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View Full Version : 2.5 TBI Daytona vs. Ka24de 240sx



Daytana
03-19-2012, 12:23 AM
Recently a friend I have not seen in a while dropped by and showed me his recently acquired 240sx ka24de. From what I seen under the hood it looked like it was a bolt on affair: Header, 2.5" exhaust, CAI, miscellaneous suspension mods, Koyo radiator. After talking I decide we line em' up and tell him he should have the obvious advantage; being that is a 16V 155HP rwd car vs. a 8V 100HP fwd car. Anyways I let him get the honor of choosing a good spot to run at and then we begin with a couple of 40mph rolls starting at 3 honks. I could already tell with the first time we were playing around I would stand no chance from a roll. Each time the outcome was obvious, after the 3 honks we are even until oldschool weaknesses prevail. I used the 2.5s torque advantage the best I could by getting the most out of my 2-3 shift which helped some but in the end only delayed the inevitable, he pulled away from me each time after around 55mph due to the 16V top end advantage. My car struggled around 90mph while his kept pulling, he had my by several car lengths at that point.

Afterwards I decide we try from a dead stop, much more competitive race. :nod: We go on 3 honks, I get the jump on him and have him to the point where he could see my tail lights for a bit until he gradually reeled me back in after my 2.5 fell on it's face on top end. We both were hype and agreed they were great runs and went our separate paths. I must say I am surprised that it was not a landslide victory for him all across the board for him since he has the drivetrain advantage and power advantage. I must say these engines really stand the test of time in not only reliability but in competitiveness in their intended category. My 91 Daytona ES is pretty close to stock besides minor mods such as: Accel Ignition coil, 0.55 spark plug gap, KM performance solid bobble strut, a/c delete, spare tire removal, open element breather, and slightly bumped up ignition timing (around 15-16*). I think now it would be a slightly better race even though I know I would still lose, I believe I ran way too much timing. I retarded it down to 13*-14* and MUCH better on top end, I have also raised up the injector base up a little about an inch which also helped in response. Yeah I know tbis are a waste of time but they make make fun daily drivers (especially coupled with a 523) with bolt-ons and mine is just that. Oh yeah 232K+ and still going! ;)

Big_P
03-20-2012, 09:10 PM
Sounds like fun man! Sometimes you know you're going to lose but it's fun to see what happens anyway.

Daytana
03-20-2012, 11:35 PM
Sounds like fun man! Sometimes you know you're going to lose but it's fun to see what happens anyway.

Indeed, it is a lot more fun actually seeing results than asking "do you think I would win or lose?". It is also a good test of who the better driver is. :)

Vigo
03-26-2012, 06:10 PM
Oh man, i hate those 'will i win or lose' threads because the race almost never ends up happening! Im all for racing for fun no matter how slow the car is. Some of the most fun i ever had was races that were so slow it was hilarious.

I remember one time racing a 2.slow (as they call them) jetta in my 2.5tbi/5spd aries. That took a long time to win but i did! lol.

Big_P
03-31-2012, 05:13 PM
I beat a 2.0 Jetta in my dad's 4.6 Econoline, heh.

Vigo
04-01-2012, 11:18 PM
I have been stomped by econoline vans before while driving slow cars.. lol. It's irritating!

Spraynlog
06-23-2012, 10:38 PM
I do enjoy my '93 Spirit with the 2.5 TBI/A523 combo. How much difference does the TBI spacer make? I've been thinking about doing it. Also, what thermostat temp are you running?

Vigo
06-24-2012, 07:55 PM
I dont know if i ever ran a regular tbi spacer. The TBI throttle body has a pipe-like thing sticking out of the bottom that extends the bore of the TB down into the manifold, and the manifold basically has a receptacle for it.. So if you just add another gasket or two you are only adding the volume of that small-diameter pipe thing x 1/4" per gasket, and then you have a nasty lip in the manifold for air/fuel to run into. Hard to explain but obvious when you see it.

I knocked out a bunch of material inside the gasket flange on the manifold to get rid of that lip and add a little plenum volume from what i was removing, and i think i ran 2 or 3 stacked gaskets. How much did i get from it?

Well, it's hard to tell, and thats where the thermostat comes in... After all the stuff i did, my tbi was eventually so far out of tune on the stock computer that it felt like it had 30 more hp when it was dead cold (i guess it ran really lean after mods). So since i didnt care about mpg or longevity (i still dont care about longevity..) i took the thermostat completely out so it would run a little better. It still felt like it lost 15-20hp when it warmed up. I calculated it to be 115hp when warmed up based on what my gtech was showing. I think it would have made 130hp if i had tuned it.

Over the time i ran that car as a tbi i got the 1/4 mile from 20.0 to 17.0 (with a lot of power missing from terrible tune) and got the top speed from ~90-95 to 115. It wasnt fast but from 0-50 or so it would make you think it was faster than it was.

The main thing holding the TBI setup back is the size of the throttle bore. At one point i noticed that you could take the top fuel section off the tbi throttle body and it fit pretty good on the end of a turbo/v6 throttle body. You could epoxy/weld it onto that and get a bigger tb with chrysler sensors, but it wouldnt bolt to the tbi manifold without an adapter AND modding the tbi manifold. One thing i would like to try if i ever get another tbi car (it will have to be free....) would be to do that, and use a carb intake which has a much bigger opening out of the box, and build the adapter/spacer to bolt the two together while adding plenum volume.

The tbi has a ~42mm throttle bore. If you add the area of the 36 and 34mm openings of the carbs on carb cars, it's closer to 50mm. I think that is the main reason why people have an easier time getting power out of carbs than TBIs on these cars.... that and the fact that all you need for fuel tuning a carb is some screwdrivers.

Daytana
06-25-2012, 12:08 AM
I do enjoy my '93 Spirit with the 2.5 TBI/A523 combo. How much difference does the TBI spacer make? I've been thinking about doing it. Also, what thermostat temp are you running?

While I do not have any dyno testing to prove any differences, I can say that car feels stronger all throughout the powerband on the butt dyno. The difference is subtle but it is definitely there. Another thing I have noticed that during hot summer days the car does not feel as much as a dog due to the spacers helping out with heat soak. The throttle body is just not raised high enough with the stock gasket to help dissipate some heat. I am running a stock thermostat.