65mm vs. 70mm Throttle Body

[DucatiRdr]

I'm lining up parts for an H/C/I in the spring:

TW FAC 170s
1.6RR
TFS-1
Edelbrock Performer upper, T Moss ported lower

I have a Ford Motorsport 65mm TB that I bought when they first came out in when...1990? I did a search and the consensus is that a 65mm should flow enough to feed my 302, but Trick Flow and Edelbrock suggest a 70mm unit. These are the guys who engineered the thing, shouldn't they know what works best with their set-up?

Does anyone have the flow rates of:

Accufab 65mm
Accufab 70mm
Edelbrock 70mm
Ford Racing 65mm

I'm sold on the idea of an Accufab, but only if its flow makes sense with my build. So, which size TB for a street driven 302? Driveability and control are important. I'm not chasing max HP, but max area under the curve.

 

[bmo37]

Personally I've always liked to match the intake opening size to the throttle body size. In that case I would go with the accufab 70mm, they always made the best quality throttle bodies imo.

 

[BYRDPE]

Personally I've always liked to match the intake opening size to the throttle body size. In that case I would go with the accufab 70mm, they always made the best quality throttle bodies imo.

i concur....

 

[Mustang5L5]

I'd go 70mm myself.

 

[DucatiRdr]

But if an Accufab 65mm flows as well or more than the competitor's 70mm, why not go for the 65mm for the improved low speed control?

 

[bmo37]

Generally a larger t-body will shift your power curve up, the more velocity (smaller t-bodys create more velocity) the more low end torque, the more volume (larger t-bodys have less speed but flow more air) the more hp. Part of matching your intake and t-body size has to do with maintaining an easy flowing turbulence free flow path and maintaining equalized pressure throughout the system. All in all throttle bodies in general always seem to be a mod that comes up too early in peoples mind sets as the gains tend to be minimal on a n/a car. The real gains are really seen in boosted setups where the velocity dynamic kind of gets pushed out the equation because the system is force feed and at that point it's all about getting as much air into the system rather than worrying about the speed it's moving at since its determined by the rpm vs psi. The drive-ability vs the two is really negligible and you probably won't even notice a difference.

 

[DucatiRdr]

BMO37,

Makes sense, but check out the following Corral thread I found this morning: What Horsepower & Torque Levels are 65mm Throttle Bodies good to? - Corral.net : Ford Mustang Forums

There is a link to an Accufab write-up that shows their 65mm TB flowing more than a 302 can pump. In that case does it make sense to go 70mm? Is bigger necessarily better? If a 65mm can outflow a 302, what's the point of a 70mm?

The technically guided opinions start at post #34.

 

[bmo37]

I usually tend error on the side of caution and best valve for money, as I see it 70mm makes the most sense in your application. The accufab data list cfm based on ci and rpm, what you need to weed through is how you interput the data. Most cars don't spin to spin to 7k especially a daily driver so that data can be specific to racing built engines, the data numbers are based off of what I assume is a stock 302ci engine now is that an equal comparision vs a modded 302ci with more flow potential utilizing larger flowing heads, intake, and cam (this case airflow demand is higher)? Also are those numbers based on a 100% VE. Most n/a cars never reach 100% loads more in the 80-90% range, generally the only time you go over 100% loads is in power adder applications. I think in the end the 70mm is still the best choice for now and gives room to accomidate mods in the future without having to buy another piece. The only other advice I can say is the two mustangs I've owned I swapped the throttle body fairly earlier in the modding process and never noticed the goosey feeling they talk about. Both stangs have 70mm's on them.

 

[NIKwoaC]

Generally a larger t-body will shift your power curve up, the more velocity (smaller t-bodys create more velocity) the more low end torque, the more volume (larger t-bodys have less speed but flow more air) the more hp. Part of matching your intake and t-body size has to do with maintaining an easy flowing turbulence free flow path and maintaining equalized pressure throughout the system. All in all throttle bodies in general always seem to be a mod that comes up too early in peoples mind sets as the gains tend to be minimal on a n/a car. The real gains are really seen in boosted setups where the velocity dynamic kind of gets pushed out the equation because the system is force feed and at that point it's all about getting as much air into the system rather than worrying about the speed it's moving at since its determined by the rpm vs psi. The drive-ability vs the two is really negligible and you probably won't even notice a difference.

I'm sorry, but this is misinformation based on 30 year old carburetor logic.

In a port injection EFI system, the throttle body is nothing but an air valve. At WOT, all you want the throttle body to do is get the hell out of the airflow's way. Velocity through the throttle body doesn't mean a damn thing, it's the job of the intake ports and the cylinder heads to ensure good flow dynamics into the cylinders, not the TB.

It is not uncommon to see guys who know what the hell they're doing put 90mm TBs on N/A 302s (usually with a carb-style intake and elbow, or a box intake). I've even seen guys fill up the bolt holes and EGR passages with epoxy so they could hog out the mouth of an EFI intake to match a 90mm TB. Most recently, I saw pictures of this done on an explorer intake.

Now, I'm not saying you need a 90mm TB (there may be some tuning issues that need addressed and most EFI intakes won't easily accommodate a 90mm TB), but I AM saying that you shouldn't limit your combo because somebody posts flow numbers in an attempt to convince you that all you'll ever need is a 65mm TB. I once read about a guy who put a 1000CFM TB on an intake that the ports flowed something like 350CFM and cylinder heads that flowed somewhere around the same. Once the TB was bolted on, he actually lost overall flow!

Moral of the story is, don't be afraid of "too much" TB.

As a side note, (and this should be a given, but it seems to escape some people) you should ALWAYS make sure the intake opening is as big or bigger than your TB/EGR bore. On most intakes, this means running anything bigger than a 70mm TB requires some grinding.

 

[stykthyn]

Fwiw my eddy performer came with a 70mm tb and egr spacer.

 

[stykthyn]

Also the eddy tb and egr has bbk stamped all over them.