RPM red line for STD A7 engine ?

[Steve Bryant]

After watching some of the trials Sevens were being used in on U - Tube and  hearing some of the high RPMs  that the engines were subjected to, I started to wonder what the red line for a stock unmodified engine would be.

Is there a "do not exceed"  number of RPMs?

Cheers,
Stephen

[Dave Mann]

I suspect that a bog standard Seven is self limiting.

[Terrytuned]

Steve by stock do you mean a crack tested original crank or 1 5/16" Pheonix as there is a big difference. Terry.

[Chris KC]

Depends how long you want your engine to last I guess. I'd always understood 6000rpm as the general limit - it's probably in Bill Williams somewhere. Dare say a well-built racing or three-bearing engine might survive more - but you explore that territory at your own peril. Your typical A7 engine touring engine will struggle with valve bounce before you reach 6000.

[Howard Wright]

A quick Google suggests that the top speed for a Chummy is a shade over 50mph. With a 4.9 axle and 19” wheels that equates to a little over 3000 revs.

My Special with a 5.25 axle has a 1 1/2” crank and other go faster goodies. It has been balanced and I’ve cruised at 50mph (3500 revs). At that speed the car seems to have some in reserve. The driver does not!

As Dave has said the A7 is self limiting …….probably more by the driver tolerance than engine strength!

Cheers

Howard

[Alan]

The limiting factor with a standard engine in good condition is probably the con rods. Some standard rods are good for more than5000 revs, but not all are, and as you won’t know until it lets go 4800 is a reasonable limit. I know others will claim more, but engine rebuilds are expensive. However, I don’t obsess over much with engine speeds. It’s the shape of the power curve that matters. With a standard engine at 4800 you are probably on the falling part of the curve anyway, so there’s not much point in being there unless you are trying to save a gearchange on the last 100 yards of a finishing straight. And, if that’s the case why are you on a standard engine.
On the other hand a properly built, forged crank and rods, balanced,etc race engine will see 7000 regularly, and more on aforesaid finish straight.

[Steve Bryant]

Thanks all.
You've sort of answered my question. I was referring to a original two bearing engine with a standard factory crank in good condition without mods or upgrades
Just curious.
Stephen

[Tony Griffiths]

For the racing boys and girls, an r.p.m. reminder: