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Old 10-12-2013, 02:47 PM   #21
Ice88
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Originally Posted by danbowe84 View Post
Sorry back tracking a little ice88 when you say cams will bleed a little of that comp ratio is that because of overlap?

And is overlap purely a way if reducing emissions/better mileage or is there performance gains to be had from it?

Does the ze have a vics manifold?
I dont mean to rag on you at all in this post man. But this is what I hate about people in a wider sense, they think that because teh car doesn't make lots of power in stock form that NA is crap.

Not that the whole point of the engine is meant for a econobox and not a sports car.

Other then a page of text to explain how cams work. The basic is that more duration and more overlap move the power band up the power band. I don't really have time to explain now maybe when I get home or tomorrow.
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Old 10-12-2013, 03:10 PM   #22
danbowe84
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I dont mean to rag on you at all in this post man. But this is what I hate about people in a wider sense, they think that because teh car doesn't make lots of power in stock form that NA is crap.
Not sure how you got that impression from anything I have said! Each to there own, some people like big lumpy v8's others like 4 cylinders that rev to 10 grand, I want a turboed 4, there's so many different paths to choose.
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Old 10-12-2013, 04:14 PM   #23
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you're delving into advanced engine tuning subjects which you may find reliable articles on the internet, but I rather recommend you to buy some of David Vizard's books... they are very interesting and informative about what does what in an engine and the results that happens from changing certain specs... the reading isn't as dry as Corky Bell's IMO, but you need to read both books... both authors run performance shops and have been doing this longer than many of us here have been alive lol

you will learn far easier and more reliably than all these Q&A posts because whatever we have learned before may have gotten a little cloudy over time... it certainly has been years since I read those books, and I may go back reading them again some time

back in the days, I could have directed you to well written articles on a US Protege forum but they are now all dead... the authors who wrote those articles also have moved on to greener pastures and cbf reposting them again on other forums still alive
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Old 10-12-2013, 06:35 PM   #24
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but to further a simple explanation... overlap helps improve intake port flow by utilising scavenging effect with exhaust pressure waves.... to understand this, you must understand how the internal combustion engine works, and to understand scavenging, you must have a basic understanding of fluid dynamics

you don't have to be an engineer to have a good enough understanding to make a faster car, but you do need to learn and understand enough to do this... so like I said, those books will really help you learn
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Old 12-12-2013, 07:46 AM   #25
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Originally Posted by danbowe84 View Post
Sorry back tracking a little ice88 when you say cams will bleed a little of that comp ratio is that because of overlap?

And is overlap purely a way if reducing emissions/better mileage or is there performance gains to be had from it?
Bleed off pressure is the best description of what is happening.

This is a very simple explanation that doesn't take into account other factors:
Imagine and engine that has a cam that opens the valves at TDC and closes them at BDC. This engine will compress mixture for 100% of the stroke of the crank.
Now to increase the rpm range of an engine the cam usually leaves valves open longer, and it's the valves still open before trapping - piston coming back up the bore - that allows mixture to bleed off. Basically you are using a smaller portion of the stroke - maybe 75% - as a trade off at low rpm so that there will be higher filling at higher rpm, hence why you increase comp with bigger cams.

Modern trends now use small duration cams, to keep the torque, but higher lifts so that higher flow can be utilised for filling.

Another factor is that the higher the VE the higher the dynamic comp.
Pro stock use calculated static comps around 16:1, but because they have a VE in the 125% range there is 25% more cylinder volume trapped at TDC, and that calculates out to 19:1 dynamic.
Old Top Fuel uses 6:1 static calculated comp, but when you add the 70cc of raw Nitro in the cylinder at TDC it calculates out to 21:1 comp
Conversely racing HQ's used to use 15:1 because the carb is so restrictive flow wise that there wasn't much mixture trapped in the first place.

Last edited by Old Grey; 12-12-2013 at 03:44 PM.
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Old 20-05-2014, 01:23 PM   #26
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if i purchase an ecu from a us fs-det im i able to use it on my sr2, or would i need to change harness, sensors and all that
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Old 21-05-2014, 07:15 AM   #27
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if i purchase an ecu from a us fs-det im i able to use it on my sr2, or would i need to change harness, sensors and all that
The ecu harness plugs are completely different between the US ecus and the Aussie ecus. The US plug is a single connector will the Aussie harness has three individual connectors.
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Old 21-05-2014, 08:32 AM   #28
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thanks:-)
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Old 21-05-2014, 08:36 AM   #29
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Would need the trigger wheel and sensor from the MSP as well
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