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| Scaffy |
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I've been looking on the net for a while for the answer to this question with no luck. Can anyone tell me what the maximum power range should be for a 75 and 80mm throttle body? On an NA application.
Thanks, Chad
_________________ Trickflow Street Heat top end kit, 70mm BBK TB & EGR, 24lb injectors, Underdrives & 3.73s: 275rwhp - 13.15@105mph NA / 12.37@116mph N20 |
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| richie |
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On the engine dyno I tested 70mm vs 75mm - made very little difference in fwhp or ft-lbs - went with the 75 as had already bought it.
Richie
_________________ 1993 ED F/mont 5.0L, Auto, Edelbrock RPM's, CompCam XE276HR, Crane Gold Race 1.7's, Edelbrock Performer, 75mm T/B, MAP, 42lb , GenIII coils, PH4000's , Twin 2.5", Thermos & underspeeds, 3.7 LSD, 2800 stall and MoTec M800, 372fwhp @ 5400rpm & 387 ft-lb @ 4400 rpm. |
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| Scaffy |
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Yeah, I think I phrased that question poorly. If I theoretically wanted 450rwhp, what sized throttle body should I be going for? But I was wondering, a 75mm tb is good for up to xxxhp and an 80mmtb is good for up to xxxhp. Can anyone fill in the xxx???
Thanks
_________________ Trickflow Street Heat top end kit, 70mm BBK TB & EGR, 24lb injectors, Underdrives & 3.73s: 275rwhp - 13.15@105mph NA / 12.37@116mph N20 |
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| BFXR6T |
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You need to find out the flow through the throttle body.
Im told the maximum speed that air can travel is the speed of sound. Using this, find out the volume that can pass through the 80mm throttle body. This volume can be calculated to determine the maximum possible power that could be produced. Keep in mind, the smallest restriction in the system will govern the overall air flow. Im sure it will be 'plenty'. |
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| EB-5LTR |
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There are graphs that show CFM flow of different size throttle bodies (try a google search). 70mm is heaps good for any worked 5ltr and even strokers. Its just going to big can hurt velocity so thats why you will hear people say that "you'l loose downlow power going to big a throttle body". If you were reving the s**t out of your engine and needed that extra couple of hp up high then id say yeh go bigger.
Hell, if i remember correctly 65mm t/b supports around 700cfm. Thats heaps enough let alone what a 70mm flows. I would say 75mm is a little too much for street. |
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| sam12h |
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Is this info of any use to you? (found on US forum Stangnet and saved years ago)
"THROTTLE BODY AIR FLOW DATA (In CFM): 1.Ford Stock 5.0L 60MM, 526 CFM 2.Accufab 65MM, 616 CFM 3.BBK 70MM, 726 CFM 4.Accufab 75MM, 845 CFM 5.Accufab 90MM, 1225 CFM"
_________________ Production Editor of Performance Motoring at Express Media Group |
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| Scaffy |
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Cheers fellas. Yeah, I know with my current 302, I don't want to be going any bigger than the 70mm. But for say 363+, I may want to step it up a bit.
sam12h, that's great, but now is there any way we can equate that to hp, or not? I guess it depends on a number of variables, but I'm wondering if there's a rule of thumb, similar to that of injectors? Oh yeah, I did spend a bit of time on google with no luck.
_________________ Trickflow Street Heat top end kit, 70mm BBK TB & EGR, 24lb injectors, Underdrives & 3.73s: 275rwhp - 13.15@105mph NA / 12.37@116mph N20 |
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| sam12h |
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http://www.pcengines.com.au/calculators.html
Lots of good stuff there, but click on; Calculate Size of Carburetor Needed in CFM It's close enough to be useful. VE is volumetric efficiency; a measurement of how much air is being ingested compared to the capacity of the motor. Below 100% is less than the engines capacity, over 100% is more. A standard 5L will have about 80%, a really well-thought-out normally aspirated carby motor (or V8 Supercar engine) can have over 100% 
_________________ Production Editor of Performance Motoring at Express Media Group |
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| Scaffy |
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I didn't think it was possible to exceed 100% VE unless you used forced induction. Because the NA motor is virtually sucking air in, it can't suck more than it's max volume. It'd be like tying to suck more air in than your lung capacity. Not possible. Stick a compressor in your mouth and seal everything up, then you'd be able to do it... with much pain. That's the way I understood it anyway. Probably very elementary.
Will have a look at that link though. Thanks
_________________ Trickflow Street Heat top end kit, 70mm BBK TB & EGR, 24lb injectors, Underdrives & 3.73s: 275rwhp - 13.15@105mph NA / 12.37@116mph N20 |
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| Scaffy |
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Hmmm, that tells me that the 70mm is more than enough for 363@6500rpm. Interesting.
_________________ Trickflow Street Heat top end kit, 70mm BBK TB & EGR, 24lb injectors, Underdrives & 3.73s: 275rwhp - 13.15@105mph NA / 12.37@116mph N20 |
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| sam12h |
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Scaffy wrote: I didn't think it was possible to exceed 100% VE unless you used forced induction. Because the NA motor is virtually sucking air in, it can't suck more than it's max volume. It'd be like tying to suck more air in than your lung capacity. Not possible. Stick a compressor in your mouth and seal everything up, then you'd be able to do it... with much pain. That's the way I understood it anyway. Probably very elementary. Will have a look at that link though. Thanks I know this is a bit off topic, but Jaguar figured how to exceed 100%VE without forced induction back in the 1950s when they were experimenting with intake runner lengths. It's pretty complicated physics, but it is a forced induction 'effect' if you like. The velocity of the air going in can be used to fill the cylinder even after the piston has begun to move up the bore, the shock waves from the valves closing travelling up the runner, bouncing off something and heading back down again helps, 'valve overlap' (where the intake valve opens before the exhaust valve shuts) is used to take advantage of the suction effect of the exiting exhaust to drag the intake air in before the piston has started to move down. It's not easy to come up with the right combo, but it is possible with a high-revving race motor. For the purpose of a street-driven modified EFI motor, just use 100% in those calculations. And you'd be surprised how rediculously oversized many MAFS, Throttle Bodies and carbies are on motors that could have used something smaller and probably had better throttle response. Bigger isn't always better.
_________________ Production Editor of Performance Motoring at Express Media Group |
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| Scaffy |
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Going by those calculators, my intake is good for 500hp and throttle body will well and truly exceed 450rwhp.
It also says I only need 290fwhp to get 13.6 1/4 mile with a 3700lb car... As for exceeding 100%VE, I think I'll leave that one to Jag. Haha. Interesting though.
_________________ Trickflow Street Heat top end kit, 70mm BBK TB & EGR, 24lb injectors, Underdrives & 3.73s: 275rwhp - 13.15@105mph NA / 12.37@116mph N20 |
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| 347xr8 |
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As I've come to understand, it all comes down to how big you're displacement is and where you want to make your power. I've got a street fords magazine here with a stroked AU, 363 cubes. That guy's running a 90mm or 100mm TB, pumping out 440 rwhp N/A. There a few other cars in magazines i've seen with 347's running 75mm TBs, still making good power.
Hope that makes sense....
_________________ SMASH THAT HOLDEN!!! |
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| sam12h |
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Yes, it depends on displacement, rpm and max VE, and every combo is different.
Here's a link I found on the weekend with some relevant info (and plenty more). http://forums.stangnet.com/690222-head- ... ation.html Two things worth noting for this thread topic; 1. Not all throttle bodies are equal (even with the same size blade the CFM can be different between brands). 2. The info on this page also leads to the conclusion that a 70mm aftermarket unit (787-790cfm) will be plenty for 363ci.
_________________ Production Editor of Performance Motoring at Express Media Group |
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| Scaffy |
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Thanks, so much great info there.
_________________ Trickflow Street Heat top end kit, 70mm BBK TB & EGR, 24lb injectors, Underdrives & 3.73s: 275rwhp - 13.15@105mph NA / 12.37@116mph N20 |
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