Racing Heads on a hi-perf. Street Car

[YouCanCallMeDave]

Ive often heard it said that this is a 'no-no' because it will greatly hamper low end torque and the much larger intake chambers for maximized flow of Racing Heads (ie : 365 cfm for a big block) will cause a great loss in low rpm torque and response.

So, im curious to know if anyone here has actually had this scenario occur by having Racing Heads on a Street car ? Ive never rode in a car like this personally so I cant say I know .

Also, im wondering how big of a problem it is providing the rest of the engine IS already setup for good low end torque which might include a lower duration Cam , mechanical sec.'s Carb having annular boosters , and plenty of ignition advance ?

Id appreciate some discussion on this as well as any personal first hand experience . Thanks.

 

[vette427sbc]

The more flow the better... its the size of the runners and air velocity that determine whether or not it will be "streetable"

 

[YouCanCallMeDave]

The more flow the better... its the size of the runners and air velocity that determine whether or not it will be "streetable"

But runners, velocity, and air flow are all related . No ? Larger the runners the more airflow, right ? Under that premise, then Racing Heads which do have larger runners , would be good for the street.....yet the talk has always been 'it will fall flat on its face under low rpms (as on the street) ' .

Second question is : HOW MUCH additional performance/hp/tq could One expect on a 468 cid , 10-1 cr , motor which is currently using Edelbrock Oval Port Heads at 290 cc intake runners.....by changing to say AirFlow Research rectangular Racing Heads at 400 cfm and higher valve lift with matching rectangular Intake , assuming the cam remains the same at a 240 duration at .050" ????? What could One expect the drivability characteristics to be like on the street ?

 

[Kid Vette]

This is from AFR's web site, "AFR heads flow more than any other manufacturer when comparing heads of similar runner size and valve angles. This means a higher velocity charge with better cylinder fill and scavenging potential. The benefit of this has been independently tested and documented in many magazines, various web sites, engine shops, and various other sources as well. Simple equation more flow and higher velocity equals more torque and more horsepower. It's the recipe for success. End of discussion!"

Racing heads would have plenty of flow but would kill the velocity giving you a very inefficient engine, bad mpg and no bottom end.

Sorry, no personal experience though.

 

[Belgian1979vette]

The more flow the better... its the size of the runners and air velocity that determine whether or not it will be "streetable"

But runners, velocity, and air flow are all related . No ? Larger the runners the more airflow, right ? Under that premise, then Racing Heads which do have larger runners , would be good for the street.....yet the talk has always been 'it will fall flat on its face under low rpms (as on the street) ' .

Second question is : HOW MUCH additional performance/hp/tq could One expect on a 468 cid , 10-1 cr , motor which is currently using Edelbrock Oval Port Heads at 290 cc intake runners.....by changing to say AirFlow Research rectangular Racing Heads at 400 cfm and higher valve lift with matching rectangular Intake , assuming the cam remains the same at a 240 duration at .050" ????? What could One expect the drivability characteristics to be like on the street ?

It's quite simple, the more cfm the head can flow, the less resistance to flow the head has. The lower the vacuum that the engine creates on the intake stroke and therefor the lower the intake vacuum, which is all important to get a good mixture in the cylinder. Therefor it will reduce low end torque.

Of course other factors are in play as well (carb size, kind of intake, valve size, camshaft) but as far as the head goes this is the basic theory.

PS : with a bigger engine, the effect of a larger intake runner will be less.

 

[Belgian1979vette]

This is from AFR's web site, "AFR heads flow more than any other manufacturer when comparing heads of similar runner size and valve angles. This means a higher velocity charge with better cylinder fill and scavenging potential. The benefit of this has been independently tested and documented in many magazines, various web sites, engine shops, and various other sources as well. Simple equation more flow and higher velocity equals more torque and more horsepower. It's the recipe for success. End of discussion!"

Racing heads would have plenty of flow but would kill the velocity giving you a very inefficient engine, bad mpg and no bottom end.

Sorry, no personal experience though.

When testing heads several factors are in play among which the actual air pressure and the bore the head is place on. There is a big difference if the head is place on a 4 " or a 4.125 or larger bore....a lot of head manufacturers play with that. You want to be comparing apples to apples.

 

[7t9l82]

engine size, compression,cam specs, header size ,gearing ,transmission type stall speed if an automatic and vehicle weight and intended use all come into play. i would recommend picking 3 head manufacturers and get their suggestions then re post it here and get everyones thoughts.you will save yourself a lot of work, the manufacturers normal get you close.