Cams and valves, cams or valves, or just one or the other?

[Badasssapper67]

How does bigger valves affect what cams you choose? Maybe not at all? How much more air do they let in with the stock valves?

Eventually the Cobra will be FI down the road. I have a set of heads Im working on was thinking about going with larger valves if they'll work with a centri or turbo.

It seems like the "average" Cobra is making 550hp and I don't want to be slower than average. Advice on how valve size affects cam size is appreciated.

 

[Badasssapper67]

No takers?

 

[01yellercobra]

I'm no expert, but I would imagine they affect the cam choice. One of the things cam grinders want to know is flow of the cylinder head. A larger valve will obviously flow more. I would think you'd be able to get away with a smaller cam to make the same power. The valve wouldn't need to be opened as far or as long since it's bigger.

I do think it's a wash without a larger bore though. The valves are already close to the cylinder wall. Going bigger just makes it that much closer. I was looking at having bigger valves put in my heads, but I also had a big bore set up.

This is just my thoughts. Take them with a grain of salt.

 

[tmhutch]

Bigger valves are worth about 20 CFM. Compared to the effects of cam timing that 20 CFM is almost inconsequential so very little will change with cam duration or intake lobe centerline, less than 5 degrees duration or 4 degrees intake centerline. Probably a more important area to look at with these engines is the intake manifold because it is the most influential component affecting cam timing. If it's the factory intake with stock length runners than you'll be limited to 7000 RPM which means cams between 212 and 218 duration will be ideal for forced induction. If you plan on lower RPM shift points than smaller cams would be better.

 

[98 N/A 4V]

Standard bore or a common .020 over I think larger valves are a waste of money. Especially with FI. We have valve strouding with stock valves. Unless the bore is opened up considerably I would keep the stockers.

There have been many people that made big power with stock valves.

-Mark

 

[Badasssapper67]

Right, good advice guys. I ask because I bought a set of heads off ebay and they had detonation damage so I might need to pull a few seats anyway. In fact, I bought them so I could learn more about our engines and I'll buy a t45 to rebuild for the same reason. So unless I can make them worth swapping I might just keep them around.
I have been thinking about going big bore, out to 3.7" but it looks like a serious, serious major operation and to me it looks like it ruins the integrity of the block. Im no expert but machining out the guts of the block to install sleeves just seems like a risky thing to do. Plus if you freeze the liners and there's a problem and it gets stuck halfway in the bore you're screwed once it gets to room temperature.
Plus I heard it cost about $1500 and that money could go towards a blower and make more power than a big bore block would. Im eccentric and I'd like to do the big bore any way but it seems very daunting.
If anyone has advice about the cost the process and wheather they's do it again that would be appreciated.

 

[01yellercobra]

I had a resleeved Teksid for awhile. The machine shop that installed the sleeves didn't install them correctly and two of the cylinders cracked. I didn't find this out until I ordered pistons. I bought an iron Boss block and ran that for a long time. I still have it with intentions of putting it in my 04 someday.

My opinion is if you want a big bore set up buy the big bore block. Don't have your stock block resleeved. If you want to keep the aluminum block then stick with the standard bore.

 

[Badasssapper67]

Hey Slo, did you have "dry" sleeves or "wet"sleeves? With the machine shop doing it did it cost around $1500, or closer or above $2000?

 

[Badasssapper67]

By the way there might be some bent valves if I have to buy one it would be better to replace the whole set, are Manley's the only game in town? And is stainless steel the way to go with both intake and exhaust?

 

[01yellercobra]

Hey Slo, did you have "dry" sleeves or "wet"sleeves? With the machine shop doing it did it cost around $1500, or closer or above $2000?

They were dry sleeves. I bought the block sleeved. It was a complete shortblock when I bought it.

The valves depend on your goals. I had a couple bent valves and replaced them with stockers.

 

[shurur]

http://forums.corral.net/forums/svt-dohc/1507401-recommended-c-head-work.html

http://www.svtperformance.com/forums/showthread.php?1046352-Reworking-C-heads

Per na svt:
"Replace the guides only if needed. Open the seat IDs to 90% of the intake valve OP and 85% of the exh valve OD."

If you go BB, you'll need to deshroud.