gollum

iTrader: (1)

When designing the new LS7 427. Why did GM choose the C5R cylinder head with short and wide rectangular ports over a ported LS cylinder head with tall and narrow cathedral type ports? I am sure there was some type of flow restriction using the cathedral heads for a "true" high performance street engine. Is there anybody experienced with C5R heads that can give use a good comment. TEA, AFR etc.

Lets keep this ***** going!

Adrenaline_Z

Taking notes from `Scientific Design of Exhaust and Intake Systems`,

the port shape is not as important as cross section, flow characteristics
and flow volume.

Having said that, I`m not keen on the flow characteristics of each port shape.

My interpretation is the rectangular port is easier to grind and shape for smoother
air travel through the port and to the valve.

gollum

iTrader: (1)

Aftermarket better hurry up. Comp Cams will need to supply affordable offset roller tappets and rocker arms. Wilson manifolds needs to design a matching intake. AFR will supply their new C5R heads for different engine combo's.

Adrenaline_Z

Are these the heads you speak of?

sross

iTrader: (1)

I agree. My understanding of the original "cathederal" ports was that it was more for injector location (direct shot at the intake valve) rather than flow. I guess it's possible that, even with the more traditional shape of the C5R and LS7 port, injector placement is still optimal due to the increased port volume.

I think if you saw the two port styles side-by-side you wouldn't refer to them as "tall and narrow" and "short and wide" (as in the first post) but instead "tall and narrow" and "tall and wide."

Richard@WCCH

iTrader: (3)

Cylinder head design is usually a series of compromise. Port shapes and cross sectional area are compromised by placement of things like pushrods, bolt hole bosses and water jackets, not to mention locations of intake and exhaust systems. Ports with larger radiused corners tend to be more efficient and therefore can be smaller in their cross sectional area than ports with tighter corner radii. These ports tend to be oval in shape and are often found in ultra high rpm drag racing engines. Often time port designers find the need to maximize port area and accept that the sharper corners of rectangular design have little effect on port flow performance for the given application.
The "Cathedral" port shape of the LSx family of heads are a unique design. Remember that the triangular shape of the port roof entrance is covered by a manifold flange that houses an injector. The actual port entrance cross section is rectangular in shape. None the less, the tall skinny design keeps the cross sectional area near optimum for the dual purpose nature of the entire LSx powertrain line. Flow tends to hover along the floor at low port speeds, while at higher valve lifts the measured velocity peaks migrate toward the extended roof line at the port entrance. IMO the GM engineers have done a masterful job of blending a high performance port design while delivering low emissions and increased fuel mileage.
Nice topic.

Richard

gollum

iTrader: (1)

Thanks for the good comments and pictures everyone. And for the certain ones that did not answer, I understand.

The correct spelling of "ca the dral"

gollum

iTrader: (1)

The GM racing team developed the C5R based on the GenIII design, but with a few major changes, the biggest being a 12-degree valve angle, from the production 15 degrees, for a straiter intake port shot. The intake port and roof were raised and widened for better flowing, easier to shape ports. They also offset the valvetrain to clear the now wider ports. All of these changes were a common sense approach at achieving higher volume air flow while maintaining good quality air/fuel mixture for a higher performing engine.

Duh........these heads heve been sitting under our noses for 8 years now and finally someone with enough common sense (GM) puts them to street use.

gollum

iTrader: (1)

Now that GM has set the standerd, it will not be long for the aftermarket to follow with a more affordable street version. My 2002 SS Camaro will be paid for in a couple of more years and then I will take the C5R route! I am sure the head will be cheaper and more common by then. Death to the LSx cathedral type head.

69firebird

iTrader: (14)

well lets not forget the chamber size on those heads is like 5cc, so youll have to run a dished piston to compensate.

It appears that all the aftermarket head companies have followded the original GM design, and kept the cathedral port shape.

As already pointed out, the cathedral part of the head is covered with the intake manifold. I just received my GMPP intake, and it has rectangular ports, and when it was tapped for the injectors you see the rectangle, and then a hole above it.

The production head is a great head, there are shops that have these heads flowing 340, that more flow than most other aftermarket heads (ford, dodge, imports, etc), and is the highest, mass produced head I have herd of.

Look at the ford production ported heads, go to patriots site, their ford ported heads, are flowing less than most stock LS1 heads.

Were lucky to have as nice a head as we do, lets not look a gift horse in the mouth
ed
firebird455@gmail.com

Tony Mamo @ AFR

iTrader: (13)

Good stuff...

What I would also like to add is the obvious big benefit the C5R/LS7 style heads offer regarding floor and short turn height. That lends itself to a much better "angle of attack" for the airstream which always helps to bolster flow numbers....especially peak flow. I was always disappointed with all the height the GM engineers/designers had to work with and the fact they still left the floor of the intake so low. I played around with a conventional style rectangular entrance raised higher off the floor in a stock LS casting a while ago with good results but without a production intake to fit the new port shape and height, it was really just kind of a fun experiment. Still, considering all the postives this new head designed offered (valve angle, lightweight valvetrain, great exh. port layout, etc.) it was still a homerun as evident by all the results we see daily on this board and others. And in ported trim, I must admit it is a pretty killer piece all things considered.

I still think it will take awhile for the newer LS7 architecture to make it down to the mainstream due to all the other parts that become necessary to run that style set-up. It wont be cheap when the smoke clears, and it is also far better suited to large bore motors, another limiting factor that will effect it's "mainstream" status. Bolting a set of these on your stock 346 shortblock simply will not be an option. I think there will still be MANY more cathedral style LS motors roaming the streets for quite awhile but a glimpse of the future is here and it is available to the people that have the money and the type of shortblock that can take advantage of it.

Tony M.

70 TA

I have heard that there may be a truck application "LS7 type" head kicking around. I didn't hear if it was a smaller valve for smaller bore blocks.

There is always something new on the horizon to entice us to spend our money on

Richard@WCCH

iTrader: (3)

Tony, do you have plans to make a intake manifold for these engines? I do believe that's becomming a limiter for the larger displacement engines. They make enough torque IMO and they could probably benefit from a shorter length runner. They need something to widen out the powerband.........

Richard

Big-DEN

"They" still haven't gotten all they are out of LS1/LS7 castings. Flowwise, yes, or close to as much as they will get.

But once you bolt the intake manifold up, most of these are under 300CFM!

Like I said BEFORE, someone needs to come up with a standard templated - port entrance for the LS1/LS6 head so that someone can make the manifold, that once you bolt it up, you lose 10CFM tops, for a 300-340CFM Induction system.

More than this, I'm sure you have to go to the LS7 offering. My guess is the LS7 will be 400CFM or very close to with some porting. Be nice if you can get to the other side of the 400CFM mark.

With a 2.2" intake valve should be easily possible, otherwise GM couldve stayed with a 2.08 or 2.100" intake valve and made about the same amount of flow as they are now.

My hope was the LS7 would be able to eclipse 300CFM@ only .400" of valve lift with some work, and hopefully 350CFM by .500", of course over about 220CFM@.300".

Wonder what the intake manifold is doing. My guess is this is out of box a 350 or so CFM piece.

THe LS7 is going to be a serious piece with just cam, headers/exuast and air filter box. Guess is getting closer
to 600RWHP and streetable.

Classic

iTrader: (3)

There are three huge concerns/problems as to why the average joe doesn't run C5R heads -- other then cost of course. First up is compression -- the chambers on C5R heads are in the mid to low 40cc range which would require a new shortblock approach (pistons for sure, rod length posibly, etc.) And you cannot just "open up" the chambers in a set without hindering that extra airflow you were trying to achieve.
Second, is rockers. Your stock stuff will not work with these heads which means you are left going to Jesel or T&D shaft rockers -- an expense the average joe does not see the need for.
Third is the manifold. There are no "reasonable" cost manifolds out there for these heads. Now, this part will change with the composite LS7 intake (as long as its priced in similar manner to the LS6/fast/etc.) However without the composite you are looking at a sheetmetal which is going to be big money, especially when people bitch about a $2000 set of heads.

Richard@WCCH

iTrader: (3)

BigDen, Let's not forget that at higher rpms once the intake valve closes on the seat, port flow continues to build in the low pressure area of the valve bowl. Coupled with inertia ram tuning I believe the loss is much less than what's witnessed on a static flow bench.
Also, as you mentioned, seeing 300cfm@.400" and 350@.500" I think it's possible to get close to those numbers, but linear flow above .500" would suffer badly. Your talking Big Block territory. Of course, wishful thinking is what's got us here today, so wish away. It may may happen sooner than we know..........

Cheers,

Richard

Classic

iTrader: (3)

There are sets of LSX heads out there that flow beyond what most consider the best heads. Now they aren't exactly attainable for the masses, but LS6 heads can get up past 350 cfm and beyond.

gollum

iTrader: (1)

I quote a recent GM news letter 2005-03-22

"GM offers the LS7 (P/N 17802397) at GM dealers in August 2005. Pricing will be announced mid-summer, however, early estimates indicate that the GMPP LS7 crate engine will sell for well below the cost of comparable custom-built aftermarket engines.

Following the release of the LS7 in a crate, GMPP will also offer select parts, such as the crankshaft, connecting rods, cylinder heads and valves seperately, and in kit form."

KICK ***!

xxxhp

I don't know if Iam missing something, but Iam not sure how much more can head porters get out of the LS7 heads. I've read somewhere that GM had those heads ported for the most flow possible. The intake runner volume is already 283cc


Even with the intake. We all saw how GM screwed up with LS2 intake. I won't be surprised if we found out that the LS7 intake is not any better than Fast 90mm intake.

Oh well, I hope that Iam wrong

Cary@Perf-Induction

iTrader: (1)

The LS7 manifold still wont fit the C5R heads. The bolt pattern is different, and the port shape is also a bit different. The LS7 cylinder head is a purpose built 427 big bore cylinder head. it does flow well though. We will be offering the ls7 port configuration, with the option of a small or large bore, as well as the smaller valve and port volume. Yes the LS7 ports are large.

There is an aftermarket head that will become avalible within the next two weeks that will offer a solution to almost everyones issues with port volumes, chamber volumes, valve sizes and is avalible in a cathederal port version and a c5r/ls7 port configuration, the price will be attractive. We will have a complete breakdown and dealer list on our website by next week. Manifolds will be avalible for the c5r/ls7 versions right behind it. One of our first releases will be our cathederal port 4.00 bore 2.100 intake valve 265 cc 11 degree valve angle. 381 cfm @ .700 lift 357cfm@ .575 lift. This is what will fill the void in the larger displacement engines 400-440 cubic inches. There is too much to list in one post. So for the guys that are currently looking for a well thought out, well engineered cylinder head, look out for the new ETP G3 15 and 11 degree cylinder head By ET Performance

BTW, The Cathederal port was a great concept by GM to get the cross sectional area they needed though the narrow pushrod restraints.