Using rectangular port intakes on oval port heads
 

Hey guys,

I decided to spin this topic off of a topic I started last
week on the '163 intake. From a few of the responses posted
it appears that other members here have had experience with
running rectangular port intakes against oval port heads.

How is it these off-design combinations even work properly?

It would stand to reason that running a rectangular port
intake mated to oval port heads would pose all sorts of
runner turbulance issues and hence cause the big block
engine to suffer performance problems. Yet, some members
have experience with this combination and claim it runs
remarkably well. How is this possible? I am hoping some
big block knowledgeable members here can enlighten me.

Steve

Re: Using rectangular port intakes on oval port heads
 

Steve,
I'm getting old so I may not explain this exactly right.

If I remember my fluid dynamics correctly, the mismatched ports create "eddies". These areas are stagnant and don't actually flow with the intake stream. They kind of create an invisible funnel effect at the oval port entrance.

As an example think of this crude comparison.
Which has less restriction?
1) a 24" piece of 3/8" id fuel line or
2) a 24" corrugated flex funnel(with 3/8" outlet)

The funnel will have a higher volumetric flow for the same value of negative pressure (vacuum), even with irregular inside surface (from the flex corrugations).
This is due to a function of laminar flow and length to ID ratios for the two flow paths

I hope this helps. Its 2 am and my brain hurts now.

PS: We used the following trick when we were to poor to afford rect port heads and wanted to run an aluminum holley intake.
We would epoxy about 2 inches of the rect. intake runners and port match them to the oval port heads. This created a smoother transition from the rect to oval runner.
This combination ran better than a full rect port setup a lower rpms, but didn't carry the power past 6500 on 396's.

That's all for tonight folks. https://www.yenko.net/ubbthreads/imag...lins/beers.gif
Eric

Re: Using rectangular port intakes on oval port heads
 

I have seen it done many times, over the years. The engine will run without trouble. I don't know all that stuff Eric was taking about, but can tell you that, IMO there is no way the Square to Oval configuration will run as good or better than the Stock Square to Square or Oval to Oval configuration.

Re: Using rectangular port intakes on oval port he
 

Lets get one thing straight...I'm not going to get into an internet Argument with anyone and obviously oval to oval and square to square is the best idea but check this out.....



Had a 70 nova with a 454 with closed chamber pistons.compression ratio ??? I bought a set of new 990 squareport heads to try instead of the closed chamber oval ports. did nothing but change the heads and put on a old sideways sqareport torqer intake. the car went from 12.70's to 12.20's.and gained about 5 mph.when it was time to sell the nova i pulled my new 990's off and all i had at the time were a set of peanut port open chamber truck heads.So i changed the springs and on they went.I never liked the sideways intake so decided to throw it on and hope it ran ok. I wasnt expecting any performance at all from this thing ,all i wanted was to sell it and move on. All i can say is ....TOTAL SURPRISE. As soon as i fired it up,it sounded good.But when i drove it,it felt better.It made a ton more low rpm torque,and just ran unbelievably well.I had to take it to the track and see and believe it or not,it ran 12.50's.Total mismatch of parts and i mean TOTAL.It had a .560 lift lunati solid cam,10" conv.,and 4.10 gears. The mph dropped about 3-4 and it didnt like to go 6500rpm's anymore,but it spun to 5500-6000 no problem.

The moral of the story is....Dont mock it until you try it,and even though on paper it should never work, you never know. I've done it and it worked.will i do it again.....Not unless i have a reason too, but i know it will/does work.


hope that helps....bob

Re: Using rectangular port intakes on oval port he
 

We took a '74 smogger 454 and added a Cam Dynamics 272 energizer cam, rectangular port intake, 750 Holley, and headers. At 3900 pounds with driver the car ran 102.4 mph with no special tuning what so ever. With traction that equates to about 13.2-13.3, if you had traction. Bottom end torque was excellent. Not bad for a total under the hood investment of about $1K including the engine. The torque felt like our L72. It was a pleasant surprise. Not many cars run as well for so little invested. Others have used this intake on race oriented oval port engines with excellent results. Add to that the hipo Chevy look and the intake is worth it even if it didn't work.

Re: Using rectangular port intakes on oval port heads
 

I have to admit that this mismatch of parts makes me https://www.yenko.net/ubbthreads/imag...mlins/hmmm.gif

Steve

Re: Using rectangular port intakes on oval port heads
 

A member on the NCRS forum posted this information regarding
the use of the rectangular port intake with oval port heads.
I thought I should share it with the group here. My thanks
to Michael Hanson for this information: https://www.yenko.net/ubbthreads/imag...ns/worship.gif

"Steve,

The stories about rect port intakes used with oval port heads are true. The combination actually does fit without leaking and it actually does make gobs of low/mid range torque. The power falls off fast at around 5000-5500 but pretty incredible at 2000-5000. It's all about port velocity at lower engine speeds. Everyone knows that the big head ports kill low/mid torque but the mismatch with small head ports and large intake ports kills higher RPM horsepower. Somewhere between is a nice balance that keeps port air velocity high. The fact that even the oval ports are large helps to off set the problem of the mismatch. There are more reasons but way too deep to cover here. Has to do with the wave bounce and speed.

In the 60's, a friend bought a new L88 short block for his 57 Chevy race car. He couldn't afford the new big port Aluminum heads for quite a while so he installed a set of oval port heads on the engine and went racing. Amazingly, the car ran times in the same range as all of the other guys that had the same L88 block assy, but with the proper big port heads. When he finally purchased the new aluminum heads, he was surprised to leard that the car ran times that were almost identical to his original times with the small ports.

In the late 60's, I was able to "make a few adjustments with the GM warranty paperwork" and help a few buddies with new 68-69 Camaros get an L88 short block under warranty to replace their 396 short block. One car was an original 375 HP with the big port heads and another was originally a 325 HP with oval port heads. For reasons I don't remember, the oval port heads were reinstalled on the 325 HP car with a new rect port 375 HP intake and L88 short block. All else was the same from car to car, right down to the header mfg and diff gearing. Both cars ran nearly identical times with the headers open but the car with the weird combo oval port heads was slightly faster on the street. "

Steve

Re: Using rectangular port intakes on oval port heads
 

This is an interesting topic since the 70 L78 I just got has the stock rectangular port intake with oval port heads. I thought it would be a terrible mismatch, but the car seems to run incredibly strong and doesn't seem to mind the mismatch. I have the correct rectangular port heads to go on it, but it might be better off with the slightly lower compression oval ports for now.

Re: Using rectangular port intakes on oval port heads
 

My 69 Camaro COPO clone runs this above combo of oval heads and 163 intake. Car cruises and drives fine. Notice Eric Jackson carb............

http://img.photobucket.com/albums/v4...8Image0005.jpg
http://img.photobucket.com/albums/v4...8Image0008.jpg

Re: Using rectangular port intakes on oval port heads
 

Next motor I build is going to have that combo. Strong bottom end with maybe 10.5 to 1, L78 cam, 163 intake, oval port heads. Add a little gear and 4 speed and watch out! I think if you have a good set of heads that have some mild work done you can probably pull real strong to almost 6,000rpm. That's enough on the street...

wilma