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Old 11-06-2011, 04:21 PM
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1.94 verus 202 valves

Is there any great advantage to having the 202 valve over the 1.94 for everyday driving . Some of the chevy heads will be the same cc but some will have the bigger valves .
I can understand the small chamber heads having big valves .. But even some of them had small valves ..

Or if you were to put the big valves into a small chamber head with originally small valves .. Would this help horse power or gas mileage etc

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Old 11-06-2011, 05:07 PM
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Unless you are a six grand shifting at every light person. The larger valves make little if any difference on an average mild street driven engine.

If the larger valves are installed without unshrouding the wall side of the chamber. The heads will not breathe as well as the original small valves.. The bigger valves get in the way of the air flow..
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Old 11-06-2011, 07:17 PM
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Quote:
Originally Posted by mike Crawford
Is there any great advantage to having the 202 valve over the 1.94 for everyday driving . Some of the chevy heads will be the same cc but some will have the bigger valves .
I can understand the small chamber heads having big valves .. But even some of them had small valves ..

Or if you were to put the big valves into a small chamber head with originally small valves .. Would this help horse power or gas mileage etc
I would agree that 1.94" x 1.5" valves are sufficient in a mild 350-size SBC. Once you get to an engine build that has a high power peak RPM OR 383 and above displacement, the 2.02" valves start to make more sense, along w/port volumes larger than most stock heads (the swirl port heads have big ports, but they're still inefficient). That's where the aftermarket and Bow Tie Vortec-type heads shine.

If you're looking for a good flowing ports and efficient chamber design for a 350 SBC, the Vortec heads have this covered. They typically use 2-4 degrees less timing for max power.
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Old 11-06-2011, 08:25 PM
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As Bob pointed out in many cases guys have the big 2.02 valves installed and they don`t have the combustion chamber wall swept back and the result is excessive valve shrouding so the larger valve flows less than the smaller valve. Just like the guys on ebay selling 305 heads with 1.94 valves installed and they did nothing to sweep the chamber. When you look at the picture you can see the valve is crammed into the small chamber. Then some guy buys them and thinks he`s got a killer set of heads until he gets his doors blown off by somebody with a smogger engine. The one area where the large chamber smogger heads did shine at was even so the large combustion chamber was inefficient burn wise it didn`t shroud the valves. This is why these heads can have a medium level port job done on them with some good necked down valves and a back cut and they`ll make more power than stock camel backs will. Even so the burn isn`t as great, the overall is flow is power.
The more flow the more power, the engine doesn`t know or care how efficient the burn is, the only thing concerned with that is the drivers pocketbook on fuel economy. If you look at Vortec heads you notice the combustion chamber is heart shaped. but when you look closer you notice the design was done this way to unshroud the valves. The intake side has alot more room to breathe compaired to the old camel backs bathtub shaped chamber. Then some guys install the 2.02 valves in Vortec heads and the flow falls off. The Vortec heads were designed around 1.94 1.50 valves. The short side radius, which is already excellant on a Vortec head was set up to match the 1.94 intake valve size.
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Old 11-07-2011, 05:52 AM
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I have a local guy who does the big valve 305-350 smogger heads. Sells them locally and Ebay..

Grinds a larger seat in stock heads. No bowl size increase, no blending, no chamber work.. Sells a lot of them..

Like hanging a 8 ft.garage door over an entrance door opening. Looks great but the opening is still only 36"

I just can't screw a customer with this type work..
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Old 11-07-2011, 06:34 AM
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Quote:
Originally Posted by BOBCRMAN@aol.com
Like hanging a 8 ft.garage door over an entrance door opening. Looks great but the opening is still only 36"
lol I like the analogy.
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Old 11-07-2011, 10:46 AM
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I remember reading an article years ago, I believe in Hot Rod magazine. They said 2.02/1.60 valves versus 1.94/1.50 valves was worth maybe 10 HP at 6500 rpm. For a street level performance build it wasn't worth the extra money if you had a good set of heads with 1.94's. This was before Vortecs.
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Old 11-07-2011, 06:12 PM
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Some times I do not ask :: in the right words ..))
If you had two sets of heads and both were the same 76 cc ..
One was 1.94 and one was 202 ..
Is there any advantage to having the bigger valves .
If there is little or no difference why did some of the heads have the bigger valves ,, some times with the same casting number .
Or was this trial and error .. But both out there and see which one stood up.
Or worked better over time
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Old 11-08-2011, 12:19 AM
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Okay lets say as you said, they are both 76cc.
One has 2.02 1.60 valves.
The other 1.94 1.50 valves.
Now if these are factory heads. The 2.02 valve heads would flow better.
As I said in my post, the larger chamber unshrouds the valve, so there`s no shrouding. Also the factory will match the size of the valve bowls to the larger valve.
But if we took two sets of 76cc heads, both came with 1.94 valves.
We have one opened up to 2.02 valves and nothing else. The power difference would be very little, maybe 5 horses more with the larger valve.
Why is the bowl wasn`t blended to match the size of the larger valve.
The power gain came from the open 76cc chamber again didn`t shroud the valve, so there was only a very slight flow gain.
So if we go back and blend the valve bowl to match the size of the valve
then it would likely pickup 15 to 20 horses. Not only did we match the size, but we also did a bowl clean up which helped flow by removing the ridge in
the valve bowl and flow is power.
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Old 11-08-2011, 07:07 AM
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There are many cases where you will lose power with larger valves- unshrouded or not. There isn't a factory equipped sbc head that needs more than 1.94" valves. on those heads the valve is NOT the restriction, the runner is.
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Old 11-08-2011, 04:51 PM
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Thanks Double Vision ..
That is what I was looking for ..
Answered both questions ..
Even if I did not ask them right .
The reason I want to know is this .. I made a post 327 -350 .a while back
I did finally get the motor tore down .. It is a 350 .two bolt main motor with 202 valves 76 cc heads .. flat top pistons -- four barrel Quad on stock cast intake . Originally was a two barrel
The reason I am interested in this motor is that it was so good on gas it would make a six cylinder jealous) And had decent power . In a 1980 chev pickup with a 350 trans and I believe 308 gears
The harmonic balancer was pressed on this crank , and lacked the bolt hole in the center. Only motor I ever saw without the centre bolt :??
The Harmonic fell off ruining the crank ..
I have another crank .. But I have a set of 64cc heads 202 valves too .
Would like the gas mileage .. Would like the extra power too.
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Old 11-08-2011, 04:57 PM
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Unshrouding the valves isn't just a combustion chamber thing. If the valve lift is insufficient it wont make much difference how much you open the chamber. On the other hand if you get enough lift it can make a small shrouded chamber act like it's not shrouded. Getting the valve up out of the way will allow better flow, but low lift will cause the best heads to not perform.
1.94 or 2.02 have very little difference. The real difference will be made in the lift of the cam used with either size valve.
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Old 11-08-2011, 07:40 PM
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I just had another brain fart LOL
If I put the 64 cc heads on the motor will the cam from the 76 cc heads work.
This is interesting to me ..
If I up the compression with the same cam.. Same intake and carb ..
What will happen to the mileage .. Should have more power..
But may not run so good on the original cam .
I would never use the same cam .. But the motor was rebuilt not very long ago .
And I believe that is where this Balancer problem came from .
They did not get it pressed on right :????
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Old 11-08-2011, 08:06 PM
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Early SBC engines did not have a hole or bolt in the end of the crank.

You will have to check the snout diameter very closely. If it is ok or has minor wear. You can use an aftermkt. balancer. The import balancers tend to be .002" or so undersize..
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Old 11-08-2011, 10:51 PM
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Quote:
Originally Posted by mike Crawford
And I believe that is where this Balancer problem came from .
They did not get it pressed on right :????
They got it pressed on "right" in that if it weren't all the way onto the crank snout the pulleys wouldn't have lined up.

BUT- if they took a flapper wheel to the damper ID to get it to go on easier (or god forbid, sanded down the snout itself), that could have set into motion the events that culminated in the damper coming off.

Most often in cases where the damper is too loose, it's because the damper was altered, but not always. Like as said above, mic the snout and examine it closely for any indications it has been altered.

More- Balancer bolt problem!
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