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Re: Higher Redline
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Posted by ErikS (more from ErikS) on Wed, 18 Dec 2024 00:46:14 Share Post by Email
In Reply to: Higher Redline, BradW [Profile/Gallery] , Tue, 17 Dec 2024 13:27:33
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Phew, we are digging in the engine physics basics now. That would be a long way to discuss every basic detail of how engines and engine tuning works.

I know some good german books about this topic to learn and educate on this topic. I am pretty sure there are similar books in english, too.

Redline can be either how high an engine can rev without destroying itself. Standard engine is 5500 rpm. This limit can go up if you install lighter valve lifters and stiffer valve springs, and good balanced pistons and conrods. Don't touch the crank besides a regrind if needed. Ligther flywheel can make the engine a bit more lively, but don't do too much as it will affect idle if you lighten too much, causing bad idle.
Lighter valve train parts will have the same amount of wear and tear at higher rev compared to the heavier standard parts.
Stronger springs will help close the valves quicker and prevent so called valve float at higher rpms. To some extent the stronger springs are also needed as bigger valves might be slightly heavier than standard valves.
The aluminium timing gears will be more robust, so that is a plus for higher redline.

So this is just about the mechanical aspects of redline. The second aspect is driveability and what characteristic the camshaft delivers. A 7.6 and 7.2 camshaft are similar, but the 7.6 gives a bit more overall power (like 5% stated in the SSR manual) and everything about 500rpm higher than a 7.2.

I rev my rally engine (specs stated a bit further up) to 7000 rpm without any issues and I am pretty sure that it would even live with a 7500 rpm redline. But, the power peaks at around 6500 rpm and starts to slightly go down after surpassing the 6500 rpm. So there is now much sense of going much higher. This is with a 7.6 camshaft and 2x Weber 45DCOE carbs. I only go to 7000 because with my short ratio rally gearbox I hit perfect power / revs when I shift at 7000.

So, to sum it up. If you are so fixed on the 6500 rpm redline, you will be fine with a 7.2 camshaft. And again, what is much more important, keep a good driveability and beefy mid range torque. 7.6 is for race use and I am pretty sure you will be more happy with a 7.2.

Cheers,
Erik

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