Z's r Best

We picked up a used 83 Z with the HO 305 and 700R4 auto for a good price. The first time I drove it hard I noticed the engine hit 7500 rpm before the thing changed gears. Of course I tried to adjust the throttle valve cable by the book, but it didn't make any difference. Of course, if you drive it normal it shifts at a lower engine rpm (about 4000), but where's the fun in that. By the way, the engine never misses a beat, not stutter, not flutter, no valve noise. I'd be afraid to wind my 81 Z's 350 up to that rpm. Any idea's why the shift point is so high?

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Z's r Best

Willie

iTrader: (1)

Personally, I believe your tach is in error. No hydraulic lifter engine can rev that high -- valve float will occur around 6,500 rpm.

Check your tach accuracy by cruising at a steady speed in the final drive gear (i.e. "D" for an auto, 4th gear in a manual). Try 30 mph for example. Please let us know what your speed, what the tach reads AND your rear axle ratio. From there, I can calculate what your rpm's are.

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Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
12.57 @ 111 mph.
12.04 @ 114 mph (50-hp nitrous).
http://members.optushome.com/au/downunder1/rides/willie/willie.html

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

My custom front marker lamp assemblies:
http://members.optushome.com/au/downunder1/misc/lens.html

Dan87IROC-Z

Yea, I have to agree, no way is that thing revving to 7500 RPM and the engine is still in one piece.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End

Current Mods: Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Coil, Cap, Rotor, 8.8mm Wires, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET : 14.32 @ 97.7mph
(corrected for elevation)

Next on the list: LT4 HOT Cam

Z's r Best

I'll have to check the rear end. I've been wanting to do that anyway. All the electrical/computer stuff works okay (at least the check engine light only comes on when their is a problem (O2 sensor went bad or if you run it hard when its cold and the engine ain't real warm yet-rich fuel mixture). It should have a 3.73 in it but the sucker only gets 11 to 12 mpg so beteen the rpm (2600 at 55 in OD) and the poor gas mileage I figured someone had changed it to a lower gear. I'll get back with you after I check the rear end. Thanks

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Z's r Best

Grim Reaper

Definitely your tach is off (or something is not right). At 60 mph, you would only turn 2,150 rpm with 3.73s and a 700R4 in OD.

Also, have your speedo checked out...it too might be inaccurate.

As for your tranny, your TV Cable may be out of adjustment and be shifting late...you could have a variety of problems all happening simultaneously.

JakeJr

I had the same problem with my 86 Vette's tach. The 1/2 shift occurred at an indicated 6800 RPM, but I KNOW the engine was no where near that speed.

My digital tach was having a nervous breakdown.

I've never tried changing the TV cable setting to make the trans shift sooner or later.

Which way does what? Does extending it make the trans shift sooner or later? How effective is using a setting other than stock?

Thanks,

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

CamaroMike

Hey, Willie. I used to shift my buddys 350 Malibu with the ENTIRE Edelbrock RPM package at 7000 RPM with a two bolt block, cast iron crank and stock rods and yes the cam was HYDRAULIC.

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84 Camaro ZZ4 with HOT cam. 1.88 60' (12.98 @ 105MPH E.T.)
Other Mods: You name it and I have probably changed it.

91 Firebird 5.0L TBI

ASE Certified Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

84FTA

Did stock tachs even ever go up to 7500? I thought l98 7000 rpms was tops. Anyway, it's probably off as most tachs are. I've taken out three tachs and each one had obvious overheating on one resistor where it actually burned in board under it.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration
13.98 @ 101

Willie

iTrader: (1)

Mike,

It is general concensus that all hydraulic cammed small block Chevy's encounter valve float at ~6,500 rpm (give or take).... this is the generally accepted figure.... but no two engines are exactly alike.

Willie

CamaroMike

I know but I just had to Razz ya.

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84 Camaro ZZ4 with HOT cam. 1.88 60' (12.98 @ 105MPH E.T.)
Other Mods: You name it and I have probably changed it.

91 Firebird 5.0L TBI

ASE Certified Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

Z's r Best

A questions about the tachs with burned components: Were they off at all rpms? Off at idle speed, off cruising, etc., or did they reach a point where they flipped out?
This one shows low rpms at idle (about 700 rpm in gear)and appears to wind up very quickly when you get your foot into the carb. Did the damage you saw cause incorrect readings all the time?

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Z's r Best