BBK 78mm throttle body gain over 70mm?

I know its probly not worth the trouble but I was thinking today about switching out my BBK 70mm TB and C&L plenum for the 78mm BBK TB. I have 24lb injectors already and Im going to backprobe my 02 sensors sometime this week to see if Im running rich at all before I decide to upgrade to the 78mm. Has anyone had the 70mm and then upgraded to the 78mm? if so is there any gain? Im not really worried about losing money for only a few HP since I could easily sell my 70mm and plenum for $100 + But like I said, Im only upgrading if Im running a little on the rich side. Im also swapping PI cams and Intake soon and figured the TB would be a nice extra boost since Ill have it all apart.
 
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The gains are on the order of ~2 HP NA when you move up from a 70mm to a 75mm. I've never seen the 78mm directly compared but I wouldn't imagine anything beyond that. The cost difference of buying new/selling old might be better spent on some SFCs or a shifter (don't know what other mods you have, just speculating). Your money, your call. :nice:
 
Why did you switch to 24s?

What mods do you have?

Did you get a tune when you put the 24s in?

If you still have stock NPI heads don't expect much from simple airflow mods on the intake side. The bottleneck in the NPI or "weak link" is the ports and valves, not the stuff up- or down-stream of the heads. You might see a bit from the PI cams and the intake is hopeless but I doubt a TB will make any difference.
 
I bought the car with CAI, 70mm TB & plenum, 24lb injectors, upgraded fuel pump, msd coil packs, UD pulleys, JET MAF, Steeda short shifter, Catted X pipe with Flows, Competition Clutch and lightweight flywheel. I have no clue why the previous owner put bigger injectors and pump in. He was in his 40s and pretty much did bolt ons and listened to whatever his friends told him to put on it. The only mods ive done since I bought it is 3.73 gears and lower it. The only thing that makes me think it might be running a little rich is that the Evap purge valve trips a code every now and then. Which is why Im going to see what kind of signal im getting from my 02s soon. I cant really think of anymore ways to get more air or back off fuel without getting a tune. I plan on getting an SCT tuner after the PI cam and intake swap tho.
 
I bought the car with CAI, 70mm TB & plenum, 24lb injectors, upgraded fuel pump, msd coil packs, UD pulleys, JET MAF, Steeda short shifter, Catted X pipe with Flows, Competition Clutch and lightweight flywheel. I have no clue why the previous owner put bigger injectors and pump in. He was in his 40s and pretty much did bolt ons and listened to whatever his friends told him to put on it. The only mods ive done since I bought it is 3.73 gears and lower it. The only thing that makes me think it might be running a little rich is that the Evap purge valve trips a code every now and then. Which is why Im going to see what kind of signal im getting from my 02s soon. I cant really think of anymore ways to get more air or back off fuel without getting a tune. I plan on getting an SCT tuner after the PI cam and intake swap tho.

Interesting.

Assuming the car wasn't tuned after these mods if you put a scan tool on it you'll likely see the fuel trims somewhat out of whack because of the larger injectors. During open-loop (e.g. at WOT) you're likely running fat but during normal driving, unless you're getting a MIL indicating too rich, the PCM is able to trim back fuel delivery to get stoich.

The evap code is probably not related to the injectors. You may have an issue at the fuel tank filler neck or evap connections. The O-ring seals there tend to harden and crack over time leading to evap and even gas leaks. Do you smell raw gas near the back of the car?
 
Interesting.

Assuming the car wasn't tuned after these mods if you put a scan tool on it you'll likely see the fuel trims somewhat out of whack because of the larger injectors. During open-loop (e.g. at WOT) you're likely running fat but during normal driving, unless you're getting a MIL indicating too rich, the PCM is able to trim back fuel delivery to get stoich.

The evap code is probably not related to the injectors. You may have an issue at the fuel tank filler neck or evap connections. The O-ring seals there tend to harden and crack over time leading to evap and even gas leaks. Do you smell raw gas near the back of the car?

I had a scan tool on it about a week ago and it was running just a little on the rich side but not much, tho all I was looking at was the 02 sensor signals. I didnt test it at WOT tho since it was just a test for my class in College. I was thinking the Evap purge valve code was coming from my car running rich and extra fuel fumes saturating the Evap canister and clogging the valve. The code hasnt returned ever since I seafoamed my car about 2 months ago tho.

Either way it will be fixed once I get a tune. Right now Im just looking for a way to get a little more air until I buy the tuner or get a dyno tune. Thanks for the input btw :flag:
 
i swapped from a 75mm BBK TB and C&L plenum to the 78mm combo...i felt a decent gain but i have cams so that's probably why i felt a gain from the combo..very nice peice though and id recommend it to anyone NEEDING more airflow. I dont know how it would flow with a mostly stock motor. Heard positive things about it on non cammed cars but i only know it personally with have cams.

like trinity said, if youre running 24lb injectors on a non tuned car your next thing to do would be a tune.. you could be running a high AFR at WOT without even knowing and thats not a very good thing at all
 
Think about this for a second before you change. By increasing the diameter of your throttle body you are allowing more air in however it will be coming in at a slower velocity. That can translate into a possible HP increase way up top but could also hurt your down low and mid range. Besides you already have the 70mm and C&L plenum don't waste your money on that. I recently installed a Vortech V2 S trim on my 04 GT (which also has a 70mm and C&L plenum) and when I asked the tuner if a bigger throttle body was needed he said definitely not! He had just recently dyno'd a blown mustang with the stock throttle body which was making ~500rwhp. So obviously the smaller throttle body was not a huge limiting factor. What else do you have done to your car? I would save the money on all the little stuff and go with forced induction thats where you really get the most bang for your buck. I also have full exhaust (BBK long tube headers, BBK catted midpipe, and flowmasters) and my car dynod just under 400rwhp and torque! Trust me the blower is the way to go
 
Use the money you're going to fork out for the throttle body toward a set of new or used aftermarket cams. Wait until you drop in the cams before you tune it. 30rwhp with cams or maybe 5hp, if you're lucky, with the tb and hurt intake velocity.
 
I had the bbk 78 mm combo and it's a pos. Cost me bottom end,bogged til 3000 rpm. A tb that big without boost will cost you velocity. I put a pp plenum and 70 mm accufab and that was a definite improvement over stock. A bit better city driving torque and pulled waaaaaaaay better after 3000 rpm. Dont waste your money on that bbk junk. My car is a 2000 2v. Buy an accufab if your gonna buy anything but unless your boosted anything over a 70 mm is too big. I didn't Know how big a factor velocity was until I wasted my money finding out the hard way.