I just finished doing all of the Ultimate TBI mods from the tech articles and my car seems slower. I read a lot about these mods making a huge difference you notice right away but there's nothing. Has this happened to anyone else?

 

you probably wont notice a difference but it allows the TBI to flow for future mods, but on a stock engine it does very little.

 

Obviously I'm not running completely stock but either way, it made my car slower. You figure a mod should be something that improves your car's performance but it completely killed it.

 

Perhaps you put somthing together wrong? I don't see how doing those mods could negativley affect it.

 

you definately did something wrong, did you make the fuel pressure regulator adjustable, if so, maybe something went wrong and now the pressure is really low. But you definately cant lose power from shaving the ridges off the tbi. Let us know exactly what you did.

 

I shaved the TBI, that's all. Making the fuel pressure regulator adjustable is pointless since there's not really an accurate way to adjust it anyway. I'm sure I didn't do anything wrong when taking it apart or putting it back together. I'm not gonna say I know everything but I wouldn't take something apart I didn't think I could get back together. Plain and simple, it's a worthless mod. Any other questions or reasons why this happened let me know. Thanks.

 

Thats really funny, I did this same mod and picked up 0.400 of a second in the 1/8mi. Went from an 11 flat to a 10.598. Go figure!

Steve

 

Perhaps you put the air filter or somthing else in wrong somehow and its not breathing like it should?

 

Thanks for the advice but at least give me some credit. I've been working on cars for about 8 years now and never had any problems doing anything I had to do. All I'm saying is the mod did nothing. To clear everything up I'm 100% sure I put everything together right. I didn't forget to put anything on and I know I didn't put anything on wrong. With all of that out of the way let me know if anyone has any ideas because as far as I'm concerned it wasn't worth my time. Thanks again.

 

You can't just know how much it did anything or not by the seat of the pants. It's just not accurate. Hell, maybe it did help, but you just don't feel what you expected. Either that or something went wrong because there is no way it can slow you down.

 

I completely feel like an @$$. When I put everything back together I didn't re-adjust my tv cable. Thanks for being patient with me on this one but in the end it was my fault. I notice a small difference now but sadly enough it's not what I expected. Sorry again and thanks for all the help.

 

if you are 100% sure that you did everything right, then we are 100% sure that you did not lose any power. It is just not possible.

 

dude, i find that hard to believe. 4/10 of a second from ultimate tbi mods alone?

i did them to my throttle body and added a 1/4" injector pod spacer and saw no gain at all at the track or on the dyno.

i think the ultimate tbi mods are worth doing, but i don't believe they're worth what people claim. you'd need something in the neighborhood of 20-25 hp and/or 20-25 lbs ft. torque to pick up almost half a second in the 1/4 mile. heck, taking the air cleaner off completely is only worth 4 hp and 6 lbs ft. torque in my car, i've tried it on the dyno.

 

I completely agree, I feel no difference at all. I've felt more of a hp gain from using octane booster.

 

Per Vizard's book on carbs & intake manifolds (I forgot the exact title), in one chapter he shows the effects of having, or lacking, a radiused transition inlet on airflow in a runner. A velocity stack is one example of a radiused air inlet on a pipe. This also applies to the inlet bore on a carb or throttle body.

IMS he showed that conical tapers are no better than just a straight tube. He also showed that any amount of radiusing helps the airflow by a few percent, and up to 5% can be had by a generous radiused air inlet.... i.e. rounding the bores. The highest number was 5.5% IIRC, and that seemed to be a limit based on the number of different shapes he tried. I hadn't seen anyone report this info on TGO so I figured this might be a good time to do it. I also went looking on the web (some time ago) and found nothing (clear cut tests of airflow, or power or torque, before/after that type of modification).

So on a 500 cfm TB (or TBI that has injectors), you could expect as much as 25 cfm. This isn't a huge gain, but it is a free gain. If the engine were properly tuned, you would likewise gain an extra 5% increase in power. If the engine isn't tuned to cope with the extra airflow, or if you aren't close to max-ing out the airflow of the stock unported TB/TBI, then the gains will be less or even nil. That's why some people who do the mod to the TBI get very little reward for their effort.

HTH.

 

first off octane booster is a JOKE it will boost the octance by either .4 or .7 not a full octance point. (so your running on 92-93 octance from the pump and you dump in one can of say STP octane booster it says increases octance by 7 points heres the break down your 7 points look like this .7), if you want booster find some racing fuel. and top off your tank with that you'll notice more of a gain vs. the crap in the bottle. or if you do some searching you can find ingredients to mix you own fuel, from like home depot or Lowes.
and a FYI
.400 in the 1/8 is small so you cant even see it except for when its on a clock, plus you have no idea what the essential elements were of "steve8586iroc's" run at the place of testing, there are so many figures that must be added in, so maybe he did infact gain something on that run. you have the weather, altitude, tail-cross-head wind to contend with, plus shift points, tire pressure, track temp, modifications to the engine and weight of car, and so many more things that relate to it.

I did the mods and then some no you cant see it plain as day, but for the future list mods it will definately help. so what did you expect a 20HP gain or what? have you ever heard this "NO 2 CARS ARE EXACTLY THE SAME"

 

Thanks AZ, You know it might have been the timing system at the track I was running at. As far as the the car goes, it's bone stock with the exception of the ult-tbi mods an afpr (also a free mod) and I cut the small end of the snorkle on the air cleaner off. Thats the extent of the mods I have on this 91RS L03. Like I said before it might have been then timing system at this track but I do have the slips to prove it. The one thing I wish I could do is go back to the 1/4mi track and see what gains (if any) it made there. My best before the mods was a 16.80 pass. Hopefully this summer I will be able to put in the 350 I have waiting in the garage, see my sig below. \/

By the way thats not my garage my motor is in, just the place I built it before my garage was competed.

Steve

 

BAM! Couldnt have said it any better myself! One thing to add is that the throttle shafts alone on a typical carb can be worth 30 cfm. Id expect similar gains on the TBI unit.


as for the guy saying theres no way to accurately adjust the fuel pressure..

How about this, go to a dragstrip (the kind that gives you a timeslip ) and start making adjustments downward of a prescribed amount (since these cars run rich from the factory) maybe one full turn down, faster? if so, do more till slower, then go back a step or two.. same goes for richer. At the same time figure out how much faster the car is pre TBI mods and after... oh.. too late now.
Of course all of this is null and void if you have other problems like a mal adjusted TPS, bad tune, etc etc.


SOTP dyno is for the birds, if you want to tune that way you are going to waste alot of gas because what feels fast when you are tuning usually is not fast. Especially with airflow mods that dont become apparent until the upper RPM range.



BTW Kdrolt, i made a very similar post to yours awhile back on TGO on this very board. Id say maybe a year or two ago, Used the same vizard book example. Didnt give any % numbers though since I was just quoting from memory.

 

You're right about trimming the throttle shaft -- I forgot that. SO between the radiused inlet and thinning the shaft, you might gain 50 cfm which is approx 10% improvement. The small Rochester TBI flows enough airflow, stock, to make 300 fwhp... so the mods are worth up to 30 fwhp (330 fwhp total).

It might be worthwhile to edit this thread and attach it to one of the stickies above.

 

I think you should look into the fuel pressure adjustment to go with this, Slowmaro91RS. When I had TBI on my car and did the porting work, it made a noticeable difference in the throttle response. however, i also had installed an AFPR before this mod, so when i put it back together i cranked up the fuel. it might just need more gas, you are getting more air into the motor now, whether you feel it or not.

in fact when i installed a 1 1/4" spacer on my 94 TBI pickup, the truck wouldn't run with the stock fuel pressure setting. i had to install an adjustable regulator to compensate, and that was without any port work.

i am not saying you are wrong, or claiming to be an expert, just telling you my experience.

 

Way back in the day, I was working on my first car, a 1978 Corolla. It had valves that needed manual adjustment. So I got the Chilton manual and adjusted them. Put all of the smog crap back on and went for a test drive.
It was an absolute slug, even for a 78 Corolla. So obviously I screwed up somewhere. Dreading now much I might have to redo and even if I could get it working again, I popped the hood.

And the cable to the carb was off the pulley. So I had basically been driving it at idle the entire test drive.