I have a 74 coupe w/ 454, auto., and 3.08 gear, street driven only. Already have an aftermatrket cam with increased duration (don't know specs). Would like to upgrade to aluminum heads, LS-6 manifold and Speed Demon carb, but the LS-6 manifold is for rectangular-port heads. I am considering the GMPP heads and am wondering how much low-RPM drivability I would lose with my set-up if I went with the rectangular ports over the oval ports. Opinions? Thanks.

 

Automatic with 3.08 gears and R-Port heads is not going to be good for a street driven car. The general rule of thumb is that unless you keep your motor running above 6000rpms a good bit of the time O-Port heads are the way to go. You also need to know what kind of camshaft you are running because you want to make sure the cam and heads work in conjunction with each other. No sense in having a cam that is done by 5500RPMs and having heads that don't start until 6000RPMs.

I have run both cast iron "215" O-Ports and some big aluminum boys that are currently on the motor. I also run 4.11 gears and a 4 speed and noticed a pretty considerable loss in bottom end when I did the switch. I do a good bit of dragging down the 1/4 mile so I don't really care too much about low end as long as it pulls hard up top. The GM aluminum heads are probably your best bet they are a good compromise between R-Port & O-Port. You can usually find some cast iron "215" or "049" heads that have been worked over with the bowls blended, 2.19/1.88 valves and some port work fairly cheap. "215" heads would give you a nice bump in compression too.

As far as the intake I did have a friend that ran a R-Port Strip Dominator intake on O-Port heads and turned 11.66 down the 1/4 with it. Personally I would make sure the intake and heads match but it worked for him.

 

That's what I thought. So if I go with the GMPP aluminum oval-ports, which manifold/carb combo would be better? (it has to fit under the stock hood): Edelbrock Torker II & 750 Speed Demon w/ vac. sec. (I've heard the runnners on this manifold are small) OR GM factory aluminum L36 manifold and 750 or 850 Q-Jet rebuilt for high performance?

My cam is a mild aftermarket grind with more duration than the stock LS-4 cam and a slight lope, but still has good low-end torque (don't know specs). Thanks for the suggestions.

 

Hello there, neighbor. Hmmm, auto, no stall and a 3.08. Stick with the ovals.

 

memphis:
If you are trying to fit things under the stock hood then your options are limited. The Torker II will fit under the stock hood. I ran this intake on the first version of my 468. The runners on the intake are small. Not the best intake out there but it's better than a stock cast iron one and it's good for hood clearance issues. I ended up getting rid of it for a strip dominator intake and an L88 hood in the quest for more horsepower.

With your application (3.08 gears, automatic trans and no stall) I think the Torker II will work well with a decent camshaft and a 750/850 Holley.

 

This sounded strange to me at first because I always thought you had to have r/port with r/port and o/port with o/port to make them run right. It's not true. It is actually better to run an r/port intake on o/port heads. The difference between the two helps with the atomiztion of the air and fuel. Troy Scott of Troy Scott's racing engines told me that is the way to go.

 

The GM-Perf heads are actually re-branded Edelbrock's,..and they call them 'roval' ports which is basically an enlarged O-port head. They recommend their intakes with the use their heads which are port matched but the intake likely won't fit under the hood. I run these on a 69 Camaro with the GMPP intake (rebranded Edelbrock RPM) that's cnc'd on a 496. With a 280H, this combo makes gobs of torque AND power up to 6000 rpm.

But for the Vette, I'm going through the same decision-making porcess as you.

The problem is the intake or intake/hood clearance,..plus I want to run my stock air cleaner and cowl induction on my 73.

I have an L36 intake sittin' around,..and maybe I could open her up a tad but I don't think the 'Roval' ports would like the L36 intake. Therefore I'm giving serious consisderation to these heads:

http://www.competitionproducts.com/p...ber=BRO2061000

Any thoughts?

 

Edelbrock does make GM aluminum BB heads. I was in their factory and saw pallet upon pallet loaded with aluminum BB heads with GM logos.

Edelbrock puts a lot of work into their head design so I'd expect their heads would be optimum.

For years I drove my 69 with a clone L88 engine (GM L88 short block) and GM iron rectangular port heads. I had a 3:08 diff and later a 5 speed Richmond (then Doug Dash). I never noticed any problems with the rectangular ports. The long duration cam and the 3:08 rear end made the car very gentle to drive in city traffic. The L88 engine actually produced very little HP below 2000 rpm. I could drive at highway speeds at 2000 rpm. Power just got explosive above 4000 rpm though.

 

73 Dark Blue 454, you are I are in the same boat.

Will an LS-6 manifold fit under a stock 74 hood? If so, and you can really run an r-port manifold with o-port heads, this may be the solution to my dilemma and the way to go. I did not know you could do that.

 

The LS-6 intake is a high-rise dual plane,..probably sits as high or higher than an Edelbrock RPM which won't fit under a 73-74 hood, and certainly not with the stock air cleaner. I don't know of a low-rise square-port intake that would fit under our hoods.

Also, I hear of some running square port intake with 0-port heads and vice versa, but that's too weird for me. I'd try the Torquer II 0-port intake or a regular Edlebrock Performer (non RPM) with the GMPP O-port heads.

 

Definitely go with ovals for your combo....but I'd look at the Brodix Race Rite series. They will stomp the GM/Edelbrocks in every category. Plus the ex ports are in stock location so no issues there.

Another alternative is the AFR 305's or CNC 315's if you want to spend a little more. Any of these will just kill the other choices.

But what pistons are in motor? If they are stock ones, then I might have to lean back to the Edelbrock EFI ovals with the 100cc combustion chambers to get your compression up a little. Or you would need to have the other all milled to get it up some. Those years of 454's were lucky to measure anywhere close to an actual 8.0 compression...often in the high 7's. That makes a real stone.

The stock hood is going to really restrict what you end up with. I think even the Torker II would be better than than the L-36. Many folks run rec intakes on ovals...but if you do, the right way is to do some port opening work to blend it in. No way that giant obstruction/transistion in flow is good for anything.



JIM

 

Yes,..the O-port Brodix heads look good here too:


http://www.jegs.com/webapp/wcs/store...tegoryId=10187

 

Ditto

 

The LS6 intake is not a highrise. It will fit under a stock 69 big block hood.

 

That's what I thought. The LS-6 manifold came from the factory in 1970 under an L-88 style hood, did it not? And I have heard that the 73-74 cowl-induction hoods, which have a slight rise to them, actually have a tiny bit more clearance than an L-88 hood, no? If this is true, I could use an LS-6 manifold with the GMPP o-ports instead of a Torker II, which I think would be better. Opinions?

 

Are you sure the LS-6 manifold is a high-rise? It obviously came from the factory in 1970 under a stock hood.

 

No GM intake dual plane intake sits higher. Compared to the Q-Jet cast iron BB intake in my 73, it has to be two inches higher. Perhaps I can figure out a way to measure. I have "163" intake and a "ZL-1" intake to compare which I assume is the same height as your LS-6 intake, or close.

Also, I'd guess there are hood height diffs between the models. Perhaps someone can detail,..but seems LS-6 cars received special hoods for clearance.

Wes

 

The LS6 intake is nowhere near as tall as the L88/ZL1 intake. Not sure if there is a Chevelle LS6 and a Corvette LS6 intake, but the Corvette LS6 is a low rise rectangular port aluminum intake and will fit under the stock big block (non L88) hood as well as all 73-79 hoods.

 

The LS-6 intake is a low rise. On the Chevelle a spacer was used to get the air cleaner up to the hood for the cowl induction. But in general they were happy they got the "Corvette" intake.
The L-88 used a high rise intake & the L-88 hi rise hood is only 7/8" higher than the 73-79 med. rise hood & allows a taller intake for BB.

You need at least about 3/4" clearance over the Holley vent tubes.

Torker II When there is room left, an insulator or spacer should help due to the flat floor.

Some use the Holley Street Dominator (Discontinued single plane).

 

Does anybody know about GM #3885069? I found one on ebay. It is also a low-rise dual-plane r-port aluminum manifold from the L-78 (396) and L-72 (427) 375/425 hp. How does it compare to the LS-6 manifold functionally and in terms of height, and would it be an alternative for me? Thanks for everybody's input - I want to try to get this right.