Another aluminum head question.

[Hipster]

Like on an L31 Vortec head?

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Mexican vortecs won't flow those numbers. I kinda look at like this. If the port stalls or goes turbulent at .500. What's happening from .500 lift to .560 not only on the upside but also down. After you killed velocity/cylinder fill on the way up then it has to try to recover and get past the wonky pressure pulse in the intake tract on the way down. On a dyno sheet if bad enough it almost looks like valve float. Everything goes erratic. Many times I've taken .580-.600 lift cams out of stuff, put similar duration back in with less lift and made more power everywhere and it runs better and is easier to tune,

 

[L31MaxExpress]

Like on an L31 Vortec head?

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The mexican heads are even worse. They peak at about 218 @ 0.450, then port stall to 210 @ 0.500. Atleast the 062s on my 2006 era crate engine did.

 

[L31MaxExpress]

Mexican vortecs won't flow those numbers. I kinda look at like this. If the port stalls or goes turbulent at .500. What's happening from .500 lift to .560 not only on the upside but also down. After you killed velocity/cylinder fill on the way up then it has to try to recover and get past the wonky pressure pulse in the intake tract on the way down. On a dyno sheet if bad enough it almost looks like valve float. Everything goes erratic. Many times I've taken .580-.600 lift cams out of stuff, put similar duration back in with less lift and made more power everywhere and it runs better and is easier to tune,

Which is why I laugh when the LS fan boys all want to rave about high lift 0.600" cams especially when combined with the stock rocker arms and beehives.

My 383 gained like 20 ft/lbs down low going from a 1.7 exhaust rocker to a 1.5. With no loss up top. So much for heads that flow worse than 75% needing a split/dual pattern cam.

 

[L31MaxExpress]

I will also breifly touch back on the LS head flow. The numbers that often get quoted showing flow increase through 0.600" are flow tested with a 4.030" bore simulated. On a 3.780 or even 3.90 bore, things change quite a bit, especially with the larger 2.00 intaks valve size. The 799/243 head castings when used on a 3.780 bore actually fall off before 0.600.

 

[Hipster]

I will also breifly touch back on the LS head flow. The numbers that often get quoted showing flow increase through 0.600" are flow tested with a 4.030" bore simulated. On a 3.780 or even 3.90 bore, things change quite a bit, especially with the larger 2.00 intaks valve size. The 799/243 head castings when used on a 3.780 bore actually fall off before 0.600.

bigger valve are not always better either, and bore size also matters. If shrouded by the chamber bigger valves may actually flow less without supporting work. If shrouded by the bore nothing you can do. Split duration cams are a band aid for a poor exhaust port, which many stock heads are guilty of, but cam manufactures also push them because the first question they get it "how's it sound" instead of "How does it perform". Sounds good but goes nowhere is not my idea of performance. People ask about "sound" over and over on this site. Wrong way to pick a cam. I think vortecs have a pretty good intake /exhaust ratio for a stock head, if that what head you talking about I can totally see it picking up torque with less lift. Also my understanding that bigger ratio rockers accentuate duration albeit fractionally.

You mentioned springs and beehives seem to be a go to choice in a lot of applications, But if a cam profile calls for a dual spring I can't see a single beehive with no damper being adequate no matter if the spring rate is close. Buy the $80 tool and cut the pockets. More to it than spring rates, it's about valve train stability over the long haul. I admit and many have read some of my posts. I'm am stupid An*l about valve springs because the resulting damage is catastrophic. Some get it. some don't. pretty sure you do.

Flow numbers are nice to have but it's just another tool to compare something against itself while modifying it, almost impossible to compare one bench to another and they don't always tell the whole story. Flow numbers are the first question a grinder will ask you for. Some of the top head porters wet flow their heads to see what the fuel is doing. Something Joe Mondello pioneered quite some years ago. Sometimes I think Mondello was a half step in front of Vizard but both brilliant guys. You can have head that has great numbers coming off the bench but on a dyno or at the track they don't perform as expected.

 

[Hipster]

The mexican heads are even worse. They peak at about 218 @ 0.450, then port stall to 210 @ 0.500. Atleast the 062s on my 2006 era crate engine did.

There you have it. Pretty terrible really. I can see why you went with the castings you did.

 

[Hipster]

Typical of conversations I'm participating in on another site that seems to have an abundance of head porters participating in and comparing notes. Most times just listen. Another brand engine where what Brodix offers as a race head for $3K bare still sucks OOTB.

"Well stated. Application is important to making decisions on valve angles. NASCAR are pretty much all using 50° to 55° seats. High lift and RPM dictate those angles. Street engines get minimal benefit from those angles. With max lift at or under 0.600" the seat curtain is the controlling factor up to about 0.350" to 0.400". Back cut intake valves and 40° exhaust seats provide a benefit to these lower RPM engines. When installing larger valves, shrouding is a definate concern considering the cylinder wall and head gasket sealing surface limit how far clearancing can be pushed. The combustion chamber wall by the intake valve seat can be relieved to aid low lift flow during the important scavenge cycle during overlap. Caution on cam dwell and overlap must be exercised to not blow too much intake charge out the exhaust at lower RPM street driving conditions."

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[DeCaff2007]

I know this thread is kinda old, but the heads I that I ordered are on indefinite back order.

Trick Flow Specialties TFS-30310005 Trick Flow® Super 23® 175 Cylinder Heads for Small Block Chevrolet | Summit Racing

Free Shipping - Trick Flow® Super 23® 175 Cylinder Heads for Small Block Chevrolet with qualifying orders of $109. Shop Cylinder Heads at Summit Racing.

www.summitracing.com

What's wrong with these heads? I'll post these on my build thread, as well.

Flotek 101-505FT FLOTEK 180cc Small Block Chevy Cylinder Heads | Summit Racing

Free Shipping - FLOTEK 180cc Small Block Chevy Cylinder Heads with qualifying orders of $109. Shop Cylinder Heads at Summit Racing.

www.summitracing.com

 

[Scooterwrench]

Looks like they would make good low end torque heads. 2.02 valves in 180 port heads seems like a waste. Powdered metal seats are porous and prone to burning troughs through.

 

[Schurkey]

The way I remember it, the Flotechs are Summit's "recommended replacement" for the no-longer-available heads that actually fit a TBI intake manifold.

Problem is, the Flotechs have the wrong angle on the center two intake manifold bolts. Someone at Summit screwed the pooch when they recommended them for TBI engines with the goofy bolt angles.

OTOH, if you're not using a TBI intake manifold that has the goofy bolt angles, they'd work just fine.

The Flotechs are supposedly Made in USA. I'd double-check that, I'm concerned that they may be ASSEMBLED here, from cheap Chinese castings.