1.94 vs 2.02
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10,722 Posts
In a majority of cases, especially with closed chamber heads, the bigger valve will flow less due to shrouding. If bigger valves are installed have the chamber deshrouded, otherwise the bigger valves are a waste of money.
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140 Posts
I think you have to multiply that by 3.14 cause it's round. That would be more like 12.5% It really depends on what you want from your motor, high revs or bottom end torque.
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199 Posts
Area of a circle is proportional to the square of the radius, which means that a 2.02 has 8.4% more area than a 1.94.
As was mentioned, though, it's not worth it if shrouding keeps more air from getting in.
As was mentioned, though, it's not worth it if shrouding keeps more air from getting in.
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3,532 Posts
The size of the valve doesn't matter. It is the overall flow of the intake compared to the exhaust. You want the exhaust to flow around 75% of the intake flow on a street driven, normally aspirated engine.
One other thing to consider other than the bulk breathing, is displacement of the eninge and what its going to be used for.
Just for an example, with The IMCA Modifieds, most of the Chevy guys around here are running the light weight 1.94/1.60 valve heads on their 350's and 400's. Not sure exactly what production head it is. Think it comes off of the 305, but they are claiming they get as much out of them with a good porting job as they do with the ported out factory heads with 2.02/1.60's.
Just for an example, with The IMCA Modifieds, most of the Chevy guys around here are running the light weight 1.94/1.60 valve heads on their 350's and 400's. Not sure exactly what production head it is. Think it comes off of the 305, but they are claiming they get as much out of them with a good porting job as they do with the ported out factory heads with 2.02/1.60's.
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7,810 Posts
I didn't think IMCA allowed porting?
porting heads
You can do pretty much whatever you want to do to your engine, in the modifieds and stock cars, as long as you are willing to sell for the engine claim.
The late model rules have gotten very convoluted and confusing.
If you are running stock unported heads you can run yada yada carburetor. If you have stock heads that are ported you have to run yada yada carb. If you are running the IMCA spec engine, which the last I knew, all IMCA late model engines had to run Brodix heads, you have to run yet a different carb etc.
The modifieds have always been pretty wide open with the engine rules, the only limitation being no aluminum heads, and limited to one carburetor.
Same with the IMCA stock cars, exept they now have to run the 350 Holley 2 bbl carb, which of course IMCA gets a kickback on each one sold, as well as they do on all the McCreary EC2 and G60 racing tires.
I find it hilarious that most of the hobby stockers around here are running as fast or faster than are the IMCA cars.
All these rule changes have caused car counts to drop off considerably and other rules changes on the modifieds are placing them out of the hands of the average Joe that wants to race.
I think the next move with the IMCA Modifieds will be to go to a spec chassis, like using the Ford Crown Vic frames, as they are the only full frame front engine rear wheel drive chassis thats on the market now thats worth a crap.
Other things that are running people off are the fact that guys like Wayne Larson, who races all over the country and has an unlimited budget has the ear of IMCA, and if they want a change in the rules, they get it.
Like bead locks. Bead locks became an issue with the Modifieds the year after I retired from racing (1992). There was a big debate about tire pressures, and guys wanting to run bead locks so they could run on 5-6 lbs of air in their tires.
So since the high rollers wanted the bead locks, They got ok'd.
Whats funny is that McCreary said the G60 was designed to run with 20 lbs of air, and not low pressures with bead locks.
The simple rule would have been to just check the air pressure of the rt rear tire on the top 5 cars at the end of the feature. Not enough pressure in the tire, you are disqualified. Simple rule and surely a lot less expensive for the average racer.
You can do pretty much whatever you want to do to your engine, in the modifieds and stock cars, as long as you are willing to sell for the engine claim.
The late model rules have gotten very convoluted and confusing.
If you are running stock unported heads you can run yada yada carburetor. If you have stock heads that are ported you have to run yada yada carb. If you are running the IMCA spec engine, which the last I knew, all IMCA late model engines had to run Brodix heads, you have to run yet a different carb etc.
The modifieds have always been pretty wide open with the engine rules, the only limitation being no aluminum heads, and limited to one carburetor.
Same with the IMCA stock cars, exept they now have to run the 350 Holley 2 bbl carb, which of course IMCA gets a kickback on each one sold, as well as they do on all the McCreary EC2 and G60 racing tires.
I find it hilarious that most of the hobby stockers around here are running as fast or faster than are the IMCA cars.
All these rule changes have caused car counts to drop off considerably and other rules changes on the modifieds are placing them out of the hands of the average Joe that wants to race.
I think the next move with the IMCA Modifieds will be to go to a spec chassis, like using the Ford Crown Vic frames, as they are the only full frame front engine rear wheel drive chassis thats on the market now thats worth a crap.
Other things that are running people off are the fact that guys like Wayne Larson, who races all over the country and has an unlimited budget has the ear of IMCA, and if they want a change in the rules, they get it.
Like bead locks. Bead locks became an issue with the Modifieds the year after I retired from racing (1992). There was a big debate about tire pressures, and guys wanting to run bead locks so they could run on 5-6 lbs of air in their tires.
So since the high rollers wanted the bead locks, They got ok'd.
Whats funny is that McCreary said the G60 was designed to run with 20 lbs of air, and not low pressures with bead locks.
The simple rule would have been to just check the air pressure of the rt rear tire on the top 5 cars at the end of the feature. Not enough pressure in the tire, you are disqualified. Simple rule and surely a lot less expensive for the average racer.
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7,810 Posts
IMCA=International Money Collecting Agency.
Probably not the right place for a circle track discussion but IMCA does nothing but require a spec sticker. Then they buy the company who makes the part. And the stickers. PM me
Probably not the right place for a circle track discussion but IMCA does nothing but require a spec sticker. Then they buy the company who makes the part. And the stickers. PM me
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1,161 Posts
i put the 202's in place of the 194's on a set of 462 fuelie heads a few yrs back and ported them also.lost alot of driving around street torque.the 194's are great from 0-80 mph and the 202's are good from there and up.i ran them for a short time on both a 350 bored 60 over and a 406 both of them built pretty good.i remember one nite in particular when i was driving on the freeway to pick up my wife at around 10 pm in the winter.some guy kept playing cat and mouse with me the whole way there when i cut loose on him.i nailed it at about 65-70 mph and that thing sat me back in the seat so hard and violently as it just ripped away.it was one of those rare times that you don't forget.at first it actually began to scare me then i got big stupid smile on my face.its a smile i've never forgotten.for the street and having fun up to 80 mph though you probably would be better off with something like a set of 305 c.i. 601 or 801 heads with the 184 valve bumped to 194.it's a closed (about 55 cc)chamber that will increase your compression and increase your throttle response greatly.
http://users.erols.com/srweiss/tablehdc.htm#Chevy
Chevy '462 Iron CCM 157/64 1.940/1.500
-
Pipe 62 50/54
108.0% 119/91
76.47% 167/121
72.46% 198/134
67.68%
407 hp 212/139
65.57%
436 hp 218/142
65.14%
448 hp
487 hp - - - - 182.8/125.4
68.60%
1.389/2.219
Chevy '492 Iron 157/62 2.020/1.600 64 - - 173/125
72.25% 198/137
69.19%
407 hp 206/141
68.45%
424 hp 209/141
67.46%
430 hp
466 hp
================================
Same intake runner, smaller combustion chamber and 2.02's made less possible HP. Although unusual not impossible. A possible case of shrouded valves as Max pointed out.
Chevy '462 Iron CCM 157/64 1.940/1.500
-
Pipe 62 50/54
108.0% 119/91
76.47% 167/121
72.46% 198/134
67.68%
407 hp 212/139
65.57%
436 hp 218/142
65.14%
448 hp
487 hp - - - - 182.8/125.4
68.60%
1.389/2.219
Chevy '492 Iron 157/62 2.020/1.600 64 - - 173/125
72.25% 198/137
69.19%
407 hp 206/141
68.45%
424 hp 209/141
67.46%
430 hp
466 hp
================================
Same intake runner, smaller combustion chamber and 2.02's made less possible HP. Although unusual not impossible. A possible case of shrouded valves as Max pointed out.
Tough question to answer without knowing the rest of the story Cause it all depends.
The induction system is just that it is a system. The size of the vavle should be kept as small as possible. Or rather as big as required. If you have intake ports that are only 165 cc's or a stock 2 barrell cast Iron intake or stock cast Iron exhaust manifolds or any other small part that restricts the flow in the induction system then even 1.84 valve is adequate and will give you bettter bottom end response.
If however you have a big 4 barrel carb on a high flow aluminum intake with intake runners in the heads about 220cc's Exhaust ports to match headers and a free flowing exhaust system then the 1.94 valves would be just like putting a cork in the end of a bottle and 2.02 or even bigger vavles would be the order of the day.
So whats the answer, "It all depends"
Ric
The induction system is just that it is a system. The size of the vavle should be kept as small as possible. Or rather as big as required. If you have intake ports that are only 165 cc's or a stock 2 barrell cast Iron intake or stock cast Iron exhaust manifolds or any other small part that restricts the flow in the induction system then even 1.84 valve is adequate and will give you bettter bottom end response.
If however you have a big 4 barrel carb on a high flow aluminum intake with intake runners in the heads about 220cc's Exhaust ports to match headers and a free flowing exhaust system then the 1.94 valves would be just like putting a cork in the end of a bottle and 2.02 or even bigger vavles would be the order of the day.
So whats the answer, "It all depends"
Ric
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