flow enough air (atmospheric pressure has further to go).
Having a short runner removes all that momentum at low rpm, and it doesn't make as much low end torque (I call this a "drop in torque" because relative to the old torque curve, it's lower in that spot). When the rpms are high, short runners flow more air and this doesn't become a restriction because the atmospheric pressure has less distance to travel.
Another spanner in the works is piston stroke length. Longer strokes give more low end torque, but can't rev as high because the weight has to change direction at a much higher speed as it's further away from the center of the crankshaft. Shorter strokes give less torque, but allows high revs because the weight is closer to the center, and the direction change speed is lower. An F1 engine is the main example. Because of the super short stroke, they make bugger all torque but make huge amounts of power because they rev very high. Why do you think they idle at 2500 rpms? Because the short stroke can't generate enough vacuum to fill the cylinder and can't overcome the engines rotating weight at such a slow speed. Putting longer runners on would help fix the high idle, but then airflow up high would be lower, thus "choking" the engine of it's power.
For forced induction, it's kind of the opposite. ITB's become a restriction so on goes a big single. And longer runners are better for spooling up turbos earlier. So lets compare a 2000cc NA engine making 100kw with a 1600cc turbocharged engine making 100kw. You could say that both would make the same torque right? Wrong. The 1600cc engine will make more torque because the air is more dense than the 2000cc engine, and denser air needs more fuel, and a bigger bang makes more torque.
But to answer your question, most of the time you don't "feel" high end torque, you feel the power it produces. All the low end stuff I am referring to is less than 3000 rpm, as that's where the G forces are more noticeable. On my car the torque curve is flat up to 6500 rpms, then it starts dropping off. But when I drive it I can't tell that it's dropping off because that's where it's making it's peak power output.
I've gone and blabbed again haven't I?
Jason Ross, current cars:
Project: 1990 SW20 GT, 1992+ brake swap, 1992+ subframe swap, 1996 Celica turbo engine swap, 1996 MR2 LSD gearbox swap, Caldina Turbo coil-on-plug ignition, Link G4 Storm, 161kw @ 10psi.
Daily: 2004 Toyota Vitz RS, 1.5L, 5sp
Tow rig: 2009 Camry, 2.4L, auto
Scrapped: 1989 SW20 GT, 1992 SW20 G-Limited, ex EssDub car, donor, 1997 Toyota Tercel 3dr hatch, front crash, 1990 SW20, G-Limited, ex EssDub car, roll crashed, donor
Sold: 1987 AW11 Supercharged, 1991 SW20 G-Limited, ex EssDub car
JasonFriday13 wrote:Well, yeah, but there is more to it.......ne, and denser air needs more fuel, and a bigger bang makes more torque.
Waffle
JasonFriday13 wrote:But to answer your question, most of the time you don't "feel" high end torque, you feel the power it produces. All the low end stuff I am referring to is less than 3000 rpm, as that's where the G forces are more noticeable. On my car the torque curve is flat up to 6500 rpms, then it starts dropping off. But when I drive it I can't tell that it's dropping off because that's where it's making it's peak power output.
I understand what you mean but you haven't worded it in the way a physicist would so I was lost
The force of net friction(air, tyres, internal) acting on the car increases with RPM so to accelerate the same mass at the same rate requires more force at higher RPM. Therefore the torque curve must be increasing with RPM to retain the same net acceleration. If it is linear there is less net force thus less net acceleration as RPM increases ergo there is less 'feel'(acceleration is what is felt).
Good point, I misunderstood what you meant the first time. Apologies
JasonFriday13 wrote:"c ITB's become a restriction so on goes a big single.
I call bull
They are just a pain to tune for Forced induction " ITB's" that is.
Boosted cars are like hot women.
A little edgy, every guy wants one,
some guys can't handle them,
and if you throw a little alcohol in them they'll rock your world.
I agree, rb26'd run ITB's for resoponce (that's all) And along with 2J's run twin turbo's because of EX pulse and shorter running on the ex manifold (that's anouther story)
ITB question is more about set up and sizing. Just note that a factory rb26 I was working on last weekend has a progressive plenum from factory, thats same as any performance single throttle intake has.
And the the opening where the throttle "would be" is around the same size.
I'd say from the people I've been dealing with building my motor that ITB's aren't that big a deal and that as to running length, trumpet size, plenum size/shape/design is rather more important
Toyota motors:
Current - 89 AW11 factory manual SC
Sold - 74 Toyota Crown wagon (MS63), Holden 308, TH400 trans
JasonFriday13 wrote:"c ITB's become a restriction so on goes a big single.
I call bull
They are just a pain to tune for Forced induction " ITB's" that is.
I guess I wasn't clear enough: [When you put a big turbo on an engine,] ITB's become a restriction so on goes a big single.
That's just what I have learned anyway, I wonder if there have been any tests done to check if this is true?
Running ITB's are good for response, because the throttle plate is so close to the valves.
I rarely blab like that on the forums, but I do it a bit more often when working on cars with other people.
Jason Ross, current cars:
Project: 1990 SW20 GT, 1992+ brake swap, 1992+ subframe swap, 1996 Celica turbo engine swap, 1996 MR2 LSD gearbox swap, Caldina Turbo coil-on-plug ignition, Link G4 Storm, 161kw @ 10psi.
Daily: 2004 Toyota Vitz RS, 1.5L, 5sp
Tow rig: 2009 Camry, 2.4L, auto
Scrapped: 1989 SW20 GT, 1992 SW20 G-Limited, ex EssDub car, donor, 1997 Toyota Tercel 3dr hatch, front crash, 1990 SW20, G-Limited, ex EssDub car, roll crashed, donor
Sold: 1987 AW11 Supercharged, 1991 SW20 G-Limited, ex EssDub car
So any day to day driving benefits of fitting the ITB's may be questionable, but I think the main point (at least for me) is that they are a cool bit of engineering, look awesome, and sound awesome. Probably not the best reasons for going ahead with a project but as far as I'm concerned owning a car like this is for fun, and if I think adding ITB's will make the driving/ownership experience more fun then.. well its good enough for me. Plus I've wanted ITB's for ages since I got into BMW's (BMW M engines always have ITB's).
Anyway I'm not even installing them right now, its a project for later on.