I am new to the Oldsmobile world and I have a question! what is a safe RPM limit for a Oldsmobile 400E block engine? I have read some where that they use to turn them 7000rpm but that seems pretty high to me! I have to much invested in my engine to just go out and blow it up!

 

Bill - I don't have a definitive answer for you on how high you can go with the RPMs, but I have a '67 400E with C heads and I've read that the 400E's are more durable at higher RPMs than other Oldsmobile BB's. The reasons I've read for the 400E's being more durable at higher RPMs are, the blocks are square ( essentially same bore/stroke), and their forged vs. cast cranks. I'm sure the experts will chime in and let me know if this is a bunch of BS.

 

thanks for answer! pretty sure I can twist 5800 to 6000 rpm but just wonder if 6500rpm would be safe?

 

Bill - I am an amateur mechanic at best, and certainly no motor expert. I've read several of your posts and know you're a car guy, so you know when you start pushing the RPM envelope there are a whole host of factors that come into play like has the entire rotating assembly been balanced, and the overall quality and precision of other internals like rods, pistons, heads, and valve train. I'm sure one of the experts will see this soon and comment. For when they do, you might want to post the entire configuration of your motor and drive line, and that would give whoever is commenting a better idea of what RPMs you can take your motor up to? Just a thought?

 

I agree with the above. The max safe RPM is dependent upon the quality of the parts and the machine work.

I have a ‘67 400 that I planned to build years ago and solicited advice. Many reported turning 6500 at the track with no issues. Light pistons and proper tolerances are critical. And then you need a camshaft that will actually make power at those RPM levels; otherwise there’s no reason to rev that high.

 

Bore to stroke ratio has absolutely nothing to do with how high you can spin anything. One of the dumbest things I’ve ever heard.
Overall valvetrain and rotating assembly will normally dictate max rpm. But if it quits making power before any given rpm, why spin it much past that anyway?
The internet can be a good place for info, OR it can be a bad place. Too often it’s bullshit that people just keep passing along.

 

Mark - Thanks for setting me straight on the stroke ratio business, I told the OP someone would. Just to provide further info, posts I have read regarding this topic, and I should have noted this earlier, said that the shorter stroke of the '66 and '67 400's vs. the '68's and 69's makes it easier to spin them up to higher RPM's quicker. Now logically this makes sense, but is it true in reality? And if true, if it spins up in RPM's quicker, is it putting out more hp earlier?

 

Two glaring limitations for revving a BBO are type of pistons and connecting rods. Factory rods are pretty soft and the big ends deform. I got a set of Scat rods from Rocket Racing and they are much better. As noted above, the valve train needs to be stable at rpm, and the cam should be making power up there.

 

what you are saying is that if my max HP was at 5800 shift to next gear?

 

The smaller bore on the 400G vs the 400E doesn’t help things,

 

Well, there is some good wisdom on this thread and myths that people read and pass along as information.

I ran a 400E with the W-30 cam of that era, and valve springs. I shifted at about 6,500 RPM's.
Now for the details: the W-30 springs were shimmed to and installed height of 1.670". I had the hydraulic lifters lashed out with Isky Poly-locks. I ran 35 degrees total advance with a Mr. Gasket quick advance kit in the stock "points" distributor and AC Delco 43 or 44 spark plugs or Champion Spark plugs in comparable heat ranges. I shimmed the oil pump bypass spring, used Valvoline Racing 30 weight oil and changed oil and filters regularly. I used reconditioned stock connecting rods and chrome rings. I don't recall what pistons, they might have been stock because the engine was not bored.

The car was a 442 convertible with L-69 Tri-carb, M-21 close ratio 4 speed, 4.33 rear gears, Hooker headers and the biggest 14" tire I could find.

Now to answer how high it buzz or whats a "safe limit" depends on things as others have said. If its not making power (acceleration) at higher RPM's there is no reason to buzz it that high. .
......Just my two cents worth.

 

As Joe, Run to Rund, mentioned above, the stock Oldsmobile connecting rods are soft and the big end goes out of round easily. Did you have your motor rebuilt? If rebuilt, was it run on a dyno afterward? What pistons and connecting rods were used? What camshaft was installed? What did your engine builder recommend? As a reference, I would shift my factory stock 1967 W30 at 6200 on the track and never had a problem with bearings. If you have the regular 442 camshaft in your motor, it probably would not benefit you to take it above 5800 RPM. Also, if the stock rods are still in it, they are sure to be out of round unless you had them reconditioned.

 

If it is the original block do you really want to twist it to the limit ? Especially if it still has stock pistons and rods.
That said - of the four big blocks the 400E is the safest to spin that high in stock form.
If you do have a lot invested in this engine I certainly hope some of that includes lighter weight forged pistons and stronger aftermarket rods and top notch balancing, if so
you have a huge improvement over stock - in just these 3 key areas.

 

Just because an engine will turn a higher RPM doesn't mean it's making power there. I would bet your engine will tap out making power between 5200-5800.

 

I had my 67 400 dynoed last year. Made 417 hp at 5700 rpm. Like the others have said. No need to rev higher past peak. It was built with custom pistons, lighter than stock . I believe they are at 510 grams. Connecting rods are Rocket Racing ,balanced bottom end. I'm sure It has the potential for higher rpm , but no need to go past peak power.

 

thanks. I had a engine builder do mine also with special piston and it dynoed at 450 hp and 490 TQ at 5800 rpm. I guess thats where I will shift at.

 

Torque peak at 5800? Wow!

 

Yeah,my peak TQ was @ about 3700

 

I meant my max HP was at 5800rpm and my max TQ was at 4100rpm, I need to get better at proof reading, I knew what I wanted to say but wrote it down wrong!

 

That sounds more like it! No need to spin it over 6K then, I guess.

 

You may want to shift at an rpm above that of max HP because in the next gear you will be below the max HP. You want the average HP within a gear to be maximized.

 

ok thanks for info!

 

Only 2-300 RPM, though.

 

Depends on rear gear ratio, transmission ratio and how far below the power band after gear change.

 

So gear ratio spacing, yes, I should have qualified my statement. 2-300 RPM usually does the trick though. A run through the gears paying particular attention to RPM after each shift will tell you what you need to know.

 

If you have a drag car you want the engines tounge out about 100" before the line.

 

???

 

Already reached max power

 

Gotcha. Plus 2-300 RPM!

 

You don't want to the car to peak @ the line, about a 100" and 500 RPM above peak power.

 

x 2

 

So 200" and 1000 RPM?

 

This (X 2) was to convey that I agreed with the gentleman (66-3X2 442) who knows what he is talking about.

Your 2-300 RPM's has been incorrect from the beginning. Believe what you want to believe, but you are wrong.

 

So, for my education and OP's benefit, what's a good rule of thumb for how far beyond the HP peak you want to rev, allowing for different gear spacing and rear end ratios?

 

Shift point takes entire package into account.
There is no simple rule. As a typical average shift RPM is usually around 300 to 500 over peek HP. As said above you are trying to get the most power to the ground. This is your higher average. There are definitely exceptions to this. A car with a numerically lower final drive and tight converter with higher torque numbers down low might benefit from an early shift point. Bracket cars are typically more consistent with lower shift points. There are too many scenarios to list.

In the end you need to get out and test.