1Boatnut

Ok guru's looking for some opinions.I already have mine but would certainly like to hear everyone's opinion...

509Ci,naturally aspirated motor.I'm running rectangular now!

What are the pro's and con's between oval port and rectangular cyl. heads..?? I have heard many differences.
I would also like what differences there would be between the 2 if they are both Stock GM. heads.
Meaning I'm not talking aluminum,although feel free to give opinions on those too!

So,lets get this discussion going

blown formula

It is my understanding that the oval ports can generate more horsepower than the rectangular ports. BUT, the ovals require a lot of work to get there... stock, the rectangular port heads are better, but harder to find than ovals. Total performance goes to the ovals though.

Dennis Moore

The rectangle port heads will be better at high rpm with large camshafts and high compression ratios. Over 6,500 rpm, 12.5:1 compression ratios and camshafts with over 250 degrees intake duration @ .050. This is the type of racing engine Chevy had in mind when designing the rectangle port heads (not marine engines). Any engine built with less will work best with oval port heads.
Dennis Moore

blown1500

Hello, Guys,
I am an oval fan on less than 500cid, less than 6,000rpm, maybe even bigger, depending on other factors. I have run the Merlin ovals with great success. They do need a litttle cleanup in the pockets, but almost anyone with the will to do it can. I have seen several boats succumb to the theory "bigger is better", take off the Merlins I installed and replace them with almost ANYTHING else, and loose power through the rpm range-I vote OVAL. Keep in mind, though, some OEM heads suck without work-maybe a LOT. Tell us which and I'm sure you will get help!!!
Have a deal if you will pm.

Nordicflame

I'm not sure which is better but my ovals seem to work very well. I use Edelbrock oval ports that have been worked over by the Chapman Racing family. They are about the largest ovals you can get and are probably over 300cc after the head work.
I run these on my 540 ci with a 232/240 114 .600/.600 Ultradyne cam with 9.2:1 CR and the motor is at it's very best around 5400 rpm.
I don't know if it would run any better with rectangles

This setup will be getting a 5 lb boost in the very near future.
This should be a good thread.

Dave

1Boatnut

Dave,,,now your talking about blowing a motor? In my opinion that is when you would want to run rectangular heads..Again,just my opinion...

blown1500,I am trying to compare stock heads.See below for reason.

Here is the reason I brought this whole question to the table...I am now running square port heads.Inconel valves,and was about to get them bowl blended...Now a buddy of mine has a STOCK set of oval ports(big chamber) that are mine for the asking...All I would have to do is transfer over my valves and stuff.He would then take my rectangular heads...

So the cost to me is "zero"...But,is there any advantage ?

Nordicflame

The data I gave you was for my motor naturally aspirated; not blown...
Sorry for the confusion,
Dave

1Boatnut

No Dave,I understood....
Sounds like your going to be adding a blower though. Correct ??

Washed Away

Can we bring mercruisers choice of rec port on motors stronger than 310-330 stockers. Seems to me that mercruiser invested loads of dyno time in these engines and rec port seemed to suit thier needs. I think that the head port design has changed on the newer mag engines (gen VI) and are a vortech style of port. So i am refering to gen IV and V. If I am wrong, please point this out.

FloridianSon

I went Merlin oval on my 502 and glad I did. Cam 224-234 110 lsa installed on a 110.My Merlins came with 2.25-1.88 valves and I got them through Summit.I wish now I had ordered them through World.I think they would have put in the extream inconel exhaust if I had asked them as they came with the sever duty exhaust .The best thing I could say is get Dennis Moore's book it will lay it all out very clearl,around here it is known as the Bible.