Extended high RPM

[another69]

I recently swapped gears in my car, and without overdrive the highway cruising is almost unbearable- the motor spins at 3000 RPM @ 60 MPH. I'm wondering if constant 3000 - 4000 RPM with my motor is ok until I get an OD? (3.50 rear gear)

Here are the basic specs:

GM 400 block (now 406) 2 bolt mains, Scat 9000 series cast crank/forged rods, speedpro hyper flattops, hyd. flat tappet 240/246 @ .050 cam, etc- shortblock built by a reputable shop.

Typical 350 trans w/ shiftkit, Denny's 1350 driveshaft, Strange 9"

Oil pressure, temp, etc are fine. I know that about 6000 RPM is max with my budget shortblock, but I'm wondering how close I can be to that on a constant basis.

[funbnme]

I'm in the same boat with a similar sounding engine. I'm not worried about the RPMs. The noise bothers me on longer drives. I keep thinking "I need just one more gear". I may drop down to 3.55's in mine..I think I have 3.73's or 4.10's even.

[Fuelie Fan]

That's a lot of cam for the way you plan to use it, isn't it?

[another69]

Yeah- one more gear would be perfect. My 17" tires measure 24.5" diameter, so that doesn't help much either. I had a 2.70ish gear before which was perfect for the highway but bogged the motor on the street. It's not so much the noise that bothers me on long drives, I just don't know how long my 3.75" stroke motor will survive at a constant high rpm. I keep envisioning a connecting rod poking through th oil pan.

As for the cam being too big- probably. My next cam will be a roller with less duration and more lift. I have pretty good heads,etc on the motor and it's what Comp recommended. The motors very responsive, even down low- my only complaint is the rough idle. It gets old after a while.

[yellow heap]

your motor will just wear out a bit faster
if your worried about tossin a rod at 4000 you have other problems.
what are you gonna get for a tranny?
Comp cam has been specing some big cams lately,overstock?
if you trust the engine build don't worry.
A tko600 would work great with a 3.50 gear.

[mongoose]

it's fine...... worst thing about it is the noise......

but if all your gauges check out fine... there's nothing wrong

[Rick Dorion]

With a M-22 and 3.55's I too turn 3000 rpm at 60 mph. At 2-3K miles a year, the engine will outlast me

[another69]

TKO 600 is exactly what I have in mind. I'll probably get one of those "all in one" kits from keisler or classic. I'm tempted to get a 700R4 or 2004R from TCI, though. Half the price and quicker shifts, still - I want a stick.
The motor is still being broken in, I guess- It only has 2000 miles on it (same with the trans), and the rear has less than 300. I hope the higher RPMs don't hurt break in, it seems the cam would just get more lube- I dunno

[mongoose]

break in?... should be done by now i'd hope....

rings should seat after 20 mins.. and cam break in.. then beat on it like to tomorrow.......

[MrClean]

i think extended high rpm is ok if you can keep the oil in you pan . i cleaned up the oil return holes on my block . 355 sbc 4 speed 3.73 gears. and a windage tray .

[deuce_454]

a reasonably ballanced SBC will run 4500 rpm forever as long as it has oil.. if it couldnt it wouldnt be much good to mercruicer... it isnt mid rpms that break rods, its suddently having to stop a piston traveling upwards at 7000 rpm if there is a miss.. then there is no pressure stopping the plug and the rod can get pulled appart..

but 3000-4000 ... rpm, dont sweat it at all....

[another69]

Thanks, guys. That makes sense about boats, didn't even think of that. As for the oiling, I have plenty of pressure with the "stock" pump, and I have a windage screen, scraper, and even a little trap door.

[ITLBTU]

Get the overdrive too! I have a mildy built 400SB with 3.08 plus the overdrive... I can do 65 at 1600RPM. The 400 has enough power to run like a raped ape even with those gears.