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Old 11-19-2012, 04:57 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by techinspector1 View Post
Brian, I predict that you're about to get an education on the importance of matching up a combination of parts toward a common goal.
A 294 cam will make power from 3000 to 7000 and will require 11.0:1+ static compression ratio.
A Torquer intake will make power from 2500 to 6500.
Your stock cylinder heads will make power from idle to 5000. They were designed to haul grandma to bingo and back, not to make high rpm hp.
Can you see a mis-match of parts?
Do you have any idea of the static compression ratio of the motor?
Do you have any idea of the squish you built into the motor?
What rear gear are you planning to run? The 294 cam will require something in the 4's.
Have you bought your 3500 stall converter yet?

Most of you younger fellows have not learned that a camshaft IS NOT a stand-alone part. You can't just grab the highest duration cam you can find, stab it in the motor and expect a world beater. It must be considered as a major part of the entire combination. If you have no idea of the exact static compression ratio of your motor, don't even THINK of trying to choose a camshaft for the motor.
A big X2 on Tech's comments!

To which I'll add that to get to the needed compression will not only involve a better than a 1970's head but you've got to consider the piston as well. A lot of research has gone into combustion over the past 20 years as a result of government mandates to lower emissions while increasing fuel mileage. It turns out that a lot of goodness for the Hot Rodder and the Racer has come out of this. Witness the Chevy LSx series, Ford's Modular, and Chrysler's Magnum; all produce power and mileage at levels not only unheard of 25-30 years ago but not even thought possible. A key (not the only one but certainly a major one) to these results is the combustion chamber shape inclusive of the piston crown. Let me say that your obsolete 1970 engine drew you unknowingly into the old hot rodders syndrome of a big cam cures your low power woes. This was thinking typical of the pre-L31 Vortec head days. Before the mid 1990's very few people including many pro-racers understood that bolting on a head with the right chamber shape could increase power output by 40-50 horses with no other changes. Then those who could afford to score a Brownfield small block head back in the 1980's surely found out and it became an immediate secret you didn't share with the competition. Even the the similar chambered and well idea advanced LT1 and LT4 of the 1990's didn't make a big splash in rodders thinking. But when the L31 Vortec arrived the community went nuts when they discovered that these things, while not Brownfields in performance nor cost, would boost power an easy 20 often 30 and if you had the intake and exhaust system optimized sometimes 40 or 50 ponies grew where there were none before. Today most heads OEM and aftermarket domestic and foreign that have gone to tight, small, heart shaped chambers where not too many years the mantra was open chambers because they breathe better at least on a flow bench while the combustion process was ignored.

The piston must be considered with the cylinder head and cam, as the cam used needs to drive the compression ratio. The greater the duration and lift the higher the compression needs to be. The down side limit is that modern pump fuels do limit how far the compression can go. But you need to keep in mind that modern heads such as the L31 Vortec do stretch the pump rated octane of the fuel by 4 or 5 more marks allowing a 92 octane to react as if it were 96 or 97. Aluminum heads will push this even further as they easily allow another full ratio over cast iron because they pull heat out faster. So you run the engine a bit hotter 10-20 degrees and run the compression up, this more than compensates for the heat loss out of the chamber and rewards you with yet more power.

Compression is everything in terms of getting the power out of the cam, in that vein you need to drive out the Dynamic Compression Ratio, this is the ratio that accounts for where the piston is on the compression stroke when the intake valve seats. It becomes a reciprocal game mathematically to calculate against the Static Compression Ratio which is the sum of all the cylinder's volumes divided by just the volume above, but including the piston crown, when the piston is at TDC. The problem long cams present is that it's hard to get the ratios up where needed without going to a domed piston where the fuel may only allow a flat top or D-dish for overall octane tolerance. So it gets to be pretty easy to over cam the engine for these other major constraints. DCR calculators are easy to find on the web, they are fun to play with and you need to do this as a means of parts selection not the other way around.

This also arrives at the ignition system. High compression and high chamber activity demand more from the ignition system. A good Capacitive Discharge (CD) with multi strike capability is a must, these are especially helpful for the engine that sees a lot of street time as high compression engines with highly active chambers can be difficult to light off in typical street driving situations resulting in missfires, fouled plugs, fuel diluted oil, etc. The head in the attached picture is not what you want, this is a poster child for inefficiency and low power output. Some where not too long ago there was a set of pictures by Cobalt or Tech, I don't recall which one put them in which are typical of what you should be looking for.

Bogie
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The Following User Says Thank You to oldbogie For This Useful Post:
Brian Morency (11-19-2012)