Daniel50 said:75mm tb wont kill power on my simple setup?
Daniel50 said:so what would be pritority tb or maf and inj?
5spd GT said:Black95GTS - Part throttle "putting around" is touchy, causing more tip-in issues. If you want to make sure you are getting all the air you can and don't worry about the cons of the bigger TB. Get it...
Just realize you don't need that big when a 65 or 70mm TB will flow enough air for you in CFM.
To many go by "size" and not actual true flow in CFM.
Black95GTS said:To put this into context: 70mm = 2.756 inches. 75mm = 2.953 inches
Are you suggesting that the increased cfm from .197 inches in diameter could effect driveability? Furthermore, any after market cold air kit pipe is at least 3 inches in diameter, not to mention that the people at TrickFlow who engineer race parts for a living designed their manifolds for that size for a reason.
I personally wouldn't think twice about slapping a 75mm TB on there. I doubt you could find many HCI owners that complain about too big a TB.
Adam
edit for spelling
5spd GT said:You go by CFM rating, not the measurement of the TB given by the company. Not all 65, 70, 75, 90. 105mm TB's flow the same when compared one of the same "size".
5spd GT said:Adam...your not thinking clearly.
The diameter on the internal lip has less to do with it, than the design of the TB. Again, and I repeat.
You go by CFM rating, not the measurement of the TB given by the company. Not all 65, 70, 75, 90. 105mm TB's flow the same when compared one of the same "size".
Yes, most cold air kits are about 3 inches in total diameter.
Part throttle is velocity. Velocity is part throttle. That blade is your vantage point. At wide open throttle velocity pretty much becomes a non-issue in most or some cases. Not all.
No, the engineers at Trickflow and other companies put the "size" because most TB's in that given size range will not flow any more than what the "size opening" for the TB will allow. Also another reason is for ease on the customer, not "port matching"...
Believe it or not, velocity is controlled during tip-in by the throttle body, despite people saying it has no effect.
The bigger surface area of the blade will allow more air in at the same degree interval of the gas being stepped on. This creates a touchier gas. This becomes more of a problem in lower gears.
Been there done that, and about to add one to my car, just to make sure I'm getting all the air flow I need...even though I may not need it. It isn't my daily driver, so I'm willing.
Black95GTS said:I agree to what you're saying to a certain point. What I'm saying though is that the TB is only 1 part of the air intake. You have to consider the size of the whole system as 1 unit. Not only does the TB need to flow X CFM, but there needs to be a smooth and uninterrupted path from the filter to the intake. Mixing and matching inlet diameters will undoubtedly negate some of the positive effects of a larger TB.
Velocity is largely a function of exhaust.
http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index.html
And I understand that more air will flow at part throttle... its a bigger tb after all. If you didn't want the car to go faster then don't mod it. If you found a 50mm TB that flowed more CFM then a 75mm TB, I would still go with the 75mm TB in this application. With FI, if the thing is too touchy at part throttle, then pull timing at those RPMs. Any competent tuner can do this. I consider myself only marginally competent and I have done it on my grocery getter. My tune is pretty harmless until 2500 RPMs then it hits like a nitrous shot.
IMO, with fuel injection, flow rates aren't as important as they were with carbs. While its very easy to over-carb a motor, its much harder to over-TB an FI one.
Adam
5spd GT said:Yes, the TB is only one part of the equation in air flow to the cylinders; never-the-less, air enters the engine from the throttle body opening.
So let's say that "50mm" TB flowed more than the 75mm TB...why in the heck would you get the 75mm TB...lol. For the "look"
Some people do not have the means or tools to pull timing at lower rpms...it isn't applicable to everyone. Just like the 75mm TB. It isn't applicable for everyone.
Also, just because someone likes to modify it doesn't mean they need to sacrifice daily driver quirks. So since I like to go a bit quicker than most I know, should I delete the a/c and powersteering. Nope, because it isn't for me. Not everyone wants to do it. Not everyone needs it. Just like not everyone wants a goosy throttle when trying to cruise around. Not everyone wants it.
Cruise control also is more "stop and go"...and that sucks...when your on a road trip. Been there, done that.
It is cfm, not size that gives you the air flow you might need.
Why get a 75mm TB when a 65mm TB might flow enough, while having a "goosy" throttle...a throttle isn't "goosy" when you punch it, it just goes. It is part throttle tip-in...
Go to www.slowgt.com and see how much cfm your engine is capable of taking in, and make the judgement for yourself...
Black95GTS said:If flow benches raced, you would be dead right.
But they don't.
I'm saying that all the CFM in the world doesn't mean squat if the combo is not well matched. How many 302 combos are there that are faster than they should be? Tons. It's all about matching the components to create an efficient power plant. Flow rates are very important, but if they don't jive with the rest of the combo they are useless. If the poster replaced his GT-40Ps with a set of worked Victor Gliddens it wouldn't matter, even though the VG's flow a ton more.
My point is that matching the components is an overlooked and undervalued strategy.
Adam
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