scottyp99

Personally, I can't figure out why GMPP doesn't just sell your engine with the Vortec heads already on them. They'd sell a gazillion of 'em!!!!


Keep the shiny side up!
Scott

nate99

They basically do with the 350 HO (330 hp/380 tq) engine, and I would have been better off starting there, though the cam they use on it is just a hair smaller. .435/460, 212/222 112.5 LSA. 9.1:1 compression, which is probably close to where I would be with 64cc heads.

That's 40 HP and ~55 tq over what mine is rated currently, assuming my cam still works as well as the one GM picked.

I'm nearly sold.

billla

There's certainly more power to be made with better heads, but the Vortecs outflow many Tier 1 heads...and do it with a great chamber and smaller ports. It's a great top for any mild 350.

JEGS typically has the best price for some reason, then it's just the rockers, gaskets, valve covers, head bolts and intake.

The rockers are P/N 12495490 for around $65.

GMPP head bolts are dirt cheap under P/N 12495499 for about $35.

Take-off valve covers I typically get for ~$20 from the Online Auction Site (you know the one )

Intake gasket is the Fel-Pro 1094...but be sure to measure deck height beforehand.

And of course, check valvetrain geometry and clearances afterwards.

63mako

I totally can't agree with this statement. Aluminum heads will allow a full 1/2 point of compression more than Iron with the same cam if your close to the detonation threshold.

nate99

Is this because the piston may be "out of the hole" too much for the thin gasket, or is this for some other reason (pushrod length, etc.)?

I'm not entirely sure what GMPP does to its blocks used for the crate engines it sells as "remanufactured". If I were being an optimist, I would hope that meant that it was not decked and fit the "brand new" dimensions, but I really don't know.

nate99

Interesting. I'll be somewhere between 9:1 and 9.5:1 with 64cc heads, if I got the particulars right on the calculator that I found, so detonation shouldn't be too much of an issue, unless there is something else that I'm not considering.

billla

...which is around 10.2 CR NA with premium fuel and full ignition advance, which we are nowhere near for this build.

I have yet to see back-to-back testing validating this perspective. Tests by Car Craft and others failed to support this perspective, while admittedly also not disproving it either. Regardless, I don't personally plan a build based on this perspective. Even if this were the case, 1/2 point of compression is worth...1-2% power on a build making < 1.4 HP/CID?

The observation that a larger cam would be required to use Vortec heads on this because they're iron just isn't applicable here - which was the basis of my comments.

billla

Deck height on any engine is a complete unknown until measured. It's typically around .020-.025...but I've seen less and more. One guy on the Forum found .040 deck height on a stock engine...so there's just no telling

GMPP block aren't machined square - the deck won't be square to the crank centerline and the deck heights can be anything, and can be inconsistet cylinder-to-cylinder. Not a big of a deal on a moderate build, as much as some will make of it.

nate99

Forgive me another engine 101 question. Is the .020-.025 and .040 you refer to the measurement of how far the piston is at TDC from the top of the block?

Labelled "deck clearance" here?

billla

Yep

nate99

So, as long as you're not out of the hole, you can run the thinner gasket, or is there a minimum additional deck height that you need as well?

billla

Apologies - let me back up for a moment.

The spec we're chasing here is quench - the distance between the top of the piston and the bottom of the head. The "ideal" quench is around .040...so we try to find a workable combination of deck height and gasket thickness to achieve that quench.

Once we know the deck height, we can see how well we can do to get around .040. The 1094 gasket is often a good choice as the stock deck is often .025 and the compressed thickness of the gasket is .015...so .025 + .015 = .040...perfection

nate99

Gotcha. I did read that .025 was the usual given spec, but as you mentioned earlier, there is a fair amount of variation.

scottyp99

Yeah, most people say deck height when they mean deck clearance. It is such a commonly used term that even people who know better say it. Don't get wrapped around the axle about it. If it's several inches, it's the actual deck height. If it's a few thousandths of an inch, it's the deck clearance. If you try to point out the difference you will just end up involved in pointless arguments.


Keep the shiny side up!
Scott

nate99

I think I'm up to speed on the concept now. I'm not one to really care about the semantics, I just did not know about optimum quench. billa set me straight.

Thanks again all.

cardo0

Yes a supercharger. It matches your heads, cam, and compression ratio. Just retard the timing. OK, i know those cast pistons won't last at high rpm and hp. But use a rev-limiter with the smaller 141c.i. blower for mostly street driving and you should be fine making somewhere in the 400hp - 450hp range. U may find u need a good transmission to handle the greater torque. In fact your trans could be slipping now so bad thinking the engine is too doggy (i upgraded my 4L60E to a BTO level 3 and wow now). IMHO bolting on a supercharger is much more fun than swapping heads and scrapping head gaskets - what till u try and get the stock composite gasket off. Blowers look expensive but once u start shopping for used 141 c.i. blowers the cost drops fast.


Yes I can't see how u can overlook the GMPP catalog for head swap comparisions - that's what i would suggest for a head swap comparo of GM crates (HO). Your current cam has more duration and wider LSA moving u higher in the rpm range for max power but idle vacuum may even be improved. So just bolting on some Votecs should see good power improvements.
But i recall u just got this motor installed and running. Don't u want to play with it a while? A low compression motor like that is very hard to break. My suggestion is maximize your tune with an O2 sensor - they're cheap and invaluable for modern tuning. Get the carb dialed in first - mid 12:1 mix at WOT and 15 something at cruise. Fuel pressure and pump shot can be concealed issues reducing power and response.
Also optimize your timing curve. Learn how to get full advance 32* at least or more in by 3000 rpm. Match up your weights and modify post bushings to get idle advance below 10*. Map the timing advance from idle to 3000 rpm and play with it to see whats best for your car.
Another bolt on is 1.6 rockers and on a mild 350" like yours i would install them on intakes only. Do you have and H pipe crossover exh - few more ponies here?
These are all very inexpensive improvements (without the blower) that take time and patience rather than much cash. But they provided very helpful experience once u step up to high dollar parts.

Good luck nate,
cardo0

nate99

None of my ideas would be happening in the short term, I just know that I will want to go for more power down the road. You are right about just getting the car running, but I just like to fit all the options together in my head and think about them for a couple of years before I pull the trigger. Tuning will be the next actual step. Any good links for learning the basics of carb tuning with an O2 sensor? I'd like to read up on it for sure.

I have thought about a small blower, but am really hesitant to cut a hole in the (or get a ridiculously high) hood. If I run across an elegant solution there, I could see myself getting talked in to it. There was a guy that had dual Weber carbs on some kind of trick B&M intake that looked really cool.

But me and dual Webers on a s/c engine would be about a dozen bridges too far.