Hilborn Stack Injection CFM?

Gotzy · Nov 19, 2009

Hey People,

Always wondered how you work out the CFM of Hilborn stack injectors for matching to a motor. Hilborn list 2-3/16", 2-7/16", or 2-1/2" bore sizes for the SBC intakes so how would you match these to a given motor.

I've got 265 and 327 project motors and a 12.5:1 350 race motor for my Morris Minor that I'm always considering stacks for but don't know what bore sizes to keep my eyes open for. I'm sorta happy to find a deal on a manifold and then build the motor that would suit it best but need the all important maths to get started, any advice out there?

Cheers

Steve

Eddie's chop shop · Nov 21, 2009

cfm is completely different when you are running individual stacks.

Running a carb through a manifold, not all cylinders are pulling air at the same time so individual cylinders are getting more air than 1/8 of cfm of carb. Inivdual injectors require much more air per cylinder since the cylinder is only getting air from that stack can't rob from a common carb while other cylinders are on the exhaust stroke.

Obviously your choice will depend on your target use and power.

Larry T · Nov 21, 2009

I think I'd give Fuel Injection Engineering a call. If they don't know, nobody does.
Larry T

rd martin · Nov 21, 2009

cannt think of the guys name at enderle injection, but he is very wise, he will put you on the right track. hes happy to talk and will explain

four-thirteen · Nov 21, 2009

The manifold is just a single part of an expensive kit. You can find a variety of SBC stack injectors in the 500 dollar range. The rest of the kit is also a lot of money. It is a lot like buying a blower. The blower isn't expensive but the rest of the stuff adds up fast.

The 2-1/16" injectors are the cool looking manifold. the others look like late model circle track stuff. http://cgi.ebay.com/ebaymotors/HILB...r_Truck_Parts_Accessories?hash=item20ae269d74

Unless you plan on spending a ton of time tuning and are going to set records, the old 2-1/16 stacks will give you almost the same performance as the larger units with the small displacement you are looking at. But it should also be noted that for a race application they are basically impossible to oversize for tuning, but might hurt the volumetric efficiency a bit.

panic · Nov 21, 2009

might hurt the volumetric efficiency a bit

How?

four-thirteen · Nov 22, 2009

panic said: ↑

might hurt the volumetric efficiency a bit

How?
Click to expand...

<link rel="File-List" href="file:///C:%5CDO***E%7E1%5CDavid%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_filelist.xml"><link rel="themeData" href="file:///C:%5CDO***E%7E1%5CDavid%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_themedata.thmx"><link rel="colorSchemeMapping" href="file:///C:%5CDO***E%7E1%5CDavid%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_colorschememapping.xml"><style>  </style> The variable, non-constant area cross section of the intake runner could affect the propagation of the transverse sound waves through the runner. For ram tuning to work properly the wave needs to be reflected off the open end of the stack. A change in cross section will also reflect the wave which would mess up the tuning by changing the apparent runner length. It would seem to be best to keep a uniform cross section from the mouth of the tube all the way to intake valve.

Hot Rod magazine has been active in this research since ramchargers started playing with it in the early 1960s. Here is a recent article from them. It is somewhat hard to follow due to the non-technical terms being used, but it illustrates the workings of the ram tuning principle. http://www.hotrod.com/projectbuild/113_9907_manifold_ram_tuning/index.html

Regarding the reflections of the sound waves, hot rod doesnt cover that well if at all. Here is a website with some animations showing the sound wave reflection off open and closed ends. http://www.phys.unsw.edu.au/jw/flutes.v.clarinets.html

exwestracer · Nov 22, 2009

One idea would be to convert the bore size to metric, and compare it with flow #s for a comparable size EFI throttle body. The info on those units is much more readily available. There is an online calculator here: http://www.revtronix.com/tech/calculators/throttlebody

Most racers don't worry too much about it, because the injector will usually flow more than the intake port it is feeding. I think that was Hilborn's (et al) theory in manufacturing them. I just figured it out for my 2.9 (75mm) Crower, and it comes up 460 cfm each. My heads flow 420 cfm at max cam lift, so the throttle body shouldn't be a restriction. If you're trying to be very precise, the type of shaft and throttle blade profile will have some effect on total flow.

Keep in mind that CFM is much more important when sizing carbs to get a good vacuum signal for metering. Obviously not a problem with stack injection.

frankenstein1948 · Nov 22, 2009

Try Spud Miller at fuel injection enterprises.1-541-990-2485
Great guy and very knowlagable about injection of any kind.
He came highly recomended to me by a couple of blown alcohol racers and rebuilt and flowed my crower stack injection set up for me.

lippy · Nov 22, 2009

How come since I switched from a tunnel ram with a bugcatcher to stack injection my vacuum wipers have been acting funny and the power brakes aren't as sensitive? This is on nitro of course.

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Hilborn Stack Injection CFM?

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