How do you determine red line?

[Trueoo7]

If you can't get in touch with the engine builder is there a rule of thumb for determining your red line limit? 302, low end cam, cast iron heads, around 300-325 hp.

Thanks
True

[kountzecobra]

When your engine's parts are scattering out on the ground and oil is pouring out of the new holes in the oil pan, you may have found your engine's true redline.
Seriously, it sounds like you should keep it under 6000 or 6200 rpm for a long happy life.

[HighPlainsDrifter]

Hi,
The red line is determined by a number of things.
- Stock bottom end should only go to 5,000 rpm
- cam profile will determine engine power range but the valvetrain must be capable of supporting it. A stock cam is good to 4,500 to 5,000 rpm.
- A performance cam may be good for 7,000 rpm as long as the valve springs and rockers,guideplates,pushrods can take it.Then the bottom end, bearing clearances, performance rods/bolts, balancing, harmonic balancer ,etc have to be up to snuff also.
- Biggest factor is money, it costs big bucks to rev that engine.
Perry.

[Excaliber]

How can you tell what you got? Watch the tach and accellerate! If you have the typical "low rpm" cam you CLEARLY run out of "power" at about 5200-5300 rpm. That would indicate your max H.P. rpm would be around 4500 rpm.

Ford Motorsports offers TWO cam that are petty typical applications for a 302. One is the "torque" or low rpm application, the most common one used. Tops out around 4500 rpm, pulls strong from as low as 1500 rpm.

The other "typical" Ford Motorsports cam is the High rpm version. Comes on around 4000 and pulls to about 6000.

Basically, accellerate and try to note when it seems like the "power" is falling off. Just BEFORE that happens is a good "red line".

Ernie

[computerworks]

Ernie...
...Finding your redline empirically is like testing matches.

[Hal Copple]

another way would be to put your car on a chassis dyno, and examine the power curve, and see where your power begines to flattenout. For my stroked Windsor, it is about 5600-5800 rpm. So i have a 6000 rpm chip in my rev limiter, and a shift light chipped for 5800.

Like the others above comment, higher than necessary rpm is really stressful on a motor. I can't afford a blown motor, so i don't rev mine higher than 6000, and rarely go that high anyway. On your motor, if it were mine, i would not rev more than 5500 rpm.

[kountzecobra]

Originally posted by computerworks


Ernie...
...Finding your redline empirically is like testing matches.

Nice one Ron!

[Mr.Fixit]

I always have confidence that the bottom end will hold up to more RPM than the valvetrain will support. So after making that decision, it is based on when the power drops off, due to cam profile (and valve float)

[PatBuckley]

True-

With your description I would make sure it has enough clean oil in it and then take it out to a deserted section of highway and roll on in third gear - keep an eye on the tach - you will feel when the power starts to drop off.

Maybe 500 rpm before that is what I would use as a red line.

[mikiec]

True,

My 302 has about 300 - 325 HP. I have my revlimiter set to 6200 RPM and the shift light to 5800 RPM. The stock EFI 302 5.0 has a revlimiter set of 6250 RPM.

My motor wants to keep pulling past the 6500 range, but I decided I wanted it to live so I limit it lower.


Mike

[Excaliber]

OK, it's like testing matches, but if you use a little common sense that is the qucikest way to find out.

The 302's are really a strong motor. The valves will float or the power will fall off before the bottom end lets go, in my opinion.

I don't know of ANY model or car offered by Ford with a "stock" 302 that will turn 6000 rpm.

Ernie

,,light 'em up!

[SFfiredog]

Originally posted by Excaliber



I don't know of ANY model or car offered by Ford with a "stock" 302 that will turn 6000 rpm.

Ernie

,,light 'em up! [/b]

Larry Shinoda is rolling in his grave after THAT comment
His '69 and '70 Boss 302 Mustangs love revving past 6000 rpm.
Actually, they love revving past 7000 rpm!

--Mike

[rdorman]

Absolutes are dangerious The Boss was special!
Rick

[Excaliber]

Like the "Boss" was anything "typical"!!

The 302 model that used the 351 heads had to be revved closer to 7000 to take advantage of the HUGE intake. Consequently they dropped the use of the 351 heads after consistently blowing up motors!

I said they were strong, not bullet proof!

Ernie

[SFfiredog]

In the early '80's I used to run a Boss 302 in a '71 Maverick drag car. I ran B/Super Modified in NHRA competition untill it got too expensive, then I just ran bracket races and, ehem... late night money making races in the deserted undustrial part of town
In it's final form it was 306 ci with a BIG flat tappet cam, re-worked stock rods and crank, 13 to 1 compression and fully ported heads. The cool thing is I had 3 sets of factory titanium Boss 302 Trans Am intake and exhaust valves that a friend got from Bud Moore's engine shop in the early '70s.
I ran a tunnel ram with 2 660 Holleys, a Doug Nash 5 speed, and a 9 inch with 6.50 gears
I would leave the line at 8800 rpm, shift at 8600 rpm, and go thru the lights at between 9000 and 9200 rpm.
It ran consistantly in the 10.00 area with a best of 9.74 @ 139.32 mph. The car did great wheelies out of the hole and shifting into 2nd, and even 3rd gear.
I have some great video of the car leaving the line on the back bumper. I have to transfer it to digital and then post some stills on the site.

--Mike

[REDSC400]

Back in the day, (Ahem) there was a great book that I just cannot find right now that was written by a guy named Bell. It was called _Performance Tuning in Theory and Practice. The author suggested, at that time, what were considered some of the performance RPM limits for three classes of engines. The first class was standard stock cast-iron cranks and connecting rod engines. The second class was forged crank and heavy duty rod and engine bearing cap and the third class engine was the all out drag racing or blueprinted race engine.

The rev limits were a function of Mean Piston Speed.

The first class of engine should not exceed 3500 Feet per minute, while the second class should not exceed 3800 to 4000 F/m while the last class could attain speeds of 5000 to 6000 F/m for just a few seconds.

Mean Piston Speed, which is a measure of Feet per Minute is an esoteric calculation of

(2 X Stroke in Inches X RPM)
------------------------------------
12

or simplified as

stroke in Inches x RPM
-----------------------------
6

Therefore, if you know your engines stroke, and you enter into the equation the RPMs of your "theoretical redline guestimate", then you can calculate the Mean Piston Speed.

Once you get the Mean Piston Speed, you can then, based upon the discription of your engine, ie: (stock, forged, race) see how that compares to the suggested limits.

Now, you should err on the conservative side. I take no responsibility for your results. I do not know how valid Bell's guidelines are regarded by todays technology.

Bell, was also one of the first folks to write about using "seasoned" old blocks for racing vs new blocks. His theory was that the seasoned old block, having gone thru many many thermal cycles of hot and cold, had all of the casting stresses relieved. Thus the old block could and would maintain cylinder hone tolerances better that a new block which still had stress.

I do not know about that theory of his?

Hope this data helps?? If not it is at least interesting.