Xterrable

Hey All

I was talking with Billla about my plans and just wanted to see what you all suggest. I want to do a complete top end on my 350 and keep going back and forth between the E-Street set up and Vortecs.

Looking for the biggest gain in torque, more so than just HP. Want something dependable for the best price possible, thus lowest priced. Dont want to high of a compression motor. And I guess that is my biggest concern as of now. I am thinking something in the 9.5:1 ratio is going to be easy to maintain as a dependable engine.

I am running an Edelbrock 650..

First, no matter which i go with, what CC head do you suggest. My 350 has been bored over 0.030. I measured the depth at what I think is TDC and found the head to be down about 0.040 to 0.045. But not 100% sure I am at TDC. My pistons are flat top's with the 4-D Shaped valve reliefs in them. Not sure of the volume of the reliefs.. I am thinking something in the 70cc range with 170-180- intake runners. But most I see are either 64cc or bigger than 70.. Suggestions? I know this is semi loaded as different head gaskets will yield different CR's.

Cam... Is it best to pick heads and THEN pick a cam? Looking for something that takes full advantage of low end. Streetable but sounds good.

Some posts I saw on here said people had issues with the Vortecs and finding headers that fit well. Something to do with the bolt patters on the Vortec heads? Then there were issues with plug wires routing etc..

I am looking for little to no custom alteration to an out of the box product. I do not have the funds available to keep switching parts due to fitment issues.

scottyp99

If you've been talking with Billla, talk to him some more. He's the guy to talk to about this sort of stuff. He is a rare dude; a guy who likes to talk about engines, and actually knows something about engines.

Edit: "what I think is TDC" is not going to cut the mustard. If you are going to be making your own decisions about building an engine, you have to be sure about stuff like this. It's not difficult, but there is a learning curve. That's why a lot of people just pay an expert to worry about stuff like that. If you are going to be the one worrying about it, you have to become an expert. There are people here on this forum who will help you find the stuff you need to learn, but none of them can learn it for you, that's up to you. Don't give up, I have been doing it for the last year or so, it's a rewarding experience.


Scott

billla

Adding a couple of comments...

A cheap dial indicator or piston stop will allow you to find TDC for sure. Nothing fancy required

The dual-relief flat-tops typically are around 12cc or so...

The decision path is to buy the flow that gets you the power level you want, then select the cam to maximize the heads...and build the shortblock and everything else to support that power level.

I haven't heard of any header fit issues myself - but I don't do a lot of R&R personally.

Xterrable

Yeah, Having never done internal motor work, I never realized that a 0.020 change in delth would make that much difference.... Eeekkk.. But then again a CC is not that much when spread over a 4 inch bore..

cv67

You can get a cheap dial indicator with a magnetic base at Harbor Brake for under $20

Xterrable

I used a Depth Micrometer to take the measurement. It was in my neighbors unheated shop. I was amazed to see the difference in measurements as the tool warmed up..

billla

A depth micrometer is great to find deck height...IF the engine is at TDC

63mako

Can't suggest how many cc's your heads should be without knowing your exact piston dish cc, exactly how deep in the hole they are. Compression ratio depends on bore, stroke, piston volume, gasket bore, gasket thickness, deck clearance. .040-0.45 is a lot and would be unusual.
How critical is it to have exact numbers? Aren't these "close enough?"
Lets figure you Think you have a 4.030 bore. a 3.48 stroke. a 12 CC piston dish. a .015 gasket and the pistons are down in the hole .045. and your running a 70 CC head. This is a compression ratio of 8.7 to 1.

Now we find out that your guess at the piston volume was off. It is actually a 3.5 CC dish (this is correct for a flat top L82 trough piston) and the piston was "not quite" at TDC so your actual deck to piston height is .025 (this is typical on an uncut deck). These seem like tiny changes right? The difference is the compression ratio has now changed from 8.7 to 1 to 9.9 to 1. This requires an entirely different cam and your best choice of head CC might be different. So come back with EXACT information and it will be much easier to make recommendations. Without EXACT information you and those trying to help you are shooting in the dark.

jackson

measure closely several times around bore.
many of the cheaper replacement-type pistons have compression distance around 1.540" ... when those installed without decking block, they do sit about 0.040"-0.045" below deck at tdc.

Some hi$ pistons also 1.540"

most 350 replacement-type flattops w/ 4 eyebrows have a dome volume about -5 to -7cc ... some depends on how large is piston's chamfer.

Xterrable

Well, using a dial indicator, I rechecked everything. And I confirmed that the pistons are anywhere from 0.040 to 0.060 down in the block. We checked each and every piston, which is where the variance comes from.

Now my neighbor also noticed that the babbitt on the cam bearings are wearing on the low side.

So I am wondering if it is worth rebuilding at this point.. I dont need a precision motor but I dont want to dump 1500 into a top end and have it grenade in a little while... But to be honest, I dont have cash to do a full tear down and rebuild.

Thoughts??

billla

You mean there's that much varience cylinder to cylinder? Uff.

This thing was fairly recently rebuilt, right? Or am I remembering incorrectly?

Xterrable

It was rebuilt 2 owners ago. The guy I bought it from owned it for 4 years and only put about 1000 miles on it in that time. It was the guy before him that must of had it done. Most of the hoses had dates in the early 90's. So we are assuming that it only has 15k on it since the rebuild... Maybe more...

63mako

.020 difference in piston to deck clearance from 1 cylinder to another is major. Put it this way .020 difference is the difference between 9 to 1 compression and 9.4 to 1 compression. Even on a crappy undecked factory block they should be within .008 max. Cam bearings always wear on the bottom side. That sees the pressure but noticable wear there now combined with the varying clearances would put me in a situation where I would either put it back together with maybe shaving the stock heads and a new cam and lifter set to get a little cheap performance for a while or rebuild it completely.

billla

I expect...in the end it's kind of a screwed-up rebuild.

If it was me, I'd do a solid shortblock overhaul and just put the stock heads back on it for now. If you're smart and careful, you can get it done well and relatively cheaply.

96 lt-4

I would assume with a 64cc head you will be fine.If you go the vortec route the improved combustion chamber will help ward off detonation.The 180cc head would be the minimum I would run.

We used the Jegs house brand alum heads with 195cc runners on a mild 350 and it made a lot of mid range with no real loss of low end.

For a cam something like the xe268 comp or similar lunati voodoo would work well.You can go one size smaller if you are running highway gears and keep the heads at 180cc if you want.170cc or smaller is fine but it will drop off from the upper midrange on.

Xterrable

So what is the downside to just doing the top end with the issues known. Loss of performance? Engine is going to break?

From playing with the compression ratio calculator, it seems that I am going to need a thin head gasket in order to keep my CR up in the 9.5 range. Whats the down side to using a thin head gasket.?

63mako

If your numbers are right you will have a .4 variance in compression ratio from the highest piston to the lowest piston. So you will need to figure the highest compression cylinder which is a 9.4 to 1 with a 70 cc head.
Felpro 1094 gasket

http://www.summitracing.com/parts/LUN-60102/

http://www.summitracing.com/parts/EDL-5073/

ezobens

I still find it hard to believe that you would have .020 difference in piston height from cylinder to cylinder AND up to .060 down in the hole unless something else was wrong somewhere. Even crappy pistons aren't off by that much in the same set?

Since you seem to have some wear on the cam bearings, I suspect you may have the same in the rod bearings, which might explain some of the variances from cylinder to cylinder.
While you are this far, it would be a shame not to drop the pan and check a few main and rod bearings, just to make sure you don't have more serious issues.
Also, have you checked the decks for flatness?
Is it possible you have warped decks that are contributing to the numbers you are getting?

Just my .02-
Elm

Xterrable

I must be doing the math wrong then.

Enter Cylinder Bore Size 4.030
Enter Piston Stroke Length 3.48
Enter Head Gasket Bore Diameter 4.10
Enter Compressed Head Gasket Thickness 0.015
Enter Combustion Chamber Volume In CCs 70
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') 6 cc
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') : 0.040

When I use those numbers, the calculator says 10.6:1 ratio. What number am I doing wrong?

Xterrable

No, I have not checked the deck for its flatness. I dont think that the tools I have will provide me with accurate numbers..

You guys are really a buzz kill today....