Thread: Could use some help on CAM specs, Timing and idea please!

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https://www.summitracing.com/parts/c...07-3/overview/ That is the CAM i'm currently running. Its in 86 K10 4x4, its a 454BBC with MSD Distributor/Cap, 750CFM Edelbrock Carb, New Timing chain, Valve spings, ect. Having trouble with timing a little bit, as well curious bout how much power it should have at this time. Its sadly only got 3.43s in rear non posi. Wanting to put New Heads and Rockers on it as well as 3.73 posi. Timing seems to be off a bit, Id like to pull distributor out make sure its not a tooth off, but not sure best way to do it? Make sure 1st Cyc top after removing distrib or... And will going from an 8" Rim to a 10" make a difference with traction. Trying to learn, can read all day on random pages. But something real time interaction(at least as up real time can get on a site) with people who've been through a bit, helps a bit more.

That cam will want 9.5:1 to 10.75:1 static compression ratio with 10.00 to 10.25 as ideal. Unless you have changed pistons in the motor, it's probably down in the 8's somewhere. Too much cam with too little static compression ratio will make a weak motor. It'll take pistons with a pop-up (dome) to make more compression. Do you have any idea what pistons are in the motor?
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I'm going on a limb and saying they're the stock Pistons. IF being so yes the Compression was 8:1, or 7.9:1 ish. So whats the next step then to increase compression. I heard this as well before but, again I'm learning as I go so any help will be much MUCH appreciated. Noted you said Pistons with POP-up, what else would be needed with this, or just for the time getting the compression right to hopefully get a bit more GO.

Welcome to CHR!

As Tech mentioned, you probably have too much cam for the compression of your engine. There are several ways to address this, but all involve pulling the engine and getting into the insides.

Do you know what the engine originally came out of? The ‘86 K10 was a small block (305 or 350) with the 454 available in the one ton chassis K30 or V30 (van).

The engine block casting number is found at the back of the block where the transmission mounts to the engine. You may need a mirror to read it, but that would give us an idea of where the engine started its life. I’d hate to see you put any more money in this until you know exactly what you have.

Again, welcome!
Glenn

Glenn the numbers come back as a 73-76 C30, Chevelle, or a Corvette. Yea, the truck was originally a V6, believe would have been a special order vehicle since its a 4x4. I'll re-run numbers again tomorrow. I had them saved when we put Cam/rebuild kit on. Leaning more towards the C30. As well any recommended sites to get the Pistons? I looked around a bit. Not sure 100% how to properly do the Ratios to figure what some of the Pistons Compression is sadly.

What do you have on it for an aircleaner???? What exhaust???????

I had a 1984 one ton crew cab with 454-----------with my back ground----------only changed metering rods in the stock quadrejet and turned over the aircleaner top-the air cleaner is too restrictive altho the factory exhaust system was acceptable-------Engine cruised at around 3300 rpm towing Chapperel trailer at 75 mph and averaged 9 mpg---------friends almost identical truck except was a dually ( these trucks were only 4 serial numbers apart) and he got 6 to 7 mpg with 410 gears and a little smaller of tire on the dually----mine had 373 gear

In my opinion, for the rpm range that these operate, the Edelbrock carb with smaller primaries will have to run with the seconaries in play and will kill mileage---------I prefer a big Holley mech sec so cruise speed/tow is on only the primaries-----

With today's pump gas quality, most fellows will limit static compression ratio to somewhere around 9.5:1 for use with iron heads or 10.5:1 for use with aluminum heads.

Problems arise when a fellow goes to aluminum heads without cutting the block decks for zero deck height. To keep squish/quench shallow, like 0.035" to 0.045" to insure operation of the motor on pump gas without detonation, they will use stock steel shim head gaskets. Look at any and every manufacturer of aluminum heads and see what they recommend for head gaskets......a composition gasket somewhere around 0.040" in compressed thickness. None of them recommend a steel shim gasket because the difference in cooling and heating between the iron block and the aluminum head can cause the head to move around and "fret" itself against the steel gasket. Using a thicker composition gasket allows the head to move around a little without fretting. I don't know what will happen with an aluminum head and steel shim gasket, but would suspect that the head will fret until it removes enough material to cause rupture of the head gasket. There are fellows who are running this combination, but my question would be, for how long?

Problem arises when the builder fails to cut the block decks when using a composition gasket, so that the squish/quench ends up at roughly 0.065" (0.025" piston deck height plus 0.040" gasket thickness) ...... too wide to help effectively control detonation on pump gas. The builder needs to either find a piston that has a taller compression height that brings the piston crown up close to the stock height deck or disassemble the motor and cut the block decks on a mill for zero block deck height. At zero deck with a nominal 0.040" composition gasket, the squish/quench is 0.040" and the motor is happy on pump gas.

There is another reason to cut the block decks to zero and that has to do with errors at the factory. No block I ever saw measured for block deck height had the decks on all four corners at the same height from the crank centerline. In a mass production shop such as the Chevrolet machining line, it would be easy for a mill operator to miss a chip in the register when cutting the block decks, resulting in block decks that are not parallel with the main bearing bore. Then, when you attach cylinder heads to the "imperfect" block, the heads are askew and the intake manifold has little chance to sealing up properly.

I'm aware that no builder wants to hear this when he is eyeballing the motor running in the truck, but that is the truth of the matter.

At least one supplier on ebay (Skip White) has addressed the problem with the small block motor. He went to a piston manufacturer and specified a piston that has a 0.015" taller compression height, 1.575" instead of 1.560" on a stock stroke 350, 1.440" instead of 1.425" on a short rod stroker motor or 1.140" instead of 1.125" on a long rod stroker motor. This reduces the piston deck height and allows a composition gasket to be used with good squish/quench when using aluminum heads. It will also allow a builder to cut the block decks to zero while removing a minumum of material for better structural integrity of the block. I know of no piston that fits this bill and is available for a BBC, but there should be.

I will edit this post to give you the math for figuring static compression ratio in a little bit......

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Well, as fate would have it. My truck decided to start hem-ridging oil from somewhere. I had already planned to pull the motor and start a tare down for pistons, but I'll do some research on having the block deck evened out. Upon that not being feasible(I live in a smaller town and the closest place that will even Port/Polish the heads I can find is 2 hours away). I'll sadly have to go with the "time bomb" combo that's being used. Thank you very much for taking the time to help and go into the detail as you have. Wasn't expecting to get a response quickly, yet alone a very detail oriented reply addressing the issue. I suppose time to buy a motor stand and get busy watching how to videos to get pistons out .

Running 3" Duel Ex with headers. Going to be buying a bigger air cleaner as well hearing it could help a bit. Eventually I'll be taking off the rear-end and again watching videos how to Remove current gears(3.43) and put 3.73 posi. Not sure if limited slip or full posi locker is a better option. I'm shooting for speed over gas mileage though as well. Not worried bout 5mpg long as the Hp match's my gas consumption .