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June 24th, 2007, 01:53 AM
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#1 |
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Regular
Join Date: Jun 2007
Posts: 61
 iTrader: 0 reviews
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High Compression and FI
Im new at all this stuff and I have seen people say that the PI heads are bad for any FI becuase the heads raise the compression. Why is a Higher Compression bad for FI?
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June 24th, 2007, 02:54 AM
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#2 |
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Enthusiast
Join Date: Mar 2007
Location: New Port, NC
Posts: 717
iTrader: 0 reviews
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FI raises the compression on an engine by cramming more air into it. If your compression is already high then you can't run as much boost without upping the octane in your fuel.
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Mustangless atm 2006 2500 HD Diesel. Built allison trans and other goodies 
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June 26th, 2007, 05:54 PM
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#3 |
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Proud American
 
1996 Mustang GT
10.76 @ 122 with d/a of 8365 ft
Join Date: Dec 2006
Location: Lakewood, CO
Posts: 10,168
 iTrader: 3 reviews
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Also with less compression and high octane fuel you can pull more timing and create more power! The 99-04 motors have a 9.6:1 CR and our NPI 96-98 motors have a 9.3:1 CR. When the PI (99-04) heads are put on our NPI motors the compression bumps up to 10.6:1. The reason being is the different size combustion chambers and different dished pistons. PI motors have a 17 cc dished piston with a 42cc combustion chamber where as the NPI motors have a 11cc dished piston and 51cc combustion chambers. So if you put PI heads (42cc chamber) with NPI pistons (11cc dish) it creates the higher CR. Now if you run low boost with your PI heads with NPI motor it wont cause a problem but you would be better off to take your NPI heads and get them Ported and polished and keep the low compression ratio to make more power safely!
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RIP Travis Billings  Special Thanks to: Andrews Racing Transmissions Baseline Suspensions Blown Small Block Ford with a hole in the block. 9.5 Dart Block 400 CI being saved for. Just because you can fuck a cactus doesn't mean you should. Never Lift Racecars |
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June 26th, 2007, 06:21 PM
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#4 |
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Enthusiast
Join Date: Oct 2006
Location: warren, Mi
Posts: 941
iTrader: 0 reviews
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Removing some of the combustion chamber will help lower the compression ratio, you'll end up with around 46-48 cc chamber. If you take to much out you will end up hurting the performance you are trying to gain. Average combustion chamber on a P.I heads is actually 44cc's they rate them at 42 as the smallest of the average, I have actually seen some measure out at 46 untouched. If you have your heads ported by a real head porter all this information should be sent to you with the heads.
Back to the topic, you can run higher compression but you will need a higher octane fuel to support it. One way around this is to adjust the timing trim around to support the added compression. Built modulars running forced induction love compression, unless you plan on digging into the lower end I would look into other options.......
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Just another 10 second Mustang, what did you expect ? http://youtube.com/watch?v=BgykaUrmfvM
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June 26th, 2007, 06:26 PM
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#5 |
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Proud American
1996 Mustang GT
10.76 @ 122 with d/a of 8365 ft
Join Date: Dec 2006
Location: Lakewood, CO
Posts: 10,168
iTrader: 3 reviews
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You will also be digging into your wallet alot with the high octane gas! lol but then again Horsepower sure aint cheap!
__________________
RIP Travis Billings Special Thanks to: Andrews Racing Transmissions Baseline Suspensions Blown Small Block Ford with a hole in the block. 9.5 Dart Block 400 CI being saved for. Just because you can fuck a cactus doesn't mean you should. Never Lift Racecars |
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June 26th, 2007, 09:12 PM
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#6 | |
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Enthusiast
Join Date: Mar 2007
Location: New Port, NC
Posts: 717
iTrader: 0 reviews
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__________________
Mustangless atm 2006 2500 HD Diesel. Built allison trans and other goodies
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July 3rd, 2007, 11:27 AM
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#7 | |
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MM Ninjas!
1990 Mustang LX
9.36@143 mph
Join Date: Jan 2006
Location: North Fond du Lac, Wisconsin
Posts: 11,375
iTrader: 1 reviews
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Re: High Compression and FI
__________________
My daily driver has 16 cylinders and 4400hp @ 1000 rpm....  ***1988 Mustang GT - Stock....almost 
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