I understand there are theories about the ideal intake to exhaust valve size ratio. To maintain that and have the valves fit in a particular bore size there are going to be a few that come to the same conclusion. Same goes for port volumes. There will be a formula that works.
As for exhaust duration many motors take advantage of the smaller exhaust valve size to leave it hanging open for as long as possible without piston to valve contact. Modern roller cams and a light weight valve train let you snap those valves open and closed amazingly fast compared to old tech.
There were plenty of other GM designs they had to draw from too. As an example Dart make a Buick head for the SB chev that uses the port design and shape from the V6. A style that looks very similar to the what the LS7 uses.
I believe these were the go to SBC head for a while in NASCAR in the 90's
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Mike Murphy
Melbourne Australia
Again, I'm not insinuating that the GM guys snuck into the Ford engineering lab or had the Russians hack the Ford computers.
I'm just saying that in comparison to a traditional SBC head, the LS stuff (most especially the LS7) is pretty closely related to a Cleveland head, where no other OEM head is.
The poor exhaust flow is just the inherent nature of some cylinder heads and it's not really related to bore size. Take a close look at some older Pontiac heads. The exhaust flow is almost 80% of the intake on some heads, and some of the early Poncho engines had some very small bore sizes: the 350 had a 3.875" bore....the 389 was a 4.060"....421 SD was a 4.090".
I've seen some high 60% numbers on some LS7 heads, which requires a larger amount of exhaust duration to crutch it.
As for port volume, it will depend on the size of the engine and the application. The 4V Cleveland head was a complete dog on a factory 351 or a 302. It takes a lot of rpm (or extra displacement) to get that big 245 cc of air moving....
Like you say, most every performance automotive engineer out there will be familiar with combinations that performed well through the years. It's hard to start with a clean slate and not take notice to things that really work or were highlights of past decades. In my mind the LS7 is a pretty sweet piece because it has enough displacement to pull on that large intake port volume and a large enough bore to take advantage of the larger valves. Both of those are Cleveland traits, but the factory Cleveland engines were really too small to really take advantage of them.
There were plenty of other GM designs they had to draw from too. As an example Dart make a Buick head for the SB chev that uses the port design and shape from the V6. A style that looks very similar to the what the LS7 uses.
I believe these were the go to SBC head for a while in NASCAR in the 90's
The 1990's was the era of the "corporate engine" at GM. Pontiac developed the 867 head for NASCAR. Buick wanted a head for their NASCAR teams so they contracted DART to make a head based on the V6 head, but NASCAR disallowed it, so the Buick head landed in NHRA. The T&D rocker arm business was built on contracts from Buick for developing shaft rocker for that head. The 18 degree high port head was the dominate GM head in the 90's until 1998 when Chevy released their first NASCAR specific head the canted valve SB2. The aftermarket continues development of the 18 degree head to this day for dirt late models and off road truck racing. The evolution has taken it from 18 degrees to 16,15, 13, 11, and now 9 degrees.
As far as the LS heads, specifically the LS3 and the LS7, being copys of the Cleveland... I don't buy it. I see more similarity to the 18 degree and its derivatives. If anything, the SB2 with canted valves is closer to the Cleveland than the LS.
I'm not the first one to notice it, think it, or mention it.....but it's usually the Chevy guys who complain about the notion of it....hahaha
Y'all have a good night.
So far I haven't read any complaining, but I can understand why a Ford guy would want to take credit for the LS7...
I can only assume that beyond the original 23 degree SBC design, you don't understand the differences in SBC heads, or how and why they were developed.
Even 'way back in the day, I was very impressed with the old Boss 302 Cleveland heads. They didn't do much at low end, but they sure liked to breathe at big Rs. Thought they sure looked like BBC heads, at the time. 'Uge Uge ports.
Seems like the really serious SBF racers figured out a way to adapt them to the far superior Windsor block.
Folks that don't have the funds for the latest and greatest have so many times adapted the best parts from various badges and have come up with surprisingly good results.
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Karlos
"In the Land of the Pigs, The Butcher is King"
Cleveland heads have always been renowned for their bad exhaust port design. I remember reading years back something about it being a design compromise to get the exhaust manifolds to fit in between the shock towers. Ideally they wanted the port to be much higher.
Racers used to machine the whole exhaust port off the head ad replace it with a new aluminum plate with raised exhaust runners.
Gains can be made by putting port tongues in the exhaust ports to lift the port floor and make it D shaped.
There's huge potential in the Cleveland heads but you guys in the US didn't get to see much of it as the motor was dropped in the early 70's. Australia kept going with the 351C in Ford sedans right up until the mid 80's. As a consequence we now have companies like CHI and others making some amazing heads for these motors.
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Mike Murphy
Melbourne Australia
Cobra Make, Engine: Harrison #100 under construction
Posts: 1,109
Not Ranked
Faaaaarrrrrkkkk Mikey, really didn't mean to start such a ****e storm!!
i only stated the facts a way an engineer not a mechanic or enthusiast would look at it !
i.e: hp per litre & hp per kilogram !
AT NO POINT was it mentioned which is cheaper to get hp from or anything else for that matter ....like maybe which is the better boat anchor etc.
At the end of the day what YOU LIKE is what suits YOUR application and if your happy with it nothing else matters to anyone but YOU
Faaaaarrrrrkkkk Mikey, really didn't mean to start such a ****e storm!!
i only stated the facts a way an engineer not a mechanic or enthusiast would look at it !
i.e: hp per litre & hp per kilogram !
AT NO POINT was it mentioned which is cheaper to get hp from or anything else for that matter ....like maybe which is the better boat anchor etc.
At the end of the day what YOU LIKE is what suits YOUR application and if your happy with it nothing else matters to anyone but YOU
I don't think of it as a sh!t storm. It's been an interesting discussion so far. I'm not an expert and I've learned some interesting stuff from this thread (always got to keep learning)
I think we are all grown up enough here to see the Pluses and minuses of each option and it's not always about max power numbers. These cars are a big part emotion.
I've said many times that I reckon over 400HP is probably a waste in a Cobra and both of these motors far exceed that.
There's huge potential in the Cleveland heads but you guys in the US didn't get to see much of it as the motor was dropped in the early 70's. Australia kept going with the 351C in Ford sedans right up until the mid 80's. As a consequence we now have companies like CHI and others making some amazing heads for these motors.
can anyone help in letting me know what sort of block those things are on in the video. i cant work it out, Cleveland or Windsor?
i cant decide if i should get a Windsor built up or put a Coyote in it.
An LS just seems like half way between the two. Not old school and not school - twin cam head with VVT.
but that's me.
mine will be going into a 40, so i need to think about gearbox and finaldrive availability. want something that will cruse at 100km/h, as well as move when in the power band and not drop out of it on gear changes.
Thanks, still trying to get my head around the options for engines. currently tossing up between a built Windsor or Coyote. The video that mike linked sugested that the coyote was short on capacity. sounds like they can take them out to 5.7L (351ci) so that would help a little, however by that stage would you be up around the cost of a built 427/434/451 as shown below?
if that's the case would it start to swing back to the old school direction?
Cobra Make, Engine: Kirkham #684, 482FE, Mike Mccluskey build
Posts: 2,520
Not Ranked
Do those heads even fit on anything but the specific block for the engine. The heads are cheap because they don't fit in anything but the expensive designated block???
20Likes
. But we werent talking about 18 degree heads, sb2, etc., we were discussing the LS engines.
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