I just went back to look at the other thread again and saw the new info that was added this morning. LSG pretty well gave the OP all the info he needs. Now it's time to start checking geometry to see if those new pushrods are the correct length.
Alex, I also want to point out that you never responded about if you have rail type rockers. You don't want to use those with shorter valves as the rails can contact and wear on the locks and retainers.
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Sounds like I'm getting an adjustable rocker arm and following the procedure posted in the video earlier in this thread.
I have conventional rockers. Not rail type!
I think those valve sizes are pretty good for a SBF head, really. 2.02's (and anything larger, though I don't know how you'd fit it!) will have problems with shrouding because the edge is so close to the cylinder wall. I think your machinist is making good choices. Good heads really make a tremendous difference on any engine, and the SBF is no exception. Like @Dan Babb
said, your engine doesn't care that they are "bow tie valves", so long as they fit I'd like to know more about the rest of the engine choices he's making!
Thanks for the reassurance. Pro Machine is the shop (Murray, UT) in case you wanna talk to him. His name is Yates.
Originally Posted by patrickstapler
If the size of the valves you posted 1.84I/1.5E is what’s installed, you will be just fine. You actually could have gone slightly larger in the intakes. When you mentioned Chevy valves did you disclose the sizes? If not, everyone probably assumed 2.02/1.94.
You will want to make sure to do some port work on the exhaust side of the heads to take advantage of the larger valves. Make sure the intake sides are just cleaned up.
The exhaust ports were ported, that much I know!
Guys, did anybody look at the other thread? It wasn't the size of the valves LSG commented on, it was the length. Chevy valves are shorter in length than Ford valves potentially causing rocker arm geometry issues. The pushrods will potentially be too long now and the contact pattern between the rocker arms and the stems of the valves may be less than optimal.
The OP needs to verify his geometry and make adjustments as necessary to ensure a good contact pattern on the valvestem. If he does that he'll be fine. If not then wear issues may show up down the road from side loading the valves. The problem comes when guys just slap it all back together without checking and then wonder why the valves and guides prematurely wore out on the heads they paid good money to completely reccondition.
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This is valuable information. I think it's pretty certain now that I'll be doing a geometry check now.
Valves just go up & down, so as long as the dimensions are right and they seal in the heads, why would the fact that they were used on a chevy motor too matter?
I had a 354 Chrysler Industrial Hemi rebuilt by a local shop (in business forever with a good reputation) and the valves use on that were the same size as some ford big block motor, so that's what he used during the rebuild. They were dimensionally the same.
Good info, thanks.
The whole 'valve erosion' thing is a bit overblown, really. With better understanding of WHY valve seats would erode, the problem is mostly gone for well-planned engines now. In fact, the biggest reason they went to Tetraethyl Lead in gasoline was to prevent this 'valve erosion' problem. It was believed that the additive helped lubricate the valves, and kept them from sticking to the seats. The added detonation resistance was also seen as a good thing. Modern research has shown that it was the octane improvement that helped, not any 'lubrication effect'. In fact, TEL was really hard on exhaust systems, with the lead salts being very poisonous to boot.
What few people realized was that engine technology of the time - cam, combustion chamber, ignition, and carburetion, combined with cheap gas, often led to conditions favorable for detonation. If it happened during cruise, (which is common due to lean mix for economy) power levels were low enough that the quiet pinging could go unnoticed. Meanwhile, the exhaust valves would get so hot they'd try to weld themselves to the head every time they closed. If the condition was allowed to persist for long enough, it resulted in serious damage to the heads.
So, they went to TEL to raise octane, which helped. And later, hardened valve seats. With modern sensors to help sort out real-time fuel/air ratios, not to mention electronic fuel injection, leaded gas wouldn't help the average modern car, even without considerations for the environment and catalytic converters. Gas quality is a lot more standardized now, despite alcohol and other additives. Thanks to modern technology, the old 'hardened valve seats' thing is usually not a big deal for cast iron heads - although I'm sure for some high performance applications, it can come in handy! It probably falls into the same category of "Well, do I need hypereutectics, or forged?" It just adds safety margin.
The camshaft's closing ramp is a lot more responsible for limiting impact of the valve on the seat than anything else.
Lots of information here that I think is above me. Definitely something to research in my free time. Thanks for the detailed info.