After a long sabbatical away from TBI I am back.

I swapped to an edelbrock 1405 carb about 2 years ago and a little while after got a Wide band o2 setup which quite simply is the holy grail of tuning tools.

I went nuts with the carb and took it about as far as it can go tuning wise, it can still get some massaging for airflow but AFRs were dead on at the track except for a weak pump shot and have given me the times in my sig.

I couldnt get the TBI to work for the longest time, i finally figured it out. My battery relocation didnt quite work as well as I thought and it was just enough voltage drop to make the ECM pissy.

I moved the battery to the front again and now Im back to TBI.

670 holley with shaved throttle shafts, radiused inlets and radiused outlets from the adapter plate. Gm injector pod with stock injectors@20 psi

I drove it on my old chip and what the wideband was telling me was downright shocking, the AFR was WAY lean under low rpm and WAY WAY rich at wot. I've since done a few burns just playing around getting the car atleast safe to drive. I hope to get serious about data logging and tuning this weekend.

my initial impressions after driving the car carbed for the past year is that once I got the tune roughly in line with the TBI it just BLOWS the carb AWAY in the low end torque department and throttle response. Flooring my car at 1500 rpm would be insane with the carb, it would probably stall.

I can do that all day with the tbi, i can just slam on the gas and go at any rpm which is quite an improvement. With the carb I needed to always keep the throttle and RPM in a comfortable unison while driving around. No such thing needed with F.I.

Im pretty excited about the whole thing, one of the absolute biggest weaknesses of the carb setup was its crap low end torque. At the track launching from 3000 rpm the car would jump and then bog past the 60ft mark where it got into its power band and took off. I never have managed less than a 2.1 60 foot even with insanely good traction because of this.

Im fairly certain I am cured of this problem now. Its just a matter of getting the mid and high rpm AFR in line (which was way off... explains my poor performance at the track with the TBI)

Anyhow, Ill keep you update on the tuning and hopefully I will be able to give a track comparison swapping the two inductions on the spot. I will have wide band data to settle any discussion about tuning also.

cya

 

thats interesting considering most peeps seem to say that carb is better then TBI-in just about every aspect of tuning and performance wise.

 

Those people probably dont know what the difference between a jet and a metering rod is


carbs are easy to get in the ballpark, out of the box mine was I'd say about 85%of it being as good as it was going to get. That last 5% is a real pain to get and then once you have that you realize that you are basically stuck and your performance still isnt perfect.

The year of serious tuning on the carb taught me alot and made me pretty profficient with the afb. In its current tune its basically as good as its going to get without getting real crazy. Its still not as good as it could be with ANY carb, a double pumper would definately be better suited to the 5 speed and single plane.

Still, I have plenty of data to show that the only thing Im hurting for is pump shot which is not a problem with fuel injection.

 

to expand on that, the TBI (just fuel injection in general) isnt quite so simple. With a stock tune my car would be almost undriveable and then to get it tuned for my setup requires a meticulous approach to tuning.

My carb has 4 jets, two metering rods and two metering rod piston springs. Thats four things I can easily change (you mostly do them in pairs) and for transition systems I had three pump squirters (i could drill them but factory .043 worked fine) and only one pump arm hole that was even close

compare that to the MAP FI system which has in the main fuel table 72 seperate data points alone. Way more precision involved.

 

Thats cool to hear you got it working agian. The volts mustve been pretty low during crank. I know that at 4 volts the ecm cuts the fuel all together and begins shutting down.

 

Glad to see that you are back. Now that you have the wide band are you going to go with a bigger cam and or more wild combo?

 

Was that 13.65 with the 305 carbed?

 

Good to see you got it running Pablo. After you tune it up I hope we can see some similar times as you had with the carb. What do you think, does it have the potential to be as fast?

 

yes the 13.65 was with the carb and both of those times/mphs were at a track early this year (i have to say that because alot of people think those are Gtech times)

I think it has the potential to be quicker, especially out of the hole. The big thing my carb was lacking was pump shot and the ability to easily and precisely tune the high rpm afr which were both lacking.

 

Was it with a 305 or a 350 and were there any other mods?

 

305

its definately not stock