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The spool characteristics of the Ct12A's

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LAG?? Learn to drive...
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Discussion Starter #1
Ok i am a NA guy at heart. i grew up around old muscle cars. my dad had one, hell at 10 i helped rebuild a 383 into a plum crazy purple 71 challenger. So when i still had my NA, i heard about the instantly spooling 1j and it sounded great, smooth powerband, with little to no lag, humm just like a NA car. 10psi at 2800rpms.....wow great sounds perfect.....yeah right

So i have had mine running for 9 months now. and i will admit it does spool fast and it has it benefits. i mean it makes me flexable when going from a roll, anywhere from 3200-6000 is a nice rpm to start at Lol. But the car still doesnt pull hard until 4500. true it pulls fine below that but not until 4500 when it really shoots forward. and pulls hard to 8K+.

But my god. i cant get more than 20mpg out of it, babying it, and keeping it under 2500rpm and under 3-5lbs of vacume. Still cant get more than 20mpg on adverage. Ive gotten 24mpg on a 150mile hwy trip cruising at 70mph with the 3.72's at 2600-2700rpm. It drives me nuts. the car is allways spooling. its impossible to keep it under 10lbs of vacume while crusing at hwy speeds. and we all know more air more fuel.

Now it does have it perks. The smooth torque curve allows the tires to hold their grip so it launches like a bat out of hell, i mean i can nock off high 12sec times and still not really loose traction in rain....unless its deliberate. and occationally i need that extra spool time, but rarely. Most of the time i start roll races from 4500+ so it defeats the purpose of the fast spool. And it makes it nice being able to cruise at 3K rpm and still be able to boost 15psi in 5th to pass on the hwy. thats nice. But im begining to hate how easily the 1j turbos spool.

So is anyone else annoyed by the ct12a's?
 

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JZA70 448 rwhp everyday
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i love mine, and i seem to get around 24 mpg on the highway, but if i get on it at all the mpgs are out the window.

~scott
 

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Republican
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8,421 Posts
yes... big turbo 1jz FTW
 

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On 2 wheels
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750 Posts
Dude, you shouldn't be worrying about mpg in a turbo vehicle...

This is actually the first post i have read that complains of turbo's spooling too fast lol
 

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Over 10 years on SF....
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7,892 Posts
mpg? who cares? :p
 

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LAG?? Learn to drive...
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Discussion Starter #6
Well i dont care too much when im racing. i look at it as im paying for my hobby. i mean no matter how high gas prices go its still cheaper and more addicting than heroin.

But as long as its my daily, i will worry about trying to get decent gas mileage out of it. And its just that im fighting the turbos, and trying to keep them from spooling so that i can concerve gas. And i am starting to run into heat issues with the small turbos at high boost. So yes i am ranting about the turbos spooling too fast. id prefer a higher spool rpm, so i could keep it in vacume and get better gasmileage and be able to run the stockers a bit higher without them heatsoaking after prolonged boost levels. That is what sold me. I am upgrading my twins for something slightly bigger and going to get 100-120whp more and 25% better fuel economy. but after 9 months of watching my boost gauge more than my speedo to try to get better mileage, im venting and seeing who else feels the same way,

plus so far no one has selected that they like the fast spool....
 

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1JZ BLING!
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Weight..

The 1J has to try reallly hard to get the heavy ass MK3 rolling. Powerband is the key, not the overall power.

I did not see a list of your mods? What do you have? SAFC is really the key to getting good gas mileage over a long distance drive.
 

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Not so boring anymore
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its still only a 2.5L

I would expect gas milage to be better though.. with a fucked up o2 sensor (running 13.5-13.1 a/f cursing) I still got 280 out of a tank and i wasn't driving nice the whole time.. (~17 mpg)
 

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67mm of pleasure
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I have intake, 3'' dp-hi flo cat-super dragger, blitz ecu, fcon, stock inj, mkiv rims/rubber, and boosting 15-17 on the highway and I can't ever stretch over 20mpg, but like Ryan said, its my hobby so I don't mind. It also doubles as my daily, but now I have a super short commute to work, so I don't mind as much. I wish they didn't spool up like they do on the hwy, but I do a lot less hwy driving than real world driving, where I really like the quick spool. I also have a bad o2 sensor that is throwing a code, so hopefully it'll go up a little bit when its replaced this week.
 

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All else being equal, the car should get better gas mileage during boost (just like your n/a 383 if you raised the compression). The car runs more and more efficient as compression increases, the only thing making the fuel economy worse is if your TPS goes past the 80% mark, and it dumps extra fuel into the mixture as a safety measure, or if boost gets far enough positive to cause timing retard. Outside of that, the mixture shouldn't be any different on boost than off, based on the o2 sensor reading.

-Ray
 

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JZA70 448 rwhp everyday
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^ yes, my wide band reads 14.6-14.8 unless i exceed about 80% thorttle and boost comes on. I have safc but it doesnt even make any corrections because im 11.5 under boost (14 lbs), and 14.7 everywhere else.

~scott
 

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LAG?? Learn to drive...
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Discussion Starter #13
SupraBlur1JZ said:
All else being equal, the car should get better gas mileage during boost (just like your n/a 383 if you raised the compression). The car runs more and more efficient as compression increases, the only thing making the fuel economy worse is if your TPS goes past the 80% mark, and it dumps extra fuel into the mixture as a safety measure, or if boost gets far enough positive to cause timing retard. Outside of that, the mixture shouldn't be any different on boost than off, based on the o2 sensor reading.

-Ray
regardless. if you are at -10lbs of vacume, you have a certain flow of air filling the intake manifold. and at -5lbs you can asume that you are using more air, i dont have the volumetric equation in front of me, but assume even that you are using near double the air to fill the manifold to create a lesser vacume. so if you are using closer to twice the air, then at the same a/f ratio you are using twice the fuel also.

and if you shift at 3K at 10lbs vacume, or 1500 at 5lbs vacume, then you essentially are using the same amount of fuel (in theory). So no matter what because of the fast spooling ct12A's, the more throttle you give it the more fuel, not to mention that we have high impedance injectors(saturation) instead of low impedance (peak and hold), meaning that the injector doesnt pulse it merely adjusts the spray. so that alone makes the car run richer than a peak and hold injector. so even though we have .5 liter less displacement than the 7m, we are not able to acheive better gas milage.

my mods are simple:
HKS intake
Sard ECU
HKS EVC
RSR Dp
3"test pipe
Tanabe Hyper medalion cat back

Stock clutch
Stock twins
Stock fuel
Stock y pipe
Un-tuned

estimated 12.7-12.9 and 109-112 traps. this is an estimated generalization. based on multiple races. Ive only been able to run a [email protected] 103 witha 2.00 60' with a dammaged stock IC, and a boost leak at my banjo bolt in the manifold for the brake booster,

Ive had a full exhaust pullied 04 cobra pull out to half a car between our bumpers from 40-95
A BPU+ evo that ran 12.5 @110 with a 1.87 60', i pull out on him from a roll and ive pulled high 1.9's with consistant 2.00 60's.
Camaro that runs 108 traps and froma roll i run away from him.

All on a clutch that slips from power after a few hard shifts.
 

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supraracer01 said:
regardless. if you are at -10lbs of vacume, you have a certain flow of air filling the intake manifold. and at -5lbs you can asume that you are using more air, i dont have the volumetric equation in front of me, but assume even that you are using near double the air to fill the manifold to create a lesser vacume. so if you are using closer to twice the air, then at the same a/f ratio you are using twice the fuel also.

and if you shift at 3K at 10lbs vacume, or 1500 at 5lbs vacume, then you essentially are using the same amount of fuel (in theory). So no matter what because of the fast spooling ct12A's, the more throttle you give it the more fuel, not to mention that we have high impedance injectors(saturation) instead of low impedance (peak and hold), meaning that the injector doesnt pulse it merely adjusts the spray. so that alone makes the car run richer than a peak and hold injector. so even though we have .5 liter less displacement than the 7m, we are not able to acheive better gas milage.
You're forgetting a key part of the equation, which is that given more air and more fuel, you are also making more power. This is why you will probably get more fuel economy out of a 7M-GTE than a 7M-GE -- the n/a variant produces power less efficiently and requires a higher RPM to move the same amount of air (and fuel) to accomplish the same work. Making more power at a lower RPM can only improve economy (case in point, the LS1 getting almost 30mpg in double-overdrive gear). Again this is provided that you don't cross the 80% throttle threshhold, which changes the ratio.

Trying to compare fuel economy between the 1JZ and 7M is almost apples to oranges because of other variables related to how efficiently the engine operates at a given RPM range.

Case in point, my other car has a supercharged 2.3L (which is a negligable difference from the 1JZ-GTE's 2.5L) and is in positive boost all the time, even when cruising with minimal load. Even pushing a car that's just as heavy as the mk3, with the a/c on, it gets 30 mpg without trying. It's just a different design.

All else being equal, if you could manage to operate with more vacuum, I can almost guarantee that your mileage would be worse, for the same reason that lowering your compression would.

-Ray
 

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jblaze said:
So are you saying that you get 30mpg out of your 1j?
No I was talking about my Mercedes. My point was that it's apples to oranges to use boost and displacement as a determining factor of gas mileage. All else being equal, it would be, but when you compare a 7M to a 1JZ, all else isn't equal, and it's the same as comparing it to a Mercedes M111. They have different optimal ranges for best gas mileage.

-Ray
 

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Akai Suisei - 赤い彗星
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supraracer01 said:
So i have had mine running for 9 months now. and i will admit it does spool fast and it has it benefits. i mean it makes me flexable when going from a roll, anywhere from 3200-6000 is a nice rpm to start at Lol. But the car still doesnt pull hard until 4500. true it pulls fine below that but not until 4500 when it really shoots forward. and pulls hard to 8K+.
I dunno about you, but my car kicks pretty good somewhere between 3k and 3.5k. I'd be worried if I didn't feel a big jump in power until 4500.
 

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Resident Smartass
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You are complaining about 24 mpg????? I get 8mpg..........but I don't mind :) He he hehe.
 

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No matter which engine you put in the supra, its not going to get good gas milage because of the weight. Obviously using a 3.73 rear will get you the best hywy gas milage because of the lower RPM's. But the fast spooling twins should not have that much effect on overall gas milage.
 

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I was depressed when I drove my 1j because it didnt lag like a DSM :rolleyes: Im getting 25 mpg constantly no matter how hard push down on the throttle. My n/a 7m got 17mpg consitantly. Yeah Im looking to ditch the stockers.
 
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