Need head/cam recipe - Impala Tech
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post #1 of 6 (permalink) Old 06-26-2019, 10:50 AM Thread Starter
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Need head/cam recipe

Specifically hoping Dave has something to say.

I have a fresh, solid 454 rebuild currently in the car but plan on replacing the heads and cam this coming spring. I'd like to keep the HP under 550, target overall driveability, and use pump gas.

Sorry Dave, but my O2 sensor design background and current occupation kind of mandate fuel injection. I'm hoping to narrow down the hundreds of head and cam options based on someone's actual knowledge and experience.

1969 Imapala convertible build thread here:
https://www.pro-touring.com/threads/...ghlight=impala
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post #2 of 6 (permalink) Old 06-26-2019, 11:47 AM
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Your best bet is to call Chris Straub at https://straubtechnologies.com/. Cam guru, he has helped many with cam and heads on team Chevelle site. Chris will spec the heads and cam to work together and you will be happy. Most likely he will save you couple of $$ too. Look him up on Team chevelle forum and you will see what people that run his cams say.

550 is easily achieved on 454 with the right combination of parts.

That being said my 468 is pushing little over 550hp with reworked GM 781 oval port heads and custom roller cam from Chris.

You ask internet and you will get 100 opinions, instead ask people that do this for living and have track proven combos out there.
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post #3 of 6 (permalink) Old 06-26-2019, 01:31 PM Thread Starter
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Quote:
Originally Posted by 67SS View Post
Your best bet is to call Chris Straub at https://straubtechnologies.com/. Cam guru, he has helped many with cam and heads on team Chevelle site. Chris will spec the heads and cam to work together and you will be happy. Most likely he will save you couple of $$ too. Look him up on Team chevelle forum and you will see what people that run his cams say.

550 is easily achieved on 454 with the right combination of parts.

That being said my 468 is pushing little over 550hp with reworked GM 781 oval port heads and custom roller cam from Chris.

You ask internet and you will get 100 opinions, instead ask people that do this for living and have track proven combos out there.
Thanks. I know Dave was an engine builder as well so trying to limit it to people who have actual experience. Street manners are my biggest concern as I drive the car when I can (just did 2000 miles on the Power Tour).

1969 Imapala convertible build thread here:
https://www.pro-touring.com/threads/...ghlight=impala
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post #4 of 6 (permalink) Old 06-28-2019, 10:38 AM
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Chris Straub is an engine builder. He is still working at it while I have been retired for the past 15 years. In addition to being an engine builder I am a degreed engineer so I have the theory and experience as a racer to bring to the mix.

That said you want streetability. That means you need to keep your engine operations in the idle to 5,400 RPM range. No trans-brake, or five series rear gear in your future eliminates cams with a duration over 234 degrees, because you are not going to see any high RPM to justify the need for a longer duration.

The wider the Lobe Separation Angle LSA the more bottom end torque you will make to break the tires loose or accelerate your car (at the expense of not making any power at 7,200 RPM). Of course this means you won't have as much of a Rumpity Rump cam sound that many feel is much more important than actually performing well; but on the plus side EFI loves a wide LSA as it smooths out the vacuum signals in the manifold.

Custom cams allow you to specify lift. The more aggressive the lash/opening ramp (or rocker arm ratio) the harder it is on your valve train (requiring frequent maintenance and spring changes), but the more power you will have. Just look at any flow bench work and you will see that the higher the cam lifts the valve the more the head flows. In general you take the head flow numbers and double them to get an idea of the power a set of heads can make.

Now about those heads. There are two parts to a heads design that will make power: the port (size shape and angle) and the combustion chamber (volume, shape and quench). Any head can be made to work. But the key word here is work, as in custom carving a head with burs and epoxy to obtain any shape, or size you want that supports laminar flow at any RPM. With a BBC under 500 cubes you need to be looking at oval port head (230 cc to 270 cc port volume). With RPM limited the smaller (stock 230 cc size) will give you the best throttle response (driveability, and to keep a MAP sensored EFI happiest).

BBC has big ports but small valves like the old nail head Buick engine. If you choose a stock cast iron head you will spend as much money on rebuilding them with bigger valves and hardened valve seats with new bronze valve guides as you will on an new set of aftermarket aluminum heads that weight forty pounds less. The BBC also has a bad exhaust port the is short abrupt as it bends the exhaust ninety degrees. This bad port was designed into the head to make a big truck engine fit in a car body.

You need a least 2.25 inch intakes and 1.88 inch exhaust valves. You don't want flat steel stock valves as they are heavier and weaker than tuliped stainless intakes and Inconel exhaust vales. Bigger the valve the more low lift flow you get. On the street low lift flow numbers are what improves idle quality and gets your car rolling.

Finally the combustion chamber needs to be discussed. The original engine designed to race in NASCAR back in 1961 had a 90 cc bath tub combustion chamber with a semi hemispherical large domed piston to match. Emission requirements killed high compression pistons and the bath tub chamber shrouded the valves which separated the fuel from the air that was carrying it (very dirty in terms of emissions).

In 1969 a new open chambered service head became available. It entered into regular production in 1971. This new open chambered design unshrouded the valves yielding nearly thirty additional horsepower in a high compression 427. That larger chamber unfortunately also decreased piston quench (used to mix fuel vapor and air before the point of ignition), which is why a SBC makes 1.5 HP per cube while a BBC is limited to 1.2 HP per cube with off the shelf parts. You can get three horsepower per inch in a "Big Bore" short stroke BBC with Pro Stock custom built Hemi heads for a 15:1 compression Pro Stock engine that Shifts at 10,500 RPM.

You want the smallest combustion chambered offered (which is why I choose an Edelbrock head over an AFR head even though without porting the AFR flows better). The Edelbrock head requires dedicated pistons to clear the smaller chamber if you are going to run a domed piston to raise the static compression (flat top piston has no worries). Chevrolet sources all of their Signature Series performance heads from Edelbrock as they are able to meet GM QC and follow Chevrolet engineering guidelines.

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post #5 of 6 (permalink) Old 06-28-2019, 10:58 AM Thread Starter
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Thanks for the summary. I'd really prefer to keep whatever pistons are in there when I get the heads off as the engine now has a grand total of 4000 miles on it. I'll be able to measure and cipher this winter.

1969 Imapala convertible build thread here:
https://www.pro-touring.com/threads/...ghlight=impala
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post #6 of 6 (permalink) Old 06-28-2019, 11:40 AM
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If it is a stock 454 out of a truck engine it will have 7.4:1 cast aluminum dished pistons, or a flat topped piston with 8.7:1 compression. You really want a 9.8:1 small domed forged piston to meet your horsepower requirements like one of these:

https://www.jepistons.com/Products/141634.aspx ,or these

https://www.summitracing.com/parts/s...make/chevrolet

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