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Duratec - Safe Rev Limit
mackei23b - 16/2/16 at 09:14 PM

Hi there

At present I have an ST150 spec Duratec with Jenvey 45s and Raceline wet sump and oil filter housing and MS3 for the ECU, everything else is standard including the big end bolts. I'm currently running a rev limit of 7,200rpm.

If I fit ARP big end bolts, but remain with standard valve springs and retainers, what is my safe rev limit?

Cheers

Ian

Paul Turner - 17/2/16 at 10:25 AM

I would expect the power to have peaked by 7200 on a standard engine (even with Jenveys) so no point revving higher. All you will do is wear the engine out faster, you won't go any faster.

mackei23b - 17/2/16 at 12:08 PM

Yes, I think power will have peaked at 7200rpm.

I'm running a standard type 9 gearbox, though I'd really want a longer first gear. For example if I hit 7,200rpm (I'm getting around 200bhp) in first and change to 2nd gear the revs drop to 3,900rpm (I'm down to 150hp) on typical Duratec dyno plot.

So it not about achieving maximum power, it's trying to keep the engine in the peak power range as far as possible, or at least improving it a bit.

Cheers

Ian

[Edited on 17/2/16 by mackei23b]

Paul Turner - 17/2/16 at 01:00 PM

quote:
Originally posted by mackei23b

I'm running a standard type 9 gearbox, though I'd really want a longer first gear. For example if I hit 7,200rpm (I'm getting around 200bhp) in first and change to 2nd gear the revs drop to 3,900rpm (I'm down to 150hp) on typical Duratec dyno plot.



You are correct, you need a longer first gear.

When I started hillclimbing I had the exact same problem so built an engine that gave a bit more power but was safe to 7800 rpm instead of the 7000 rpm my original engine was limited to. It helped but not that much. With standard Escort Mk 2 ratios the rev drop only changed slightly to about 4700 instead of 4300.

Then I learned about close ratio boxes. Bought a Quaiffe Escort kit and a mate built me the box. Rev drop using a 7800 rpm limit was them 5100 rpm which was noticeably better.

My suggestion for you is to contact Steve Perks at SPC 01527 894232. He does a kit that changes 1st gear in a type 9 (works with both 4 cylinder and V6) and using a 7200 rpm limit in 1st your revs would drop to 4800 rpm which is much more like you need. The kit is about £250 from memory, by far the most cost effective way to get decent ratios.

Hope that helps.

RussH - 20/7/18 at 12:06 PM

Slight thread resurrection - what mods did you need for 7800 rpm?

My big end bearings let go on my current engine due to a lack of oil pressure on a very hot trackday. Internally standard aside from cams - I was taking it to 7500 regularly for the last 6 years.

I've got a replacement unit to go in shortly, i'll be swapping the cams over and would like to increase the rev limit a little further if I can easily / at low cost. I like to keep the internals reasonably standard for ease of replacement (as proven in my current situation!)

Would ARP rod bolts alone see me at 7800, or would I need anything else (stronger valve springs?)

I already have a close ration box btw.

Andy D - 21/7/18 at 03:33 PM

Hi Russ. Although it doesn't say what the safe rev limit is, the Burton tuning guide does suggest the rods and pistons aren't too safe over 200 bhp. I think I'd be keeping the revs down to nearer 7000rpm than 8000..
http://www.burtonpower.com/tuning-guides/tuning-guide-pages/ford-duratec-he-tuning-guide.html