Hello all,

I've been doing a lot of reading and searching, and there's still a few questions I'd like to have answered that I haven't been able to get clear yet.

I have an '87 LG4 305, already has shorty headers, custom y-pipe, Edelbrock cat-back, MSD coil, EGR delete, some other stuff, and a really strong bottom end. I don't want to ditch it for a 350, it's just too good of an engine, but I would like to squeeze a lot more out of it. Here's what I have planned:

113 Aluminum Heads, rebuilt
XR258HR-12 Comp Cam
Performer Intake
Quadrajet Carb

Now for my questions:

At a 9.3:1 compression ratio, will the Aluminum heads be effective? If not, what would be the best way to bump up the CR? Can the heads be milled down a few CCs, thin head gasket, something like that? I'd really like to get it up to around 10:1, but i'd be worried about valve clearance with the 305 cylinder walls. Is this a problem?

Also, will I be able to use the stock lifters, pushrods, and rocker arms from my engine, assuming all are in good shape and within specs? I've read some about pushrod length being hard to figure out, but I would assume that with 113 heads being a stock unit for a SBC, this shouldn't be an issue.

Obviously valve springs will have to be changed with that cam, already planned on that.

That's really the short and sweet of it, I think I can figure out the rest of it just by searching.

Thanks guys,

-Levi

 

checkout my post- it's very possible the 113 heads have different bosses, causing you to change the serp system.

 

When I used the Vette heads, I had to drill and tap the holes for the brackets where they needed to be. Easy enough as I had swapped to a Serp setup at the time. If you have the factory front multi-vbelt accessories, you'll have to tap the holes too I expect. The meat is in the castings for the holes, it was just never drilled and tapped.

The 113 heads have a 58 cc(or was it 56?) cc chamber, so your compression ratio should not go down any. Use some thinner head gaskets, but I wouldn't use the steal shim gaskets. get factory TPI 305 gaskets from GM. Thats what I ordered when built my 305 years ago.

Cam looks like a good choice for the engine.

 

The 113 chambers may be the same volume as the 081 305 heads, but being aluminum, the effective CR will go down.

Remember, 113's were used on 350's, with equivalent iron heads for TPI 350's having 64cc chambers. The reason is the greater heat loss through the aluminum heads, not only allowing higher static CR, but necessitating higher CR to get the same power out of them as iron head produce.

 

Is the effective compression ratio you mention the same as dynamic compression ratio? If so, I don't see how aluminum vs iron makes a difference.

 

Ive been trying to research this some myself, the aluminum vs iron argument.

In favor of the argument that iron heads give higher effective compression ratio, Ive found a quote from a cylinder head r&d guy for a race engine manufacturer that stated iron on iron engines will make the most power, aluminum on iron will make less power and aluminum on aluminum will make even less power. I also found somebody referencing smokey yunick as finding that aluminum heads make less power, he would coat his aluminum head in some goo they used to preserve eggs in to help the heads hold heat.

On the other side of the argument I found this, http://www.carcraft.com/techarticles...est/index.html .

I dont think five7 and others are wrong but Im starting to wonder if maybe the difference is far more negligible than some people think as far as compression. At least the test above would leave one believing that the benefit of the weight savings far outweighs the miniscule loss in effective compression.

edit=changed dynamic to effective to reflect five7s argument more accurately

 

Interesting article. It would be even more interesting to see a cut-away of the two heads to see if they cast them any different. Thicker aluminum would reduce heat flux.

I don't recall hearing about Smokey's "goo", but ceramic coating is being used more & more on chambers and exhaust ports to reduce heat transfer.

"Dynamic" CR is not what I meant by "effective" CR. Dynamic CR takes the cam into account for the volume that is actually in play due to valve opening/closing and overlap. It doesn't take head material into account.

"Heat" and "power" are measurements of "energy". The more heat you dissipate, the less energy you put out through the crankshaft. That's one of the reasons car companies went to higher temp thermostats to improve fuel economy.

 

I'm researching a 383 I'm building and I had just delved into dynamic CR for the first time(never looked into it on prior engine builds due to ignorance I guess)...hence the confusion about aluminum vs. iron. I googled effective CR and I saw lots of references using dynamic and effective interchangeably.

Coated combustion chambers have been discussed as well in some of my readings. Don't remember the reasoning for it, though as I've also read about using cooler thermostats to wick away the heat quicker. Those contradict each other so I'm sure it was two different places.

 

I'll read that article at home tonight. Not going to make any difference for me as I already have AFR190s on the current engine...but knowledge is good...even if it takes reading 10 articles to form an opinion on something.

 

So,

Facts:

1. Both heads are 58cc combustion chamber
2. 113 casting is aluminum
3. Factory casting is steel
4. 113 casting has bigger intake valve, and new valvesprings compatible with my cam (the set I snagged for this build does)

Now, if I understand correctly, the difference in effective compression between the steel head and the aluminum head is so negligible that people don't even really agree on the fact that it matters. So, even if I lose a few horsepower, I'll make up for it in weight savings of the aluminum and the flow of the bigger valves. Also, I'll save money by not having to change out the valve springs, and I'll be able to use the standard pattern intake I have setting around and not have to buy a more expensive angled plug intake.

Now, assuming that eventually I'll want to reuse these heads on a 350 when the old 305 kicks the bucket or i get more time to work, should I worry about milling them or just say to heck with it and run them like they are? Would .030" flat milled introduce other problems with valvetrain alignment, cylinder bore clearance, head warping, etc? Would it introduce compression problems later on a 350 because the ratio would then be too high? (Shouldn't I just be able to use a thicker head gasket then to make up the difference?)

How much is too much, and what isn't even worth messing with in this case?

Thanks,

-Levi

Oh, I almost forgot, the car has the combination serpentine belt/v-belt set up from 1987. Will this be a problem with the head bosses on the 113s?

 

I'm in the process of installing 113's on my 350.

I am noticing the difference between a .039 gasket and .041 gasket equates out to almost .1 difference on the compression. I think you would have to shave off quite a bit on the heads to get down to 10. Then you could possibly have problems on all the parts bolting together and having leaks/etc. Along with alignment on pushrods and etc.

I have not changed my pushrods or rockers. Hopefully it all works correct.

I did notice that my passanger bracket is missing one bolt hole in the head. Has anyone tried to go to the vette bracket? Power steering/alt bracket bolts up fine.

 

I'm running .028 thick head gaskets on my car. They are a GM p/n that I have no idea what they are. They are a nice composite material and I plan on running them again if I have to.

Anyway, I'd run the 113s as is on the 305 that way they are transferable to the 350 whenever you build it. They will be better untouched so that you can resell them later too if you upgrade.

Also, you may have to drill the bosses in the front of the head for your accessories. Sounds more daunting than it is. Get the proper size drill for a 3/8" tap...then tap it. I tapped shallow on mine out of fear of breaking through.

 

Nice thing about being an engineer here is that I have access to a first rate machine and fabrication shop whenever I need it. Drilling and tapping for a bracket should be no problemo.

Will the 113 heads make any difference at all, or would I be better served just sticking with the factory castings and only changing the cam, and keeping the aluminum heads aside for a later 350 build?

-Levi

 

I 'think' that the Vette heads flow better than the 305 heads. The bigger valves would be a plus. You might do some research on some David Vizard suggestions on the 113 head and where improvements can be made with some simple porting.

The 305's small bore really limits valve size and breathing of the engine...but the vette heads should help out a bit. I think its worth the effort, especially if you plan to put them on a 350 later...they will transfer straight across which is the beauty of the SBC.