question about engines

[yokinazu]

ok heres the question. im building a 350 chevy motor punched out 60 over, makes it somethin like a 358 i think. but any way im geting ready to start doin my heads and valves. heres the question would you port or polish? or both?
please give your reasoning. i know what im goin to do, im porting. but i would just like some other persons opinion on the matter.

yokinazu Reviewed by yokinazu on 12-20-2007. question about engines ok heres the question. im building a 350 chevy motor punched out 60 over, makes it somethin like a 358 i think. but any way im geting ready to start doin my heads and valves. heres the question would you port or polish? or both? please give your reasoning. i know what im goin to do, im porting. but i would just like some other persons opinion on the matter. Rating: 5

[Rusty Trichome]

If you are spending all the time and money for high performance, I'd spend the extra for polishing, too. Smooth, unobstructed airflow is a good thing.
AircooledTech.com - Port & Polish Your Heads

[Frickr]

it depends on what your going to be doing with the motor, if its just going to be a drag motor, and only go a quarter mile at a time, then the polishing will help out. but really, if its a street motor, polishing can actually hurt your performance. in your combustion chamber and in your ports, there is small pours in the metal, all of those little raises and indents will actually help absorb some of the heat from the combustion, and cool the air going into the chamber. when you polish it, all that heat is just reflected back so you might have problems with hotspots, or dentonation. if you do a good port job, match your intake and and header to the head, and smooth out and open up alot of the intake and exaust runner, you should get a pretty substancial gain. despite what you have heard, you can actually make more power with a castiron head then with a aluminum head. the castiron takes longer to heat up, and disapates the heat more efficiently then aluminum which spreads the heat throughout the entire head. the major reason why alot of racers use them is wieght. the 5 extra hp that you could have with the cast iron, is about equal to the small amount of wieght that you trim off.

if your bored 60 over, and your only looking at a little over 350, you must be running a low compression ratio. im looking at that number with a stock compression stock pistion 350 with a big cam intake header and carb. with a good vlave job, and some porting, nothing major, its not going to help that much unless if you got high compression pistions, a huge cam, and a big carb. but if you have all that, then i wouldnt even mess with stock heads in the first place. i would buy a nice set of dart or edelbrock heads.

[yokinazu]

i already know how to build high power motors. im just wonderin what other peoples take on this is. aint payin extra nothin for polishing or porting i do it my own self.
by the way 358 is my final displacment not horses.
also i aways been told either port or polish but never do both. when you do both you will not have enough turbulance to properly mix fuel and air.

i build trannys fora livin and its gettin a th400 that will about throw you thru the back window when it shifts. i would like to get away from the torqe converer and put a hydrostik in it, thats basicaly a clutch if a dont know, but i aint seen one in years.

[Frickr]

look at the circle track stuff, they have a valve body thats controled by a clutch peddle, and the torque converter is replaced by a dumby that just makes the connection between the motor and tranny. I think TCI makes it, hang on ill find it for you.

[Frickr]

its only for a powerglide TCI Powerglide CNC Clutch Pedal Kit - JEGS

then the front drives TCI Circlematic Front Pump Drive Kits - JEGS

and valve body TCI Circle Track Valve Body - JEGS

[xcrispi]

You must be a real old gearhead to have seen the old clutch flite transmissions .
Things are antiques and not many ppl. run em - collectors item man . Ppl. are running brunos , lencos , G force w/ dbl. disc setups and floaters in the real fast cars now.

We need more info like other dude said . He's right too about gasket matching the heads to the intake it can gain you almost as much H/P as the port -n- polish job .

We need to know what this motors primary use is gonna be . RPM range ? hyd , solid , hyd roller , solid roller cam ? lift / duration at .050 too . compression ratio ? , choice of intake manifold - single / dual plane ? Rear gear ratio and tire height ? How heavy the vehicle is ? Is it gonna get sprayed ? steel , aluminum , titanium connecting rods ? Gasoline or alcohol ?

If it's a high rpm motor polishing is to your benefit due to greater air/fuel speed velocity inside the intake plenum and intake runners - air/fuel mix. goes through so fast gasoline / alky stays better atomised and particles don't get the chance to become larger .

On a hot street motor the fine grainy texture -aka- "as cast" is to your benefit because the air/fuel mix. is moving through the intake plenum and intake runners at slower speeds / velocities and the grainy texture helps fuel stay atomised .

350 + .060 is a 360 I think . It's been a while since I played w/ small blocks . Life begins at 500 cid .
Crispi :jointsmile:

[MadSativa]

just do it..........its a stock 350, your not gonna rocket anywhere with stock heads, besides a port and polish makes better performace, when you add more air and fuel to the mix, so think about a small turbo or even a small supercharger, but just do the port and polish for shits and giggles, so later on you can add more air and fuel.

[Frickr]

if i were you, i would try to find some 327 corvette "camelhump" heads. just portmatch those, and they should be good for up to 450 hp no problem. unless if your going for 700 plus, it really doesnt add that much more hp with even the most radical port and polish. sometimes if you get to durastic, you can hurt performance. just like putting to big of an intake on a car, it will decrease the performance unless if the motor is built for it. and if you plan on doing it yourself, its a risky thing. you have to get each chamber identical, each runner with the same CC. the only way to measure that is if you have all the plates and burettes and stands to measure all the volumes. if you just go in and smooth out some of the ridges that are left from the casting that should be good enough. maybe where the valve guide is, smooth to increase flow around that. other than that i really wouldnt do to much unless if you really know what your doing.

[Mississippi Steve]

Port the heads, polish the exhaust, but leave the intake rough to help the fuel to attomize and vaporize. then have the heads flow tested, as well as have the intake manifold match ported and flow tested also. Oversize valves, 3 angle grind with stelite seats. Solid lifters with a gear drive cam is the way to go.

Remember, your making the horsepower in the heads.

BTW... boring the cylinders is not a good thing.... you don't want to do this unless you *absolutely* have to. It reduces cylinder wall thickness and the larger pistons increase the internal rotating mass. You *DO* want to have the engine fitted with 4 bolt mains if it doesn't already have them, then have it ZERO BALANCED. You will probably also need to go with an aluminium flywheel and scatter shield. BTW... Borge and Beck multi plate clutch is a good thing.

Unless your building an engine that will be run wide ass open *ALL THE TIME* like a NASCAR engine, then your probably going to want to have the cam ground for mid-range hp and torque. Figure to have it kick in at around 2800rpm with a shift point around 5750/5800. If you don't have him beat by then, hang it up.

I am assuming direct port induction and 5spd manual trans.... if you can get hold of 4 2bbl 42mm down draft weber carbs, you shouldn't have any problem at all getting 500 - 600 *RELIABLE* hp on the street.....and if you can keep your foot out of it, get 20+mpg

Don't forget to upgrade the trans, drive shaft, and rear end, to handle the extra power.
Then you also gotta upgrade the brakes..... the fastest car in the world isn't worth a crap if it can't stop.

Might want to think about suspension and tire/rim upgrades.... make it quick, make it fast, then make it turn too. Got to be able to get the power to the ground.....hopping axles and smoking tires ain't gonna do anything but lose races and cost you money.


BTW... I built a 235hp 1600cc pinto engine(no blower or turbo) and dropped it into a Cortina..... ran like a scalded cat and handled like it was on rails. those guys in their big block Camer-slos got rather upset when they got their doors blown off by a little 4-banger.