I recently purchased a C20 350cu t-400 tranny 4.10 rear axle ratio. It has 4.10 rear axle ratio,the engine was rebuilt (bored 30 over) 12000mi ago. My concern is,how much extra wear and tear are the 4.10s going to cause on the engine as the truck is driven quite a bit on the freeway (65+mph)? At those speeds,the engine sounds like it is really revving. It is a 1985 model Any help would be appreciated Jeff
your engine can handle it,but you will be lucky to get 12-14 m.p.g. at most depending on your driving style...(that is a generous estimation mind you) you are most likely turning around 4500+ rpm I would imagine.. the redline for your engine in stock form should be around 5500-6000 depending on if you have hydrolic lifters (valves start to float around 5500 )or solid lifters get a little more rpm.. eugene my 76 blazer runs 3500 rpm at 65 mph with 3:73 gears.. just changed out to 3:08 now I turning around 2000 at 65 m.p.h eugene
>I recently purchased a C20 350cu t-400 tranny 4.10 rear axle >ratio. >It has 4.10 rear axle ratio,the engine was rebuilt (bored 30 >over) 12000mi ago. >My concern is,how much extra wear and tear are the 4.10s >going to cause on the engine as the truck is driven quite a >bit on the freeway (65+mph)? >At those speeds,the engine sounds like it is really revving. > >It is a 1985 model > >Any help would be appreciated >Jeff HELLO JEFF, YEP THAT 350 IS REALLY SPINNING AT 65 MPH WITH THOSE GEARS. HERE'S A MATH FORMULA TO HELP YOU FIGURE OUT EXACTLY WHAT RPM YOUR MOUSE IS RUNNING AT WHATEVER MPH YOU ARE GOING rpm = (mph x gear ratio x 336) / tire daimeter USING THIS FORMULA, WHITH MY 72 CHEYENNE I AM DOING 2900 OR SO AT 65. THATS WITH 373'S AND 28" TALL TIRES. USING YOUR INFO AND A 28" TALL TIRE, THE RPM IS AROUND 3100 AT 65. I'M GUESSING YOU ARE RUNNING A TALLER TIRE THAN ME SO YOUR RPM'S ARE LESS THAN 3100. STILL BUZZING AND NOT TOO GOOD FOR MPG. THE BASIC FACT IS THAT RPM'S ARE WHAT WEAR OUT AN ENGINE. THE HIGHER THE RPM, THE MORE WEAR AND THE WEAR INCREASES WITH THE ENGINE SUSTAINING THE HIGH RPM FOR LONG PERIODS OF TIME. IF YOUR 350 WAS ASSEMBLED USING GOOD PARTS AND THE OIL PRESSURE AND TEMP STAY GOOD YOU SHOULD HAVE NOTHING TO WORRY ABOUT. A STOCK SMALL BLOCK CAN HANDLE THOSE RPMS EASILY. STOCK 350'S STOP MAKING POWER AT 4200 ANYWAY, ESPECIALLY IF USING A STOCK INTAKE/CAM BECAUSE THAT IS WHERE THEY STOP FLOWING AIR/FUEL EFFICIANTLY. HOPE THIS HELPS, BRANT
I have a 79 C20 with 3.73 and factory tach. I run 3000 at 65mph and 3500 a little shy of 80mph, 4000 at about 90. I have put the tach to the peg (5000) at over 100mph (do not know how fast, just past the century mark) . It sounds like a banshee past 65-70mph because that is when the secondaries on the carb kick in full time and gas milage goes to about 9, below 65 I have seen 10-14. It does not kick into passing gear past 50-60mph and has unreal interstate passing power. Since you have 4.10 gears and the same size tires (245 75 16) you might be turning 3400-3700 at 65 with the TH400. This is not bad, just not practical unless you can afford the gas. The Chevy 350 is a tough engine. Mine is original with 128K and 25 years of age, drives the interstate 60+ miles on a regular basis, no problems, just it only goes 180-240 miles per tank max. Look on the web and find a tire size/engine calculator. It will tell you all you need to know. Keep that classic going Jeff. You take care of it, it will take care of you. 79 C20 Bonanza 350/400 4bbl Q-Jet 3.73 14-Bolt Corp.
Thanks for answering! I should have mentioned the tire size 265/75/16. As you mention,the passing power is unbelievable! The truck has very little rust,but I intend to repair the small spots. Jeff
