I'm considering going with the rectangular port heads as there are so many additional choices.

How do you guys like them for streetability and low end power?

Thanks!

 

I have Merlin rect port, 310cc intake runners with 119cc combustion chambers. If I had to do it again I would go with oval port style for sure. The rect ports are great for the strip but I believe now that oval ports have a big advantage on the street and still offer very good top end power. I am sure someone else will chime in here but my 2 cents worth stick with a good set of oval ports!!!

 

I agree with 467-Ratman. On the street they suck. At low rpms oval are better but from 5000-7500 they rock.

 

The larger oval port heads have about 290cc intake runners. The smallest rectangular has 295cc intake runners. I wonder how they would work????

 

BLUNSFORD......if you can get your hands on a few back issues of Chevy High Performance they had a series of articles comparing the two styles of heads. One set of test on a near stock n/a motor and another set on a blower motor.

With a not so radical motor......the ovals came out on top as far as hp and tourque went.

-Rick

 

You can go to their site too and look up the flow #'s for various heads.

 

It depends on what you want the motor to do and what rpm range you want to do it at. There are a few variables but generally I think the 600 hp range is where ovals need lots of porting or go to a good set of small rec ports, 650 and you need bigger heads yet.

Cubic inches also has a lot to do with it, a 396 - 496 can do a lot with good ovals or a small set of rec ports, the 305 AFR's are great heads and I would not hesitate putting them on a 550 -650 hp 427-496. The new Brodix (Race rite) ovals look very promising (tremendous flow #'s from small ports) and the Dart ovals are pretty good to. The G.M and Edelbrocks (ovals) are the same castings with the G.M's having 2.25 intakes and there for a little better flow.

Post your combo, intended usage, and HP goals and we can give better advise.

 

i have LS6/LS7 heads on my 454 and have no complaints what-so -ever...
they are open chamber 118cc, 325 cc intake runner...as far as i know they are stock....the motor pulls really hard right from 2000-5500 rpm...

 

It really depends on your engine set up, cam, exhaust, compression, etc.
Factory intakes/heads for the high RPM & compression Big Blocks were all rect ports. Lower compression motors and passenger car BBs got the ovals.

Here's a pretty good rule of thumb:

Soild Lifters = Rect port heads
Hydro Lifters = Oval port heads

I went with the Rect heads on my 396/425 as I used solid lifters, lumpy cam, headers and big exhaust (2.5 id) pipes. You'll pay a little more for the Rect ports, but if you need the extra flow they are worth it.

I think the rects and the oval feel about the same on the low end with a dual plane intake, it's above 4 grand when the rects show their stuff.

 

A rule of thumb I heard is that rect is for higher rpm motors and ovals for lower rpm motors. Just something I had heard. True or not, I am not sure.

-Rick

 

I do not disagree that 325cc heads will work on a mildish 427-468, but worked smaller port ovals will work better. To make usable power throughout the rpm range you want to cram as much air through as small of a port as possible, todays 6.7's 207 mph prostock motors use MUCH smaller intake ports than the 8-9 sec. cars of 20-30 years ago. The new pro stock heads flow much higher #'s at a MUCH MUCH higher velocity. To be frank the older design 325 cc G.M castings are outdated, not saying they are junk, but there are ovals that you can get off the shelf that out flow them by quite a bit. The newer AFR small rec. ports and Brodix Ovals are fantastic heads and would make 75+ HP over the G.M castings if a decent sized street roller cam was used. They would also have much better lower rpm throttle responce.

For a comparrison my ported Edelbrock ovals, solid roller and Holley 1000 made max power (495 rwhp) at 6500 rpms and goes 125 mph in the 1/4 in a full bodied 69 on the motor.


[Modified by 69 N.O.X. RATT, 12:54 AM 10/31/2003]

 

I've run sq. ports on my 68 from the day I got the car, course it's a factory L-89. I have ridden in a number of 427/390 vettes, and each time, mentaly, I've compared mine to my friend's as they were going through the gears. I've concluded that I would leave them in the dust. Yeah, sitting in the passangers seat vs. the driver's seat is not a good barometer, but the seat of the pants feel just wasn't there in the 390 horse versions. Keep in mind, that the cars at that time were bone stock, mine as well as my friends'.

I was running consistant 13.0-13.1 times at 105-107mph, this with a 3:55 and close ratio 4 gear. My friend, with his 66 427/390 3:70, close ratio was turning 13.7-13.9's. I'm sure the guys running the oval ports will say you have to do port work to make the heads work....why? Why not just put on square ports and dispense with the work? My thought process is such...if the same amount of work is put in square ports, then the square ports will be that much better, and be a better performer, yes?

The point of the matter, ovals are no match for square ports on the track. Street should not even be part of the equation...it's a no no to street race, plain and simple...irresponsible, but that's a topic for another day. Square ports will get you from point A to point B just as fast as ovals.

 

I wouldn`t have anything but. They work great. However square intake heads are for higher RPM`s They make a ton of horsepower because they are used on solid lifter engines with at least 11-1 compression in the higher RPM range. They are a waste of time to bolt them on a low HP hydraulic cammed engine limited to 5500 RPM`s. :)


[Modified by wallyknoch, 10:44 PM 10/30/2003]

 

Thanks guys, a lot of really great input here but a few have missed the point of my question.

I understand why rectangular ports flow better, etc, etc and that they make more HP at higher RPM.

My question is, on a motor with a hydraulic cam with duration of 230 deg @ .050 with 10:1 compression, 2500 stall converter - how would the in traffic street response be? I don't want stumbling or hesitation or bad low end.

Thanks again for all the input.

 

Not really, as long as you use a solid lifter cam. The converter will probably work also. The heads work best at higher RPM`s. and a hydraulic cam will kill the advantage of the big heads as it will never rev up to its peak potencial. It will not be the correct combination. Stick with the original oval ports with a hydraulic cam, it will be slower, but again run very good. If it was me, "SOLIDS" and 3/8`s push rods. :cool: By the way, I have a set of nearly new LS7 heads with 3/8 pushrods for a grand if you don`t have any. :yesnod: :thumbs: