SB Engine build......300hp

**Duke W.** · May 17, 2006, 05:15 PM

Re: SB Engine build......300hp

It's going to need boring and .020" is the smallest oversized piston I know of. I'm not sure of the compression height of the OE pistons so you need to find that spec so you can compute the actual crankshaft C/L to deck dimension, which is nomially 9.025". Replacement pistons might have a different compression height, so you need to take that into consideration when you compute the CR with the new pistons.

Engine Compression Ratio (CR) Calculator

http://www.csgnetwork.com/compcalc.html

This calculator is designed to show the different Compression Ratios for different sized engines.

I think the KB/Silvolite KB152 have 1.678" compression high and a 7cc valve notch, which should yield about 9.75 with nominal deck height, which is right were you want it. This is computed with an OE type .018" or so steel shim gasket, which will yield a quench clearance of about .040", which is also right on the money.

That's with a 62cc chamber and you should measure at least a couple to verify.

If the decks and heads check out with no warp using a machinists bar and .0015" feeler they are flat, and a steel shim gasket will seal, and NO METAL NEEDS TO BE REMOVED FROM THE MATING SURFACES FOR THE PURPOSE OF "TRUING".

As long as you're going to have to send the block to a machine shop for boring, have the machinist skim .006" off the left deck to get equal deck height, but make sure he feels comfortable making this fine and accurate a cut. You best sit down and have a long heart to heart talk with machine shop manager. If you take it to a typical "we do 'em all that way" joint they're probably going to deck both sides and wipe out the ID numbers. Many guys have been screwed by machine shops. Make sure the work order specifies ONLY the EXACT work you want done. Maybe you can get referrals from the local chapter to a shop that understands Covette engine RESTORATION, as apposed to some "production" rebuild shop that might screw you.

I'm not up to speed on the latest guide rebuild and seal technology (and I assume a guide rebuild is in order), but make sure that the seal type matches the guide type. Some guide materials require a little more oil than others, so the seal should be matched to the guild technology and material. If the guides are rebuilt with pressed in iron sleevs, I don't see any need for a "seal upgrade". Use the OE type O-rings and shields, but try to find viton O-rings as they will outlast nitrile at least 2:1. Maybe someone else will chime in or you can do some research on available methods and let us know the results.

If the head mating surfaces measure flat, they don't need to be milled. Watch out for this just like block decking.

The 300 HP engine responds very nicely to typical pocket porting/port matching/multiangle valve seats. It's time consuming work, but will increase top end power a good 10 percent with less rolloff past the peak and increase useable revs by 500-1000, which will create signficantly more "area under the curve" at the top end. Also, if you pocket port the heads, install the OE replacement cam (1408839 or equivalent) retarded four degrees. This will shift the POMLs four degrees from 108/116 to 112/112. It will loose a little low end torque but will create a very nice power band "dome" from 4000 to 6000, but won't affect idle characteristics.

You should also mount the bare heads on the block before before either goes out for machining. Mark the combustion chamber overhang and bevel it away keeping in mind that the walls will be .010" further out after boring. It's usually worst on the exhaust side. This will add a cc or so to the chambers. You can measure the volume after the heads are assembled and do a little more grinding as necessary to get them plus or minus about 1cc of nominal.

Carefully inspect all the valve gear. If the pushrod, rocker, and ball wear points are smooth and burnished, they can be reused. Keep each set in a baggy and mark them for installation in the original position (same for any valves you reuse). Replace the valve springs with the '66-up 3911068 OE springs or equivalent. "Upgrading" the studs with bolt-ins is insurance, but if the head has no history of pulling studs, I don't think it's necessary with any OE cam.

Inspect the valves for seat and stem wear. Assuming they have not been previously ground they can probably be ground and reused if stem wear is not more than .0005". You will probably find that the exhaust valve stems have more wear than the inlets.

You didn't say the year, but if the rods are the early design, get in on Boyan's Crower Sportsman group buy. If the later design they should be Magnaflux inspected and are okay to reuse if crack free.

Use GM EOS as an assembly lube for the cam and valve gear, HD diesel engine oil for everything else and for crankcase fill. Change the filter after a few hundred miles, but it's okay to leave the original oil in for the full term of a few thousand miles or one year. Continue to use HD diesel engine oil after that.

The 300 HP engine is underrated and under-appreciated. As OE built it will make about 190 RWHP@4000-4500 and be out of breathe at 5000. If you do all the under the covers work I outlined it should make around 220RWHP@5000 with a little rolloff to 5500 and rev usably to about 6000 - almost as much RWHP as a good OE built L-79, but it will produce signifantly more low end torque and idle butter smooth at 500. That's about a 15 percent increase in peak power with a much broader power "sweet spot" under the curve - up to 1000 more useable revs - with only a slight loss of low end torque and NO HOTROD PARTS from Jegs and Summit!

For the way most of use use these cars nowadays, the operating characteristics of a "blueprinted and tuned" 300 HP engine are hard to beat! If I was restoring a 300 HP engine, this is the way I would do it.

Duke

**Jim V.** · May 17, 2006, 05:50 PM

Re: SB Engine build......300hp

Your help is invaluable. Thank you.

Did you mean KB156?....they are the forged 7cc flat top...they do come in +.020

What do you think of the Hypereutectics?...Was thinking of the Speed Pro H660cp

Any special advice on rings with either the forged or hypers?

BTW...I recall, from your prior help, the OE piston compression height to be 1.671 for low horse and 1.675 for the SHP.

When you talk about beveling the heads to the cylinder, how much head material are you suggesting be removed...just a straight run down to the cylinder perimeter?

Next up...find a machinist as anal as I am...should be a challenge

Thanks
JimV

**Rob A.** · May 17, 2006, 07:15 PM

Re: SB Engine build......300hp

Jim,

While the heads are off, have a machine shop check to see that none of the pressed in rocker arm studs have pulled up or loosened. This often happens with age. If any of them have, this would be the time to have them replaced with new, oversized ones. (You can do a quick check yourself with a straight edge along the top of the studs on each head). Most machine shops won't check this unless you request it. I had a '66 300hp, stock engine that had a couple that pulled up slightly and had them replaced while the heads were reconditioned, with no further problems.

**Carl S.** · May 17, 2006, 08:10 PM

Re: SB Engine build......300hp

I am about to rebuild my 63 300hp engine. I have found 3 studs have pulled up, one on one side and two on the other. Has any one heard of screw in studs?

My big question is about harden seats? I have heard secound hand both sides of the harden seats. I have yet to hear from anyone first hand who had bad luck with or with out them. My rebuilder thinks they are the best thing since scliced bread, however I dont think there is enough room for them or do I think the process is falt free. Since I do not expect to drive over 3K a year I dont think I need them. I think more harm can be don by messing with the heads.

**Kevin M.** · May 17, 2006, 08:36 PM

DON'T DECK THE BLOCK

If you didn't already know that. It's the pad with VIN and engine ID you want to protect.

Kevin

**Duke W.** · May 17, 2006, 10:24 PM

Re: DON'T DECK THE BLOCK

It's okay to cut down the LH side if it is high relative to the right side. The LH head completely covers the left side block deck. There is no way to determine if it's been machined in the field with the head installed.

Duke

**Duke W.** · May 17, 2006, 10:37 PM

Re: SB Engine build......300hp

You don't need hardened seats. Risks are penetrating the cooling jacket or the seats coming loose in service. Plus it's going to add significant cost.

With proper seat minimum widths - .040" on the inlet side and .060" on the exhaust side (and proper valve clearance with mechanical lifter cams) and a few thousand miles of yearly use freshened up valves and seats should outlive most of us.

Back in the seventies GM found some seat erosion on truck engines with unleaded fuel. Truck engines operate at a much output/RPM than a Corvette engine other than Corvettes that see serious road racing.

That's the origin of the myth, and it just won't die, but it provides a good revenue stream for machine shops. If the shop won't back down, I'd look elsewhere to get the work done.

GM didn't start induction hardening exhaust valve seats and add exhaust valve rotators until several years after the introduction of unleaded fuel - late seventies IIRC.

Duke

**Patrick H.** · May 17, 2006, 11:24 PM

Re: SB Engine build......300hp

Duke,

The induction hardened seats started in 1973. I have a few heads with them, including one currently on my 71.

Patrick

**Duke W.** · May 18, 2006, 12:07 AM

Re: SB Engine build......300hp

I should have said "a couple" rather than several as I did not recall the starting date. I think the SB exhaust valve rotators started in '77(?).

Weve seen busted rods, worn out valve guides, stuck rings, scuffed cylinders, occasional pulled rocker studs, but burned valves on unhardened seats are rare. Burned or busted pistons are also rare, too.

There are still a few factory built engines out there and many rebuilds including many older rebuilds with non-hardened seats, but I can't recall anyone reporting a burned valve or excessive seat recession.

This particular engine only has 90K miles, but is 40 years old. Head underside photos show more sludge than I would expect on a well maintained engine. The cylinder leakage problem is likely due to stuck rings from varnish and crud because of deferred maintenance or sitting for a long time with dirty oil. I'm sure the valve guides are well worn, and the valve seats may also be leaking.

In the long run corrosion can take a severe toll on an engine that is not well maintained. That's why the oil and filter should be changed at least annually, even if the car sees only a few hunded miles of use in a year.

Cosworth Vega engines get eaten up from the cooling jacket side because aluminum (including Corvette radiators) is unforgiving of poor cooling system maintenance (periodic antifreeze changes to restore the corrosion inhibitors), but cast iron will also suffer from poor cooling system maintenance, given enough time, and brake systems get eaten up by corrosion due to lack of brake fluid changes.

Duke

**Patrick H.** · May 18, 2006, 12:54 AM

Re: SB Engine build......300hp

Duke,

If I could ever find them I'd show you the pictures of the valve seats from my 71 when I took the motor apart at about 110,000 miles. The valve seats were very, very worn; so much so that I could not reinstall 1.94/1.5 valves again without really having them recede too far into the head to be useful.

My machinist and I talked about causes. Valve seat recession? maybe. Based on some other similar age heads he was working on, our suspicion was that the valve guides had worn enough to allow the valve to return to the seat "off center" and eventually wear the seat.

Patrick

**Duke W.** · May 18, 2006, 01:35 AM

Re: SB Engine build......300hp

Isn't it past your bedtime, Patrick, back in EDT Michigan. You're going to give a patient the wrong medication tomorrow because you're so tired!

Worn guides can beat up seats, but I got lucky on this issue. When I decided to change the valve seals on my Cosworth Vega a few years ago, I found all the stems were pretty loose, one quite severely. It was "notchy" - like it had formed a "second seat", and I feared the worse. I pulled the head, which has Stellite seats, but the valves and seats were all in excellent condition.

After installing and reaming new guides to size, I mearly lapped in the valves and they seated very nicely.

From papers I've read, the effect of TEL is long lived. This suggests adding some leaded race gas or 100LL avgas in the first few tanks of fuel just to get the valve seat benefits of the TEL. Then maybe throw in a little leaded gas every few thousand miles.

I also like to grind both valves and seats at 45* then narrow to the desired width and thoroughly lap them in. GM cut the head seats at 46* and the valves at 45* creating an "interference seat". Basically the valve just pounded in its own seat over the first few hundred miles. Hey, it lasted for the warranty period!

Starting out with well formed and lapped seats is the way to go and a few gallons of leaded fuel once in a blue moon is good insurance.

Also, back in that era we only expected maybe 100-125K miles on these engines before they needed a major overhaul, and a head refresh at 50-75K was not considered outrageous.

Nowadays with decent maintenance we expect at least 150K miles from the head and 250K miles from the short block of modern engine.

Duke

**Jack H.** · May 18, 2006, 08:52 AM

Piston size can be dictated...

The 30-over, 60-over sizes are made for the convenience of stocking warehouse distributors in reducing inventory proliferation. If you're willing to go to the piston mfgr direct and pay a special handling fee, you can get pistons in any size you want...

The last time I needed to overhaul my '71 350, it was at 40-over. A borescope analysis said the engine would 'make' at 42.5-over. So, instead of boring excess 'meat' out of the original block, my machinest ordered a set of hand selected pistons. It cost an additional $25 in special handling fees plus the freight direct from the mfgr and loss of discount(s) provided by the local stocking distributor. But, the car's alive and well today running nicely at 42.5-over.

Why cut out more iron in an original block than you really have to? With the crazy prices original blocks are commanding these days, why not go 'optimize' the number of rebuilds you'll get before eventually being forced into an 8-hole sleeve job?

**Jack H.** · May 18, 2006, 09:06 AM

Re: SB Engine build......300hp

When no-lead gas was phased in Daimler-Benz published a nice white paper on the subject since customers were concerned about what would happen to their previously built engines... The upshod was interesting. Benz engineers concluded:

(1) So long as no-lead fuel quality was maintained, there was no problem running that fuel in an engine originally designed for leaded gas.

(2) Any engine designed for leaded gas that had seen +5000 miles of use on leaded fuel, had accumulated ALL the lead it'd need for the rest of its economic life.

(3) Benz would NOT deviate from their warranty obligations on previously built vehicles designed to run on leaded gas because of the use of no-lead.

Now, on the issue of hardened seats or not, at our shop 100% of the cylinder head work we do includes cutting hardened seats in. While this may be 'overkill' we do it for several reasons:

(A) We also build/crew vintage race cars and they see AGGRESSIVE use including heavy acceleration to red line and lots of WOT operation. So, the machinests we use are CRACK and simply don't make seat installation errors.

(B) Because we do as many engines as we do, the added cost of cutting hardened seats into the heads is almost chicken feed.

(C) We've never had a 'botched' job and the finished head product is good for MANY years to come.

(D) Although most cars built for the street will never see the abuse of a dedicated race engine, you simply can't predict what kind of 'stunts' a novice weekend warrior owner is going to go pull with his classic Corvette!

**Clem Z.** · May 18, 2006, 10:23 AM

amoco white gas,lead free was around in the

40s so i think lead was just added for a quick pump up of the octane

SB Engine build......300hp

SB Engine build......300hp

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