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Old 04-09-2003, 03:47   #1 (permalink)
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Barra XR8 - Built to rev but can't

Are there any people out there with some technical knowledge about the new 5.4l Boss engine.
It seems that it has great torque and is designed to rev, however the mags are saying the long stroke prevents it being revved over 6000rpm without letting go.
Thus we have an engine that breathes very well but it can't rev any more than 6000rpm. It is something of a paradox.
So I suppose the question is, is there any room in the current block for increasing bore size and then being able to shorten the stroke to increase rev potential? If not, the holden unit will still have the wood on the XR8 and GT (even though it uses more oil than petrol).
This then would be a very bad thing.
Please respond
Stephen
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Old 04-09-2003, 05:10   #2 (permalink)
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The Mustang Cobra R 5.4 4V revved to 7000rpm with the aid of a forged steel crank and Carillo rods. Based on that there shouldn't be any reason why FPV can't engineer it to rev to 7000. To answer your question, yes it can be de-stroked but i'm not to sure about bore increases
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Old 04-09-2003, 05:19   #3 (permalink)
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Any engine can rev. It just depends on how much R&D you are willing to spend to acheive a reliable motor. 10,000 rpm XW anyone?
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Old 04-09-2003, 05:52   #4 (permalink)
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I can honestly tell you that the Boss motors don't need to rev past 6000. They pull like a steam train from low down & by the time you hit 6000 in 2nd gear you're well & truely flying.
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Old 04-09-2003, 06:33   #5 (permalink)
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The only problem I find with mine is that I reach 6000 very very quickly. I wish I could go more before having to change gears at the second blink of an eye.

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Old 04-09-2003, 09:42   #6 (permalink)
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I have been told by a mechanic who has modified the Sohc 5.4 in a F series truck that it can be safely revved out to around 5600rpm+, so i would guess that the Boss has a little more in her but 6000 is a safety margin.
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Old 04-09-2003, 16:30   #7 (permalink)
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It's true, the 5.4 will never rev much past 6000rpm in street trim.
Even with some very strong (read expensive) internals, it is unlikely it will go past 6500rpm reliably.
It has to do with with it's undersquare bore/stroke ratio, it's very diesel like in it's config.
It would very likely throw conrods and/or split bores if revved beyond 6500rpm.
6000rpm is a safe limit for road use.

Have you ever heard of a high revving Ford I6?
It too has an undersquare config and won't rev for the same reasons.

Rick.
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Old 04-09-2003, 16:49   #8 (permalink)
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You have 5.4litres that breathes very well and that makes good torque down low. WHY would you ever need to rev beyond 6000rpm?
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Old 04-09-2003, 18:31   #9 (permalink)
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I think the journos are talking through their butt. It's like they talk about traits of certain IRS types, struts etc. I reckon if you put them in a car where they didn't know the tech stuff up front they'd be hard pressed to know what's going on. Like the Control Link on Holden IRS - in reality the difference is very small and hard to pick unless you know it's there.

Same thing for engines. The Ford Modular engines are at max bore size already and the engine was originally designed to run at 4.6 litres. Obviously Ford Oz decided the torque was important and went for the 5.4 crank. It still revs to 6k and seems to do the job.

There are so many more considerations than bore x stroke, however there are advantages and disadvantages for both. Like 2 valve versus 4 valve - the LS1 has much bigger bore so the flow of its larger two valves is obviously not that much less than the smaller valves of the Boss which are limited by the bore size (this engine would not be real happy with 2 valves for this reason.

All that matters is what happens when right foot meets plush pile carpet and the tacho starts arcing around - LS1 and Boss are both fantastic
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Old 04-09-2003, 20:15   #10 (permalink)
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Quote:
Originally posted by Aussie Pete
All that matters is what happens when right foot meets plush pile carpet and the tacho starts arcing around - LS1 and Boss are both fantastic
Exactly Petey Boy.. The performance market in Oz has finally delivered some goodies from both sides of the spectrum. If people aren't happy with either a Boss or an LS1 then you will never please them. It's that simple..
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