wont go past 4k RPMs?

[zonacats]

I finally got around to putting a tachometer in my blazer and I've been testing it out today. Everything seems to be working fine but I have a question about RPMs/shift points. The truck runs great (new crate 350 with new edlebrok 600cfm with about 4k on it so far) and the tranny was rebuilt about 10k ago. Now that I can actually see my RPMs I've noticed it never goes above 4,000 in any gear, even at wide open throttle. I know this isn't gona be an 8k RPM race car but I feel like there should be an extra 1k up there and I'm missing out on some top end power. So my first question is, is that normal for an average gen 1 350 + 700R4? Or should it be going up to say 5k under full throttle?

Some additional info that may effect this.... I got 4" lift with 35's. Truck has 3.73's....

 

[kennyw]

With OD, 3.73 gears, and 35" tires, you should be near 195 mph by the time you get up to 5k rpm.

 

[zonacats]

Well, im not wanting, (or trying) to hit 5k in OD and cruse down the highway... Maybe I wasnt clear but lets say im at a dead stop and give it full throttle... It will shift into second at about 4100, then if I stay on it it will shift into third at like 4000, etc. I have always just assumed I was getting at or close to 5,000 at each shift before I installed the tach. Maybe the lift/tires are holding me back, but I don't think so. The thing runs great through all gears and doesn't seem like its falling flat before the shifts. Which leads me to think I should have some more RPM and power that im missing out on...

 

[ryoken]

it really depends on what yr mill, mileage, etc..... huge dif in cams, heads, etc thru the yr's, and that's the stuff that affects rpm's.. if everything is working correctly..

heck, be glad you don't run TBI, they hit 4 g's and it's like running into Kim Kardashian's arse.... sb and bb..... Mutt couldn't spin 5 g's if you rolled it down Mt Everest...

 

[wage92]

If it is shifting before you get to your desired rpm, that has to do with your trans. You can put a shift kit in it that will alter your shift points, if you feel you want to rev higher. I put a shift kit in my th400 and one of the features it has was that it will hold any gear if you are full throttle and it will also downshift to any gear.

Just a thought, they are not hard to install but if you have never had an automatic trans apart you might want to find a buddy that has.

 

[ryoken]

very true.. I was talking manual... just run it in second gear physically and see if it'll rev higher...

 

[Greg72]

My old BBC fell flat at around 4K....

I ended up selling it before I ever figured it out, but my theory was either a bad mechanical fuel pump, or undersized/clogged fuel lines.

I don't think it's fair to assume that a 40+ year old fuel system is going to be in perfect condition anymore..... The lines could be all gummed-up, clogged or just not up to the task of feeding a much larger, thirstier engine.

It might make sense to connect a fuel pressure gauge near the carb somewhere you can read it while driving, and see what kind of fuel pressure you have as the revs climb up toward 4K.... You may be surprised to find that there's no more fuel available.

Next time around (aka: this time) I'm going to design a fuel system from scratch....with correctly sized lines, pumps, fittings, etc. There's no way I'm going to ask a factory fuel system to feed a big-displacement BBC.

 

[Stomis]

heck, be glad you don't run TBI, they hit 4 g's and it's like running into Kim Kardashian's arse.... sb and bb..... Mutt couldn't spin 5 g's if you rolled it down Mt Everest...

I can vouch for that, like hitting a ****ing brick wall.






Adjust the TV cable properly?

 

[zonacats]

it really depends on what yr mill, mileage, etc..... huge dif in cams, heads, etc thru the yr's, and that's the stuff that affects rpm's.. if everything is working correctly..

heck, be glad you don't run TBI, they hit 4 g's and it's like running into Kim Kardashian's arse.... sb and bb..... Mutt couldn't spin 5 g's if you rolled it down Mt Everest...

Its this exact engine, bone stock, with brand new everything (intake, carb, distributor, etc.)

http://www.summitracing.com/parts/nal-10067353/overview/make/chevrolet

Its really got no trouble getting up to speed and going through the gears. Im pretty happy with it for my needs. Just dont want to leave something on the table (power wise) if its there and im just not using it.

 

[kennyw]

You have a truck, not much use for engine RPMs above 3000 for most applications. Racing is about the only reason to go into 4000-5000 range.

 

[Stomis]

You have a truck, not much use for engine RPMs above 3000 for most applications. Racing is about the only reason to go into 4000-5000 range.

Maybe on the street, well not even. What about long climbing grades? Wheel speed for loose stuff like sand and mud? Hill climbs where you have a short distance to run at something?

4500-5500rpm is a normal redline for a gas truck IMO

 

[diesel4me]

Maybe the throttle isn't opening all the way when he floors it?...floor mat too thick,cable too slack,etc?..choke not opening fully,or closing at high revs some?..could be restricted exhaust,catalitic converter might be blocking up perhaps?..

I had a truck I bought once--on my way home I could barely get it over 45 mph...kept bogging down,I thought the fuel pump was dying,started getting nervous!--pulled over to see if the choke was closing,and when I took the lid off the air cleaner,a mouse came out of it,and all around the air filter was packed full of jute padding from the floor and some cheese-it crackers!....I dumped it out in the bed,put it back on,and drove home with 100 more HP !..

 

[kennyw]

Maybe on the street, well not even. What about long climbing grades? Wheel speed for loose stuff like sand and mud? Hill climbs where you have a short distance to run at something?

4500-5500rpm is a normal redline for a gas truck IMO

That is a normal redline for a gas motor, but not something I would expect even a dune truck to use regularly. Then again, I buy trucks to haul big loads since I grew up on a farm.

 

[diesel4me]

Good thing he doesn't have a 6.2,he'd run out of revs at 3600 rpms...just like a Briggs & Stratton!.....weird thing is ,if I let mine hit the govenor,it sounds more like 5000 rpms,even though its not...

 

[n4xplay]

New motor after a trans rebuild... your trans vacuum modulator could need adjusting, that will change your RPM shift point.

 

[pblaze725]

That Edelbrock has a rod on the side that can be adjusted if the secondary isn't opening all the way.
Make sure when you pull the throttle cable that bad boy is fully wide open throttle.

I had to adjust mine.

 

[Blue85]

First of all, check the TV cable setting. There are several threads here about how to do it. If it was too loose your upshifts would be low. Worse yet, the trans would get abused and fail. 2nd - verify the tach. Maybe it's wrong.

Are you running out of power or does it still pull hard when the shift happens? If it's out of steam, check all the stuff mentioned above - fuel filter, plugged cat, etc.

Now the truck 700s often came with low shift points for reasons stated above. But it's easy to change just by modifying or swapping the governor (of course you would make sure everything else is OK with the vehicle first). This comes out easily without even dropping the pan. You can grind away on the weights - the more you remove, the higher your shift points will be. If you can get a governor from a Camaro/Firebird/Corvette 700, you will see they have no weights added to them, so it's not a sensitive adjustment. I run a Camaro governor in my truck tranny and i have to lift my foot from WOT to get 2nd gear. The 1-2 is at like 5500 - above my rev limiter. The 2-3 shift happens at least a few hundred rpm lower (as you noted).

Shift kits adjust the shift firmness/characteristics, but usually don't change the shift points.

 

[zonacats]

Ok, thanks for the suggestions. I will look into some of this tonight. It feels like it pulls strong all the way up to the shift point.