17059216 new issues vs old issues

[Cliff Ruggles]

186 castings from 1969-1970 are about at good as it gets for a factory iron head.

I don't buy them these days simply because by the time you completely rebuild them and convert to screw in studs, guide plates, hardened exhaust seats, etc, you can purchase a complete set of World Products SR heads (for example) for about the same money.

The 186 castings are pretty much duplicates of the older 291/461/462 castings that had the "double hump" on each end and no accessory bolt holes, but the 186's have the flat machined pads and the bolt holes.

I wouldn't stick my nose up at a set of them, they are actually pretty valuable to restorers, but take into consideration the cost involved with getting them rebuilt and up to par for this new fuel.

Also consider that the ports are apprx 165/65cc and the SR heads are 170cc, and they come with 2.02/1.60 valves, so have improved flow potential plus all the additional benefits mentioned.  Going from memory they are available in several versions, 67cc combustion chambers, 76cc chambers and even a smaller offering for 305 Chevy engines.........Cliff

[77cruiser]

With the 882 heads you probably don't have any where near 9.5-1 C/R unless the block has been decked or you have a .015 shim head gasket.

[Cliff Ruggles]

Good point Jim.

Very few of these engines are anywhere near as high in compression as the owner/builder thinks they are. 

Quench distance is a very important part of engine building, and folks don't put enough compression in these engines anyhow.

SBC engines absolutely LOVE very tight quench.  I shoot for around .030-.035" for my engines.  The tighter quench improves combustion efficiency, it will run cooler, take less timing/fuel to be happy, and less octane at any given compression ratio.

Higher compression also improves idle quality and low speed manners with any given cam choice.....Cliff

[blazer74]

Flat tops can be quite a bit in the hole depending on brand and deck height, ask me how I know.

I run 64cc Vortecs with flat tops. lucky to be around 8.7 or so doing the math.

[von]

I have #3973487 heads on my 350. How are they at performance potential? I know the combustion chambers are large for the lower '71 compression ratios.

[Cliff Ruggles]

487 castings are excellent.  Pretty much identical to the 1970 441's but have the smaller tapered seat spark plugs.  They have the larger combustion chambers, most will be 1.94/1.50" valves and pressed in studs.  Very late production versions may have hardened exhaust seats but most will not.

To this day I'm not sure why many aftermarket pistons end up WAY down in the hole at TDC.  I suspect that the folks making them as "replacement" pistons didn't want to raise the compression ratio with the larger overbore sizes. 

I've seen this sort of thing with a LOT of TRW and Speed Pro forgings over the years, and I avoid them for that reason.  Not uncommon at all to see them .030-.035" below the deck at TDC.

Almost all of the engines I build here get decked and squared, so we mock them up and measure how far the new pistons are below the deck, record the information, then take it apart and send it to the machine shop.

Pretty easy to establish tight quench using a Felpro blue head gasket that crushes to .039".

For SBC builds I've also left the pistons in the hole .015-.018" if the surfaces were in great shape, and use .020" steel shim gaskets same as the factory did for many years.

What most folks do here instead is they don't even check piston to deck clearance, and run out a buy a gasket set with thick "rebuilder" head gaskets in it.  They think their new build is 9.5 to 1 compression (for example) and it will be at least half a point, if not quite a bit lower. 

Building one of these engines with a lot of quench in it works against you in just about every area.  They will run hotter, make a LOT less power, use more fuel, takes more timing to make them happy, and less vacuum produced at idle plus worse throttle response/street manners with any particular camshaft.

Establishing tight quench with your engine build is just one area that you can gain significant benefits.  There are quite a few other places to improve engine power and efficiency, and when you put all of them together the differences between two engines using very close or the same parts can be amazing.......Cliff

[von]

Thank you. I agree that quench is important but missed that boat with my 350. I bought this engine as a completed fresh rebuilt long block. Bone stock 350 with cast dished "rebuilder" pistons. Even though the deck had a clean-up cut the pistons still measured around .020 down in the hole. I had the heads off to measure deck height and have a look at things and should've used steel shim gaskets to bring up the CR some, but used the .039 Fel Pro units. I calculated 8.0 compression ratio. One advantage though is that it runs great without a hint of ping on 87 octane and 38 deg total timing plus 12 deg manifold vacuum advance. It runs surprisingly strong (a relative term) for what it is with stock .390 lift cam, stock iron intake and exhaust manifolds, tuned Q jet, and points type ignition with Pertronix I ignitor.

[Cliff Ruggles]

Most of the engines I build here make best peak power with closer to 30 degrees total timing.  This shows us how important tight quench is far as combustion efficiency is concerned........Cliff

[68rs/ss]

30 degree's is not what I was expecting for total timing. Alway's thought the SBC liked 34-36 or a little more. At what RPM is the timing all in?
Phil

[Cliff Ruggles]

Tighter quench, more efficient combustion chambers, optimum compression ratios for the octane, and very well chosen camshaft will require LESS fuel and timing to make best power.

Couple of years ago I built a 455 for my Ventura.  It was very tight quench, exactly zero deck, good flowing heads, well chosen cam, etc.  It went on the dyno and cranked out 455.4hp and 540tq, and only required 30 degrees total timing to make those numbers.  That engine was used as part of the High Performance Pontiac and Popular Hot Rodding articles for the KRE aluminum head testing.

A customer of ours set out to duplicate that engine, used the exact same heads, cam with the same .050" specs but "modern" lobe profiles, same stock iron intake, q-jet and HEI.  He took that engine to the same dyno and made 390hp, 499tq.

Turns out that his attempts to "duplicate" our engine came up a bit short, simply because he failed to follow the "recipe" exactly and just figured a little extra quench and "modern" cam with less seat timing but more lift would get the job done. 

I was lucky in this deal as very early on I used .020" steel shim head gaskets on all of my SBC engine builds simply because that's what was there when I took them apart.  The "rebuilder" gaskets are much thicker, usually around .040-.060" and they lower the compression close to half a point and increase quench distance at the same time.  Nearly every single SBC engine that gets "rebuilt" will have the pistons pretty far down in the holes at TDC and a thick head gasket on it.  Folks come up considerable short on engine power all the time with that deal, even following engine builds they read about in magazines and on line, and never know why more times than not they don't make the grade.

I've also had some in here to tune that ran pretty hot and sensitive to low octane fuel when they shouldn't have, mostly because they simply had WAY too much quench in them.

Thinking back the worst one we worked with here was a Pontiac 400 with "builder" pistons that were nearly .040" below the deck at TDC and it had really thick Detroit head gaskets on it.  Although the compression ratio was only about 9.3 to 1, it ran hot, overheated and POUNDED like sledgehammers with any attempts to put some timing in it to make acceptable power.  This was quite a while ago and early in my learning curve so it took me a while to figure it out. 

We ended up pulling that engine and replacing the pistons with a much better flat top design with 2 valve reliefs, zero decked it, .039" thick head gaskets, then a cam with 10 degrees more duration to compliment the new compression ratio just over 10 to 1.  The result was an engine that idled better, didn't even think about running hot, overheating, pinging on pump gas, and it would literally tear your head slam off when you went to full throttle!  It literally felt at least 100hp stronger than before, yet same CID and head flow.

No need to mention how thrilled the owner was with the end result, and we once again educated ourselves as to how important these things are when it comes to building engines.......Cliff