Cylinder head work

[blown motor]

I have a 340 with 10:1 (10.5:1?) compression, X heads, stock intake, 650 Eddy, TTI, 2 1/2" Magnaflow exhaust with X-pipe. Is it worthwhile for me do any head work to gain HP? What work? How much will I gain?

[jimynick]

Murray, the ball park figure that I've heard for a normal, non 10-10ths porting job is 30-40hp with more available based on the thickness of your wallet. But, don't forget, what we're talking about is basically an air pump and while you can gain advantage in certain areas, you then need to improve others and in a porting deal, that sounds like a cam and intake mods as well as exhaust work. I'd call Indy and ask them what they think and you could call Edelbrock, too, and get truly professional opinions. Ian 

[Chryco Psycho]

You can definatly make gains porting X heads but by going to 308 swirl castings & some decent port work you can gain 41 RWHP over X castings

[cudabob496]

other things can make your car perform like its got more power, as in cold air induction,
steeper rear gears, and a race stall converter.  I just put a 3200 stall, and 3.76 rear gears,
in my 99 Trans Am, and its like a 50 hp gain, as far as quickness.

Also a race type double pumper carb may give a noticable kick in the pants.

And, as mentioned above, if your heads have the air flow room, a different cam
might be noticeable.

[blown motor]

I forgot to mention it does have a Lunati cam but I don't know the specs on it. It was in there when I bought the car. Also it's bored .060.
Neil, are you saying that ported 308 heads will deliver 41HP over ported X heads or stock X heads? I'm leaning toward staying with X heads to keep it stock and reduce the cost.
So let's say I got the heads ported and gasket matched, then air flow tested. Then I put on a carb that will supply at least that much air which may even be the 650 that I have. Would that be the correct approach? Is the stock dual plane intake adequate or too restrictive? I know there's a lot of talk about Eddy RPM intakes. Will a different cam help? Right now it seems to have great low end power which is what I like. It's just a street car.

[cudabob496]

need cam specs, to match with the head flow rate.

[jhaag]

Right now it seems to have great low end power which is what I like. It's just a street car.

Because this is a street car and you like torque, porting heads should be put on hold. You should change your intake, and check the cam specs. You will get more bang for your buck in these areas as well as a convertor and gear swap, as mentioned above. Once you start down the path of head porting all of these will enter into the equation anyway. Typically you will move your torque curve higher in the rpm range with head porting. This is not the most desirable thing on a street driven car. 

[blown motor]

Typically you will move your torque curve higher in the rpm range with head porting.

Did not know that. I learn so much from you guys 

[Strawdawg]

If you have enough torque to spin the tires from a standing stop on good pavement, then a higher stall converter will only hurt you.

Porting heads can hurt low rpm power because it reduces velocity thru the ports, but, again, without knowing how your car currently performs with its current combo, we don't have any basis to say that it will be appreciably negative, or not.  For sure, it will help the top end.  How much it helps will depend upon your combination.  If the cam is relatively small and does not produce a much higher power band than stock, porting will not make a great difference.  If, on the other hand, your cam is large enuf to extend the power band appreciably above the stock engine range, then porting will have a much more substantial gain.

Of course, if the cam and porting presents a significant potential gain, your current carb will probably become a much greater restriction so the gain will not be as much as it should be.

Or, if you have stock exhaust manifolds on the engine with small pipes behind them along with restrictive mufflers, then you won't see as much of the potential gain as you should either.

In other words, you have to look at all elements of the drive train to be sure they work together in order to obtain your money's worth.

[blown motor]

TTI headers with 2.5" Magnaflow exhaust with X pipe. I think we are ok on that side of the equation. If the carb ends up being the resticting factor that's an easy one to solve. Just spend more 

[jhaag]

Strawdog is correct in that the entire combination needs to be optimized, to work in concert. Hence my point that porting heads is rather far down the list until stock ports become the restriction. As Strawdog pointed out, after you do port work you need to change other parts of your combo to maximize the increased flow. All comes down to how many $$$ you want to spend and where you want to end up.

[Chryco Psycho]

We went from ported but not sure how well as I did not port the X heads to Ported 308 heads , most of the porting I did was not about making the port much larger but more about removing restrictions & turbulence & enhacing swirl & fuel atomization , so I would disagree & believe the gains would be significant using 308 swirl heads cleaned up properly , you do not even need to use the larger 2.02 valves to make significant gains but I do agree that the colpete pkg including cam intake & heads all need to work together for max gains

[moper]

There's always power to be found by cleaning up factory heads. Simply by using a good shop, with top of the line equipment you can gain up to 15% more airflow with no change in peak power rpm. I think it's a little incorrect to say "porting gets you power but raises the rpm". It doesn't in and of itself unless it's taken to a much deeper level than "cleaning up". That's because generally by increasing flow through the open valve at higher lifts, you sacrifice flow at lower lifts. So you need a bigger cam, and that cam won;t make power until higher rpms where the engine can actually make good use of that extra airflow.

In the case of stock 2.02 or 1.88 X/J/O/915 type factory 340/360 heads... Have a 5 angle valve job done, making sure the guides are perfect. If they are stock valves replace them with performance stainless that are back cut, and if the heads are 2.02/1.60, go 2.05/1.65 and have the seats pushed out into the chamber as far as possible. Give the shop a few hours of labor to bowl blend the throat cut and shape the guide boss, and gasket match the intake side, and slightly port the exh side. Those changes alone should give you another 30-35 cfm with really good low and mid lift flow. That's enough to make another 40-50hp with a small to medium sized cam.
The strength of the 308 heads is not the intake port but the exh port which is basically the Magnum design and much better than earlier heads. The intake port doesn't flow much different from earlier heads.

[Topcat]

As far as the intake manifold goes...
I recall Nell (CP) once saying that the OEM 340 manifold design was one of the best out there?

The earlier design were close to a square bore then changed to a spread bore.

[AussieMark]

Right now it seems to have great low end power which is what I like. It's just a street car.

Because this is a street car and you like torque, porting heads should be put on hold. You should change your intake, and check the cam specs. You will get more bang for your buck in these areas as well as a convertor and gear swap, as mentioned above. Once you start down the path of head porting all of these will enter into the equation anyway. Typically you will move your torque curve higher in the rpm range with head porting. This is not the most desirable thing on a street driven car. 

Exactly the bigger the ports the slower the air speed and fuel will become less atomized and start puddling on the port floors at low rpms do what Chryco recommends and get the better heads more power no side affects.