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Top Fuel
https://www.slantsix.org/forum/viewtopic.php?t=45734		 Page 1 of 1
Author:  icepaddles [ Tue Jul 26, 2011 3:31 pm ]
Post subject:  Top Fuel
I understand that Top Fuel class runs a low compression,
6 to 1, 7 to 1, but (maybe) blown alcohol runs high compression.

I suppose that is due to the facts that 1. The blower overdrive will stuff that much more fuel into the chamber from it having more volume. 2. nitro methane conducts electricity so it burns before it compresses much anyway.

So, could a gasoline engine benefit from running more cylinder volume (higher deck) and more boost, assuming you can keep the intake and the head gaskets from blowing out and an intercooler is used?

It seems that stuffing more air/fuel in would increase what comes out.
Author:  kesteb [ Tue Jul 26, 2011 8:31 pm ]
Post subject: 
Yes, look up Porsche Turbo Carreras from the early to mid '70s. The practical minimum compression is something like 6.5:1. Anything less is too down on low end power and has a problem igniting the mixture.
Author:  Dart270 [ Wed Jul 27, 2011 11:04 am ]
Post subject: 
Yes, large chamber/compression volume and more boost and fuel will make most power. If you are trying for 600+HP, you might spend a lot of time thinking about this. Otherwise, 8 or 9:1 will work well with moderate boost.

Lou
Author:  icepaddles [ Wed Jul 27, 2011 3:45 pm ]
Post subject: 
It makes sense to use less boost for economy it also makes sense that using high cylinder volume would be good for time spent at around 2000 rpm (probably not spinning the turbo fast enough to fill the cylinders).

It seems you could get away with more than using high compression ratios, since it would take filling the cylinder with mix to get compression higher - thus - it would be at higher rpm with less likelihood of detonation.

Thanks all, Ill be reading somemore about it so I could decide.
Author:  kesteb [ Sun Jul 31, 2011 9:24 pm ]
Post subject: 
The turbo books usually suggest less compression and more boost to make power. But you are free to do as you please.
Author:  Shaker223 [ Mon Aug 01, 2011 12:25 pm ]
Post subject: 
Quote:
It makes sense to use less boost for economy it also makes sense that using high cylinder volume would be good for time spent at around 2000 rpm (probably not spinning the turbo fast enough to fill the cylinders).

It seems you could get away with more than using high compression ratios, since it would take filling the cylinder with mix to get compression higher - thus - it would be at higher rpm with less likelihood of detonation.

Thanks all, Ill be reading somemore about it so I could decide.
A high compression turbo build is documented over on moparts. A lot of power was made and it did not end well because the margin for error is extra small on the tune.
Author:  icepaddles [ Mon Aug 01, 2011 2:01 pm ]
Post subject: 
That would tend to be in line with the design of a forced air cam (if my memory serves me) where long duration is called for. (1). with a need to fill more volume and (2). a higher compression requires closer piston to valve relation, thanks.
Author:  bigslant6fan [ Thu Aug 04, 2011 3:47 pm ]
Post subject:  .
It's true that a lower CR will allow more boost with the same octane fuel,but below 8:1 CR will reduce fuel economy and drivablity on the street. It's true the early Porsche had 6 1/2:1 CR,but they were hot running,air-cooled engines with out an intercooler.This caused them to be detination prone.
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