What valves is everyone running in their ported/cammed heads?
What valves
- Thread starter eaglesnick
- Start date
I knew you were running the oversized manley valves, but I heard the stock valves flow better/more than the manley's.
Let's try this another way. Below is independent flow testing for my CNC ported heads @ 28" of water for comparison. The heads have backcut 1 mm oversize stainless steel valves. The intake ports may show 5-10 CFM more at all levels according to test facilitator. He did not have the correct intake orifice and molded a facsimile. Also note the exhaust valve testing was not done with a flow tube. The flow numbers are less without it, and this is an important consideration for comparison:
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Let's try this another way. Below is independent flow testing for my CNC ported heads @ 28" of water for comparison. The heads have backcut 1 mm oversize stainless steel valves. The intake ports may show 5-10 CFM more at all levels according to test facilitator. He did not have the correct intake orifice and molded a facsimile. Also note the exhaust valve testing was not done with a flow tube. The flow numbers are less without it, and this is an important consideration for comparison:
Pardon my ignorance, but I have no idea what any of those numbers mean. You mentioned your valves are backcut 1mm oversized SS valves , but didn't mention the brand. Also how strong/stout are the stock valves.
Those are the flow numbers in cubic feet per minute (CFM) of the intake or exhaust passage air flow under consistent pressure (28" of water) with the intake and exhaust valves at different lift heights off the seat (.100", .200" and so on). This is an overall representation of the heads flow capacity and characteristics. It is used as a baseline and to determine the effects of changes to the valve, ports, bowls or valve job. It is repeatable and comparable with the same head design or others. These are very good numbers to know and ask about when considering porting, competition valve jobs, valves or the heads themselves.
I use SS valves in rebuilds as they are generally stronger and lighter then stock valves. This is important as spring pressures increase. I got a package deal for valves, guides, springs, CNC porting, repairs and assembly from one of the major mod motor providers. I am not sure where they got their SS valves. Although my heads flow well for what they are, I do not want to give the company any credit. My heads needed $400 in repairs right out of the box from the provider for issues that are visible to anyone giving them even a cursory look.
Thanks for the explanation, sucks that the shop didn't do the job right the first time. However noticed at the top of the page it says the heads combustion chamber is 50 cc are your heads cobra heads? I thought cobra heads are 52 or 53 cc. Anyway the valves we decided to put in my heads are Ferrea back cut 1mm oversized.
The OS valves take up more room in the chamber. My heads were surfaced by the provider after welding up detonation damage also removing chamber volume. Then the heads were returned to me with chatter marks from a dull cutter that required another .003" from the surface (valves were also not lapped). This further removed chamber volume, and 50 CC is all that was left.
The service that made the repairs to the repairs (local) also CCed the heads and checked the head flow. The repairer of repairs is very well known and highly respected in Buick circles for his head work. I was suspicious of the actual flow numbers since the workmanship had been so poor from the original provider, and I needed the head CC in order to select the right pistons. Turns out the heads flow well for 4.6 heads, but the original provider does not specify what 4V heads are flowed to give their advertised numbers. So be careful to get 4.6 head flow numbers and not 5.4 head flow numbers from GT heads. What I got was not what I thought I was getting in so many ways!
The service that made the repairs to the repairs (local) also CCed the heads and checked the head flow. The repairer of repairs is very well known and highly respected in Buick circles for his head work. I was suspicious of the actual flow numbers since the workmanship had been so poor from the original provider, and I needed the head CC in order to select the right pistons. Turns out the heads flow well for 4.6 heads, but the original provider does not specify what 4V heads are flowed to give their advertised numbers. So be careful to get 4.6 head flow numbers and not 5.4 head flow numbers from GT heads. What I got was not what I thought I was getting in so many ways!
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Let's try this another way. Below is independent flow testing for my CNC ported heads @ 28" of water for comparison. The heads have backcut 1 mm oversize stainless steel valves. The intake ports may show 5-10 CFM more at all levels according to test facilitator. He did not have the correct intake orifice and molded a facsimile. Also note the exhaust valve testing was not done with a flow tube. The flow numbers are less without it, and this is an important consideration for comparison:
Your flow numbers are impressive but I don't see how relevant it is to what the OP was asking. Some comparative data would interesting to see. These numbers are what you typically see on heads that have extensive mods.
Getting back to the thread; I don't think there is a big incentive to replace the OEM valves. You won't see big improvements in flow numbers with just a valve change and the factory valves are very reliable and seal the chamber as they are supposed to. I would put the money elsewhere unless to have to replace them if they are beyond their service limit. Manley is a good choice
I'm not a big fan of oversize valves. They will improve flow numbers but the size only goes up 1 mm which isn't much of an increase. What you’re doing taking this route is removing more material that the seats rely on to stay imbedded into the cylinder head. The area directly between the 2 exhaust valves now has a narrower heat path as the rest of the seat. That area already runs hotter than the rest of the circumference of the valve because of their close proximity. What little material it left between the valves seats after they are opened up for oversize valves is scary. It's best to have as much "meat" surrounding the seat as possible. Sometimes it's better to leave things as they are. Besides, this is an FI engine not NA, any gain going to oversize valves would be like a flea landing on the passenger seat. Porting is what nets the biggest gain in flow numbers not like our engine needs it with a blower in front of everything :rockon:
Sorry Russ, I started to type a response, but decided it is just not worth my time. OP, you know I am happy to converse with you here or again through PMs.
Over sized valves do not necessarily increase the peak flow numbers over a stock sized valve. They will however increase the flow in the lower lift ranges. Torque can be picked up here whether it is normally aspirated or force inducted. However, if the bowl area above the valve seat has not been opened up to match your increase in area ( pocket porting to match valve diameter ) any increase in flow will be minimal at best. The stock valves with a back cut and bowl work can see an easy 25% increase in lower lift range flow. I have done it, even without large increases in cross section area. That is where most of the porter's time should be spent. The "GT" heads already have larger exhaust valves from the factory. By 2mm, they are 32mm in diameter and they have the same basic constuction between the valves as the Terminator heads. There is no coolant flow between the stems or right above the seats there either. Plenty of material. The "GT"s are force inducted too. If you are having your heads worked over and can afford the increase in price and the heads will be ported to match the increased diameter available I say go for it. But, remember you will not see dramatic increases at the dyno. A 1cfm increase in flow is a potential increase of 2hp. Then again a restrictive intake can still hold back a good set of heads no matter how the engine breathes...
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hey Quick Strike you a smart Guy sorry to hijack for a second.but with a larger bore which I have 3.700 the heads will flow more cfms correct due to the unshrouding of the valves to the cylinder bore.? I got stock Ford revised heads non ported I have a book that states a 20/30 cfm increase due to the bigger bore.
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Gary, I have seen that figure in a magazine article as well. There was no data or comparison to back it. It did not say if this was an overall gain through all lift points or just in a particular lift range. I am sure unshrouding by .075" on each side will provide some improvement in flow (probably greater in lower lift figures), but I have not seen any back to back comparisons showing them.
I was not trying to raddle your cage. If you installed larger valves chances are the mods on your heads are quite extensive which makes it hard to get your head around how it compares to just installing larger valves. I think the cfm numbers you posted are pretty close to the best flow you can get out of a set of Cobra heads which is nothing to sneeze at :rockon:
With regards to unshrouding the heads on the Boss block. You can open up the chamber walls on a 3.700 bore motor to match the clearance with the 4.6 but doing this makes it a dedicated big bore head.
Here is a photo of a 3.700 bore gasket and the relationship to the chamber.
I think unshrouding the valves on a big bore block would show some pretty decent improvement on flow into the chamber as I would say about 20% of the circumference of the valve is obstructed by the 4.6 cylinder and chamber walls
I would have posted a pic of the finished head but for some reason I didn't take a picture of it yet and I don't want to pull them off the engine that is waiting to get clearance honed and assembled
My heads are done other than cutting the seats and valves but this is a good comparison photo showing the degree of unshrouding that can be achieved.
This removes a sizeable amount of material in the chamber so keep that in mind when considering the piston dish and what compression ratio you want. I haven't put a cc plate to these chambers yet but it's more than 52.
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