Thread: Rect. vs. Oval

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I have a question of price vs performance. I have a mildly built 468 chevy big block with 9.5:1 compression. The heads on it are Chevy production aluminum, rect. port from the early 70's. I know these heads are way too big for this application, but how much would I gain in HP and overall performance by spending $2000 on a set of oval ports. On that same note, I have a set of 049's that have never been worked on. By the time I spend money on new seats, valves, springs, etc., I'd probably be ahead by buying a new set. The factory aluminum heads have 124cc chambers so I could gain a little compression by going with a 119cc chamber not to mention better cylinder fill. If there will be some noticable improvement, I wouldn't mind doing it, but if it's just minimal I don't need it. Can someone give me an idea?
Sorry for the general description, but I don't have the numbers right in front of me.

You didn't mention which cam you have. The 049's are a good oval port head. Exhausts are nicer than most ovals. No gain in HP but you will move your torque and HP bands down to a more reasonable range to make you happy on the street. If you are going to have head work done, I wouldn't mind one bit that a set of 049's went on any big block for the street. By the way, are your machine shop prices that high there? 2000?

I'm at work and don't have my cam #'s. I did forget to mention that this is a motor in my 19' V-drive. As far as machine shop prices, they vary, but a comparable set of cast iron heads out of the box might gain better performance for the price. I'm assuming The 049's don't have hardened seats or bronze valve guides, as they were designed for leaded fuel, I'll need new valves, springs to match my cam and the labor. Are you saying I'll see no HP gains?

Gains can be made with anything. As a bolt on HP swap, no. The rect's move everything up in the powerband. Ovals bring them back down to a more managable rpm band. You might feel a performance advantage, but it's not an increase in HP, just putting things back to a reasonable, workable area of the engine's capability to work this engine where you have control of how you work it. I say this because you just told me it is in your boat. Depending on prop pitch and varieties of props you might change over to etc, the 049's will give you versatility in performance on the water with what ever plane system you're running and the amount of skiers you run (gotta get them out of the water smooth and quick). What out-drive do you have? You have to consider that. It really blows when you're out on the water and the darn thing breaks or gives you fits because of an engine that was too tempermental at the wrong time. Do a bit of research on these heads and mull it over. I think you'll be happier with the 049's.

OK, I see what your saying with moving the HP down to a workable range. I guess that would be the real question. Would I get my peak HP down to around 5K rpm with the oval ports and would it be noticable? I understand the rect's don't do you much good without high comp and high RPM, but are they hurting me that much. I've been running them for years with no problems but was getting curious as to the noticable gain I could get with the ovals, and if it was worth it.

In a boat, you'll be happier and the "feel" will be noticable.

the 049 heads would be ok but heavy. to do them up you may be better with a new set of alum O port heads and there would be less weigth on the transom may help get the boat on plane .better short side radius on the ex port just a better head .but if you do not have the coin the 049 would work . you may not see any thing if not prop out right . how do you know the heads are to big ? i put two sets of 049 heads on a 39 foot stinger the boat run about the same it had rect ports 375 hp engines in it heads were crack so i used the 049 heads with stock size valves

I guess I don't actually KNOW the rect's are too big, but based on all I've read and the recommandations given for mild/street engine builds, they are always opted out for the oval ports. I guess you get better cylinder fill at lower rpm's because of the smaller intake ports while not loosing any breathability. My initial guess was I would gain a little compression and better cylinder fill, and as Nitro said, this would put my power down into a more usable rpm range. I just didn't know if it was worth it...financially.

Originally Posted by DennyW

Or, if you blend the square port to enter in the right spot as the flow enters the head port, square ports will give added low end, and good top end.

What do you mean by that Denny? I don't understand what you're saying. Do you mean portmatching?

well your heads you have are alum and the 049 iron heads are heavy . the 375 hp mercruiser did run rect ports . why not just take your alum heads and cut them to get the cr up . your 049 are not in stock form going to run better then the rect ports at 5000 rpm i really do not think so very low rpm maybe like off idle but i work on many boats never seen to many just idle what is the casting number on the alum gm head that are 124CC??? you have a 19 foot v drive you would be nuts to run them heavy boat anchor 049 heads if you want this thing to move you have to run it were it makes power the boat is not heavy?? 19 feet of boat? run the rects heads cam it to make power run the right prop

Originally Posted by pat mccarthy

well your heads you have are alum and the 049 iron heads are heavy . the 375 hp mercruiser did run rect ports . why not just take your alum heads and cut them to get the cr up . your 049 are not in stock form going to run better then the rect ports at 5000 rpm i really do not think so very low rpm maybe like off idle but i work on many boats never seen to many just idle what is the casting number on the alum gm head that are 124CC??? you have a 19 foot v drive you would be nuts to run them heavy boat anchor 049 heads if you want this thing to move you have to run it were it makes power the boat is not heavy?? 19 feet of boat? run the rects heads cam it to make power run the right prop

The casting numbers on the aluminum heads are #3946074. They are advertised as a 114.8 cc chamber but have been worked extensively, as have the runners. The cam is a Clay Smith 240 duration at .050 and .570 lift on both valves. I know a 19' boat does not sound heavy, but this one is heavier then most which is nice for ripping through the chop. It's a '73 Schiada if you're wondering.

I need a new monitor.
This one is a bit fuzzy.
I read the header as "Rectal vs. Oral"
Ewww

well the heads could be over work they are not stock. but what you have to ask your self if 60 pounds or so of iron going to help move this boat ?i would think by the time you get the 049 to work you may want to buy better heads like a small alum rect or O i do alot of big blocks and all the machine work block / heads the 049 /781 with 2.19and 188 bowl work hard seats and all the other stuff you will have alot in to them heads

Originally Posted by deepnhock

I need a new monitor.
This one is a bit fuzzy.
I read the header as "Rectal vs. Oral"
Ewww

hey as long as your not getting the rect

Originally Posted by pat mccarthy

well the heads could be over work they are not stock. but what you have to ask your self if 60 pounds or so of iron going to help move this boat ?i would think buy the time you get the 049 to work you may want to buy better heads like a small alum rect or O i do alot of big blocks and all the machine work block / heads the 049 /781 with 2.19and 188 bowl work hard seats and all the other stuff you will have alot in to them heads

A LOT into them! Thats exactly what I was thinking. Either way, it's alot and I'm still trying to figure out if it's worth it for me to do it.