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The lean mean donut machine
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Discussion Starter #1
I've got a 400HP 350 that uses ported 305 heads and 11.7:1 compression. I only got about 203 cfm after porting and only 1.84 valves, so I'm looking for less restricting heads. I want to keep the high compression so I want the same 58cc chamber size, and I also want to do some more porting for experience. I happened to come across some L98 corvette heads on ebay and they have the 58cc chambers, however they are selling for $400 US. Is it worth me to port these heads heavily with bigger valves or are they a poor casting? $400 is a lot to start with if I still have to invest in building them.
 

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They are decent castings, and I wouldn`t go up on the valve size unless you plan to deshroud the chambers, I would just bowl port them and leave the valves stock, and unshroud the chambers some to help flow. Honestly, I don`t see you making 400 horses with 305 heads, the 1.84 inch valve can`t flow enough to support that power level. I would also hope you aren`t using pump gas with that compression ratio. Rather or not they are worth it are up to you, do they need rebuilding? new guides? if so you`ll have another $300 to $400 invested, with that money spent you could have a set of Dart heads.
 

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The lean mean donut machine
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386 Posts
Discussion Starter #3
203 cfm computes out to a max HP of 417, and I know by my combo I'm pushing the heads to their limits, as my HP seems to flatline from 5300 to 6000. The heads also have great low lift flow as well. The increased CR and decent quench help me make the 400HP, along with some other goodies. On a regular 9.5:1 engine with a .025 deck height I would be lucky to get 350HP. I use octane boost and premium gas all the time, I have never had detonation problems.

As for the L98 heads, they come with screw in studs and guideplates, and they have been checked for warpage with a machine straightedge, so it looks like they don't need any more work that way.

I would definitely deshroud the chambers to fit larger valves in, and I plan on getting swirl polished undercut stem valves to help flow a little more. What is the biggest valves I can fit in these heads?
 

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The money you'll spend putting bigger valves in those heads won't be worth the return in hp. Spend the cash on a decent 5 angle valve job with a bowl cut. Valves with undercut stems are worth the effort.

Larry
 

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The lean mean donut machine
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386 Posts
Discussion Starter #5
you talking about putting undercut valves in the heads I have now, with a 5 angle grind? If so, how much improvement will it make considering I already have a 3 angle grind on the stockers?
 
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