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Throttlebody conundrum


Guest Anonymous

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Guest Anonymous

I posed this to Blkmgk in a private email, but I think I'd like to open it up to discussion since it seems relevent with everyone wanting to go EFI.

 

Why is it some smaller engines use TB's that are larger or the same size as larger engines? Case in point, the 4.0 explorer TB = about 60mm I'm told. Stock mustang 5.0 = 50mm (correct that if I'm wrong please).

 

Another example, a 16v VW progressive 2 bbl throttle body has butterfly's that are like 35mm primary and 51mm secondary, yet a TPI has what twin 48's (or is it twin 24's?)? Big difference in displacement.

 

Any commentary why this is, and would the throttle body I saw off the VW work on a custom EFI system for a Chevy? I like the fact that it has a small butterfly so the tip in would be real easy to take (not overly sensitive), yet have that big throttle bore for the WFO excursions that will surely take place.

 

Am I overlooking the flow through the rest of the throttle body or is the butterfly diameter not a reliable means of measuring a throttle bodies potential?

 

Any info would be appreciated,

 

Lone

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ford does things like throttle body size to limit warrenty claims-the 5.o was choked for that reason.the late model explorer tb's i sent out for almost free were 65 mm.part of that can be explianed by stall speed in torque convertor and a heavy vehicle and an abrupt tip-in to make vehicle SEEM like it has power.a turboed engine cam use a little smaller tb than a na motor cause the turbo will pressurize intake.the late model 5.0 explorer has a large tb.vw has to design for autobahn.this monthes sport /compact car mag has a test on a focus with a bigger aftermarkit tb-it lost midrange torque but the kiddies that use daddies visa will order this stuff anyway .some of the american lemans series cars had air restrictors in the air box to make cars equal-the air goes supersonic in thse things if not designed correctly.us mature engine builders dont care where parts came from-the cheaper the better.just the dyno print outs and no bs.

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Guest Anonymous

Thanks, Randy, for the explaination, that explains the mustang/explorer thing real well, I had wondered why the explorer was bigger. (gives that feeling of grunt... icon_smile.gif )

 

Regards,

 

Lone

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Guest Anonymous

Heh, Tom, I was just showing off hehe, probably should have used the word 'Problem' as some probably thought a conundrum is something to eat, probably why there was few replys on it (either that or they just looked at the person posting it and went icon_rolleyes.gif )... icon_razz.gif

 

Regards,

 

Lone

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Heh, I think you guys covered it well. However my understanding of TBs has always been that the motor would take what it needed if the TB was "too big" and that it wouldn't hurt anything. Tip in throttle response sux of course but I didn't think that the power would be hurt since the restriction past the TB ends up being the bottleneck. Progressive TB might be nice for my project, I don't need a hair trigger thanks!

 

Still need to send my intake out to be converted (sigh). Just haven't had time!

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Guest Anonymous

Well maybe you guys can answer a question for me. I was going to use a Victor Jr manifold on a 383 SBC and wanted to use a throttle body on it. I have been told that a big block throttle body fits on the small block manifold so some guys were swapping to get more flow. The reason I ask is because I can get the throttle body harness and comp cheap at a U-pull place and need max flow for a 388 stroker with a roller train. Grunt-grunt! Any input? weird.gif

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Guest Anonymous

I was a little confused as to why I can run a 750 holley but need a 1000+ cfm throttle body. Is it the actual flow that is the problem or is it the amount of gas.

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  • 3 weeks later...

--------------------------------------------------------------------------------

for those of you that are thinking of changeing to a different throttle body,

the following are the surface areas of the throttle body flow areas

80mm-single bore....7.80 sq inches(about 950cfm)

58mm-twin bore......8.20 sq inches(about 1000cfm)

52mm-twin bore......6.59 sq inches(about 800cfm)

48mm-twin bore......5.62 sq inches(about 670cfm)

and just to add to the possiably useless info I picked up 2 mph and 3 tenths when changeing from a stock 48mm throtle body to a 58mm edelbrock BBK throttle body on a full roller , 6" rod, 11 to 1 compression 388cid engine in my vette!btw just as more silly info nascar restrictor plates that (limit) the car engines to about 700hp have about 3 square inches of area but everything in the engine and intake is designed to work around that restrictor plate because with better flow much cheaper and easyier hp is available, its not so much the size of the throttle body as it is how your engine is set up to handle the available airflow (but in all cases more airflow has the potential to make more power!)thats why nascar has restrictor plates because they know that if the teams could use the flow available from lets say a 58mm twin throttle body the hp/speeds would increase dramatically (yes I know they run carbs)but the airflow idea is valid!and don,t try to directly correlate carb cfm numbers to throttle body numbers because EFI works much better with a larger size rateing because EFI can handle lower air speeds much better because the air flow need not keep fuel in suspension nore does EFI rely on air speed over a venturi to pull fuel into the fuel/air mix

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BB throtlebody bolts on to a carb intake? Is that for port injection or TBI?

 

Interesting numbers Grumpy. I'm going to probably go with a 75mm Ford TB. Single blade and much cheaper than the GM stuff. It'll be placed on a sheetmetal adapter elbow facing forward it looks like - I'm hoping it won't be too tall (ahem). Price is right for the conversion and the elbow so I figure it's worth a shot.

 

What fuel pumps are you having good luck with? I've got an SX, am considering an Aeromotive, and have been pointed towards Walbro($). Don't need a zillion galaons an hour and will only be running about 30lb injectors. The AEM ECU can be had for under $1700 but I'm waiting a bit before jumping on that. I've got 4 WB heater box kits coming and two display kits coming - under $200 total. Just need some $117 UEGOs to go with them and I'll be in buisness! WB has gotten much cheaper now icon_wink.gif

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Has anyone tried to fit 2 single trottlebodies on a tunnelram instead of a tpi intake. Its easy so find 55-65 mm trottlebodies almost for free. Wouldnt it give a better airflow distribution for a high rpm engine.

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I believe I remember one of the Hybridz members doing that...they used a dual carb manifold outfitted w/two TB's.

 

I dont remember who it was but I do remember the conversation being discussed.

 

Maybe you might want to post a new thread asking, "Who's running Dual TB's" and surely someone will answer..or point you to the correct sourse.

 

BTW: along those lines...does anyone make a dual butterfly AFM...say for a TPI set up whereby a smaller butterfly, that is linkage operated, is super-imposed by a larger butterfly overlaying the smaller one that opens at WOT(?)..that would be interesting: kind've like a 4bbl carb opening up at WOT(?)hmm.

 

Kevin,

(Yea,Still an Inliner)

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