Throttle Body - What size do I need? 3

[Spimage]

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.

 

[patprimmer]

More than you have.

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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[RRBD]

If it is a 4 bbl throttle body,with 1-5/8" bores it is more than enough. Think of the popular 3310 Holley of the old days. I would start looking else where. What heads & intake,what valve springs, what cam(LCA&DUR@.050)? If you're using an old HEI, it may not be up to task. Need more info about your combination. Haltech is great choice.

 

[patprimmer]

Opps, I missed the 4 thing.

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.

 

[Spimage]

Thanks for the response guys and hopefully the following info will answer your questions.
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

 

[RRBD]

What devices are you using to provide feedback to the Haltech? MAP sensor,TPS,and o2 sensor? What are you running for headers and where is the o2 sensor located and what style is it(1 wire,3 wire)? What is your BSFC or AFR at peak? If you are using a MAP sensor,it may be telling the Haltech wierd stuff based on your manifold vaccum or lack of it. In my experience, I've found that EFI likes a cam with a wider LCA(112min) with less duration in order to function properly.If not already doing so, you may want to create your fuel map and base it off of throttle position. It is way less efficient,but it will tolerate a cam with a narrow LCA and alot of overlap. Oxygen sensors can be a pain when using one that is not heated or in the wrong location. This may not be of any help as I don't know your entire combination, but is some insight from my experience.

Scott

 

[patprimmer]

The cam sounds a little short in duration, but everything else sounds like it should make more power than it does.

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

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[benn73]

I have a 900cfm holley TB that has 4 x 1.5" bores. Yours is bigger that this, so you should not be short of air.

 

[Spimage]

Thanks guys for the response, it would seem that the throttle body is ok, that being said, could it be excessive back pressure in the exhaust system?.
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.

 

[schmidtj86]

Did you tune the Haltech? EFI out of the box is usually worse than a carburetor, but I've seen people do it (and don't take offense if you have tuned it - I'm used to the tech calls and have to start with the simplest possible solutions first, hehe).

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?