anyone seen any kind of issues like this with your TBI projects?

 

its a 355 with Flat tops, 72CC heads, LT1 cam, edelbrock intake, Holley TBI. Motor is fairly fresh with about 10,000 miles on it.

 

If the Air Fuel Ratio graph is accurate, that engine is running too lean. The dips in the graph might be the ECM pulling timing out.

I wouldn't take it to WOT again before more fuel is added or you may risk engine damage.

I'll even go as far to say, that dyno run should have been aborted by 3800 rpm.

 

What kind of 72cc heads? The lack of flow in the upper RPM's will shock the power band like that. I also agree that the engine is running a little lean. Did you play with fuel pressure at all?

 

You are running extremely lean. Do you have the stock fuel pump? What kinda of chip burning did you do? I would start with those problems. You dyno chart looks like a bolt on LO3 should.

 

so a 355 with a LT1 cam should not look that way correct?

 

you are running way too lean, at WOT i believe you should have around a 12:1 A/F ratio. And you are very very lean in the lower RPM areas.

 

Correct. Most stock LO3's will produce a graph like that. You should be making at least 220 to 240 at the wheels (those heads you have are not the best for top end). You need fuel bad. I mean really bad. Your AF ratio is not safe at all for your motor. What size injectors and fuel pump are you running?

 

He's not that lean. It only gets kinda bad in the beginning and high rpms, but if you look at the AF graph and compare it to the graph, it doesn't match up. You definitely need to work on getting more fuel, but that's not your only problem.

 

Well thx guys, was just hoping someone had a clue what would have caused it, raised fuel up, I will try to log it this week i guess.

 

Hes only about 13.8:1 @ WOT in the mid range. He needs to get that number to 12.5 or so. I would worry about it if he was going to put a constant heavy load on it(WOT racing).

Does this car still have the 305 injectors on it? If it does it seriously needs 350 or 350 9C1 cop car injectors and maybe an AFPR.

Depending on what LT1 cam he has that looks about right for the LT1 cam in a TBI motor. If he has a B-body cam those are all about low-mid range torque. Even some of the early F-bodies use the B-body cam.

 

what size holley injectors? what fuel pressure? data logging will tell you nothing about WOT( IMO). you may need to datalog to get the "underlying" fuel tables in line(datalog) and then back to dyno for conformation of subsequent WOT improvement. i would record the beginning datalogs, make your changes and then back to dyno to see if the WOT is improved(enrichened). the next dyno run can tell you if you are moving in correct direction.

 

Logged car today, I have raised fuel pressure, made some timing adjustments, will redyno next week and see what happens.

 

i put a 355 in my car also.. had a 305 LO3 stock.. what kind of a fuel pump would you guys reccomend? i have the 350 injectors. mine seems to have alot more power then my LO3 had.

i've got and lt1 cam also
305 tpi heads (58cc)
edelbrock performer tbi intake
federal mogul pistons.. the guy said they have a little dome but not totally flat
decked block

thinkin about getting 350 tpi heads for over winter project in the moths ahead.

 

Before you spend money on more dyno time it would be a good idea to make sure that your fuel pump is maintaining the new fuel pressure setting at WOT. If the pressure falls at WOT, dyno time will be a waste.

Another thought, if you make changes to the timing and fuel simultaneously how will you know which one gave you an improvement? Or worse, how will you know which one caused you to lose power?

 

Walbo 190 or 255 unit.

 

what is advantage of walbro over GM TPI OR LT1?

 

Reliability. TPI pumps will work but you can't use an LT1 pump. Some aftermarket pumps can be used in both generations though. Anyways, GM pumps are junk and crap out unexpectedly with little to no wear on them.

 

I know this topic is over a week old, but look where his peak HP and torque is, ~3700 RPM for HP and ~2800 for TQ. Is the reason for this the cam or the poor tuning or the heads? His numbers are shifted waaaay in the lower range and just dies after 4K rpm.

 

well it would seem that the timing and fuel both played parts. they was not changed at the same time however. The fuel problem was do to the fact that one of my Holley injectors took a crap on me, it went out completey on th eway to FG8 this weekend. Changed that injector and man you talk about a difference in a car. and as far as teh dyno time, its nice to have one at my access and disposal

 

my guess is that it is a combination of factors.

1) that cam is pretty small in a 350.
2) Fueling/tuning is def. an issue.
3) I dont' know what his comp. ration works out to, with flat tops i assume he is in the right range for the compresion ration. that doesn't however mean there isn't a mismatch in heads/intake/cam combo i may have missed it, but i did not see exactly what heads he had.