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Discussion Starter #1
Hi everyone, I'm new to your forum and am looking for confirmation that my math is right and I'm not overlooking something .
Fair warning : I'm already committed to the project and just looking to work out a few details.
So far I have in stock:
1970 Mach I, Full Alston tube chassis, A arm/Ladder Bar, 9" rear 4.88 gear, w 32 x x 14.5 x 15 tires.
Should finish out at 2400 lbs or less.
Mid plate is a Coan SBF to GM trans adapter.
I have a 3800 stall, a T350 and a Powerglide . (please save the GM sarcasm)
1969 351 4bbl Windsor (standard bore, standard rods and mains)
CHI 3V 208 cc Cleveland heads
CHI 3V single 4 barrel intake (4500 top)
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OK, so here's the math as I understand it:
Deck Height 9.48
Rod length 6.250 (Eagle 2.1 rod journal)
Stroke 4.00 (Eagle 3.00 main)
Comp. Ht. 1.235 (Trick Flow Flat w 1 valve relief (2.5cc))
Comp. thickness head gasket .041 (Felpro 10111 )
Chamber volume 60cc

If my math is right that puts the piston .005 out of the block netting a .036 Quench and 12.78 to 1 compression 408 CID.
I've put a machinist's strait edge to the deck and it appears flat so I shouldn't lose much when it is decked.
Cometic offers gaskets up to .065 thick in small increments if I need to make up the difference to get to .035-.040 quench.

I've been out of the loop for awhile.
Am I missing anything ?
 

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This sounds like an awesome project!

Your math could be right but you posted the factory advertised spec for an early block so I have you ask--Did you actually measure the true deck height? Production variations can change it (even rods and pistons can have some variation-although modern fabrication practices has improved this.)

Personally, I'd start by mounting the crank in the block and install a couple of rod/pistons (front and rear) and verify what you have before setting your calculations in stone. That would give you an idea of how much should have removed from the deck to meet your goal.
 

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I'll reiterate what Dennis said. When trying to be precise with a bunch of 50 year old parts and aftermarket parts from various manufacturers, it pays to mock everything together before ordering the head gaskets.

As Dennis said, the earlier blocks had a 9.48" deck height, and the later ones were 9.50". Of course, with production variances and lack of machining precision back then... once the block is cut square to the crank, as well as 90 degrees side to side... it could be completely different than it is right now. Get the block cut, mock the rotating assembly together... and THEN order head gaskets.

You can get an rough idea of what deck height you are dealing with using a 12" dial caliper. Measure the distance from the main bore to the deck and write it down. Now measure the diameter of the main bore, and add half of that measurement to the first one. This will give you the distance from the centerline of the crank to the top of the deck. (deck height) This will let you know where you are starting from.

If you're wanting to turn any rpm with the 3" main of the 351W block, you'll want to make sure you have PLENTY of main clearance. I would insist on having between 0.0030" and 0.0035" on that large main bearing. If they still sell the 3/4 groove mains for that engine, I'd try to find a set of those as well. Too tight chokes off oil and spins bearings. A little loose is simply good insurance.
 

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+1 I don't like spinning 3" mains over 7-7,200 rpm , ESPECIALLY in a two bolt main block. Your engine has EASY 600+ hp potential and is in the territory of a four bolt main block for durability reasons. Others may have a different opinion than my somewhat conservative one.
Randy
 

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Discussion Starter #5
Thanks for the reply Dennis. I'm kinda leaning toward n20mike's approach with a dial caliper as I haven't ordered the rods,pistons yet.
Short of a custom piston, it comes down to a 6.250 rod with the piston .005+ out of the block OR the 6.200 rod and needing to mill as much as .035 off the deck to tighten up the quench.
I'm not sure milling that much is a good idea.
What do you think ?
 

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Discussion Starter #6
Thank's for the reply Mike. Good call on the caliper idea.
Without a doubt I won't order the head gasket until the short block is complete as it is the only dimension still adjustable at that point.
Good tip on the main clearance. Ill research the bearing story.
Would like your thoughts on my reply to Dennis Re: deck milling.
Any thoughts on how tight the quench can be in this application ?
BTW, the top end/cam combo is designed for 3000 to 7000 rpm max.
I think that with a 3 speed/4.88 I'll be shifting at 6500 and 6800 thru the lights.
 

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The most important thing is to determine the actual block height. Then it is easy enough to have a piston made to fit your needs and they aren't terribly expensive. Try to maintain .040 net piston to head clearance with .035 being the absolute minimum.
Randy
 

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Discussion Starter #8 (Edited)
Thanks for the reply Randy.
I too tend to be a bit conservative in my approach.
I don't intend to spin this above 7000 and I already have plans to buy a main girdle and studs.
I'm pretty much down to picking the rod length and determining allowable deck milling to achieve the minimum quench that is acceptable.
My target is 600 HP and 7000 RPM max on a soft tune and no power adders.
If that gets me in the high nines I'll be overjoyed.
If this combo lives for a season or two the next short block will be bigger CID and way more money as I'm barely tapping the potential of the heads and intake.
BTW, my research shows a starting cost of close to $800 for custom pistons versus $480 for the Trick Flows ???
 

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The biggest issue that I can think of in decking the block excessively will be that you will also need to remove similar material from the intake manifold (or intake surface of the heads) to match the head ports. In the end you will have made parts that are unique to only that engine combo. If you should need to do any replacements you will need to duplicate the process to the new equipment.

I have my old windsor build sheet that I used a 4" stroke, 9.482 deck, 6.250 rods and it had a JE 1.230 compression height. It was used with 58cc AFR head .041cc head gasket. Piston was .002" in the hole IIRC.

My current combo uses the same basic combo with a 1.220" compression height which is about a tight as you can get without putting the pin in the ring land. The pistons stick up .002 after I had the deck squared. The pistons were custom from Racetec and they were about $900.

I'd prefer to limit my stock block builds to 7K using a shorter rod (which cuts down on side load.) You also have to be mindful of cap walk when you push the crank that hard.

In the long run an aftermarket block is the best choice for your build as it will all)ow you to spin the crank much higher, plus you can use a larger bore piston to better take advantage of that wonderful top end. I'd certainly recommend building one from the get go as many of the parts that you will put into the stock block will probably be unusable in the big bore version aftermarket block (with the typical Cleveland sized mains.)
 

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Thanks for the reply Randy.
I too tend to be a bit conservative in my approach.
I don't intend to spin this above 7000 and I already have plans to buy a main girdle and studs.
I'm pretty much down to picking the rod length and determining allowable deck milling to achieve the minimum quench that is acceptable.
My target is 600 HP and 7000 RPM max on a soft tune and no power adders.
If that gets me in the high nines I'll be overjoyed.
If this combo lives for a season or two the next short block will be bigger CID and way more money as I'm barely tapping the potential of the heads and intake.
BTW, my research shows a starting cost of close to $800 for custom pistons versus $480 for the Trick Flows ???
Buying through an epay seller like Shannon's Engineering (507-445-3235) could lower the cost significantly on the 800 figure.
Randy
 

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Discussion Starter #11
Thanks for the replies guys.
Dennis, an aftermarket block breaks my budget for this year.
Guaranteed on the next build I will include it.
Soo...., tomorrow the block goes in for hot tank, magnaflux, and deck verification.
My machinist suggests going with the longer rod and making up the height with the head gasket.
I'm going to hold my decision until I get the results back.
As usual it comes down to money.
For $2500 I can finish the short block and be on track for next spring.
The alternative is waiting for another 18 months to complete a higher end build.
If this isn't feasible, I could build a "grenade motor" with the stock block,crank,rods, C9OE heads and KB pistons for roughly the same money.
Less rear end gear and lower RPM, just to shake the car down and get some laps in.
I was trying to avoid this given the cost and work that goes into fabricating the headers (among other things).
Don't get me wrong, I don't mind building headers, it's just a lot of work.
Looks like I have a decision to make.
 

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As long as you have good bearing clearances... 0.0030" to 0.0035" on the mains and 0.0025" on the rods, the block should hold up just fine. Keep the RPM under 7000, and it will be fine. I've had friends push those blocks incredibly hard on multiple stages of nitrous, and still have an extremely long service life as long as RPM is kept in check, and they didn't do anything excessively stupid. One guy used two stages of nitrous to push his to 5.92 in the 1/8... and that was an OLD 426 made with a modified 400 crank and Chrysler rods. lol Ran it for a few years, then sold it to a guy who ran it some more, minus the nitrous.

The 351W block is a strong piece... MUCH stronger than the 302. Keep the RPM in check, and as long as the machine work is good and clearances are right, you'll be just fine!

Yes, a big bore kit would be nice with the big heads, but you can start saving for a dedicated short block as an upgrade as you dial the car in with what you've got!

3" mains are NOT the end of the world... Look at all the big blocks out there being raced! :)

Good Luck!
 

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Discussion Starter #13
Thanks Mike, I haven't built a hot rod small block since 1982 or so and my last real performance build was damn near 20 years ago (Yeesh !).
Most of my experience is in BBC and BB Dodge stuff.
My old motor head friends are having big fun with me for not only building a Ford (God forbid),but, a small block at that.
I'm digging it.
I never was much good at following the leader.
A motor is a motor.
Ya' just gotta figure out what it wants.
You guys are helping to make the learning curve just a little shorter (and hopefully cheaper).
I'll keep this thread alive as I go along just in case someone else can get something out of it.
 
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