C2 300hp Head rebuild... 1.60 exhaust?

[Jim V.]

I did a mic on the valve stems and it appears the exhaust stems are worn and all stems are rough. The exhausts were .339 and the intake stems are .341 but pretty rough. So...if it is time for at least new exhaust valves (probably Manley's)...what is involved in upsizing to 1.60 exhaust valves? Does this decision cascade into more $$$ for new seats...? I spoke with a machinist yesterday who is understandably pushing for hardened exhaust seats. My initial decision is to decline on the hardened exhaust seats but if I go up to 1.6 exhaust valves, which may require new seats anyhow, might as well go to the hardened seats...right?

I have yet to ball gage the guides...that is next. I assume they need work as well. The debate continues on going with the cast vs bronze (thin wall Kline or thick wall) guides.

Also, can anbody ID these positive valve seals. The top shows BAF 241 & 1811
Valve guide bosses are machined to an odd size of .560"

Thanks in advance for your feedback!

Jim

[Michael H.]

Re: C2 300hp Head rebuild... 1.60 exhaust?

Jim,

Just my opinion but I would never spend the money to install 1.6" exhaust valves, no matter what. I promise, you will absolutely positively never feel any difference or HP gain. Also, I'd stick with my original feelings on the new hard valve seats. Not needed and definitely not recommended, unless your planning another 100,000 miles of driving.

I hope I'm not coming down on your engine rebuilders recommendations but he's there to make money and the way to do that is to sell additional services.

If you already need all new valves, it may be worth considering just going to the next oversize stem and reaming the guides to this new size. I never did care for bronze guides in a street engine. With the improvements in todays oils, I would think that a new set of valves in fresh guides would last much longer than any other means of repair.

[Jim V.]

Oversize valve stems.....

Thanks Michael for the feedback. I guess the philosophy is simply KISS.... Can you recommend any particular valve manufacturer for oversize stems. I understand the only downside would be the additional mass associated with the fatter stems.

Thank you.

[Duke W.]

Re: C2 300hp Head rebuild... 1.60 exhaust?

There's only a marginal benefit, at best, from installing larger exhaust valves. Larger inlet valves might be worthwhile, but it depends on what you do with the heads. If you pocket port them the E/I flow ratio will improve from about 0.65 with OE machining to 0.85, so the exhaust flow becomes quite generous, and the inlet flow is still limiting.

For a 300 HP engine I don't recommend increasing the valve size as the 1.94/1.50" combination seems to be pretty immune from developing a crack between the seats that the 2.02/1.60" combination is known to do. Leaving that extra material between the valve seats is worth the slight loss to top end power for bulletproof longevity.

The best improvement you can make to the 300 HP engine without changing its overall character is to pocketport/port match the heads with a multiangle valve job (with .040" inlet seat widths, .060" exhaust for a street engine), and retard the OE ...929 cam four degrees. There will be a slight loss of low end torque, but the benefit is that it will pull strong all the way to 5500 rather than rolling over at 4500 as it does as OE built.

As OE built the "300 HP" engine makes about an HONEST 225 NET at 4000-4500. With the above changes the peak will be around 270 net @ 5000 - about the equal of an OE built L-79 with a slight rolloff to 5500 - about a 20 percent improvement in peak power at the cost of about five percent low end torque, but without changing the overall normal driving character of the engine including idle characteristics.

For guys who aren't out trolling for street races, a massaged 300 HP engine has terrific torque bandwidth from normal driving.

I recommend Federal-Mogul replacement parts. (They are the supplier of many of the internal engine parts that GM sells). The FM Speed Pro S2323 1.5" SB exhaust valve is 21-4N stainless, fully machined, plain stem, which is the best material you can buy, but it's probably overkill for your application. Others are available in less overkill alloys. If the exhaust valve stems are worn .002" they are not serviceable, and the guides are probably worn more as the cast iron is softer than the steel.

Whatever valve guide rebuilding process you go with be sure that you understand the valvestem finish and seal requirement. It will vary depending on the material. For example some guides may be best with chrome flashed stems. Others are okay with just polished base material, and different guide materials have different oiling requirements, so that dictates the seal type.

Do some research on the guide manufacturer's web sites and whatever you finally select, go with their recommendations for valve stem finish and seal type.

I think seat inserts are a waste of money, but it's your project.

I don't recognize the valve stem seals.

Duke

[Phil P.]

Re: C2 300hp Head rebuild... 1.60 exhaust?

pretty sure the guide seals are perfect circle---logo at about 11 o'clock looks like perfect circle scribe--- i have used these in the past---long time ago--and think i remember them needing an off size machining the 560 versus the norm of a 500---

[Jim V.]

Phil.... about how long ago...

I am trying to do some detective work on the motor history and that info would be helpful to me.

Thanks