camaro8811

my car (305 tbi with 700r4) when at WOT shifts at about 4500-5000 rpm. this seems way too high and is right around the redline of the tach. my dad thinks it could blow the motor. is this bad? if it is what can i do to lower the shift point?

rjt76

your fine dont worry about it.

chupalupa

ya my 700(with 100 or so miles on it) shifts right at 5k, want it to shift sooner so as not to blow the motor? give it less pedal :P

sofakingdom

iTrader: (1)

Or, fix the "tach", so it's not broke any more and doesn't read so high.

Batass

lol. I have a 6k rev pill in my msd, still stock tach. Says I hit 7k very often.

Good for nothin tach.

camaro8811

who said the tach was broke? yeah i said tach.

Batass

theyre broke from the factory aka not accurate

sofakingdom

iTrader: (1)

Right; that wavy pointer thing in your dash, that moves up and down along with engine RPM, is not an "instrument"; it's a "trim package". It isn't really a tach, it only sort of resembles one, and is intended to convey a sense of "sporty image" to the car's original purchaser. The ones in these cars VIRTUALLY ALWAYS go bad, and the way they go bad, is by reading high, by some multiplicative factor. Out of the ones I have, there's one that reads ALMOST TWICE the actual RPM; and others here have reported ones that read 3 times actual (reads 6000 when doing 2000 )

Therefore, if you're seeing what seems to be real high "readings" on the "tach", the first thing you need to do, before getting all worked up about whatever the thing that a high "reading" might mean (shift points, idle speed, converter stall, gear ratio, etc. etc. etc.), is to verify the inaccuracy of the "tach", using a tach.

camaro8811

so your saying get an aftermarket tach. the only thing is that the idle is right where it should be. but i'm guessing that when you said it was multiplicative (i think that was the word) the higher the rpm the farther away it gets from actuality.

sofakingdom

iTrader: (1)

No, I didn't really say that. Although that certainly is one way to deal with it. OTOH, it's not like having a tach is of any particular benefit in a TBI/auto car anyway; in that application, it's STRICLTY an "image" thing. Just there for looks.

What I said was, check your stock "tach shaped object" against a REAL tach of known accuracy such as a tune-up analyzer or even the car's own ECM data stream. The ECM is usually within a percent or 2..... FAR more accurate than the trim package.

Yes the error is multiplicative, as opposed to additive. Meaning, the tach isn't "800 RPM" off, or something like that. Rather, it reads 1.2, or 1.45, or 1.8, or however many, times reality. So if it's, let's say, 33% off (1.33), then it will read 33% higher than actual at any RPM: 800 at 600 actual (200 RPM off), 2400 at 1800 actual (600 RPM off), 4000 at 3000 actual (1000 RPM off), etc.

25thannivZ28

I wouldn't worry about "Blowing the motor up" at all. I've got the stock block & crank with factory dished pistons & I've already pinned my Tach to 7k countless amount of times over the past year. Though, i have a different top end than what you have and a 350 vs your 305, but still. First time I did it i was floored and worried that I was gonna break something & thought i'd never do it again. Second time I was a bit more comfortable and then the third time it was just awesome!! Now its like a daily thing. ha, but knock on wood.

Silver87

Wow! I didn't realize that our tachs were that bad. I like the 'trim package' joke. It reminds me of what Ford does or still may do with their oil pressure gauge. Found it out on my 93 F150 XLT fully loaded with everything. It had the nice instrument cluster with gauges instead of just idiot lights. Problem was the oil sending unit was only a pressure switch wired in with a resistor somewhere in the line. Crank it up and as soon as oil pressure gets up above like 9psi, the gauge goes to 3/4 way. When you come to a stop, the oil pressure gauge doesn't drop to half way like our Chevys do. Makes you think your Ford is much better than a Chevy until you find out the truth about the oil pressure gauge. Now that's bad!