Fox Can I Run A Dr With My Stock T5?

[jrichker]

Oh! There is your issue! Your stock tach is definitely going to be off at higher RPM more than it is at lower RPM for you're probably looking at with your timing light. I've never seen a stock tach that was accurate at the top of the power band. Also, I believe that the best way to get a sense of where you should shift is to put the car on the dyno and look. I'd be happy to help you with it if you posted the graphs. You are likely to shift at over 6000 RPM to optimize the combination you listed. I think you're giving up all your mile per hour right there.

He's right about the stock tach being inaccurate at high RPM. I tried calibrating the stock tach and It was off 500-750 RPM or more when I set the middle RPM ranges to be the most accurate. If I set to be accurate at high RPM. it was off by the 200-400 RPM at midrange. You pay your money and take your choice of where you want the error to be.

My personal choice would be a tach calibrated for most accuracy at mid range and a shift warning light set for high RPM. The last time I looked, shift warning lights were somewhat primitive, but that was 10 years ago or more. Look for one that is easy to set and has multiple LEDs to help clue you in on when it is time to shift.

I just looked at shift lights and they are ridiculously expensive because there is maybe $15-$25 worth of electronics inside a $5 plastic mounting housing.

 

[FastDriver]

While I understand what Fastdriver is saying I will try and clarify my opinion on shift points.

Yep, dude, I totally agree with you. Nothing beats a scientific approach using experimentation. I'm just ballparking where this combination will/should end up if everything is working right. Your question about his shift point and stock tach was right on the money. He's intentionally shifting at 5500 rpm on a stock tach which means he could actually be shifting at who knows? 5000, 4800? Even if it miraculously is 5500 it's still costing him! and probably by a lot.

it gets complicated... it's not as much about where the car makes peak power (lays over) as it is about your shift recovery.
power under the curve... you want to use as much average power as your trans gearing will allow, so, often times with n/a cars that are weaker down low, it means taking it past peak power so upon the rpm drop associated with the next gear you are still using the max. "power under the curve".
My current combo makes peak power at 6400, but it's drop off is slight, and it's bottom end is hollow (relatively speaking)... it likes shifted at 7200rpm... almost 1000rpm over peak.

Yeah, you're right, the discussion can get stupidly complicated, but it does boil down to something pretty simple: Just shift when the hp at the rpm in the current gear matches the hp at the rpm in thenext gear or at redline, whichever comes first. It takes a couple minutes to look at a dyno with the trans gear ratios to figure it out. In the next gear power is on the way up; while in the current gear power is on the way down. When they cross, you shift. In the end, you'll end up doing exactly what you just said and maximizing the "power under the curve." Disclaimer: Some adjustment is required based on the driver's shifting habits. For example, powershifting will lower the shift point slightly. Slow granny shifting where you could eat a sandwich between gears would mean shifting at slightly higher RPM. lol

Most of the time, modern performance cars are limited by redline before the power drops enough to justify shifting. So, you just end up shifting at redline. Our mustangs, when stock, were an uncommon exception. After we add the go fast heads, cams, intakes, exhausts, we're usually right up against the "redline" imposed by the stock fuel cutoff or other mechanical considerations (valve float, clutch disengagement, transmission lock out, etc...)

 

[PakstinN]

it gets complicated... it's not as much about where the car makes peak power (lays over) as it is about your shift recovery.
power under the curve... you want to use as much average power as your trans gearing will allow, so, often times with n/a cars that are weaker down low, it means taking it past peak power so upon the rpm drop associated with the next gear you are still using the max. "power under the curve".
My current combo makes peak power at 6400, but it's drop off is slight, and it's bottom end is hollow (relatively speaking)... it likes shifted at 7200rpm... almost 1000rpm over peak.

now THAT was the explanation I was needing. you shift high to stay in the power as you grab the next gear. I do notice as the engine winds to around 3000 it seems to kind of "come alive" so to say..that is probably the case with every 302 I realize, I just never looked at it that way. the theory was when I feel the curve start to drop off I need to be shifting cause the power is no longer there to keep pulling, but I definitely understand what you meant by using higher rpm to keep in the power after an upshift. Will definitely try this at the next test and tune. thanks!