Author Topic: Preformer rpm  (Read 805 times)

Offline old cars

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Re: Preformer rpm
« Reply #15 on: December 31, 2020, 12:47:18 PM »
Yes an under square engine compared to a 454 BBC. Different needs. Thanks for filling in the blanks.

Offline Cliff Ruggles

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Re: Preformer rpm
« Reply #16 on: December 31, 2020, 01:12:25 PM »
You are most welcome.

I'd also add that Pontiac cylinder heads used machined flat combustion chambers with 30 degree intake seats (with few exceptions) designed to enhance low lift and longer seat timing plus wide LSA.  The cams for them were no more than .406" lift with the exception of the RAII/RAIV camshaft which was only .470".

As crappy as all that is they will run pretty good if you know how to exploit their best attributes........FWIW.....


Offline Kenth

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Re: Preformer rpm
« Reply #17 on: January 01, 2021, 03:30:24 AM »
RAIV was .516" due to usage of 1.65:1 rockers for this engine.

Offline 68rs/ss

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Re: Preformer rpm
« Reply #18 on: January 01, 2021, 05:16:01 PM »
Interesting to hear how much power power was found by one part change. I know you had helped me with my 355sbc q-jet rebuild & tuning. Used your cam suggestion over my Extreme energy choice and made huge improvements in tuning, power, drivability and mileage.
Building a 396 and will be calling soon for rebuild kit and guidance on Q-jet for it. I'll run my cam choice by ya too for a educated opinion.  :)
Have a Happy (and better than last) New Year.
Phil

Offline Cliff Ruggles

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Re: Preformer rpm
« Reply #19 on: January 04, 2021, 02:25:15 AM »
LOTS of opinions when it comes to camshafts.

I'm going to be one of the very few who has actually rented the dyno time and back to back tested multiple cams to see how these things really work.

I've also advanced and retarded cams then street and track tested after each movement. 

Plus I tune for a living and get to see all sorts of troubled engine combinations brought here that need help. 

As mentioned earlier the WORST cam you will ever put in a big CID engine is short seat timing and tight LSA.  I could write a couple hundred pages here with details and specifics related to that topic, but it sort of goes against the grain and too many folks who are disciples of some of the famous "guru's" in this hobby get their panties all wadded up about it.

Just like the dyno sheet I put up earlier here.  We made ONLY a cam change, the engine was on the dyno and pinged hard enough with the small cam on a tight LSA to require rod bearing replacement.  With the larger cam it idled better, improved throttle response, and WAY more power across a much broader RPM range.

Sadly this sort of information just goes on deaf ears as folks get pretty set in their ways and refuse to see the forest for the trees.

What also adds to the confusing with these things is miss-information on the Boards.  The biggest myth in the hobby these days is LOWERING compression to 9.5 (or less) for pump gas.  Not sure who came up with that nonsense but for sure stuffing a small cam in there on a really tight LSA with early intake closing is NOT going to bring back all the lost power nor will it necessarily make that engine pump gas friendly. 

I custom tune on weekends, have now for nearly 20 years.  I get a LOT of those engines brought here where the customer, all his friends, beer drinking buddies, local shops and all the "guru's" in his area have taken a stab at fixing it with no success.

To date the record for longest distance a vehicle has been brought here to custom tune and correct running issues with is 1800 miles one way!  Most come in from 200 miles or less.  Believe it or not the customer who brought his vehicle here 1800 miles needed a $30 part to fix his issues!  I also went back thru everything in his carb and distributor as too many hands had been in that stuff, but the MAIN culprit as a simple part that took less than 2 minutes to install!

Remarkably most vehicles brought here to tune are fixed by going into the distributor before I even touch the carburetor.  I've come to LOVE these cheap POS advance weight/spring kits.  Absolute and total JUNK and cause WAY more running issues and poor end results with these engines than any other reason.  99 percent of the HEI "clones" and aftermarket "bug zapping" distributors aren't making the grade either and I've seen enough of these points eliminating modules throwing a monkey wrench into the deal to avoid them completely, but all that stuff is stories for another day........Cliff