Does port velocity really matter?

[RCCDrew]

 After looking at a 426 hemi last week, this question came into my mind.  The ports on the heads are Huge! But the hemi is still one of the most feared engines out there. There has to be very low port velocity on those heads. So what gives? Is port velocity a good thing or a bad thing? Looks like you could max port every wedge head out there and not come close to the hemi port volume.

[1 Wild R/T]

But Hemi's aren't known for low rpm torque..... Till you build them bigger.... I know guys with stock stroke semis that have spun them past 8,000 rpm's cause thats where they are breathing good...  Personally I don't want to spin a big engine that tight....

On the other side EFI makes port velocity less of a concern.... You don't need velocity when the fuel is atomized by spraying it at high pressure....

[Oldschool]

The HEMI is a diferent animal when it comes to velocity. Folks get fooled into thinking that with those large ports, they don't have good low end velocity. When you consider how the HEMI is designed, that is not necessarily true. On a BB Mopar with stock ports, they have great velocity on the low end  --  but the valves are a lot smaller and the wedge head suffers from considerably more shrouding of the valve than the HEMI. The BB has 2.14 intakes which are shrouded a ton more than the HEMI intakes. The HEMI pops open 2.25 intakes with minimal shrouding. That said, when those 2.25's start coming off the valve seat with such a small shrouding effect, they are already moving big air. The 2.14 BB valves aren't moving a ton of air coming off the eat compared to the HEMI. So, when you figure the difference in valve layout and valve size, the HEMI is moving a lot of air at low rpm. I have taken care of many BB's from all makes on the drag strip and some can run with the HEMI off the line. But because of the huge ports, larger valves, and lack of valve shrouding, when the big ole HEMI gets rolling it just gets stronger and stronger all the way down the 1/4 mile. The conception is that the HEMI was slow off the line, but the huge top end pull just makes it look that way...   

[jimynick]

If you look at port velocity as a function of filling the cylinder, you'll also notice that this is not a determining issue at low rpm. Where the hemi shines, is it's straight through, linear gas flow that doesn't require a change in direction between intake and exhaust flows. That's why every successful top fuel car runs this type of engine/cylinder head layout. As Oldschool mentioned, when the rpm's rise, the hemi layout just keeps getting better in terms of handling the amount of flow to make the best HP at those elevated levels and in the case of the factory 426, it had enough size and compression to carry it past the low rpm levels/speed operations into where it really shone- the higher rpm levels with a load on it and the SOB thrives on it. Lucky us, eh?! 

[brads70]

In stock form they were a bit of a dog no?    I say this as I have a local buddy that spent 40K installing a 426 into his 71 Cuda  .Spent big money on date code dual 4bbl carbs, shaker hood, etc...  I can't say I'm very impressed with the performance of it?  Sure a race engine or one done up with aftermarket parts is a stout  piece , but a stock Hemi?
Not trying to start a war or anything but this is the only Hemi I've had "experience" with.     He wasn't to happy either when I went by him like he had a 318 or something? I only have 8K into my lump?   Maybe it's not tuned right or something? 

I'm sure Oldschools Hemi would make mine look like a 318 or even maybe a /6    I've heard lots of talk from street racers from the 70's that will say a 340 could beat a stock Hemi?

[Chryco Psycho]

Velocity is critical , it keeps the fuel suspended , helps cylinder filling , rod ratio / piston speed comparative to port size etc make a big difference also.. But yes the Hemi is a different beast you can look right through the head through the ports & once that air flow gets moving in a straight through shot it is amazing .
 The street Hemi is an odd beast as it really was never meant to be , it was severely detuned for the general public with hyd cams the worst possible carbs etc even the 340 Had the better AVS style carbs  . The real legend was built at the tracks in almost every form of motorsport where it was tuned for max power & is still the only engine in any compedative top fuel or alcohol class and still owns the SS/A & SS/AA class even 52 years later . The nasar Hemis were making over 600 HP on a single carb / Dominator !! & the SS cars make over 800hp    alcohol are over 2500 & there is no way to measure Top Fuel but estimated at 7500 hp +

[Topcat]

The HEMI is a diferent animal when it comes to velocity. Folks get fooled into thinking that with those large ports, they don't have good low end velocity. When you consider how the HEMI is designed, that is not necessarily true. On a BB Mopar with stock ports, they have great velocity on the low end  --  but the valves are a lot smaller and the wedge head suffers from considerably more shrouding of the valve than the HEMI. The BB has 2.14 intakes which are shrouded a ton more than the HEMI intakes. The HEMI pops open 2.25 intakes with minimal shrouding. That said, when those 2.25's start coming off the valve seat with such a small shrouding effect, they are already moving big air. The 2.14 BB valves aren't moving a ton of air coming off the eat compared to the HEMI. So, when you figure the difference in valve layout and valve size, the HEMI is moving a lot of air at low rpm. I have taken care of many BB's from all makes on the drag strip and some can run with the HEMI off the line. But because of the huge ports, larger valves, and lack of valve shrouding, when the big ole HEMI gets rolling it just gets stronger and stronger all the way down the 1/4 mile. The conception is that the HEMI was slow off the line, but the huge top end pull just makes it look that way...

I can relate to what Ken is saying.

Opening it up and it seems like I can't find the peak end where HP starts dropping off.

I haven't put it over 7K RPM yet.

You can rev Hemi's more per shift because of their design as well.

[mopar jack]

the hemi is awesome and I would love to have one but I remember talking to Rich Nedvile (performance west) about how the Hemi dominated top fuel and his response was it's the only head allowed per Nhra rules.

[Chryco Psycho]

Other have tried with crossflow heads in Ihra or Ahra without success with enough $$ & time I am sure the tech is out there to  compete though

[HP2]

Port velocity is why a well tuned 440 could put the smack down on a street Hemi in the stop light drags.

[moper]

Port velocity is critical - but one has to account for the overall design differences. A Hemi port and channd chamber allow for a MUCH faster port that still has stable flow characteristics. The wedge design simply does not. So while "velocity" is important, it's also subjective relevance. That's why more time is spent on matching port volumes to displacement on a wedge head, and velocity is left to measuring during port modifications. There is such a thing as too much vlocity, both overall in a port, and localized, in a wedge design. With a hemi there really isn't any, hence the higher rpm performance.