Throttle Body - What size do I need?
Throttle Body - What size do I need?
(OP)
I have a 377 cu in Chevy V8 with all the mod-cons incl. the "Haltech" fuel injection / management system. My problem is that on the 'Dyno' it is peaking at 200 kw at 5500 rpm and holding this through to 7500 rpm. I suspect this due to restricted breathing, the size of the throttle body is a 4 barrel 41.25mm (1 5/8") Does anyone out there know how many CFM it would need to flow in order to continue making power above 5500 rpm, and if so, what size throttle body I would need ?. Any input in this regard would be greatly appreciated.
Warren.
Warren.





RE: Throttle Body - What size do I need?
Bigger than you have.
Seriously
What RPM do you want to achieve.
What is the throttle bore ob a Gen 111 SBC with factory rating for 300 Kw or about 400 HP.
Sprint card run about 2.25" or bigger throttle blades I think.
I would guess you could run at least 2.5" and up to 3" would run OK, but the throttle night get touchy.
It really depends on how much more power and how many RPM you want to run, and how much you are prepared to give away to get it.
It also depends on port and valve size and cam timing etc.
Regards
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RE: Throttle Body - What size do I need?
RE: Throttle Body - What size do I need?
You have 8.3 sq inches. I was thinking you had 2.1 sq inches
You need I would think about 6 to 7 sq inches.
As RRBD says, look to other areas for the performance boost you require
Regards
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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Throttle Body - What size do I need?
Heads: Brodix Track 1 CNC Ported
Intake: Victor Junior ( At the time, not 'Port Matched')
Valve springs: 240 lbs seat pressure
Camshaft: Comp Cam part # 12-705-8,
Mechanical Roller
Lift: .575" at valve, both Inlet & Exhaust
Duration @ .050, 225 deg " " "
Lobe Seperation: 110 deg.
Valve Lash: .020
Ignition: Crank Trigger, Wasted spark ( No distributer )
Multipoint feul injection.
Regards,
Warren
RE: Throttle Body - What size do I need?
Scott
RE: Throttle Body - What size do I need?
Is the exhaust adequate for the power you seek.
I have no experience with electronic engine management systems, but can, and if so, have you tried adjusting timing and fuel supply on the dyno by overriding the "O2" sensor and whatever else controls it to give an A:F ratio of something like 12.5, presuming the fuel is petrol.
Another thought, what is the compression ratio, and do the piston domes interfere with flame propagation in the combustion chamber.
Regards
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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Throttle Body - What size do I need?
RE: Throttle Body - What size do I need?
I am using 4" side pipes with 2.48" perforated inner pipe (+ - 40"), Any ideas as to what the max back pressure should be.
Regards,
Warren.
RE: Throttle Body - What size do I need?
Are you running the 4 barrel with 8 MPI injectors on the runners, or are you using a 4 barrel with 4 TBI injectors in the TB? What was the observed air fuel ratio during these pulls? How about fuel pressure? How much ignition timing are you running? Have you verified the ignition timing?
Was it an engine dyno or chassis dyno? If chassis, what transmission?