odddoylerules

72 350

Was just gonna put seals in, check it out and put on a dual roller timing belt, strap on these 66 330 heads and go, but pops thinks he wants to help me have the rebuild done for my bday. I'm afraid it'll be too hot for my gf to daily drive. What do you think?

The car: 72 cutlass sport coupe w/ac
342 LSD
Th350/shift kit
Edelbrock performer intake
Thorley 4-1's
X-pipe and FM delta flow 40's

The options:

Stock cam and pistons
66 330 heads w thick gaskets for near stock compression

Or

Probe SRS flat tops
Stock rods
JM 16-18 w31 update cam from mondello
Small chamber 66 heads w fat gaskets

My worry is compression is gonna be too high. I'd like to have the stock 7 heads redone to moderate things, but I got other crap to do!!

If it ends up bring a little hot I'm sure I'd love it, but thats not my point. I'm selling the crown Vic to work on her 4x4, so in reality it'd be best if this could end up a reasonable driver, and in that regard I'm also worried about forged pistons.

Anyone run similar combos?

I've never jacked up cr like this, so please share your thoughts. Those 60 cc chambers w flatties are gonna give quite a bit more pop than smog heads and smog pistons

CORRECTION - cam is mondello grind JM 18-20

odddoylerules

I'm honestly hoping to not need a rebuild

Smitty275

The only thing I'd NOT do is the Mondello ancient technology camshaft.
Put the 330 heads on it. You won't have an issue. Also have a cam ground for the combination your going to end up with. Proper camshaft can deal with compression. Your not going to be excessively high cr anyhow but a proper cam can make or break any combination.
Absolutely nothing to worry about should you decide to put a set of forged pistons in it. I've never seen it be the cause of any issues. Just make sure they have the proper piston to wall clearance.

olds 307 and 403

With stock 72 24cc pistons, .041" gaskets, .025" pistons in the hole with 60cc chambers with give 8.3 to 1. Good for cruiser.

odddoylerules

That's what I'm hoping is the case, but what's wrong with the updated w31 cam? We have it on hand so its free, and if it ended up being 10:1 or greater cr, wouldn't that be similar to what the w31 was?

Smitty275

Not sure who told you its an "updated" version of a W cam or where they even came up with such a term. Its an OK cam and since you have use it. But with advancements in camshaft technology since that cam was put on the market well over 30yrs ago there are much better options.

cutlassefi

Smitty, I'm assuming he's talking about various Muscle car cams that Comp and others have available. The have the same @.050 numbers on the same lsa's but have more modern lobe profiles.
Even with that they're too much cam for most sub 9.0:1 applications imo.

captjim

Also, for less than $100 you can get a custom "D" shaped dish milled into the flat tops to fine-tune the CR.

joe_padavano

The 1966 330 heads and the 1972 350 heads will have just about the same chamber size (roughly 60 to 64 CCs). Variation is due more to production tolerance than actual chamber design changes. Of course, how the valves are cut will also affect CCs.

BlackGold

I don't know who told you that a JM 16-18 cam is an "updated W-31" cam, but nothing could be further from the truth. Mondello describes the cam as "Towing/Motorhome" and it's optimized for low RPM. Specs are:
0.472/0.488" lift
256°/260° advertised duration
210°/216° duration at .050"
112° LSA

I'm not trashing on the cam; it might be just what you need. But it's not anything close to the high-RPM 308-deg W-31 cam. It's important you (or your builder) knows this so you can match the rest of the components and intended usage.

HWYSTR455

What the pros are saying, listen to them. Target your CR, then choose a cam, properly is key. The target CR will dictate the general category of use of the engine. For today's fuel and mild performance, 9-9.5 is a good range. 9.5 allows for more options when it comes to cams, and would be my suggestion. (most prefer higher CR, like in the 10:1+ range)

And of course, the performance level your girlfriend can handle depends on your girlfriend's abilities!

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odddoylerules

Actually the gf comment had more to do w avoiding knock w strategic application of throttle than w performance... Hold on, I'm gonna look up the cam quick. We bought what was listed in mondello as a w31 can upgrade, similar power and rpms, but you could run power brakes might not be that 16-18

odddoylerules

Jm 18-20. Its a split pattern w more lift and less duration than factory w31 and is ground by Engle on a 112 lsa

odddoylerules

Totally agree bout listening to reason and experience, hence why no thought of 8.3:1 cr + the cam....

odddoylerules

Getting the pistons machined seems like a reasonable option for that price. I really dislike dealing w knock

odddoylerules

Dude I just found the invoice, it was ordered April 17th 2001, that cam has been gathering dust in its box for 13 years, today!

odddoylerules

**Sigh**

I know. The 7 heads have an eroded ex seat from not using enough lead substitute, so I was gonna have some mild porting done and back cut valves installed as a part of their freshening. The 66 heads were just to make it a driver again.

I was gonna do the rebuild w the flat tops as is and have the chambers massaged to get a lower cr, I think pops is rushing this.

I would hate to machine pistons, then slap hot heads on it just to have the cr lowered to below what the cam likes

HWYSTR455

Quench and cam selection will do more to prevent det than anything.

A solid built short block is the foundation for a long lasting engine. I think your dad's plan is a good one. Rush it, and you most likely will have to do it again.

You can cut a 5cc relief in the pistons and still have decent static to work with. Depending on the heads, you can be in the 9.75-10.2 or so range. All compatible with pump gas as long as you choose the cam properly.

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odddoylerules

9.7 might be OK, 10.2 definitely not so DD status friendly. What influences quench on this type of head?

odddoylerules

What is the piston deck clearance generally in the smog 350s? I'm trying to run some cr calculators

HWYSTR455

And that is the biggest variable. They are all over the place from what I understand, which is a good reason to rebuild. That way you can control it. Optimum is roughly .003-.006 below deck, depending on the head. You should shoot for .005.

I see lots of folks use .025 in the hole for general calculation, but it's just that, general. Maybe Joe P could chime in and comment on what the range is from the factory.

10.2 is still ok for pump gas, IF you choose the right cam. Many are running that much or more on the street without det. (ones that properly tune and choose cams). Lower is safer, and you really don't loose much power. As long as you are 9.5 or over, you have a wide selection of cams.

Quench is a factor of chamber design, not much you can do about that, unless you go to aftermarket heads. Just make the best of everything else, and you can get reasonable quench from OE iron heads. At that point, you can play a little with head gasket thickness even, tailor the static to your needs. As a reference, quench of .040 -.050 is optimum, depending who you ask. (Example: .005 in the hole + .040 gasket = @ .045) So in theory, you can go from a .040 gasket to a .050 gasket and still be ok. (Plug that into a static calc and you will see the range.)

Here's an ok overview of quench:

http://www.chevyhiperformance.com/te...earance_guide/

Once you know what your static CR is, you can calculate dynamic CR, which is a more relevant factor in det resistance. A DCR from roughly 7.25 - 8.50 is what's considered the range for 87-93 pump gas.

Here's an online DCR calc that's very popular:

http://www.wallaceracing.com/dynamic-cr.php

Plug in different intake closing events and bang, pick your poison.

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odddoylerules

Super sweet. Great info

captjim

What exactly is the goal? I had a 9 to 1 355 with the engle 16-18 cam in a G-body wagon with 3.42 gears. Car ran a high 13 (12.7 with a little shot, but that's another story), had great street manners, smooth idle, excellent part throttle acceleration and decent (16 +/- mpg) economy. Car was dead-nuts reliable, could drive it anywhere, and was fun to drive. What more do you want in a DD?

odddoylerules

Yeah that's what I was thinking, if it was the 16-18 cam I would probably just rering and deck the block for a bit better pop. What did it run off the bottle?

Goals include daily drivable, into the 14's, and sounds good, but it already does the sound thing

odddoylerules

Oh wait, 13s. Srry

captjim

IMO, you don't need or want 10 to 1 Cr to run low 14s with good manners. I ran 12.8@ 108 with a > 100 shot.

odddoylerules

Yeah....I never wanted a motor I needed to retard or run expensive gas in. If I can't pussyfoot down the highway on 89 or hammer it with premium in the tank its kinda pointless. I'm honestly hoping I can save the forged pistons for when I need them down the road.

HWYSTR455

Guess you guys didn't understand, you can do 89 in a 10:1 engine with the right cam. The previous build I had in the clone was 10.03:1 with the Crower #56263 cam had a DCR of 7.43 and was able to run 89, full advance and a decent curve. I could have gone to 10.5:1 and still only been at 7.76 DCR, can easily run 91 octane on that. My daughter drove that config, and even with 342 gears, we would take in on trips to the beach and mountains. It's going to be her daily driver.

Forged pistons are a no-brainer. The cast pistons are a gamble at best, and because of the compression height, they are more prone to det. It's the in-the-hole that kills you. If it's apart, it's pointless to re-use the OE pistons.

Why not call a builder and ask some questions? Like Rocket Racing? Or Wise? See what your options are. Don't have to take my word for it, sure they have way more relevant experience.

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odddoylerules

OK, well if the cam goes in the pistons go in, and I guess I'm gonna have to wait up til I get the can card to check out that dcr calculator. The motor has 60k original miles on it so if there's nothing scuffed up when we pull the heads and if the mains look good it won't be coming totally apart. But message received. DCR is king

HWYSTR455

To calc intake closing from advertised numbers, use this formula:

Take the advertised intake duration and divide by 2.
Then you add the LSA to this number.
Then you subtract out the ground in advance.
Then you subtract 180

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odddoylerules

Read ur build posts dude, ur a savage! Thanks again for the great info.

HWYSTR455

Ah, thanks! Reminds me I need to update that thread!

You saw the 1/2" fuel system upgrade thingee too?

https://classicoldsmobile.com/forums...tml#post669931

Need to update that too, mounted the relay and fuse harness for the pump...

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odddoylerules

Will a mechanical pump really suck that bad?!

Imm gonna quit posting so much til we get it out. Just saw that pulling my motor post and it made me jealous.

HWYSTR455

Only mechanical pumps that are performance capable are the RobbMC pumps, and they aren't cheap. Depending on the power level, the Carter pumps may be able to keep up. I've heard some have success with the Airtex pumps, but I wasn't going to take any chances.

An electric pump with a bypass regulator will fight any chance of vapor lock, and will certainly provide ample fuel, with the correct lines and tank pickup.

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odddoylerules

Yup yup. This car has hella spiders in it, I need a shop vac