Join Date: Jun 2002
Location: Riverview N.B. Canada
When considering a cylinder head purchase, it is EXTREMELY
important that you are completely honest with yourself ,
as to what you intend to do with the car .
Is it a street car only ?
Is it a street / strip effort ?
Pure race car ?
This is critical , because cylinder heads are designed to some
things very well ,but, not all things .
Race heads on a street car , and street heads on a race car
usually give lackluster results . For opposite reasons .
IMHO , the most widely misunderstood , and promoted ,cylinder
head feature , are the flow numbers .
The most under explained / promoted feature is velocity .
Yes , I know , buy the ones with the biggest flow numbers , right ?
To get the best results , you really have to determine what you
want to do with the car , and what rpm range you want to
maximize the power .
For the street , velocity is king . So , look for a blend of good
flow numbers , but , with a small intake port / valve .
For the most part , the larger the port , the slower the velocity
at any given rpm point .
The lower the velocity , the lower the mid range torque .
Roush 200 heads are a very good head , but with a very large
200cc port . This kills the velocity at low and mid rpm ( and the
torque along with it ) . At high rpm ( or with added displacement ),
they are great . But , on the street , by the time you get to a high enough rpm ,the race is already over .
That is why it is very important to do your homework before hand
if you are going to send a set of heads out to be ported .
The ultimate secret , is to improve the flow numbers , but do it by
removing as little material as possible . Some guys just grind the
port bigger . Bigger port , better flow numbers on the flow bench
but give a reduction in velocity , and the car accellerates slower .
Shape of the port is just as important as size .
It takes a pro porter to do it right .
Always remember , we do not drive a flow bench ( or a dyno ) , we drive cars . Numbers on a flow bench can be VERY misleading .
For the record , I currently use a set of ( old tech ) GT40 iron
heads with 1.94 / 1.6 valves . They flowed ( only ) 210 / 165 .
Crappy by comparison to todays 250+ cfm heads .
But these heads made 370hp @ 5500 rpm on the dyno
and 360+ lbs of torque as low as 3500 rpm ( peak of 377 @ 4500 ) .
They walked all over a set of Edelbrock RPM 2.02 / 1.6 and
Dart SR 's ( both of which flowed larger numbers on the bench ) .
On the street , the car works awesome . Instant power everywhere ( from 2000 - 6200 ) .
When it comes to heads , bigger is definately not better .