I have a book by Vizard Building horsepower and he says that bigger exhaust valves help fuel economy and they should be 90% of intake valve. Why is that?
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“Cars are the only thing on earth that will beat you, break you, make you bleed, make you cry, spend all your money, spend all your time, not work and not care that you will love more, the more they abuse you.” -Anonymous -
V.e.Builder/Owner of Badass Panther Wagons
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Has to do with once the energy is expended from the air fuel mixture it reduces the volume needing to be removed from the cylinder.Scars are tatoos of the fearlessComment
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American engines, especially the older ones, tend to have valve sizes that are substantially smaller with respect to the intake valve than a Japanese DOHC counterpart. I assume American DOHC engines are the same way (as the Japper DOHCs).1992 CVLX. 5.0 HO/GT40P/T5/3.73/trak-lok with bolt ons. 02 front CVPI setup, rear HPP setup, CVPI shocks around, F250 radiator, e-fans, and the power of 3G. 15.92@89mph, 2.4 60', 4700' elevation (5500' DA) with 3.08 open rear and the old oil chugging 289. RIP.Comment
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another bit of it is that you want the exhaust gas to go out at a high velocity. If you tune things just right, you can actually create a little bit of vacuum in the cylinder to get a more full air charge on the intake stroke. The technique is called scavenging. Too small though and you risk not getting all of the exhaust out, and thats no good.86 Lincoln Town Car (Galactica).
5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley
91 Lincoln Mark VII LSC grandpa spec white and cranberry
1984 Lincoln Continental TurboDiesel - rolls coal
Originally posted by phayzer5
I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousersComment
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ahh yes scavenging reminds me of those old 2 stroke detroit diesels i worked on in high school. nothing makes you think WTF? like the first time you pull the heads on a supercharged v8 with 4 exhaust valves per cylinder and no intake valves.Comment
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Intake air speed in theory desired is 300 FPS exhaust is 200 FPS. Exhaust flow with a smaller valve is usally comensated with a split cam ..more duration and lift on exhaust. As the exhaust air flow reaches around 80% of the intake flow a strait up cam is usally more desireable. Most engines need work to get there. When they do and a split cam is used power will be just blown out the exhaust.
Creamys engine is close to 89% between intake and exh flow so I selected a straight up cam.
Gadget your heads are close to the same percentage as far as your heads are concerned. Intake and exhaust selections can effect that.Scars are tatoos of the fearlessComment
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How do you measure this on a running engine?Originally posted by turbo2256b View Post
Yeah, I'm parroting what I've seen asked elsewhere, but I'm also interested to know!2012 Mazda5 Touring | Finally working on the LTD again!
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I have a theoretical approach that would work, but am not certain anyone would actually go through the trouble.**2012 Ford Mustang Boss 302: 5.0/ 6 spd/ 3.73s, 20K Cruiser
**2006 MGM,"Ultimate": 4.6/ 2.73/ Dark Tint, Magnaflows, 19s, 115K Daily Driver
**2012 Harley Davidson Wide Glide (FXDWG):103/ Cobra Speedsters/ Cosmetics, 9K Poseur HD Rider
**1976 Ford F-150 4WD: 360, 4 spd, 3.50s, factory A/C, 4" lift, Bilsteins, US Indy Mags, 35s Truck DutiesComment
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You could spell it out in a separate thread and see how many people tell you to get lost?2012 Mazda5 Touring | Finally working on the LTD again!
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It would take a lot of equipment. Alot of mods to the intake and exhaust with sensors to data log air speeds and temeratures.Originally posted by 1987cp View PostScars are tatoos of the fearlessComment
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Variable exhaust valves like a 2 stroke?Originally posted by P72Ford View Post1989 Grand Marquis LS
flat black, 650 double pumper, random cam, hei, stealth intake, Police front springs, Wagon rear, Police rear bar, wagon front ,exploder wheels, 205/60-15 fronts 275/60-15 rears, 1 5/8" headers, 2.5" offroad x pipe, Eclipse front bucket seats, Custom floor shifter, 4.10 gears, aluminum driveshaft and daily driven. 16.77@83mphComment
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So ..... (again, admittedly parroting what I've seen elsewhere)Originally posted by turbo2256b View Post
- How do you know when you're getting close to the air speeds you quote as desirable?
- How do you know those air speeds are desirable in the first place? (probably from your experience at Ford, but a little background in laymen's terms might be helpful)2012 Mazda5 Touring | Finally working on the LTD again!
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