I'm making some good progress with my engine tuning, but I'm still a rookie at this and need some ideas/suggestions on the latest issue.

When I step on the gas the motor makes good power, then just steadly pulls....until 4500rpm. At that point the motor really pulls hard until right up to 6000. It would keep going if I had my rev limiter set higher. It's making power in the upper RPMs that I could only dream of with the TPI intake.

So what's going on between 1500 and 4500? I can be at wide open throttle and the motor steadly climbs. I should be able to put the pedal to the floor and jump up quickly in RPMs. The motor is not reacting this way. Any ideas?

 

I diagnosed a TPI car with similar symptoms...gas pedal was like a wet sponge, no bog just no power, then all of a sudden it would wake up. Distributor got bumped and was only 4deg BTDC initial advance (PROM was burned at 10deg BTDC).

Setting the dist nailed the problem, 6deg of advance makes a huge difference. Whip out your timing light and re-check, make sure the ESC is disconnected and you're looking straight down at the timing tab so you get a straight line between the balancer's zero mark, the tab, and your light.

 

Base timing is set at 6 degrees and the motor seems to run best there. Moving more or less results in idle problems.

 

to the top

 

getting any knock retard? are you extremely lean?
whats your blms?
Whats your mods?

 

Spark Retard:
Once in awhile I get spark retard...it's not very frequent.

My BLMs aren't always right on 128, but I'm getting it closer and closer with every run. Sometimes I'm lean, sometimes I'm rich, but again that's not usually excessive.

The motor is a 355ci, LT1 Intake, SVO 24# injectors running at 27.2#, pro topline heads, LT4 HOT cam, 1.6 roller rockers, headers, and a 730 ECM.

Besided getting my BLMs closer to 128, where should I start looking for this problem? I'm still learning and not sure where to go from here.

 

Getting your BLMs closer to 128 will not help your problem of being a little boggie until 4500RPM. If your BLMs are between 122 and 134, you are perfect.

I would suspect upon tip in of the throotle, that you are either suddenly rich or suddenly lean. I have seen some other posts about bogging problems with the LT1 intake. The LT1 intake is better than the TPI for top end power, but lacks on the bottom end and at midrange as compared to the TPI runner system.

You can do a search (which you may have done already) on this matter. Try to identify tables in the 730 ECM that may tend to improve the tip-in throotle problem. If the 730 ECM is a SD system I would look at the VE table and the timing table.

We talk about your injectors before,,, maybe you are suddenly rich at throotle tip-in causing the engine to feel boggie.
Those 24# injectors are great at higher RPM, but at lower RPM, they may be flooding the engine as the TB opens.

Hey, I'm guessing here, please bare with me.

 

What is the compression ratio of the engine and intake closing timing? (Chamber size, piston config, piston to deck height, head gasket thickness).

RBob.

 

Yes, but if you set the timing to 10 deg BTDC (adding 4deg across the board) does the mid-range get better or worse?

RBob.

 

I don't know the fine details, but the motor is about 10:1. I'll try adjusting the timing tomorrow night. I can only work on the vehicle on the weekends.

Thanks for the replies guys! I'll be sure to keep you updated. If anyone else has any ideas, I'll certainly try them as well.

 

Yeah I would try giving some more advance earlier also see if that helps,also if I recall the pro heads are very large runners are they not?
What convereter are you running?
If those heads flow what I think you are not going to have
stout lower rpm power especially with the LT1 intake and if you are using to low a stall then it will feel really weak.
Not real bad but nothing like the Long Runner intake was.

 

I'm running a Syclone (yeah, the pickup) torque converter. I think it's about 2000 stall.

The Pro Topline heads are 200cc.

Regardless, I should still have more power than I'm getting in the mid RPMs. Thanks for the suggestion...I'll play with that timing and see it it helps at all.

Moving the base timing vs adjusting the spark advance is the same thing, right? Guess I'm not sure why I would have to move the base timing if I can adjust my spark tables in my prom.

 

Well, you mentioned that you changed the base timing and decided against it because it messed up the idle. The problem isn't the idle, it is the mid-range, so the question is, what happened to the mid range when you changed the base timing? If the mid-range got better/worse when you added timing then you know which direction to go in.

RBob.

 

give the ae tables a tweak for more fuel. the air is stalling in the port as the valve noses over the top of the lift curve.your basically dealing with a bog more or less. either that or go into the PE tables and richen things up a bit ans see if it clears up. id also see just how much PE timing your running. might not be enough or could be to much and if its advancing the flame front to far ahead in the cumbustion cycle itll be dropping off TQ.

 

I like the stuff above from Rbob and funstick. The idea of Rbob is really a good one. You set the static timing which is applied across the board, while the ECM controls the dynamic timing in a table. So, if you set the static timing up to 10 degrees (OK, maybe the idle is worse, but) does the bog at mid-range go away or lessens. If it lessens, than you know to set back the static timing to your 6 degrees for a good idle and burn a new chip with more midrange timing.

Fundamentally, the air flow is stalling at throotle tip-in as I said and funstick has expanded upon. You have an SD system, so some work on the VE table might help you also.

 

Did I not just say the same thing?
Why the disrespect?

 

S10Wildside, you asked earlier about moving the timing via distributor or chip. I answered differently.

Yes, you can move the timing via the chip, by reducing the initial timing term in the chip you can add timing across the board. If the initial in the chip is 6 deg, setting it to 2 deg will add 4 deg across the board. And the opposite may be done.

When it comes to problems such as you are experiencing a lot of times it just takes trying different things and noting how the engine reacts. Such as: a chip w/more timing, one with less timing, another with 10% more AE, then another with 25% more AE, then go out and try each one. Be sure to drive long enough with each to be sure of the results.

RBob.

 

Can you explain what seems to be an inverse effect on timing by adjusting the initial timing in the chip?

 

Sure. Example first: typically the physical base timing (distributor) is set to the same timing as the chip's initital timing value. Say they are both set to 6 deg BTDC. The code subtracts the initial from the final SA value with the distributor putting it back in. So it is a wash.

Now, lets leave the distributor at 6 deg BTDC and then set the chip's initial to 2 deg BTDC. The ECM will now subtract 2 deg from the final SA value. The distributor adds 6 deg back in for a 4 deg increase across the board.

RBob.

 

Can you data log a run?.
Maybe post the VE, Timing and PE Fuel stuff?.

Without being able to look at anything, there is little you can do other then just shoot in the dark, and hope to hit something.

At a min, you need to actually measure something performance wise, so you can decide if a change helps or not. SOTP just wastes gas.

A really good running car tends to *feel* slow because it pulls so smoothly. All you notice is being pinned to the seat.

 

87_TA: No disrespect was meant here, yes you said a similar thing, I was concentrating on the last two posts, thats all.
You seem a bit too sensitive, I meant no disrespect, so please excuse me, TIA, Doc.

S10, you have alot of good stuff listed above concerning your problem, this should keep you busy for a little while, anyway good luck, I think that you will get to the bottom of this. Please keep posting, I am very interested in your tuning issue.

 

The end result is identical to what most guys do by "mechanical methods" to add 4 extra degrees of base timing. They adjust the distributor to 10* and leave the eprom at 6*.

The difference in the "prom burner's method" mentioned by RBob is that it doesn't get your hands dirty.

 

Thx doc

S1O,how weak does the truck really feel? Thats the part im lost on..
Does it seem to not respond well,bog,or just no pull real hard?
Please elaborate.

I was just looking at your heads in summit,They flow 278 cfm @
.700 lift. Those are extremly well flowing heads and im positive are going to favor high rpms.

What gear are you using with that converter?
If you have a tall gear with that low stall its going to be pretty weak at the bottom till it gets into range.
Not saying it can't be improved upon with some tuning,but I would not expect great launching capabilities.
Like grumpy says ,dont trust the butt-o-meter always.

Do a 1/4 calculator off craigs software ,allowing little or no spin I found it to be very accurate.
Lets get some date here.

 

Which of course is the best part. I remember having a letter published that mentioned something about being able to tune while wearing business casual. . .

RBob.

 

espcially with an emulator.

 

Well, it'll be awhile before I do further diagnosis. I think the problem has been a transmission problem from the start. It has felt like the transmission would not shift into passing gear when I go WOT. While out getting data today the transmission started acting funny (like the engine was working harder than it should and the transmission was sluggish), then I smelt something burning. After that I no longer had 3rd gear. I had to drive home in 2nd gear.

I have played with that TV cable from one extreme to the other and everything inbetween. It's going back to the guy who built it next weekend so he can look at it. The transmission was just rebuilt before I got the vehicle going again. Less than 20 miles and it's already busted. The transmission fluid level was full, I'm sure of that.

I'm frustrated.

 

Sounds to me that the guy who built your tranny didn't do a very good job. Now you will find out if this guy "stands by his work".

The question is, can you trust the guy to do the job right? My experience is that you will most likely have "problem after problem" and it won't get fixed right until you get someone else. But you should be discussing this on the Tranny Board.