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Discussion Starter · #1 ·
My specific questions is shifting gears, is it better to do it at peak HP, Tq or redline. Here's why I'm asking.

Nailing the throttle from a standing start with no brakes spins the tire (Open rear) for about 5-6 feet, leaving a pretty nice patch for a 40" tire, the motor redlines at 6,200, I have the chip in the MSD box set for 6,000 rpm, I usually shift right around 5,900, which translates to about 58-60 mph in first. Second gear brings me to 93-95 mph. Knowing I'm nearing the end of the quarter mile should I be shifting into 3rd somewhat sooner to keep the engine in it's powerband or keep it in 2nd and bring it to redline so that no time is lost between the 2nd to 3rd shift? What's you opinions. Will I make a better run going to redline or shifting before the end of the 1/4 mile (at say 5,800-5,700 rpm's) and let the engine stay closer to peak. I'm just curious what some of you guys who make multiple and frequent passes on the strip think?
 

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Big question is, what's your combination? Lots of things determine shift points. Personally with your 6000 chip, I'd shift at 5600. Because there's going to be a small amount of time between gears that the engine will rev up a few hundred rpms. If you're to close to the chip, it'll loose power.
 

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Discussion Starter · #4 ·
My truck is ....unique. It's an 89 Ford F-350 pick. Lifted, 4 wheel drive. 39.5 inch tires 4:56 gears. It has a 408 stroker motor with 9.5:1 compression ratio. No name heads (Strikeforce from PBM) with 2.055 intake valves 1.60 exhaust, (Heads Flow 280 int @ .600 lift), 1.6 ratio rockers. Cam is 224/234 @.050 and 290/300 adv dur. It has an Edelbrock performer RPM manifold, MSD everything (Distributor, ign box, coil), Holley 750 with vacuum secondaries, Stan's Tri-Y headers with 1 5/8 primaries. Dual (Short) exhaust go from headers maybe 18 inches of 2.5 in pipe, dual flowmasters and out the side. C-6 has a 3,000 rpm stall speed converter. Truck weighs about 6,000lbs with me in it.
 

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Relating to your other post, if you buy your G-tech it is very easy to work this out. Once you have done your "runs", shifting at different points, and downloaded them....you can overlay multiple runs on the graph/s and you'll soon see what works and what doesn't.
 

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Discussion Starter · #6 ·
That's primarily why I would use it, right now the engine makes it's peak tq at about 4,500 and HP at 5,600.
 

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It's typically better to slightly over-rev an engine at the end of an acceleration run than it is to sneak in an extra shift right at the end. Ideally you'll gear/tire the car to hit peak power just a tiny bit before the end of the track.

If you have a dyno graph, even if you peak at 5,600RPM, I doubt your HP is going to decrease to below the point of where the next shift will put you. If it does, it might be worth a shift, but if your power at 6,000 is above that at 4000, don't bother to shift it. Or you can just do it at the track and see what it likes best.

If it were a stick, I would say definitely don't shift it, but with an auto, you don't lose power on a shift.

<font size=-1>[ This Message was edited by: thekingofazle on 11/9/06 4:56am ]</font>
 

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Discussion Starter · #8 ·
That's what I was thinking, it is still pulling VERY hard at the top end (Near 6,000's) and your answer sealed it because at 4,000 I'm much further down the HP scale. Good way to think about it!!!
 

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After you shift your RPM should never drop below your peak torque RPM.
You stated that as 4500 rpm so when you shift your rpm should always be above that 4500 rpm mark. That is where you get the best acceleration. if you are waiting too long to shift you might be costing yourself time and mph. Maximum torque always equals maximum acceleration your best times come from shifting when the shift puts you back at your peak torque.
 

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Here's a spreadsheed in Excel to tell you where you're going to be shifting at.
http://students.ou.edu/B/Wesley.E.Blackman-1/FM/ShiftPoints.xls

If you don't want to download it, what it says is that, with:

1st Gear Ratio 2.46
2nd 1.46
3rd 1
Axle Ratio 4.56
Tire Dia (in) 39.5
Convertor Slip 5%

And,
Shift Point 5700 RPM

At your specified shift point of 5700:
After:
1st Shift - Speed=57 MPH
Entering 2nd, engine RPM=3374 RPM

2nd Shift- Speed=96 MPH
Entering 3rd at 3894 RPM

Redline in 3rd at 140 MPH


If you had a dyno graph, I could fit an equation to it and actually tell you if you'll have more average horsepower shifting once or twice.


<font size=-1>[ This Message was edited by: thekingofazle on 11/9/06 4:27pm ]</font>
 

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Discussion Starter · #13 ·
My motor is running strong right up to the 6,000 rpms. (As I matter of fact, if the tach wasn't saying 6,000 I would probably hold it longer because it feels so strong) But to protect the motor which the engine builder said redline is 6,200, I'll shift it at 6,000. I think based on the info here (and on that earlier post from 2002) shifting would cost me some time and MPH. So I'll tach it out to 6,000 which should bring me to about 100 through the 1/4. That's not too bad for an 8ft tall truck weighing 6 G's. While painted Kandy Apple red/maroon, it's not exactly a "Sleeper" but it's definitely got the GO to accompany the SHOW.

Now when I talked to the engine builder about it's use, he said he would build the engine to have 400 RWHP. When I had someone put the specs of my motor onto the Desktop Dyno program he came up with 385 hp at the Crank! Yet when he did his he said his was putting out 450 at the crank. Even HE admitted he was wrong because he has a lo-rider 2wd and I WASTED him when we were together at a local show. He said he would have to rerun the numbers through. Can someone here put my stats in and come up with what this think should be putting out? I know it's a pain in the ass but in order to have 400 hp at the wheel, it should have somewhere near 500 hp at the crank. What specs are needed? I'll input what I have to make it easier but any help I can get to determine what the output is will be great. And here's the thing, if it's less than it was supposed to be I won't be upset....because it's already scary fast for me as it is and anything more isn't necessary. I'll post up what I have....Thanks!!!
 

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Discussion Starter · #14 ·
By the way...thanks for the spreadsheet on shift points!!!!!
 

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Discussion Starter · #15 ·
Stroke: 4.00
Bore: 4.030
Intake: Edelbrock Performer RPM
Carb: Holley 750 Vacuum Sec
Port Volume: 215cc
Chamber Volume: 65cc
Intake/Exhaust Valves: 2.05/1.60
Header: Stan's Tri-Y headers 1-5/8's primary 3" collector
Muffler: Flowmasters, 40 Series, 3 inch
Compression Ratio: 9.0:1
Dish Size?: 27.5 cc (They are Kieth Black Pistons (P/N KB319)
Cam: Adv Dur 290/300, @.050 224/234, Lift .496/.520, 110 lobe sep.
Cam is from PBM Performance P/N 160170.
Heads flow 290 int @.600 lift, 200 exh @.600

What else do you need to run a desktop dyno sheet?
 

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Discussion Starter · #16 ·
I just double checked the flowbench numbers for the heads those readings are actually at .700ths lift.
 

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are you 100% positive your truck weighs 6000lbs.??? if so i would guess your engine makes somewhere close to 550HP at the flywheel. get your truck on the scales,then you can get a better guess at the HP thing
 

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Exactly!

Cris
 

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Dosen't mattter what it weighs... If the Engine has 550 hp then it has 550 wether the truck weighs #5,000 or #1,500.....

The desktop dyno will give him a good approximate. Timing him in the 1/4 with a known weight and gears will then give him very close #'s to what his engine is putting out. I say very close because I can take a 700 HP) engine and do the 1/4 mile in 25 seconds and nobody in the world can figure out my HP rating even if they do know my gears and weight...

That makes sence don't it?

FE
 

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On 2006-11-09 14:40, FALCONAROUND wrote:
Dosen't mattter what it weighs... If the Engine has 550 hp then it has 550 wether the truck weighs #5,000 or #1,500.....
Hmmm.....

On 2006-11-09 14:40, FALCONAROUND wrote:
Timing him in the 1/4 with a known weight and gears will then give him very close #'s to what his engine is putting out.
Hmmmmm......

On 2006-11-09 14:40, FALCONAROUND wrote:
That makes sence don't it?
=D

Cris
 
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