Straight vs Angle Plug Heads
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Joined: Sep 2006
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Straight vs Angle Plug Heads
Can someone give me a quick synopsis on the advantages and disadvantages of the two types of heads? Aren't the factory small block heads "straight" plugs? I am getting a set of aluminum heads with 2.02 x 1.60 valves, 185 cc runners and will make around 10 to 1 compression if that helps. I have had ugly (and painful) experiences with headers on street cars in the past so will be keeping the stock exhaust manifold.
Thanks.
Thanks.
Burning Brakes
Joined: Nov 2004
Posts: 1,028
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From: San Antonio Texas
i have aluminum heads with angled plugs with headers on my 79 L82. if they weren't angled i'd never be able to get standard plugs in due to headers (might be able to use shorty plugs).
Le Mans Master
Joined: Apr 2006
Posts: 5,403
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Yrs ago when the norm was to make good compression with big dome
pistons (12.5/13.0 race engines) they found by cutting a notch in the
dome of the piston and angling the plug they could get back some of
the good burn across the cylinder that a flat top allows. Today with
so many heads availible with small chambers, 12 to 18 degree valve
angles they can build very high compression with little or no dome on
the piston, getting rid of the big domes on pistons made them lighter
for high rpm engines. Angle plugs on a flat or dished piston street
engine, no real advantage.
pistons (12.5/13.0 race engines) they found by cutting a notch in the
dome of the piston and angling the plug they could get back some of
the good burn across the cylinder that a flat top allows. Today with
so many heads availible with small chambers, 12 to 18 degree valve
angles they can build very high compression with little or no dome on
the piston, getting rid of the big domes on pistons made them lighter
for high rpm engines. Angle plugs on a flat or dished piston street
engine, no real advantage.
Last edited by Little Mouse; Nov 30, 2006 at 02:23 AM.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I have found the only thing angle plug heads do over straight plug heads is angle one or two plugs directly into primary pipes so you have to ding them or, as I had to do on my Hookers, cut a tube and weld a piece in to lengthen it so it would clear the plug 
Le Mans Master
Joined: Mar 2004
Posts: 7,493
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From: Little Rock AR
Angle plugs were used on performance replacement heads to reduce detonation tendancies. The plugs are angled closer to the exhaust valves. I do not run them as they seem to cause more problems and issues than they solve when it comes to fitting the other parts around them. 
-Mark.
-Mark.
Drifting
Joined: Oct 2004
Posts: 1,496
Likes: 1
From: Lafayette Louisiana
I don't think the angle plugs give any performance advantage. I run angled plugs, headers and standard length spark plugs with no problems. With any change you have to do your homework. After I bought the heads, I searched for a header that specifically said "use with angle plugs". You can't buy parts and then hope they fit. Thats when the problems show up.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
Chevy first came out with angle plug SB heads in about 1972. These heads were #492 castings and only thing done was relocation of spark plug to cylinder heads. Design change was for high dome, high RPM motors. All the aftermarket heads with straight plugs have relocated plugs to top of combustion chamber so only advantage of angle plugs would be if you were building 14:1 compression engine with BIG domes on pistons and modern theory say to reduce chamber volume and run as little of a dome as possible. HP effect is very slight, maybe 8-12HP at most on angle pugs over straight plugs and that is with a BIG dome on the piston.
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Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
i have a set of the 492 on a '70 350-370hp engine now, and it seems like i recall that they were only available through GM parts beginning in '71. a lot of folks put them on their '70 350-370hp vettes and camaros in '71. that's my recollection anyway . . . i recall the 10 hp claim using the 11:1 factory pistons back in the day. no idea what was reality. i don't think most folks can feel 10 hp in the seat of the pants
Last edited by S489; Nov 30, 2006 at 01:03 PM.
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Originally Posted by kevinator80
I don't think the angle plugs give any performance advantage. I run angled plugs, headers and standard length spark plugs with no problems. With any change you have to do your homework. After I bought the heads, I searched for a header that specifically said "use with angle plugs". You can't buy parts and then hope they fit. Thats when the problems show up.
Also I run raised exhaust port heads so no off the shelf header that states it will fit angle plug head is guaranteed to fit.
Oh and just one more thing came to mind, the angles on the spark plugs can be dramatically different from one head to another, take a look at two different manufacturers heads you willl see what I mean.
Drifting
Joined: Oct 2004
Posts: 1,496
Likes: 1
From: Lafayette Louisiana
Originally Posted by MotorHead
The selection of headers with over 1 5/8 " primaries that fit C3's is limited....to 1, so not alot of homework is involved here because there are no 1 3/4" headers made to fit angle plug heads
Also I run raised exhaust port heads so no off the shelf header that states it will fit angle plug head is guaranteed to fit.
Also I run raised exhaust port heads so no off the shelf header that states it will fit angle plug head is guaranteed to fit.
I bought 1 5/8". Only one, that explains why they were hard to find, huh?
Dynomax ceramic, vendor's add stated "angle or straight plugs"
