Sorry if this is a stupid question, but what factors do I use to determine this? I have:

- 406 cu in
- Comp Cams XE274; operating range 0f 1800-6000 rpm
- Edelbrock Performer RPM air gap intake; operating range of 1500-6500rpm
- Edelbrock Performer RPM heads
- Milodon oil pan with crank scraper
- studded main bearings
- Eagle 4340 forged "I" beam rods; 640 grams each
- Eagle 4340 forged crankshaft; internally balanced
- KB hypereutectic flat top pistons; 564 grams each
Would I be safe to assume that my redline is 6000 rpm due to the cam?

 

I have the same intake and heads on my 406 and I can tell you for sure that you are wasting your time trying to go over 6500 RPM. My cam is a nowhere near yours though so I can't get any closer than that.
The is a forum member that uses the same cam that you have in his 406 with a better flowing set of heads. Maybe he will chime in and provide more information.

 

Yes and no. Redline is considered the maximum safe engine speed. Your cam determines the operating range and that operating range may also coincide with the redline. If your cam gives its all at 7k rpm and your reciprocating and rotating assembly aren't proofed above 6k rpm, then your redline is still 6k rpm. A lot of times, the powerband in many engines falls off substantially before redline so there's nothing more than making noise by buzzing the engine to a mark on the tach it has no desire to be in.

A smallblock factory bottom end with nothing more than a good forged piston can easily live at 6k rpm. It's helpful to use a lightweight custom piston (not the off the shelf TRW-type stuff) since the most stress occurs from the piston putting the rod in tension on the exhaust/intake transition event. A preped rod and a good, cast even, crank and good bearings and you are good to go.

 

With that XE274 your going to be limited by your hydrolic lifters. Maybe a quick burst to 6500 but only 6200-6300 on a steady pull or you will float a valve

 

That about covers it. Keep in mind that the length of the stroke has a lot to do with the maximum RPM for any given engine. The short stroke 327 will rev much higher without falling apart than a long stroke 400 with the same quality internals. The redline was set by the engineers and the warranty people. A factory LT-1 would have a redline of 6500 RPM based on the parts supplied but you would probably lower that if you were using a 3.75" stroke crank with all else being equal.

Hope that helps.

-Mark.

 

Engage throttle fully. When engine blows, notate the RPM level at the time explosion occurs. This is your true redline.


I know I am a smart ***.... But that was kinda funny.

 

It seems like no one really knows how to determine redline accurately, I guess it depends on the parts used, and even then it seems like an educated guess. I am going to assume a 6000 rpm redline for my engine, based on the cam parameters and hyd. lifters. Here is a thought; what about if I get the car dyno'd, wouldn't that be a good indication of how high the engine makes power to? I just want to determine what rpm to shift at without damaging the engine.

 

Yes, you are correct. Nobody here has the total combined engineering expertice and financial analysis resources that the General had when he determined the red line for their products. We can only guess.

The base engines were probably safe to the factory redline under normal use. The SHP engines with all the best factory parts were red lined at 6500 max (someone correct me if I am wrong). If you have the valvetrain up to factory SHP specs and the bottom end up to SHP specs you can probably run it that high safely.

You are running an aftermarket engine with upgraded everything so you are safe to some higher RPM but, the valvetrain looks like the limiting factor here to me. If you use the cam grinder's specified parts, you would expect that the valvetrain would be able to perform as designed. The bottom line is that the bottom end will live longer at high RPM than the valvetrain here in my opinion. Based on what I see you should use the cam grinders RPM limit as a red line because that is the weakest link in the chain. The valvetrain will float long before the bottom end would let go if all the parts are good so there is the limiting factor. You may put the car on the dyno and find a lower RPM shift point is appropriate for this combo and if so, you have a healthy cushion of safety. No need to rev any higher than that.

Sounds like it will realy RIP when finished

-Mark.

 

Your goal should be to determine what rpm to shift at to achieve the quickest rate of acceleration, i.e. lowest ET at the drag strip, rather than how high can you rev without damaging the engine (assuming the best shift point is below the engine damage rpm, and it usually is).
You can easily accomplish this with a few runs at a track, if you can launch the car consistently.

 

Yes, I know the point is to find the rpm to shift at to find the fastest rate of acceleration......as it stands now the engine easily winds out to 6000 rpm and feels like it is still pulling, but I am afraid to take it any higher for fear of damaging the engine. Here is another point to ponder: I have a full MSD ignition system including a Pro Billet tach drive distributor, and I have started to question the accuracy of the stock factory mechanical tach, I just have a feeling it is not right. I don't want to mount an aftermarket tach on my steering column because there just isn't any room due to the tilt function, and there is no way I will screw one to the top of the dash either. I may end up using a stand-alone MSD shift light. Anyone using one of these things?

 

Do some arithmetic to verify your tach reading using your trans gear ratio, rear end gear, tire diameter and speedometer reading - if that is accurate.

 

My speedo is not accurate yet, I have changed rear gears, and have yet to change the speedo gear. Another reason I want to determine maximum rpm is to know what "pill" to instal in my MSD 6AL to protect from accidental over-revving.

 

By the sounds of your engine internals it is built with good parts.... so this willl not determine your redline.

What is left is you heads and cam... The best way to do this is to put it on desktop dyno and see where your power peaks. Then find out how much your rpm drop is per gear in your tranny. You want to shift into your power peak for fastest acceleration.

I did this on my last engine... I was shifting to high at the strip(6500) I went and put my engine into DD2000 and found my cam peaked at 5700 so I shifted at 6100-6200 so my rpm drop (my ST-10 has a 500rpm drop per gear) would bring me into my power peak. This alone netted me 1/2 sec at the strip. I tried to further lower my shift point but resulted in slower times because I was shifting too soon.

 

Hey MikeC, howz your restoration coming along?
Wouldn't a chassis dyno show the same thing, but more accurately than DD?

 

My restoration is slowly progressing still hoping for this spring but doubtful it will happen. It should probably be out in June or July.

Yeah a chassis dyno would show this more accurately. Any kind of real dyno would show it better than a computer program.\ but I have found that the torque and HP curves are extremely accurate in shape its just they are a bit optimistic on the actual output.

 

Not for those of us with 700R4's...