adk61

iTrader: (5)

you may find this hard to believe, but that procomp head isn't a bad head... just buy the empty castings and do the work and put proper parts in them... as for the head it works well for a budget build... just my $.002

JimV

iTrader: (1)

I made the post and stand behind the data and my flow bench. I don't know why would you ask a question you don't want an answer to. I'm sorry your flowbench dosen't tell you how to port a head, build a motor and what prop to use, mine dosen't either. My flowbench provides data, period. It's up to the operator to desifer the numbers and decide were to go from there. For those of you who don't know I flowed the stock cnc exhaust port, modified it and got an average gain of 26 cfm from .200 to .700 lift. Peak gain of 38 cfm at .500. To answer your question: AFR uses a cheater pipe when they flow there exports. A cheater pipe is a 6" pipe that does nothing but enhance the numbers on there flow bench, my flow bench and your flowbench if you were to dig it out of the trash. I'm not sure where they get there advertising numbers on the web site... hmm... maybe a FLOW BENCH. A flowbench is to provide a measurement
The data from my flowbench tells me how efficient a port is. Example, I know from flowing more ports that I can remember that a 1.880 exhaust valve can flow in the 330+ cfm no cheat pipe on a old style Dart Pro One head. The new ones wont do it, different story. It's obvious on the video's, the port volume, crossectional area and area at the flange are different than the much smaller AFR's Flag up excessive exhaust pressure. The piston has to evacuate the cylinder, a choke in the port means more pressure on the piston along with other potentiual problems. Maybe one of those engineers can give you the psi. I don't have that number. The second video shows the modified afr port. There is an editing error, at .500 It should read 286 cfm. The multiplier is .318 times the percentage
The second part of reading data is airflow increase between the lift points. The stock cnc'd head shows near peak flow at .500 lift whereas the modified port at .600. The data from my flow bench data also shows if the flange size is correct for the application. Reading the curve, if the venturii, bowl, short turn is correct the higher lift numbers will flatten out considerably. It really pisses me off hearing of the few broom stick cowboy internet engine builders out there that don't have a flow bench, or do have one and do not know how to use it, or even worse owning one for a status symbol and are giving advice and BS because the profit margin. I got one down the street from me. I was in his shop a couple of years ago looking at what he said flowed 300 cfm on a fluffed up set of Darts. He backed himself in a corner and was able to bring him back his 260 cfm heads he sold as fully ported. I did ask one of the members here on OSO to dyno one of his sets of the cnc'd afr's he had up for sale, against a set of my heads, appearantly he drank the kool-aid too and declined.

Video 1: https://www.youtube.com/watch?v=lefrYoaVsCk
Video 2: https://www.youtube.com/watch?v=9SP9vzIFifc

Video 3: cheater pipe racing : https://www.youtube.com/watch?v=C9AQzI-pfdo

buck35

You obviously know heads and flow, ... but how can you possibly call any exhaust fitted to the head a cheater?
In the real world isn't said cheater going to end up perhaps being the limiting factor?

MILD THUNDER

iTrader: (3)

Buck, some heads are flowed with a pipe, and some not with a pipe, when publishing flow numbers to help sell their heads.

As for JimV, he does know heads and flow. And knows engines as well. Having worked for Roush, Dart, been involved in development of cylinder heads for big companies, modified tons of head for oso members over the years. I personally feel his resume makes his words worth listening to. He is by no means, a ''monkey with a dremel tool". He is a guy worth having around on oso in my opinion.

buck35

I totally understand that and give him all my respect, but heads are designed to have an exhaust bolted on. I've never seen a set of cheaters , be they dry or wet.
absolutely no disrespect intended .

Cole2534

iTrader: (1)

Who cares what's bolted on? Find out how they're flowed at the factory and take that into consideration.

offshorexcursion

iTrader: (5)

The pro comp head can be worked to flow good numbers.

IMO the cheap casting can not reliably handle a lot of power though.

Even with the best parts installed, shaft rockers etc, the casting will fail.

Black Baja

iTrader: (2)

The steady, low pressure airflow testing described for intake valves often fails to adequately predict the performance of exhaust valves/ports. Inconsistences frequently occur where enhanced flow bench performance leads to decreased engine performance. This is a result of the considerably different exhaust port flow environment, which includes higher pressures, compressible flow, and products of combustion. Early gas exiting occurs under high pressure as critical, or choked, flow then transitions to sub- critical flow under lower pressure ratios. Normal practices are to ensure the exhaust port flow capabilities are at a minimum of 60-80% of the intake. This however does not ensure the most efficient geometry and can lead to larger than required valves/ports or a restrictive exhaust. Excessively large diameter exhaust valves leave less room in the cylinder head for the intake valves, while a restriction can significantly lower the capabilities of the engine regardless of intake flow improvements. Other general findings include maintaining a minimum area throughout the port or increasing exhaust port volume can often increase engine performance. It would be desirable to have improved methods of analysis specifically designed for exhaust ports during critical flow to understand these findings and produce more efficient port geometry. This would be of particular interest to high performance engine designers within the motorsports industry.

Copied from a research study Unniversity of Miami. And the main reason why I began the thread the way I did. The flow bench is a poor piece of equipment to be using on the exhaust port. My question is was the flow bench the final test done with the exhaust port? Was there and kind of dyno testing before and after? Track, water whatever kind of testing before and after the work was done to the port?

With page upon page of combinations putting up big numbers AFR's port with the cheater pipe seems like it has done very well. I'd really like to see some more real world testing cause as stated the flow bench testing doesn't really mean anything. Maybe the port wasn't fixed and instead broken.

Rattlesnake Jake

iTrader: (2)

When I looked into them I was told if going over 600 lift to use Girdles.

F-2 Speedy

iTrader: (6)

I would recommend running stud girdles on about any high performance engine regardless of the cam profile, stability is key, heck I use to run them on 450 hp small blocks back in the day, jmo