×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Intake to Exhaust Valve Size Ratios

Intake to Exhaust Valve Size Ratios

Intake to Exhaust Valve Size Ratios

(OP)
I’m currently cad designing, cnc machined, billet 4v heads for several ENDURANCE engines.  I’m building them for both na and turbo applications utilizing a maximum rpm of 9,000 to 10,000 rpm.  These are water cooled engines, utilizing thermal coatings (pistons, chambers, and ports) built for high output on pump gasoline.   

I have been researching many different head combinations from 2 to 4 valves and analyzing their intake to exhaust valve size ratios.  I understand that flow ratios are what you really look at but I also understand flow starts with and is limited to the valve size.

The ratios that I’m looking at are the Surface Area of the Intake to exhaust valve.

Everyone agrees that they would go to a smaller exhaust valve if they could utilize a larger intake valve.  Everyone agrees that you give up energy through increased pumping loses but gain more from increased airflow and more power.

My question is:  Do you also gain heat or longevity issues.

Out of everything that I’ve analyzed so far, drag racing has the smallest ratio (biggest intake valve and relatively small exhaust).  I don’t see any endurance engines that have this small of ratio…. Is it because of heat and reliability?

I see pro stock running 2.6 in and 1.7 ex which is a 42.7%.  
Alan Johnson sbc heads running 51.5%
Chevy LS2 and LS6 at 63.4%
ZO6 LS7 at 53.6%
Sport Bike Heads from Honda, Kaw, and Suzuki all at about 75 to 79% in the 1980’s…
They all now run between 68 and 69% currently.

My question is: How small on the exhaust is too small and what are you sacrificing in terms of reliability?  Is it heat and is this why you only see this extreme trend in drag racing and not on endurance engines?

Thanks for any help.
682-558-9275

RE: Intake to Exhaust Valve Size Ratios

This has a lot to do with your head design and reversion tunning.

I have looked for empirical formulas and looking at everything from Ducati race bikes to Alfa Romeo

The secert lies some where between 1.22 and 1.3 or 1/X .

My guess is the pro stock boys with their huge intakes and 600# springs are sacrificing exhaust flow for the huge intake charge.

Also the scavanging of the long tube headers probably help with evacuation.

Regards

RE: Intake to Exhaust Valve Size Ratios

I think the measure you want to compare is "valve curtain area  times duration". Valve curtain area is the circumferece of the valve times valve lift. This measures the wall of the cylinder that the valve moves through, which is the area of the opening provided by the opened valve. Using this measure of area instead of the area of the head of the valve eliminates the squaring effect. But you also have to consider the difference in the intake duration to the exhaust duration. As a former drag racer, I'll tell you that I found that most of the popular cams had longer exhaust duration compared to intake. This usually had to do with the fact that most american pushrod engines don't flow enough through the exhaust port to match the intake port flow.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources