Intake Runner Height & Camshaft Design 1

[mred2nice]

Good Afternoon

Shopping for some help with camshaft design in relation intake port height. I am working with Pro Action 12 degree high port cylinder heads. Teh intake ports are 2.85 inches off the deck. As oppesed to a std. height 15 degree SBC head, does anyone know what camshaft design piece I will need to change?

For example...if the ports are higher then you need to open the intake valve sooner.

Thanks for the help,
Ed

 

[patprimmer]

I don't see how the port height has much effect on valve timeing.

It might have an effect on maximum lift, as it will tend to increase airflow at higher lifts.

The factors affecting valve timeing are mainly the RPM you wish to operate in, and stroke. If all other factors remain the same, a longer stroke needs more cam duration.

Regards
pat

 

[ShaunT]

I assume you are asking your question as it relates to cylinder fillin. The best thing to do to design a cam to meet specific air flow requirements, is to start by having a flow curve of the head you are using. Put it on a flow bench and flow it at.100 lift increments.

Then after a couple of other variables thrown into the mix, coming up with a base line duration,lift, and basic cam profile configuration is pretty simple.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[htwls]

Mred,
Port height doesn't necessarily affect the camshaft profile. Now the flow numbers off of a flow bench (as stated earlier) and the cross section of the port are much more important factors to consider. Make sure you consider the exhaust to intake flow ration when choosing a camshaft also. High ratios do not need as much exhaust duration as a head that has a lower ratio.
My experiments with raising port location came to the assumption of higher port = increased flow. Thus a smaller port cross section ( increases velocity ) and keeps torque up acrossed a wider powerband, without sacrificing large amounts of horsepower in the upper end.

 

[ShaunT]

Also consider flowing the Exhaust with a Tulip headded valve along with a comp. of the same port with a conventional Nail head valve. I bet you see a nice gain with a tulip. That gain translates into smaller exhaust duration that you need. ALso, longer rods typically like a little tighter LSA.
I put in a cam with a 110LSA into a motor with a 2.1:1 rode to stroke ratio. I installed it on a 104 intake C/L. IT was also 10 degrees shorter intake duration than a previous piece, but considerably faster opening as evidenced by both intake and exhaust being .040-.060 less lobe lift and 15+* bigger duration at .200.(All that with an 8* shorter seat timing intake cam) The previous piece was on a 112LSA that the cust. put in at a 114 intake C/L. The motor gave an extra 60 HP at the same RPM the previous cam peaked at. It also picked up almost 80LBS of torque. It held within 20 LBS of peak torque for over 2000RPM. BTW: it not only picked up the numbers that I stated, it did it with absolutely NO changes to the motor accept the cam AND 5 jet sizes smaller than previous.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[Andy330hp]

5 jet sizes smaller? If that is correct, I wonder how much of the gain was the camshaft, and how much was no longer blowing black smoke through the exhaust? If you really improved airflow and STILL had to reduce the jets, he must've been disgustingly rich before.

 

[ShaunT]

Actually, we were at a .5 BSFC before, and that is what we had to do to get back to the same BSFC.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[ShaunT]

Sometimes, less jet is needed because the new cam puts a much stronger signal to the carb.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)