Thoughts on NOT porting intake?!?!

[Anlushac11]

My machinist and I were talking and he was saying he would not bother trying to port too much on the intake side, just concentrate on the exhaust side. Since the intake will be under pressure dont need to do much there.

The machinist also said for same reason I dont need to go to a larger intake valve since the intake side will be pressurized its not as important.

My thought was yes he is right...BUT...

The better the airflow the more power that can be made with less boost. I know on the Ford 2.3L turbo's you can make 200hp with 16lbs boost but port the intake side and lower intake and gut the upper and you can make 200hp on 12lbs of boost because you have reduced or eliminated the restrictions. This also means more power with the same amount of boost.

My dad was recommending bigger valve and porting intake, according to my dad the intake porting and bigger valves help to make power. My dad said in his experience turbo motors love big valves on both sides and he recommends back cutting intake and exhaust.

I was also thinking since a stock log head flows like a sewer pipe any head porting that can increase the amount of head flow on intake and exhaust can only improve things.

I will be using a cam recommended for log head and turbo:
CI 272deg/.450"lift/ 110deg lobe centers.

Thanks for any input.

 

[CZLN6]

Howdy Back:

YOu might do a recap of your build plan. I don't remember the details. What year casting are you building? In general, I'd go with larger exhaust valves if I had to choose. I'd back-cut the intakes, but not the exhaust. I'd be concerned about the cylinder pressure and added heat in a blown engine. For that reason I'd use a little wider margin on both intake and exhaust seats. I'd spend alot of time on polishing the combustion chambers. Polishing will remove hotspots and a polished surface reflect heat better. I'd spend alot of time on the exhaust ports.

In the intake ports, I'd spend time blending the transition between machined and as cast surfaces, and rounding the short sides of any bends. A quality three angle seat should be a minimum.

And, as always, listen to your Dad!

Adios, David

 

[Anlushac11]

Here is the build so far based on the parts paid for and ordered:

1978 200 block bored .030" over. O-ringed, .086" copper head gasket, ARP head and main studs.

Stock crank ground .010/.010, my machinist does not do dynamic balancing but he contracts out to a guy who does.

C3 170 forged rods. Polished beams, lightened, shot peened, nitrited, ARP rod bolts, rifle bored to oil free floating pins. (My D8 rods are cast iron...not comfortable running those on a turbo).

Stock oil pump with port matching

Pistons are JE forged flat top pistons with metric rings, chrome top ring.

Classic Inlines hydraulic cam, 272deg dur, .450"lift, 110deg lobe center dialed in at 107deg.

I have already converted a 2.3L TFI distributor to run in the inline six.

Still have to order double roller timing chain, Michigan 77 main and rod bearings, engine rebuild gasket kit.

Will be using lots of dry film lubricant and oil/thermal dispersant coating where practical.

Top of pistons will be getting thermal barrier coating and exhaust port and combustion chamber will be getting thermal barrier coating.

My dad will be doing port and polish on D8 log head, have figured for a 57cc chamber.

Not decided on running EFI port injection or a GM TBI injection. Either will be controlled by Megasquirt.

 

[Asa]

in a sense he's correct.... but at the same time, anything you can do to help that turbo will help make power, you won't be running as high of boost, the turbo won't be spooling as fast, everything should last just a little bit longer due to that

plus, when you want more power, then it's easier to make and you don't have to pull the head to port everything then

 

[Mercury Kid]

Leaving the intake side alone on a forced induction motor is an old school of thought. Kind of like using a single pattern cam on a nitrous motor. It works, but not to the fullest extent that it could. If you wanted to save the time and some money you could leave the intake alone, but you'd be leaving some cards on the table so to speak.

 

[Crosley]

It is not so much as the boost level as the air flow level.

Boost may be higher with less air getting into the chamber than with lower boost number and better air flow with port clean up work and larger valves.

The larger valve addition I could see not doing , but the port clean up and bowl area under the intake valve should be done in my opinion.

 

[Broncitis]

I guess I didn't realize you were not using the AL head, with all the specialty work I just assumed you were, alot can be compensated for with using boost, I'm having trouble with this computing.

 

[CobraSix]

the above statements are right. Sure, the turbo will still be making boost and forcing air/fuel into the cylinders. What is affected by the 'smoothness' is how that mixture is moved.

Think of it this way, if you are adding plumbing to your house, would you use really rough pipe or smooth pipe? Same principle. Both systems under pressure.

Will it make a huge difference on this application? Maybe not, but a difference it will make. With all the work you're putting in, unless this was a temporary head, you might as well spend the few hours and clear up the ports some. Remember, smooth ports will keep the fuel from dropping out of suspension when compared to rough surfaces.