Untapered throttle body

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CrazyAzn

CrazyAzn

Senior Member
okay so since i got my car dyno'd i have been wondering why my power drops off so badly after like 7500 rpms. I thought it was the exhaust and header, but i then realized i have a 68mm holley throttle body on it. BUT this throttle body is 68mm all the way through, it is NOT tapered and lacks the velocity stack that all throttle bodies have.

my question is, could this throttle body actually be costing me power? Since i would believe at 8k you would need all the flow you could get along iwht the most acceleration. if someone could help me out here that would be awesome, im not all that sure of flow characteristics or dynamics, but if honda designed a velocity stack, im sure theres a reason.

Note: THe power just drops like a rock after like 7500, also dont mind the juice stain on the paper

DynoChartb18c-1.jpg
 
It looks more like a fuel cut issue than an airflow issue. If it were an airflow issue, you'd likely see a plateau in the power as a result of maxxing out the flow potential of the system. I'd bet on a fuel issue. The stock tapering is just there to allow a higher flow velocity at lower rpm, boosting midrange rpm, and assisting in smoothing out the transition from intake to manifold plenum.
 
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interesting. . . i was thinking that too. . .but wouldnt my AFR go really lean if that were the case or not necessarily? i have rc 310 with the stock fuel pump, has anyone had an issue with the stock pump not being able to feed 310's or a 1.8 GSR?
 
what engine and what cams are you using


questions to ask your self

is vtec working

are the cams to big causing valve float

look at your fuel map is the voulmetric effiency of the engine droping like a bomb if think about what would cause this im sure its not the throtle body did you have the intake re bored so the plenum will accept the new size throtle body if not you are causing a ton of turbulance in the plenum /throtle body
 
CrazyAzn said:
interesting. . . i was thinking that too. . .but wouldnt my AFR go really lean if that were the case or not necessarily? i have rc 310 with the stock fuel pump, has anyone had an issue with the stock pump not being able to feed 310's or a 1.8 GSR?
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Yeah, you would most likely see a rise in afrs, but not necessarily - If the TB is causing the airflow to choke out prematurely, you could see the AFR's go more rich as well. Try replacing the TB with a stock one and see if that hurts/helps the situation. Also, despite the fairly poor grammar of 97hatch's post, if you didn't portmatch the IM to the TB, you might have some serious turbulence in the plenum, which in turn could cause some serious dynamic pressure differences in the runners.
And yes, a stock pump should be able to adequately handle 310s. Also look at your fuel map, and see if there may be any problem areas with timing or fuel around 7500 at WOT.
 
I also realized it could be my stock clutch slipping. . . I think this because the sound of my motor changes around the pt where i lose lots of power. . If my clutch were to slip on the dyno, that would cause the loss in power, correct? just brain storming ideas as to why my car is being stupid. . . LOL

my step up is a 1.8 gsr bottom end, b16 pistions, PnP b16 head, itr cams, dual valve springs. Those are the major things that are worth mentioning.
 
Yeah, a slipping clutch would be a problem.
 
Does a dynapack load the wheels like a Mustang dyno? Could be the weight set up all wrong, my car almost died on the dyno becuase it was setup poorly. Killed my clutch too. But then again, I've heard that name Church on here a couple times, I would assume they know whats what.
 
yeah it loads the wheels like a mustang dyno. . . and church does nothing but tune cars, both for race teams as well as the everyday shmo. . . but i think my clutch slippped up high, because the power keeps climbing then all a sudden peaks and drops, also the motor sound changes around that rpm. i cant describe it in type, but it has a diff sound that your motor does when your smashing regluarly.

also its a stock exedy replacement clutch. . . i wasnt planning on making that much power. . . guess i was wrong (not syaing 180 is alot, but way more than stock )
 
My buddy is using a Exedy Stg1 Organic and making a lil more then 300whp on his Teg. Time to upgrade :)
 
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