how many cubes can my heads handle?
how many cubes can my heads handle?
(OP)
I am building a motor starting with the heads. I have a set of Brodix BB2-plus heads and would like to run 540 cubes or more. Brodix says that these heads are good up to 522 cubes if ported and flow about 370 CFM @ 28". The BB3 heads flow the same but have a larger intake runner volume so they say it can handle more cubes. My question is that if the heads flow the same why can't they handle the same size engine? What do others think of the heads I have, can I run a 540 or more through them and how well will this combo do? Looking for others opinions/experiences.
Thank You.
Michael
Thank You.
Michael





RE: how many cubes can my heads handle?
To test this theory, you'll need the head volume.
RE: how many cubes can my heads handle?
The CFM of your heads and the CI displacement of your engine need to be matched to the power output and engine speed range you require.
Compression ratio will be dependant on a number of factors, being combustion chamber volume, deck clearance, head gasket thickness, piston crown shape and the cylinders displacement.
The phrasing of the OP indicates maybe you are in over your head, and therefore not seeing through sales hype and very broad generalisations. Do you know a good reputable engine builder who has built similar engines for similar applications. His advice might be valuable.
If you want more advice from here, you need to give more details of the other engine components and your application and aspirations.
Regards
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RE: how many cubes can my heads handle?
Unless you are going to build engines professionally I would not recommend using all those expensive parts as a learning curve...
Cheers
I don't know anything but the people that do.
RE: how many cubes can my heads handle?
Michael
RE: how many cubes can my heads handle?
Port, or intake runner, volume plays a big role in charging the cylinder. Small port volume is for smaller displacement -OR- lower power range. An example would be a 300cc port on a 500 cu in BB. It would be a stump puller but also would be falling short at perhaps somewhere around 5,000 to 6,000 RPM.
RE: how many cubes can my heads handle?
For max power... CSA x 184,136/Stroke x Bore2=Max RPM
RE: how many cubes can my heads handle?
Michael
RE: how many cubes can my heads handle?
Problem with using cross sectional area is it's only considering a 2 dimentional cross sectional area cut in a plane and not looking at 3 D effects of the port geometry such as flow shear, flow break away, etc etc.
A steady state Flow Rig (which is where the CFM numbers come from)does. Granted, it only allows deductive reasoning from obeservation and may not allow you to really understand why (you need CFD for that) but I think the CFM numbers are useful. I once worked with Ford but now have gone all metric I'm afraid, so am using AlphaKs (relative to bores)and metres cubed per second, and then use a 1 D code to evaluate. So I can't help the original poster right now I'm afraid.
RE: how many cubes can my heads handle?
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.
RE: how many cubes can my heads handle?
Have you taken a look around the Airflow Research (AFR) website? There is some good info there. They have done a tremendous amount of development for BBC heads and are about the best in the business.
http://www.airflowresearch.com/index.php
RE: how many cubes can my heads handle?
Michael
RE: how many cubes can my heads handle?
Whenever you set out to build a particular engine combination there are several things to consider. One thing I am amazed that no one has asked you yet is the type of car you are going to run, how much it weighs and several other variables. The first thing you need to do is determine what you want to accomplish and design everything toward that goal. Now, if you already have the -2 heads as it appears from your initial post then why don't you consider building a smaller engine. If you have no parts and want to build the bigger engine then you need to consider the requirements to build that combo successfully. Airflow is certainly important but there are so many other variables to consider. The intake runner size/volume will go a long way to determine where in the RPM range you are going to make power but also you need to remember that it takes a certain amount of volume to feed certain size motors efficiently.
It sounds as though you need to consult a reputable engine builder in your area or a good cylinder head shop to help you make the right decision. These resources are available to you so why try to make such an important decision on your own? One last thing is that you need to be realistic with your goals for this combination a take everything into consideration. Especially your financial situation.
I am not trying to muddy the waters here but if you were going to have to buy a new cylinder head you should probably consider the fairly new Brodix -3XTRA series which has been rolled to 24° instead of the standard -3.
Good Luck
Larry
Larry Coyle
Cylinder Head Engineering, LLC
www.cylinderheadengineering.com