BenB
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| posted on 14/12/12 at 01:22 PM |
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Fair enough- although I don't see how the risk of detonation when you have boost and a high CR ration is fundamentally changed by the method you
have created the boost!  The Rotrex chargers are centrifugal which means they don't heat up the inlet charge as much but a good intercooler
will sort that out. I can't understand also how the centrifugal fan changes the cam problem- I suppose the centrifugal blower creates a
disproportionate amount of it's boost at high RPM when the degree overlap will obviously be the same but the actual time of overlap will be
less....
From the sounds of it people have got these chargers to work with high CRs and rad cams- I just can't understand how...
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JAG
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| posted on 14/12/12 at 01:50 PM |
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Ben; fundamental physics/thermodynamics haven't changed.
The way I read this thread these guys have simply created a relatively tuned NA engine and then slapped on a 'charger (doesn't matter what
type) and run it at low boost levels to avoid detonation.
Your comments about valve overlap, detonation and heat still apply to these engines. The method that has been used has simply changed the balance
between power WITHOUT boost and power WITH boost.
On older boosted engine designs the engine-without-boost made less power and the boost was used to increase power.
On the new designs the engine-without-boost makes more of the overall power and the boost simply adds the last little bit.
By doing this I guess you can create an engine that behaves more like an NA engine whilst giving the specific power outputs associated with boosted
engines.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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jeffw
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| posted on 14/12/12 at 01:54 PM |
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Exactly this. My cams are not big lift, somewhere between 285 Piper and mild race. They come in around 3k and are all over and done with at 7.3K.
As the Rotrex is at max rpm at 7100rpm in my car this is ideal so there was no point in changing. Race cams wouldn't be any good but fast
road/rally cams are fine.
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Oddified
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| posted on 14/12/12 at 04:59 PM |
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quote:
Originally posted by jeffw Race cams wouldn't be any good but fast road/rally cams are fine.
Or dial some of the overlap out with the cam timing/vernier wheels.
Ian
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laptoprob
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| posted on 14/12/12 at 05:40 PM |
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quote:
Originally posted by BenB
Back to the original question, you actually want quite a tame cam. Sporty cams generally have loads of overlap to encourage scavenging of the exhaust
from the cylinders. In a forced induction setup you don't want oodles of overlap because you'll wee away all the PSI you've been
lovingly creating.
Regarding compression ratios it all depends on what boost level you're using, what fuels you're going to run, what level of intercooling
you're going to have, whether you'ld consider water or methanol injection etc etc.
You can run an engine on RON95 at 11:1 but you'ld be restricted on boost levels (prob high single figures) even if you run a goodly size
intercooler.
In my photo archive there's a scan of graph from G.Bell's Forced Induction Tuning showing recommended boost vs CR.
Hi Ben, i had heard this before about the overlap but wondered if i can gain anything much by adding some lift etc.
Ill have alook at the graph, thanks for that.
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jeffw
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| posted on 14/12/12 at 07:15 PM |
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Atspeed played with the verniers when they mapped the car and we saw a big jump in torque while moving the exhaust cam.
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laptoprob
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| posted on 14/12/12 at 09:42 PM |
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quote:
Originally posted by jeffw
Atspeed played with the verniers when they mapped the car and we saw a big jump in torque while moving the exhaust cam.
I know that you can add an XE exhaust cam to a C20LET engine and swing the cam a few degrees and it gives big torque gains which sort of ties up with
what Atspeed have done.
Maybe they dialled some overlap out and gained some boost back hence the torque?
Either way i,m going to go down the fast road cam route and do some work on the vernier pulleys once its on the rollers.
Thanks for your input fellas (especially Jeff,great inspiration). Watch this space.
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laptoprob
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| posted on 14/12/12 at 09:45 PM |
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quote:
Originally posted by jossey
Rob,
How am I supposed to keep up with you now.....
Right I need a hayabusa now.
Good luck with the project though.
Just a quick question.... Say you put the supercharger on and let's say it touches 320hp??? Ish... Then what's next?
Haha, i reckon at Blyton power doesnt mean everything anyway. Its such a short circuit it really gets down to some good handling.
If i hit 320hp(which is doubtful) then i may need to go back to 2 wheels to quench my thirst.....if the wife allows it that is
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jossey
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| posted on 14/12/12 at 09:57 PM |
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Well good luck with the winter upgrade. If I can get hold of a 3.38 diff then ill goto other tracks but currently the 3.92 n 3.62 are all I have an I
lost the details for the guy who said he could change the pinions in the 3.62
Speak soon.
Ps I can't beat you on handling but mine is a little lighter than yours so maybe that will help ... In the dry
David
quote:
Originally posted by laptoprob
quote:
Originally posted by jossey
Rob,
How am I supposed to keep up with you now.....
Right I need a hayabusa now.
I
Good luck with the project though.
Just a quick question.... Say you put the supercharger on and let's say it touches 320hp??? Ish... Then what's next?
Haha, i reckon at Blyton power doesnt mean everything anyway. Its such a short circuit it really gets down to some good handling.
If i hit 320hp(which is doubtful) then i may need to go back to 2 wheels to quench my thirst.....if the wife allows it that is
Thanks
David Johnson
Building my tiger avon slowly but surely.
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Craigorypeck
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| posted on 18/12/12 at 10:26 PM |
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I'm running 11:1cr with newman fast road cams very modest 6psi but it goes well. dialled out some overlap and got a bit more boost.
found this useful. ezinearticles.com/?Supercharger-Tuning-Through-Cam-Selection-and-Cam-Timing&id=2473412
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laptoprob
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| posted on 21/12/12 at 08:08 AM |
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quote:
Originally posted by Craigorypeck
I'm running 11:1cr with newman fast road cams very modest 6psi but it goes well. dialled out some overlap and got a bit more boost.
found this useful. ezinearticles.com/?Supercharger-Tuning-Through-Cam-Selection-and-Cam-Timing&id=2473412
Cheers for the link, very informative. What did your engine do on the dyno? And its a Zetec i take it? Any other head mods?
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Craigorypeck
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| posted on 21/12/12 at 03:48 PM |
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Not dynod yet.. running in new block atm.
Yb engine with ported head.
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