Engines

p8ntman442 · Post by **p8ntman442** » Mon May 05, 2008 7:07 pm

why continue the graph past the peaks? You should be shifting.

Aaron · Post by **Aaron** » Mon May 05, 2008 7:22 pm

Wrong. You should shift when the power level in the current gear after the hp peak equals the power level you'd be at in the next gear. On a Z34 5-speed, it is just about 6500rpm with every gear change. The engine peaks at 5800.

On that 2.0l turbo, say you lose 3,000rpm with a shift. If we continued the downward slope after the peak on the GM graph, it'd be at the same hp at 7,000rpm as it would be at 4k. Thus the best shift point would be at 7,000rpm. Now consider the hp doesn't dive nearly that bad, in fact it stays flat, arguably gains going high. So hopefully you can rev it out far past 5300, 6500 at the least.

Atilla the Fun · Post by **Atilla the Fun** » Mon May 05, 2008 10:20 pm

aaron is absolutely correct, both in my own experience, and in numerous independent tests.

Kohburn · Post by **Kohburn** » Tue May 06, 2008 8:11 am

while thats true if you have an engine where the hp drops low enough before redline to happen it is just a dumbed down way of explaining the true nature of your shift points.

your shift is determined by the area under the curve of the HP. depending on your RPM drop you want to maximimes that area. essentially is maximizing your hp through the powerband. since gearing changes and your rpm drop can change with each gear you have to look at each gear individually. sometimes your ideal shift point will drop a couple hundred rpm with each gear. it all depends on the full dyno graph.

Aaron · Post by **Aaron** » Tue May 06, 2008 9:25 am

Kohburn wrote:while thats true if you have an engine where the hp drops low enough before redline to happen it is just a dumbed down way of explaining the true nature of your shift points.

your shift is determined by the area under the curve of the HP. depending on your RPM drop you want to maximimes that area. essentially is maximizing your hp through the powerband. since gearing changes and your rpm drop can change with each gear you have to look at each gear individually. sometimes your ideal shift point will drop a couple hundred rpm with each gear. it all depends on the full dyno graph.

You're right of course. But looking at the area under the curve is exactly what I said to do, figure out your rpm drop, and find the point after the peak where it will equal the point before the peak with that drop., This maximizes the area under the curve.

You do need to look at each gear, I was just explaining it without getting into too much detail. However, that being said, in the Z34 5-speed with a stock 3.4 DOHC, every shift point was within 200-300rpm, all right around 6500.

Kohburn · Post by **Kohburn** » Tue May 06, 2008 2:32 pm

Aaron wrote: You're right of course. But looking at the area under the curve is exactly what I said to do, figure out your rpm drop, and find the point after the peak where it will equal the point before the peak with that drop., This maximizes the area under the curve.

i don't think you read what i said. the point after the peak will only equal the point before the peak if you lose enough HP in the end to drop it that far.

if your hp does not drop enough to do that then you shift at redline.

Aaron · Post by **Aaron** » Tue May 06, 2008 5:02 pm

Ok now I understand. If that's the case, then you need to raise the redline! Only if the engine can handle it of course...

Atilla the Fun · Post by **Atilla the Fun** » Wed May 07, 2008 7:22 pm

Aren't we all now just saying what 3 of us knew, in various terminology? At any rate, I know my '84 Trans Am's original 5-speed gad progressively closer ratios, while my Fiero is much less like that.

Kohburn · Post by **Kohburn** » Thu May 08, 2008 7:40 am

Atilla the Fun wrote:Aren't we all now just saying what 3 of us knew, in various terminology? At any rate, I know my '84 Trans Am's original 5-speed gad progressively closer ratios, while my Fiero is much less like that.

yeah the RWD transmissions have always had better ratios available.

cactus bastard · Post by **cactus bastard** » Sat May 10, 2008 12:26 am

Atilla the Fun wrote:I'm seriously thinking a 5.3 with an aluminum flywheel might not kill my trans. ... 270 torque

Just don't drive like an idiot.
People at that level of torque are not blowing trannies while smoothly accelerating, they are applying huge inertial loads instead. The aluminum flywheel will help you a lot.

Series8217 wrote: DI Ecotec turbo powerband:

Holy shit; that thing is amazing! (haha, electric)

Atilla the Fun · Post by **Atilla the Fun** » Sat May 10, 2008 12:18 pm

I cashed in a certificate of deposit that just matured wednesday, and Thursday I bought a 5.3! Dad is home from the hospital, too! My 5.3 came with everything, as my pictures this week will show. It's from a 2001 Silverado, with 112k miles, for $500.
I know Aaron thinks wiring this will be worse than a DOHC 3.4 that I couldn't find, But I will use the Painless harness, as it requires just 7 connections to the car: 1)check engine light (2) tachometer (3) ground (4) constant hot (5) ignition hot (6) cooling fan relay (7) fuel pump relay.
At first I will use my Muncie.