RPM Question - Team Camaro Tech
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post #1 of 23 (permalink) Old Jan 21st, 08, 03:26 PM Thread Starter
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RPM Question

Just got my '68 on the road this week after two years in the garage. I'm running a 350 4-speed (rebuilt Saginaw trans) with a 4 bbl and electric choke. The rear is the original 10-bolt 2.73. After warming up, the idle settles in at around 1,000 RMP. But at 55-60 MPH the tach is clocking 2,700 and it feels like I need a fifth gear. Maybe this is normal for the set-up I have but it just feels tight. I was told the engine is out of a '93 Chevy pick-up and has 37,000 miles on it.

Any thoughts?
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post #2 of 23 (permalink) Old Jan 21st, 08, 03:33 PM
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Re: RPM Question

Taching 2700 at 55-60 sounds about right to me with 2.73, but the 1K idle rpm is too high for a 4spd. I have a 350 (with 5spd), 750cfm carb, mild cam, and my idle is good at 600-650.

Have you tried to adjust the idle down?

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post #3 of 23 (permalink) Old Jan 21st, 08, 04:10 PM
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Re: RPM Question

Quote:
Originally Posted by dbx1969 View Post
Taching 2700 at 55-60 sounds about right to me with 2.73,
If you had a 20" tall rear tire. With a 25" tire you should be running about 73 mph at 2700 rpm.
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post #4 of 23 (permalink) Old Jan 21st, 08, 04:32 PM
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Re: RPM Question

man would I love to run 2,700 at 55-60!!!!


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post #5 of 23 (permalink) Old Jan 21st, 08, 04:35 PM
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Re: RPM Question

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Originally Posted by onovakind67 View Post
If you had a 20" tall rear tire. With a 25" tire you should be running about 73 mph at 2700 rpm.
Yes, you're right. I should have used the on-line calculator. By memory, it seemed right thinking back to the Saginaw I had before the TKO swap.

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post #6 of 23 (permalink) Old Jan 21st, 08, 05:20 PM Thread Starter
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Re: RPM Question

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Originally Posted by dbx1969 View Post
Taching 2700 at 55-60 sounds about right to me with 2.73, but the 1K idle rpm is too high for a 4spd. I have a 350 (with 5spd), 750cfm carb, mild cam, and my idle is good at 600-650.

Have you tried to adjust the idle down?
Not yet, but that's the first thing I'll try this weekend. It's been 16 years since I owned my last '68 and I may just not be used to the feel of a muscle car. It just seemed really tight. My father thought maybe the choke was sticking or not set up right. Just looking for ideas to hunt for.
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post #7 of 23 (permalink) Old Jan 21st, 08, 05:43 PM
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Re: RPM Question

We gotta know what your definition is for 'really tight'.

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post #8 of 23 (permalink) Old Jan 21st, 08, 05:49 PM Thread Starter
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Re: RPM Question

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Originally Posted by Fred Ficarra View Post
We gotta know what your definition is for 'really tight'.
2700 RPM at 55 MPH and a slight bit of whining that leaves me feeling like I need to shift one more gear. That's the best I can describe it. Like I said, it may be fine. I've only put 10 miles on the car. Just looking to see if anyone could suggest where to start looking first or if that sounded right.
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post #9 of 23 (permalink) Old Jan 21st, 08, 06:08 PM
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Re: RPM Question

55mph @ 2700 rpm in 4th gear with a 25.6" tire (ie, 225/60R15), you must have a 3.73 gear, not a 2.73. And/or your tach or speedo are reading incorrectly. Or you aren't in 4th gear. Or the clutch is slipping REALLY BAD.

Tip: most GPSes have a very accurate speedometer feature (on flat roads at least) to verify the speedometer reading.


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post #10 of 23 (permalink) Old Jan 21st, 08, 06:13 PM
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Re: RPM Question

4th gear is all the way over toward the pass seat and down!

Sorry, I'm in a good mood and just being funny!


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post #11 of 23 (permalink) Old Jan 21st, 08, 06:17 PM
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Re: RPM Question

Quote:
Originally Posted by dubs68camaro View Post
4th gear is all the way over toward the pass seat and down!

Sorry, I'm in a good mood and just being funny!
Unless you are using 3spd shift levers on a 4-speed saginaw... the only way to make it fit is to flip the 3-4 lever upside down which makes the pattern look like this:
1 4
2 3

My old 67 was like that when I got it...


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post #12 of 23 (permalink) Old Jan 21st, 08, 06:42 PM
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Re: RPM Question

LOL.....dang.....than maybe he does need to shift again!


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post #13 of 23 (permalink) Old Jan 21st, 08, 07:01 PM
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Re: RPM Question

Looook see if you taco meter have numero of cylinders selector sweeech señor

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post #14 of 23 (permalink) Old Jan 22nd, 08, 05:13 AM
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Re: RPM Question

One mile covered in 60 seconds = 60 mph. Yes, with a 2.73 gear, cruise rpm s/b around 2100-2300 rpm. OE size tire (check glovebox door for decal), correct speedo gear, and 3.73 gear = 3000 rpm.

Match with a following vehicle, or as suggested a GPS unit.

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post #15 of 23 (permalink) Old Jan 22nd, 08, 07:17 AM
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Re: RPM Question

My vote is for the speedo being off. What's the rear tire size, and do you know what color driven speedo gear you have in the Sag?

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