At 60mph, engine rpm's are at 4000. At least that's what the stock tach reads. What is the chance this number of 4000rpm is off due to a 700r4 to th350 and 305 to 383 swap?

 

welcome to thirdgen.org, i'd say the chance your RPMs are off due to a trans or engine swap are zero. they may be off because the tach is wrong or out of calibration, factory tachs aren't known for great accuracey.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

Thank you, looks like a great source of information.

Is 4000rpm bad for 60mph? (2.73 rear)

 

I've got a 700r4 with 2.73's and a 305tbi, and at 2000rpm's I'm around 70-mph, so, I'm pretty sure something's off with your tach.

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89 iroc-z 305 tbi
k&n filtercharger, open element air filter. nuffin' else

 

Well you have a th350 in there, but the last gear I think is a 1:1 ratio so if you put it in the calculator thing it comes out that you are going slightly over 100 mph. have you ever wondered why people seem to be going really slow on the highways

 

I would try getting an aftermarket tach. The stock tachs were never accurate anyways, but you definately want to know what rpms you're running. The height of the rear tires will affect your gearing as well. But I wouldn't think by that much.

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"Putting any amount of money into a RICE BURNER is like wiping your a$$ with a turd. "
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

 

I'll have to try that after market tach. I hate incorrect information from guages. I have had my wife drive next to me at the same speed in her car and I am actually going 60mph @ 4000rpm. Anyone know a good user friendly brand? Thanks.

 

I would say way off!As long as its a v8 the calibration is the same (incorrect or not) I have a tb350 behind my 350 and 75 is still 2800 rpm, well it was when I had the 2:73's in it . From 305 to 350 with tb350& 2:73's 2800 rpm, stock 14 wheels.
I would say you tach is screwdup. 4:11's wouldent even be 4k @60 mph.
SSC

Edit: sunpro= cheap & reliable.
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85 Camaro, 355/400 "drag car" current DD 13.1@ 101mph on its last season run.
Plans: Possibly add N20 for next season.
82 Firebird, 355/350, as soon as the powertrax gets installed. "dyno time"

[This message has been edited by SSC (edited November 22, 2001).]

 

I really like the tach I have. My Dad bought it from Autozone for $120 but summit sells it for $100. He bought it thinking it had a rev limiter on it, but it doesn't. And are you sure you have 2:73s, maybe a previous owner swapped gears. I would recheck just to be certain.

------------------
"Putting any amount of money into a RICE BURNER is like wiping your a$$ with a turd. "
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

 

I had 3.23 stock and at 70mph my tach read
2200. I now have 4.10 and my rpm at 70 is
now 2650, mybe this will give you an
idea of how off your tach really is..

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86 T/A L98 with T-5(orig an LG4)
Hooker headers
Performer RPM intake
holley 750cfm carb
cast iron 76cc heads with
2.02-1.60 valves
B&M ripper
Richmond 4.10's
Flowmaster
9.43@74mph 1/8 mile.

 

Not really, he has a T-350 tranny, no OD.

 

well it's still pretty off though..
cuz if he has the gear ratio he was
saying.. thats a road gear bigtime..
even with the th350 he should be
running low rpm's at 70mph with the
rearend ratio.
4000 rpms @ 70mph, haha that would
be more like if he had a 411 rearend.

 

Thanks a bunch for the feedback. Although my tach is wrong, it's good to know my engine isn't working it's a$$ off at highway speeds.

 

Are you talking just regular drive gear, or OD?

 

I used to run at about 3000 rpm at 65 with the 2.73 gears and 200c trans. That was without the lockup turned on.

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'82 Z28
LG4 305 .030 over, performer intake, holley street avenger 670, xe 256 cam, tes headers, 3 inch single exhaust, spintech muffler, 14 x 3 inch drop base k&n.