Yesterday I ran a 15.97 with my setup. Everyone and their mom knows that is ridiculous. I obviously have some issues with some TPI and I need to figure out which path to take before I spend a dime.

Here is what I need to make my TPI run good again.
-Knock sensor
-Electronic Spark Control Module
-A New ECM or MEMCAL (trust me one of these are bad)
-MAF sensor needs to be replaced.

Tally everything up and I could easily get a great carb setup?

So I must ask myself... which path? I mean carbs have been around since cars were born. They have proven themselves very reliable in any climate, they have awesome throttle response. By having a carb there are less things that can go wrong. Keep your carb clean and you are set.

TPI/ FI Been around for 30 years, you can tune it without opening the hood. You have computer diagnositics. Reliable in any climate, better gas miliage. However sensors are expensive, alot of things that can go wrong.


I am not trying to say one is better than another. I am at my wits end here and I need some serious advice. I need someone to help me get through a bad time here. When you put well over a 1000 man hours on a car and have it laugh in your face at the end it makes you want to give up completely.

My goal is a high 12 in the quarter. I am running a 16. Something is not right.
I want to be fast just like anyone else, but a reliable car day after day is my top priority. Whatever is wrong with my TPI setup electrically cannot be good for my engine so I need to nip this in the bud quick.


Today I am going to switch MEMCALS to see if a computer problem that I know I have will go away, if it doesn't then it is obviously an ECM issue.

Like I said, before I spend X amount of money I need some reason folks to help me decide the best route in according to my current setup.

 

First out, im going to point out im a TPI user, TPI lover, etc, so my opinion will be somewhat bias. As i am not a carb user, i dont nessecarily like the carb (will go into details later), and i dont know all that much about them, i will spill my guts about the TPI system to the best of my knowledge.

I have been researching the TPI system for the last few months endlessly trying to figure out how to improve upon the stock system, and retain the LTR set up for the max power.

I will go into some details on how the system works, and how to make it work better.

How it works:
The tuned port injection system, is actually extremely simple. Air flows into through the throttle body into the plenum, where it goes out into the 8 different runner tubes towards the cylinders. On its way the injectors spray fuel in creating the a/f mixture, which goes into the cylinder and combusts.
Think of it as a Big room, a Large front doors and 8 doors elsewhere in the room, everyone flows in, and flows out, Rather simple at this point, but its yet to be at the more complicated parts.

The stock TPI system was designed to work on a 5.0L engine, and does not nessecarily flow an extremely large amount in stock form.

I dont know of anyone who makes a An aftermarket plenum, but the stock ones with a few man hours can flow extremely well. From here, you want some aftermarket runners, the semi-siamesed SLP runners are Exellent, and with a little porting, can flow some extremely good numbers. If these are the runners you choose to use, then here you can siamese the plenum openings to the runners, by cutting the middle wall between the pairs of runner tubes. From here an edelbrock base works extremely well, and all the other bases are made by edelbrock anyways.
A good way to bring up the amount of fuel going in is by adding bigger injectors, LT1 24lb injectors are a good choise, and can be found cheap and are well made.

The Stock Throttlebody flows well with an airfoil, and doesnt need much more then that.

If you are having problems with an MAF, potentially look for a car in a yard with a good MAF, and ECM.

also look at your cam specs. The TPI system, or any EFI system is somewhat picky with the cam used in them. While lift is not as much of a factor as duration is, the TPI system doesnt like to be held up to long.

Have you done any chipwork with the TPI system? While the MAF responds better to change then the Speed density does, with a bore, and that much cam difference, it will certainly need some chip work.

The powerband of the TPI system is the downfall of this system, it produces LOADS of low end TQ, but falls flat on its face around 5500 - 6000 RPM depending on what parts used in it, any porting etc.

Now, onto the pros and cons of the TPI system

Pros:
Loads of low end TQ
Good fuel milage
Look Nice
Electronic control
Responds well to computer change
Easy to ajust
Reliable in any whether (depending on application, and set up)

Cons:
Short Powerband
Electronic, more potential for things to go wrong
Harder to set up

Reason i dislike the carb:
The carb doesnt have any good fuel mileage if this is a regualar driving car. The carb doesnt work as well in damp weather, and the carb is actually more complicated on the inside.

I have gone though as much as i can think of, chances are ill post up again today with more i forgot to mention.

hope this helps.

sheldon

 

Umm.. I know alot about "flow" since I port intakes and such as a second job. I know how to get power out of a TPI. What I do not get is why a stock TPI L98 does better in the quarter than my 355 with globs of mods.

I have learned today my MEMCAL is bad, in theory if the memcal is bad the computer is using default programs in which could be making me run like crap.