Flat spot at 4,800rpm

[Dan B.]

Went to PRP tonight. Took the '88 Thunderbird Sport w/ the '88 5.0 HO swap, T5 and some other stuff. Got four passes in. I made three passes (#1, 2 and 4) and I let a friend drive the third pass. It was running a set of 26x10.50-15 MT ET Streets on turbine wheels with 20# of air. Should have dropped them down but it slipped my mind. Don't laugh at the times but you have to start somewhere and I've not done anything to tune it at all.

Pass #1 was a 1.96 (60'), 14.1 @ 95.6 mph.

Pass #2 was a 1.95 (60'), 14.06 @ 96.5 mph.

Pass #3 was a 2.1 (60'), 14.31 @ 98.1 mph.

Pass #4 was a 1.91 (60'), 14.05 @ 96.6 mph.

The good news....I'm pleased. There was a Lincoln spec'd out about the same as the 'bird (HO, T5) that was running high 14's and low 15's. On my passes it was launched at 4,000 rpm and shifted at 5,800rpm. The one down side is a dead flat spot at 4,800rpm. It pulled hard to 4,800, flattens out then pulls slow up to 5,800...this happens in each gear and I'm pulling into 4th about 100' before the traps (so three times). This flat spot is costing me "at least" two tenths. I had noticed this on the street also so I was aware of it before going down. I'd be at least solid 13.75 (or quicker) car without the problem.....and I'm happy with that in a fully dressed '88 Thunderbird running 3.55's.

Any ideas of what may be causing the problem?? Timing is 16 degrees, FP is 42#, MAF is stock, stock 19# injectors, TB is 70mm Edelbrock, intake is Explorer, stock '88 HO heads and cam.

Just throw some ideas out and I'll start tuning.

[yeahloh95]

Have you tried short shifting it at 5k

[Dan B.]

Have you tried short shifting it at 5k

On the street, yes and it seems to run good but tough to say if its any quicker. Last night was the first time at the track with it so next trip I'm going to try that.

[PaxtonShelby]

Is your tach accurate? The Ford factory tachs really suck - at least in the older cars.

[Dan B.]

Is your tach accurate?

Good question. I did have it bumping the limiter earlier than I thought it should have on the first burnout. Thinking it was cutting out at 6K and I thought they were set for 6250 in the computer.

[cam303]

You are pulling that engine way out of its power band. Try shifting it at 4800-5000 and it will run 13's if it ran 14.0 shifting at 5800.

[Dan B.]

You are pulling that engine way out of its power band. Try shifting it at 4800-5000 and it will run 13's if it ran 14.0 shifting at 5800.

Yeah....just used to running my Ranger. After some looking I see that I was just wasting track going over 5K.

[badstanglx]

Just put e303 cam be done with it

[Dan B.]

Just put e303 cam be done with it

Find me an ExploDer motor!!

[SK@StreetLethal]

Honestly on my stock 5.0's the quickest times I ran were shifting at 4500. It may be running lean to that will also cause it to nose over.

[Mark Aubele]

Dan I didn't realize you were shifting that high when we talked last night. Just like was said above, I always shifted at an indicated 5100 or so with stock 5.0s.

[Dan B.]

If the weather holds out I'm going to head back this week and give'er hell......but at 5K this time!