Porting heads go big valves or stock size
- Thread starter jetmech
- Start date
If had a 4.1 you may be able to better benefit from a larger intake. Theres not much room unless you move the valves away from each other. Its more effective to back cut the stock valves than just about anything. You will see a sharp ridge on them. You could go with 1.77 intakes. Thats only .06in more than stock. Hardly worth it imo. The heads flow like crap. Theres a lot to be gained in the bowl area and the valve job.
I think thats the direction im going w/ cam 218/218
J-B Racing
Forced Induction
- Joined
- Sep 16, 2003
Like Bison says...Stock Valves will work fine. I have compared on the Flow Bench and it`s not worth the money to with bigger Valves. A good Porting Job with Stock Valves will do the Job very well.
Joe
Joe
from what i learned from an engine and head builder here is Cali is that , stock valves will work just fine, bigger valves on turbo cars are not necesary, think of it this way, you have a forced induction (TURBO) pushing air in the car if you have good flowing heads and a nice cut on valves and seats you will do just fine, bigger valves get to close to the cylinder walls and could basically create turbulance in the piston chamber blowing out spark plus you loose velocity with bigger valves, put your lips on the end of a straw and blow through it you will feel lots of air and high velocity on the other side, now blow through a garden hose you wont get the same feeling and you loose velocity on the other end, one thing to do is to replace the exhaust valves with stock size ones but use the stainless steel one since the exhaust valves are the ones the get the most abuse over time...
Ive also found the stock exhausts to be very durable over time. They are tremendously hard and can often go longer between cutting than replacement stainless valves. Inconnel is the way to go if you want to run it on the edge.
knperformance
knperformance
- Joined
- May 4, 2006
The stock exhaust valves if back cut will give great results almost as well as aftermarket valves, the intake on the other hand through extensive flowbench testing are not worth using even with a back cut they give up after midlift . Also be careful when selecting after market valves i have tested other brands and some lost as much as 20 cfm . I only use ferrea valves because they gave best flow numbers in the heads that i do.
So your saying stay with the stock exhaust and go w/ the larger intake valve.
J-B Racing
Forced Induction
- Joined
- Sep 16, 2003
What I have been doing for a few years now is that I ONLY change the Exhaust Valve to a 1.56`` and leave the stock 1.71`` Intakes. I have noticed the Engines have a better Throttle response and a little more torque.
The 1.56`` I take them from Pontiac V-8 Exhausts. A little Machining is required. But this is much cheaper than buying a set of S/S all around.
Good Luck on your Project..
Joe
The 1.56`` I take them from Pontiac V-8 Exhausts. A little Machining is required. But this is much cheaper than buying a set of S/S all around.
Good Luck on your Project..
Joe
marred4life
Banned
- Joined
- Mar 15, 2002
i have full ported stock irons with bigger valves and a 212/212 cam that sound and feels awesome
TurboTnZ06
Go on red!
- Joined
- May 7, 2002
Yeah I run 210/210 on a 110 billet hyd roller using stock irons with manley severe duty SS stock sized valves with extensive bowl porting only. 127 mph in the 1/4 works for me.
What I have been doing for a few years now is that I ONLY change the Exhaust Valve to a 1.56`` and leave the stock 1.71`` Intakes. I have noticed the Engines have a better Throttle response and a little more torque.
The 1.56`` I take them from Pontiac V-8 Exhausts. A little Machining is required. But this is much cheaper than buying a set of S/S all around.
Good Luck on your Project..
Joe
i have been researching this for a while and i agree on how the engine reacts anyhow. The exhaust side on a turbo car is the problem side on our cars cause the valve is not big enuff to the flow the extra air that is packed in back out on the exhaust stroke. That why the exhaust valve gets opened a tad early to help try and vent the cylinder better with less self EGRing. The down side to that is by opening the valve early we are giving up some of the cylinder's charge that could actually do more work by pushing the piston down the bore. better mileage and better power.
a flat back exhaust valve works great.
See if only we had a bigger exhaust port and a bigger exhaust valve. that where the bueaty of a set of champion GN1's are because they have bigger valves on both sides of the engine.
this thread has some good info in it please read
http://www.turbobuick.com/forums/ge...68993-increasing-exhaust-valve-size-head.html
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