I Equalized combustion chambers on stock heads after pocket port and came up with 65.2 cc on each chamber, which is about 8.7 compression ratio.

If I mill the heads .020 I will have a compression ratio of about 9.05.

If I go .030 on the heads, the compression ratio will be the actual advertised compression ratio of 9.3.

With the price of gas and non-availability of 92 octane (at times) should I go with a 9.05 compression ratio and avoid detonation problems with low octane fuel, or go with a 9.3 and let the knock sensor take care of this problem when I have to use low octane fuel.

This is my daily driver.

 

89 octane would be fine at 9.3 to 1, I need 93 in the blazer motor, but it is at 10.5 to 1 on iron heads

 

How often do you plan to use less than 92 octane? I don't know too many stations, actually hardly come across one, that doesn't ahve 92 octane. Even the ones out in the sticks have 92.

 

My '90 Iroc came with 64cc iron heads and a ratio of 9.3:1, 91-92's had 9.8:1...and I always use 92+octane in mine to keep the knock down and ECM out of the igmition timing. When it gets involved it "over-corrects" and your motor falls flat on its face...milage goes down, power goes down too...I have gotten as much a 10.4* knock retard on 87 octane on a hot summer day..

 

Out here in Arizona/New Mexico/Nevada/California the gas stations offer 3 grades...87, 87, 91...except where there is boat gas which is 100+ (which is $4.00 +++/gal).

The altitude also varies from 500 ft. above sea level to 7000ft above sea level.

My goal is to use as cheap a gas as I can, while still having as much power as I can.

 

A couple of things I've heard helps:
1)Zero decking the block, improving quench.
2)a longer 6" rod, iproves the rod/stroke ratio
3)rounding any sharp edges in the combustion chamber/cyl..

I've got a good article here on octane, I'll look it up..

 

should have read 87, 89, 91 gas (not 87,87,91)

Sorry.

 

The "advertised" compression ratio on the 1989 350 TPI is also 9.3, but I will almost guarantee if you had taken your motor down the actual compression ratio would have been in the 8.7-8.8 range.

I had heard this before I tore this engine down...now I believe that they all are actually lower than advertised for reliability problems which translates into less warranty work.

But the bigger numbers sound good in their printed text and there are always variations in any assembly line product. One cylinder was 2cc too small; the rest were within .5cc. So, it should run a lot better after all are equal.

 

It's in the Feb 2001 Chevy High Performance issue.
titled: 411Hp on 87 Octane
355ci 9.4:1 smallblock with forged 5140 steel crank, stock rods, speed pro slight dished pistons, 0.005 deck height, TFS aluminum heads, holley 750 D/P'r and headman Elite headers, 38* total ignition lead, and keeping the engine temp down to 180*-190*.

Quote:
Conclusion:
....a few warnings. First, pay close attention to the timing curve as well as cool inlet air temp, cool engine temp, and employing a well designed combustion chamber that doesn't require as much timing to the same power....

 

BTW, my engine IS torn down, and still on a stand as we speak...I've just finished buy some undercut-swirlpolished valves and am still finishing up a sweet port-job, and although they cc'd pretty much "on the button" the pistons were in the hole a little and still would've only managed roughly only 8.9:1...

 

Mine is also on the stand. I swirl polished and undercut the stock valves. Saved a few bucks.

Had some problems when they shipped the rings, the plasma rings they sent had 5/64" oil rings. I am still using the stock pistons...the stock ones were only 1/8", so had to buy a set of Perfect Circle rings just to get the correct oil rings...I guess nothing is ever easy that is worthwhile!

 

Heard that!
I also reused my stock pistons, they were fine, and of a higher silicon variety, but I got lucky and received the right rings..
I also went with a ZZ4 cam, and found out, after measuring, that my intake valve seals were going to hit my guide bosses.. it's always somethin...

 

I am using a stock cam, have headers (ceramic coated inside & out) with actual dual exhaust 2-1/2" thru Flowmasters.

Had a 700R4 beefed up by COAN to put behind it, worth the money.

3.41 rear axle ratio, seems to work pretty good out here in the mountains.

Looked at doing a 383, but decided to wear the stock setup out first.

Appreciate your info.

 

I too though hard about a 383, but the more I did the math, I know I can hit really close to the same numbers from a properly spec'ed 350...I'm not ready to build an entirely new package from the oil-pan up..for just a few ponies..
I rebuilt and beefed up my own 700r4, got the video from Summit and the TCi kit and Vette servo etc..should be enough for my 400hp..
I did go up from a 3.23 ratio, when I parked it to a 3.73 now, which should put my rpms right where I want the at the traps, tho I'll probably have to play with the tranny governor to get my shifts just right..
I got a set of Flowtech shorty headers and a custom true-dual 2 1/2" exhaust routed like factory with 2 ELD-RPM mufflers in the Corvette's location..
I thought of doing the kit coating on the headers, heard anything good/bad?

 

I'll give you a few of the facts I know about coated headers. When we were moving from Indiana to Arizona my truck was equipped with the standard set of headers. We were pulling a trailer that weighed between 9000-10000 lbs.

A lot of grades in the west are 6%+ and maybe anywhere from 6-20 mi. long. When you pull something that hard, that long...when you stop you don't need a light under the hood...the headers especially in the sharp bends are glowing a bright red. You could light a cigarette off the headers.

I knew many more trips like that I would have burn-thru. So, I had "Jet-Hot" coat my headers inside and out. If you only coat the outside it stops the heat from coming thru the header, but the inside of the header is even hotter because the ceramic coating does not allow the heat to escape. But if they are coated inside and out, it lets the heat go out with the exhaust and makes the underhood temperature at least 20 degrees cooler.

If you have a fuel or oil leak that sprays on the headers that have been coated it does not ignite instantly and, may eliminate a fire altogether. Coated headers are also a lot easier on the body if you inadvertently touch them while working under the hood. You may get a slight burn, but nothing like your skin turning white and raising a big blister immediately if not sooner.

I think it is a pretty good investment in both performance and safety. Plus, they are a lot more durable.

Heat out here in the desert is a big problem. During the summer the temperature reaches 120 degrees F. A lot of vehicles burn to the ground on the interstate because they develop some type of leak that translates to fire and by the time they get it stopped, it is toooo late.

I took my latest set of headers to Phoenix and had them coated inside and out...cost about $365...well worth it. And this is on an old "beater" we use in the desert. I'm going to have the headers for my 350 TPI coated also by "Jet-Hot" (when my piggy-bank gets full). Probably the last big expense before I put the engine back in. HOpe this answers some of you questions, and maybe even gives you some more.