so i have a perfectly fine bottom end laying around, its a 4 bolt 350 with flat tops, and 1 pc main. I just wanna build this little engine with some budget pparts. With my old 64cc my compression was about 9.2:1.
I am interested in bumping my compression up to about 10.5:1 so i can run the xr288hr. I wanna go with procomps because its a spare budget engine..
My question is what cc should i go with to bump my compression to 10.5:1??
I was thinking 62cc??
I will not cut them i will get them in that cc btw.

 

going from a 64cc head to a 62cc is only going to bump your compression up about .25

 

try 58 cc heads from a 305 that will bump it up.

 

depending on your piston-to-head clearance, and the amount of overbore, a 350 with flattops and 64cc heads is around 10.2:1, not 9.2:1 10.2:1 with aluminum heads is fine on pump premium unleaded.

 

All the statements you just made were way too generalized... head material has very little to do with what fuel you can run and nor does static compression ratio. You can build a 10:1 motor that won't run on pump gas and you can build a 13:1 motor that will, it's all in the dynamic compression ratio.

 

The block is completely stock bore and deck. I put some 4 valve relief flat top pistons. I beleive when i did the math like 2 years ago with the 64cc heads i was around 9.2-9.4:1. I would just like to bump it up to around 10ish:1 and i am now confused on what cc i should be looking at.

 

yes, It was generalized, and yes, you can build a 10:1 engine that'll detonate or a 13:1 that won't, but neither of those qualify as smart builds, and as I've been building hot street engines for a living for over 9 years, with not one complaint in the last 8, you can understand I stick to smart builds. And a 10.2:1 350 with iron heads is NOT a smart build. Period.

 

what cc on the heads would you recommend then for a flat topped 350??

 

whatever heads you were looking at that are 62cc are fine if they're aluminum. You can run 10.5:1 on pump premium with a streetable cam. That's in the upper reaches, but it is still realistic. And considering the price of Patriot's Freedom heads, there's no need to buy iron. Freedom 185cc/64cc heads $575/pr bare, plus free shipping, plus $10 handling. Then new stainless valves, $80/set. (www.competitionproducts.com) Add another $15 for seals, you should already have springs, retainers and locks, That's under $700 for a pair fully assembled. Yes, iron Vortec heads are going for like $580, but they require a new intake manifold, and there goes the price advantage, plus they weigh another 20 pounds each.

 

so with a set of 62 cc heads and the flat tops that should put me in the 10ish:1 area compression ratio??

 

yes, probably somewhere around 10.5:1, with a piston-to-head clearance around .040", no less than .035" This includes both the thickness of the head gasket, plus how far below the decks the pistons are at top dead center. If the block was never decked, it should be around .020"-'030", and that's fine with FelPro steelshims. If the block has been zero-decked, any of the common .038" gaskets should be okay.

 

Why? With all things equal in regards to flow and velocity, chamber shape, a 10.2:1 350 with iron heads would make the same power as around a 10.8:1 350
with aluminum heads.

I kind of like the idea of using Iron better because you can make more power without crazy cranking pressure on the same cam profile.

For example, I'm considering around 10.2-10.5:1 with iron heads, which with my camshaft (57 degrees overlap, 106/106) would produce between 8.6-8.8
DCR. If running aluminum heads, I'd be shooting for something closer to 9.2 DCR, and a much smaller chamber. Now with the higher cranking pressure, the advance curve would have to come in slower.


I'm not entirely convinced the weight savings is worth it. I've yet to see any data proving any power gains are made over aluminum, and while the argument that you can run more compression or more advance holds true it's only to get you to where you were if you ran Iron.



-- Joe

 

I've only heard Dynamic Compression Ratio mentioned once or twice in this discussion. The DCR should be the objective. The static compression ratio will need to suit the cam selected.
10.2 SCR with iron heads is entirely streetable. See my sig. Now keep in mind that as Atilla says, it's not necessarily a smart build however I'm still NOT on the edge of detonation because I've been careful in selecting the rest of the components, keeping the engine cool and always use premium fuel. I may not build an engine like this for a customer. If they overheat it, or mess with the timing then it could cause problems.
What I like about aluminum is the ability to run another full point of compression. In my application the extra point in SCR brings my DCR up another .5 point and bumps the power up by another 5%.
Like Anesthes, I understand iron's ability to keep the heat in and heat equals power however I like the added compression and feel that there's something to be gained.

 

Why do you like the extra compression?

Ideally, a street motor should have between 160-180psi of cranking pressure. By running higher static compression to make up for thermal losses, you end up making the same power throughout the curve but you run the risk of detonation under the torque curve which requires timing to come in later.

There are pros and cons to iron and aluminum. For a good amount of years I was a fan of aluminum, but, for the reasons mentioned previously, and issues with threads pulling out, the fact that you have to run a higher operating temperature to get the same efficiency, it doesn't seem to justify the minor weight reduction.

Again, the higher SCR and timing is noted, but your just making up for the losses. I've yet to see a head test where two equal flowing and velocity heads, with equal chamber design have shown a power difference between aluminum and iron. In fact, check out this article:

http://www.carcraft.com/techarticles...est/index.html


-- Joe

 

Interesting article. However what they didn't do was explore the limits of static compression on both heads. Because of the heat dissipating qualities of aluminum (as you have pointed out) it's possible to run a higher SCR than it is with iron. More compression means more power. (That fact is indisputable.)
The difficult part is ensuring that you don't run into detonation and because the average guy tends to run a lower than optimal SCR, aluminum heads offer a greater margin of safety.
There are tests showing the significance of running a higher scr (it's really dcr we're after though) and software simulators that demonstrate the additional power that can be produced. My dyno 2000 program shows my 350 makes 355 hp at 5000rpm with 10.12 scr. Bumping the scr up to 11.12 yields 371 at the same rpm.( Unfortunately for me that SCR IS too high for my iron Vortecs!) I was just reading a magazine article by Steve Dulcich (from Engine Masters) where he takes a Mopar V8 and adds head gaskets (to the tune of .25"!) to lower the compression ratio. 4 dyno pulls in all and each test with a lower ratio yields less power. The general rule of thumb is that a full point of compression is worth about 4% at full power. Keep in mind too that the area under the curve gets a boost as well. Greater output overall.
I won't argue with your 180 psi of cranking pressure is appropriate for a mild street engine, however I tend to shoot for about 200 psi. Just watch the engine temps.

 

Right, more compression is more power, but are we making back power to equal what was lost thermally, or exceeding? I'm not convinced that higher compression aluminum makes more power than lower compression iron, I think that the ability to run higher compression is simply making back the lost power. No more.



Right. So if you sat down and said, "No matter what, I'm doing this motor 10:1, but I'm using aluminum for safety" you will run slower than if you chose Iron.

What the article did test, if I recall, is changing spark advance and so no measureable improvement.

Again, all spot on, but I still offer the question. Does the increase in compression exceed what was lost thermally.



-- Joe

 

I would have to say " Yes."
If only because the OEM's have made the move to aluminum engine components AND higher compression. This is not to discount the strides made with modern engine management.

 

Sorry I've been away, but I'd like to pursue this. For those who want to have their cake and eat it too, there are thermal barrier coatings for the aluminum heads. When I type anything on here, it has to be the same as for my customers. Telling people how to push the limits is not for me. I give safe, proven combos that make most enthusiast customers happy. For them, I agree with 160-180, and I believe in using measured cranking compression over calculated DCR. I've found 200 psi to be safe on pump premium, if no power adder like nitrous or boost, and I've had to go over 11:1 to get there on some builds. 200 is fine for modern combustion chambers, whether iron or coated aluminum, usually any issues come from not deburring everything. But do I let anything leave the shop that cranks over 190? Only if it's my personal property. No exceptions.

 

That makes perfect sense. Much like the carb manufacturers providing out of the box jetting that's likely to be overly rich for most applications or cam shaft companies that build off the shelf cams with too much LCA to compensate for the enthusiast that overcams his engine.
Still for me, I try to wring out what I can from my own combination. I suppose that shows in the advice I dish out. I only relate to my personal experience and try to qualify my reasoning with an explanantion and/or a warning.
The thermal coating thing is something I'd like to pursue. I have an intake manifold and a set of headers that I would like have done. As I'm close to the edge on DCR and ignition timing, I think there would be a benefit to keeping the intake charge as cool as possible (along with a quality CAI set up) and keeping a little more heat in the exhaust.
I hope goes12s is still listening!

 

While it's true that aluminum intakes do get hot, the air in there is only in there for less than half a second. Go in your kitchen, turn your oven to 200 degrees, when it gets there, stick your hand in for half a second. how hot did it get? If you want to spend money improving the intake manifold, start with an RPMAirGap, then have it Extrude-honed. Then have it welded up and machined down to accept 8 injectors. The smoothing of the extrusion will ruin it for carb or tbi, the roughness helps keep the fuel suspended. But the extrusion will radius the transition from the plenum to the runners, without having to cut the thing apart, hand port it, then weld it back together. Start with the best, then make it the best it can be made. The extrusion process will reduce surface area by smoothing everything, and less heat will be transferred to the fresh charge of air.

 

The RPM Air Gap I have already.
As you are aware as the air/fuel mixture (yes, it's carbed) passes the through the manifold, the charge will try to absorb whatever heat is present. An injected manifold, which would have no fuel in the manifold as such, is less sensitve to the heat as you suggest with the hand over the stove element experiment. Because of the fuel present in the incoming charge and it's propensity to want to evaporate, it will consume whatever heat there is. Much like soaking a twenty dollar bill in lighter fluid and setting it on fire. The fluid will ignite however the bill doesn't burn because the lighter fluid is absorbing all the heat as it evaporates.
I would think the whatever could be done to keep the intake cool, both from under hood heat and lifter galley heat, would be of some benefit. Wouldn't you agree?

 

8 injectors has/have? many advantages over any carb, especially since this intake won't accept the QJ without adapting, and this is one of those advantages. If you do the extrude-hone, the ports are too slick for any coating, unless it's electrostatically applied. And while the coating is good, the extrusion radiusing the transitions is more helpful. If I was staying carb'ed, I'd be inclined to coat a new generation Super Victor, whichever one has the proper cross-sectional area and plenum volume to match the heads. The Super Victor has no inaccessible transitions, thus the extrusion is not worth doing. Either way, this or the last proposal I described, is getting awfully invested in an engine not worth it, since better results can be had for far less $ from an LSx swap. There, some are finding HP porting the thermoplastic intakes, so extrude-honing would help, but the real question is when will some company offer us an LS6-style intake, re-sequenced for the SBC? And while they're making insane profits selling them for $600+ for the LSx guys, they actually cost less to manufacture than aluminum, and the SBC guys won't pay that, plus the volume wouldn't much surpass the LSx demand, but the SBC guys would feel differently, and then the company in question would have to sell the LSx intakes for less, and why trade 1 slow dime for 2 quick nickels?

 

Seems to be the way doesn't it?
I love the idea of an all aluminum 427.