Adaptability of GM Tuned Port Injection?

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^^^ this ^^^. gauranteed improvement based on original post, and lowest risk to the owner/seller and buyer.
 
Originally Posted By: A_Harman
Comp Cams has a small selection of Computer Controlled cams that would be appropriate for this application.

http://www.compperformancegroupstores.co...gory_Code=HFTCC

Is there such a thing as engine builder malpractice? Whoever put the Thumpr cam in this engine should have known better.

I'm starting to think that's the route I'm going to go.






Originally Posted By: Trav
Sorry Eric but IMHO your getting the dirty end of the stick with a 3K budget on this thing. A 2800 stall converter and headers then fuel system work/chip tuning and god only knows about the heads is going to burn through 3K quicker than wild fire.
On top of all that if this is sign of the work of the guy who put the engine together who know whats going to happen to it if you get it to make some decent power, that engine should be well over 400 HP when done right.


You're right- 3K won't really get the job done. I would like to figure out why this thing runs so terribly though. I'm not totally convinced that the cam is the sole problem, especially when this thing pings SO easily when you just poke the throttle. I'm guessing there are multiple issues in play...






Originally Posted By: mk378
Originally Posted By: The_Eric
His end game is that he wants it running "good enough" to sell.

Stock cam then. Fortunately the rest of the car is still stock. A car that is in good stock condition is worth more than some unknown mod job, even if the new owner wants to modify it.


I don't think a stock cam will fix ALL of the issues. I do believe a milder cam is in order though.





If I think about it, I'll post up the dyno sheet- it shows an impressive amount of fail!
 
Did someone do an air pump/EGR delete on this car? Its been over 30 yrs but I remember one that pinged like crazy when the air pump was removed. Does this distributor have a vacuum advance? Was the timing set with it connected? How is the base timing? Did someone put lighter springs on the centrifugal advance weights?
 
Air pump and EGR are still there. At a minimum I'm suspicious of the EGR, as I know it wont respond to vacuum and the idle doesn't change at all with vacuum applied.

Base timing is 8* BTDC with the connector unplugged. That's about as much as I know for now because the customer dropped off of the face of the earth for a while and couldn't get auth to spend more time/money on it. Now that I do, I need to work it back into the schedule somehow.
 
Dyno sheets. The first is HP/TQ, the second replaces HP with AFR

tBXRD2n.jpg

aDfODbG.jpg
 
Am I seeing that right 16.9? its going full lean over 3200 RPM. I wouldn't start the cam but injectors, throttle body and a chip tune first, you need to get some gas to that motor. Throw a set of header on it while your at it so it can breath a little.
Its still going to be a bit of pig off the line with a stock converter but it should be much better than it is. I was thinking about this, going back to stock cam is all well and good but its not a stock engine anymore its got more cubes and will still need more fuel and a chip tune.
 
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I don't think you are? Yes, it starts the pull at 16.9:1 and drops as the pull progresses. By the time peak torque rolls around it's about 15:1 and at peak HP, it's where it should be- around 12.6:1. Definitely not saying it's correct though, but it seems like it's got the ability to provide sufficient fuel enrichment for the power it (barely) made and probably enough to (barely) support mid 300's (probably wide open)?

I do agree though- if this thing starts running as it should, it'll likely need injectors and a tune.
 
Ok, I was looking at the what looks like a red line where it appears to be going lean at 3200 and up. I cant make out what the lines represent on the bottom.
 
The blue is TQ, the red is HP and purple is AFR. On the top graph, the left side is the scale is TQ, the right side, HP and the bottom is RPM. The bottom chart is the same, but exchanges HP for AFR on the right side.
 
So it runs lean on the bottom end, and rich at the top? Strange. I can't figure out which one is AFR.

Cam timing?

For $3k to fix I wonder if it'd be faster to find a stock long block. I'm guessing though that is close to labor. But maybe the 383 can be sold for someone else, thus recouping the price difference.
 
Originally Posted By: supton
So it runs lean on the bottom end, and rich at the top? Strange. I can't figure out which one is AFR.

Cam timing?

For $3k to fix I wonder if it'd be faster to find a stock long block. I'm guessing though that is close to labor. But maybe the 383 can be sold for someone else, thus recouping the price difference.


Well 12.5:1 really isn't rich when you're WOT making peak HP. The lean on the bottom (at WOT too, since it's a dyno pull) could be form a sluggish O2 sensor- not reporting back to the computer fast enough.

I'd really like to figure out what's going on FIRST before replacing cams and engines (even though it may well need a cam change). I want it out of my hair, but I'm not going to start tossing engines at it to make it disappear!






Also I'd like to know what about the TPI system doesn't like lumpy cams if there is no MAP sensor.
 
Fair enough, makes sense.

I was kinda confused by how lean it was on the bottom end too.
 
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