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Old 07-18-2008, 10:17 PM
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Performance Gains from Larger Valves?

Hi

I have a street-driven supercharged 400 Small Block Chev, which is running standard heads with 1.94 inlet & 1.5 exhaust valves.
I have the opportunity to purchase some heads with 2.02 & 1.6 valves.

Could anyone tell me if there would be noticeable performance gains from the larger valves?

Cheers

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Old 07-18-2008, 11:25 PM
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If your 400 has stock smogger heads (882, 624, 993, etc) now and you are going to another crappy stock smogger head but with 2.02's don't expect a lot of gain.

If you are switching from a stock smogger head to a aftermarket high performance head like say a Dart 200 or 215 Iron Eagle Platinum or RHS iron Lightning or EngineQuest EQ lightning head with big 200+cc ports with 2.02's yes you will see a big gain in power. Like night and day. These heads flow a lot lot more air than a stock GM head and have a much better combustion chamber.
What head castings do you have now?
What head are you swapping to?

More detail on your 400.
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Old 07-19-2008, 02:54 AM
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Current heads are original smoggers with some port work done (3973493 - 76cc).
Heads I'm looking at are also smoggers of the same era, just with bigger valves (3973487 - 75cc). They're originally from a 350, so I'd need to drill steam holes in them.

Engine is a 4-bolt 400, with nothing radical done to it (other than the blower).
It has an ARP head stud kit, Summit cam (#1105), dual valvesprings, Harland Sharp 1.6 roller rockers and stud girdle, MSD ignition.
The bottom-end is pretty much standard, just with good quality rings and bearings. This is because I don't want to invest in expensive pistons/rods/crank etc for the 400, because it's already bored to it's limit. Otherwise when it's time for a rebuild, I'd need to find another 400 so I could re-use my good parts.
I'd rather wait until it gives up, then get a new 350 block, and invest in quality parts for that, which I can re-use in future.
In saying that, I fitted the blower in 1997, so the motor is doing pretty well!!!
I nearly forgot, blower is a Weiand 6/71, with dual Holley 600 vac-sec carbs, which I'm currently rebuilding and boost referencing the power valves.

I've always wanted/planned to buy good aftermarket heads, but was gonna wait until I got a new 350 block first, which might be years away!!!
That's why I was wondering if the gain in performance is worth the trouble/expense of fitting similar heads with larger valves.
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Old 07-19-2008, 02:59 AM
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I would pass on that deal. Get some heads that really flow and are a more reliable casting.

http://aaeq.net/Enginequest/Cylinder_heads/flow_numbers

I would suggest something like their CC220BA head (also
available with a larger chamber volume)

As you can see from the chart they flow huge.

(your heads with a lil port work are likley in the 205-225cfm range.)
probabily not more than 230cfm
A smogger head with just 2.02x 1.60 valves will flow less. 195 to 210 depending on the valve job.)

And step up the cam to a Comp Cams Extreme Energy XE284H-10 pn 12-250-3 minimum.

Or if you like power, this Crane F-280-2 #114681 street/strip mechanical will wake er up
http://www.cranecams.com/?show=brows...tType=camshaft
This cam actually starts to justify using a stud girdle.

It's very hard to put too much head on a 400.

Make these changes and you'll think you bolted on an afterburner.

These EQ heads are cast in Australia I believe.

If you take care of your 400 it will out live you.

Last edited by F-BIRD'88; 07-19-2008 at 03:36 AM.
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Old 07-19-2008, 05:09 AM
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Thanks for the info.
(The stud girdle is only there because I got it for free )
I used to look at heads on the internet, but got frustrated finding good flowing heads with large combustion chambers. Most top quality manufacturers I looked at only really did high compression heads, although I see there are a lot more options now.
Then I think about having to drill steam holes in brand new heads , and eventually come back to the plan of building a complete new 350 engine.
And my 400 is still going strong, and making enough power as it is. I mainly use it just for cruising now anyway.
I've decided not to worry about the heads. I'll just keep an eye out for some aftermarket ones advertised for a good price, or most likely wait and splash out if I decide to build a complete new engine.
Cheers.
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