[Cobrascort]

With the rx7 maf, you get an extra 5hp above 6000rpm, some of the guys with this mod are shifting at like 7200rpm and that doesn´t make any sense. I shift at 5900-6000rpm because that is where you peak in horse power. If there is a explanation for this I would love to know.

 

[James92Scort]

Well, one explanation is that 2nd Gen EGTs max horsepower occurs at 6500 rpm. Does that help?

Red 92 EGT

 

[Cobrascort]

realy? I thought it was at 6000rpm, well if that is so I will have to try testing that out, cause I don´t really feel any power after 6000rpm

 

[Pimp_scort_89_GT]

Geez 6k RPM??? I barely ever rev over 5500 anything more than that seems usless, because the engine only pulls until about 5000-5500. after reding this I tried to take my engine to 6k, but there was just no power up that high, and it sounded hella nasty. My Mustang on the other hand gets shifted at about 65-6800 RPM on the track, and it pulls all the way there. I rarely go over 3k when on the road though. It just doesn´t need that much pedal to get up and go. The scort on the other hand almost always makes it up to atleast 4k before I shift, 5500 if I´m really getting on it.

 

[Cobrascort]

I think your car doesn´t pull at all above 5500rpm because you have the Ford 1.9L HO and I have the Mazda 1.8L DOHC motor which doesn´t create hp until the upper to high rpms

 

[Pimp_scort_89_GT]

Ahhh yes, that is right, you own a Mazda. I forgot about that.

 

[MXTurbo]

Another thing to consider is the optimum shift point is where the horsepower is closest before and after the shift. Lets say at 6000 RPM´s you have 120hp, you shift and the RPMs go to 5000 with horsepower of 100. With the stock VAF (its not a mass air sensor) there is no hp made above 6k. So lets say you shift at 6800 with hp at 120, rpms fall to 5800 horsepower at 110. This is all hypothetical of course but it is the correct theory. In a car like the EGT with the 1.8 BP the best shift point is at or near redline since that is where the horsepower peak is at. In a different motor the best shift point may be a while before redline, since the motor does not make peak horsepower at higher rpms. With the RX-7 airmeter the shift point should be at redline for maximuim performance.
the horsepower peak is not the best shift point, it is usually after the peak, but with the RX-7 meter the redline is just about where peak hp is made so you have to shift there.
_________________
´89 Mazda MX-6, 356 wtq
´93 EGT, 55 shot N2O

[ Edited by MXTurbo On Date 09-27-2002 ]

 

[Dustin]

If you want to get right down to it. Ideally you shift at peak horsepower and the rpm drops to peak tourqe. The span between peak tourqe and peak horsepower is refered to as your powerband. That is a perfect shift. Now however on the 2nd gen. egt´s if you shift out of first gear at 6500 rpm you are gonna drop way below peak tourqe. And as most 2nd gen egt drivers know. They loose power quick below 4000 rpm. So you have to shift at a higher rpm to keep yourself on the powerband. On most (not all) engines it is faster to go over the powerband than under, do to the fact that it looses power slower over 6500 than it does under 4000. You just have to find out where your optimum shift points are, based on how your car is geared.
For those that are confused by the concepts of hp and tourqe, there is a great article that blade summited on this site. I really recomend that you read it.

_________________
A car is only as fast as the driver allows it to be!

[ Edited by Dustin On Date 09-28-2002 ]

 

[MXTurbo]

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%>[TR][TD]Quote:

[/TD][/TR][TR][TD]

On 2002-09-28 03:05, Dustin wrote:
If you want to get right down to it. Ideally you shift at peak horsepower

[/TD][/TR][TR][TD]

[/TD][/TR][/TABLE]
No, that is incorrect:Lingenfelter Performance Engineering, Inc.

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LPE Drag Racing Tech Tips:
BFG #6 Proper Shift Points

As previously promised, we will try to explain proper shift points. Whether you drive an automatic or a manual transmission equipped vehicle, shift points are an important factor in obtaining the best performance at the drag strip. Even in an automatic equipped vehicle, you can have varying amounts of control over shift points. Many automatic transmissions will allow you to manually shift the transmission.

To determine proper shift point, it is important to know the gear ratios of the transmission and the power curve of your engine. Some owner´s manuals will provide the transmission gear ratios and may even have an engine dynamometer power curve of the engine. If possible, a chassis dynamometer test of the vehicle in each gear is the most helpful. Because the transmission ratios are rarely evenly spaced, your optimal shift points may not be the same for each gear change. Also, because shifting actually takes time and full power is not applied to the wheels during the shift, it can often be advantageous not to shift if the shift is going to occur just before the lights.

In choosing the proper shift point, you are trying to maximize the power delivered to the ground. In terms of the engine power curve, you are trying to maximize the area under the curve. As an example, in a stock 1995 manual transmission Camaro Z28 you have the following:

Ratio Shift RPM @ MPH Drop to RPM
1st gear = 2.66 5500 45.6 3680 25.60 = tire diameter (in)
2nd gear = 1.78 5500 68.2 4017 3.45 = Rear ratio
3rd gear = 1.30 5500 93.4 4231
4th gear = 1.00 5500 121.4 4070
5th gear = 0.74 5500 164.1 3716
6th gear = 0.50 NA NA NA

As you can see, despite the 5600 rpm shift point in each gear, the different gear spreads result in different rpms that the engine drops to when shifted into the next gear. This engine makes its peak horsepower of roughly 255 hp (at the rear wheels) at 4900 rpm. At 5500 rpm the engine is still producing 247 horsepower at the rear wheels. The engine also makes 247 horsepower at and above 4500 rpm. At 3700 rpm the engine is only producing 215 hp so if you shifted at 5800 rpm out of first instead, you would drop to 3880 rpm and the engine would be producing 225 hp at that rpm. If you had an engine that lost power more quickly after it reached its peak it might not be advantageous to shift so far past the power peak.

When determining proper shift points it is also important to consider the safe operating speeds for your engine. Consult your owners manual or your engine builder when selecting shift points. Shifting after the redline or past the safe operating speed of the engine can result in premature engine wear or damage.

 

[James92Scort]

Dustin: If you shift at 6500 rpm you´re only going to drop to 5000 rpm which is slightly above peak torque ratings ([email protected] rpm) in the 2nd gen EGTs (well, at least in mine). Also, to point out something i´ve noticed when driving... when you shift between first and second gear you drop roughly 1500 rpms, between 2nd to 3rd you drop 1000 rpms, and between 3rd to 4th you drop just under 1000 rpms.

Red 92 EGT

 

[Scortadict]

so what will be the shift point on a n/a EGT and on a n/a EGT with RX-7 vaf??

i shifted mine at 7000 each gear on the drag strip last month and i did a good time for a n/a EGT.

 

[FourDiceS]

scortadict: Did you get those clearlights from a tracer?? if so, could you please tell me from wich model. Thanks

 

[Scortadict]

i buy this clear corner at http://www.zx2racing.com/store/

 

[TheBlade]

This post is WAY late, but with all the stuff I´ve read, 1.8L EGTs are at peak torque at 4500rpms and horsepower at 5400 rpms. I usually shift at 6200 because it leave the car running beefy after the shift.

 

[MXTurbo]

actually, the BP´s peak horsepower comes at 6500rpms