What Happens When..............

General engine tech -- Drag Racing to Circle Track

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vortecpro
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What Happens When..............

Post by vortecpro »

What happens to power when you build a engine with a factory GM cam. The engine: 427 BBC 9.8 compression, 4.350 X 3.766, RaceTec pistons with a 1.5 1.5 3.0 ring pack. Ported 820 GM oval port heads, 1.880/2.190 valves. Comp cams roller tip rockers, factory cast iron Q-Jet intake with a Q-Jet, 4 quart factory oil pan. Now heres the thing: I used the factory 396/350 HP 427/390 hyd cam, .461/.480/214/218/112 camshaft, why because I was curious and wanted a dead smooth idle. The oval port 427 was rated @ 390 HP in the Corvette with a factory rating of 10.25 compression, The question is: how much power will my 427 make with 9.8 comp and the factory 390 HP 427 hyd cam and ported heads? Pictures of the build to follow.

1. Do ported heads help when the cam is the cork?
2. Where will peak HP be made?
3. Is the factory 390 HP 427 HP rating correct?
4. I'am I wasting my time?
5. How good is the factory cast iron intake?
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PRH
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Re: What Happens When..............

Post by PRH »

If I’m not mistaken, the factory cam had a LSA of 115.

Will you be testing with the correct exhaust manifolds for a 390hp 427?
Somewhat handy with a die grinder.
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Re: What Happens When..............

Post by vortecpro »

You are absolutely correct, I had my cam grinder copy the factory cam on a 1960s cam core and I had him change LC to 112. I used 1970s NOS TRW hyd lifters. I did use 2 inch headers.
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Re: What Happens When..............

Post by BradH »

Not an apples-to-apples comparison, but it might give you an idea of what to expect:

Took a stock "rings & bearings" BBM '70 440 9.0 CR engine w/ a 6-bbl intake, factory stamped 1.5 rockers, 1.75" headers, and 222 @ .050" x .455" (1.5 rocker) on 112 LSA HFT cam

In my E-body Mopar weighing around 3700#s w/ driver it was a 13.2s @ 103 MPH car on sticky street tires

Swapped the stock '906' 2.08/1.74 heads for home-ported '452' 2.14/1.81 iron heads (later generation BBM passenger car heads) which had been milled a bit (probably about .5 CR increase) and put on Crane 1.6 iron rockers while the heads were being changed.

Next time at the track the weather may have been slightly better (figure early spring vs late fall for the previous tests), but the new heads & rockers combo picked up big time... 12.5s @ 109 MPH w/ the rest of the car being the same. Yeah, I was "pleasantly surprised" at that much of an improvement for just those two mods. Oh, it didn't idle totally smooth, but didn't have an excessive lope, either.

So, even w/ the small cam, I still believe there's the potential for noticeable improvements w/ your build.
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mt-engines
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Re: What Happens When..............

Post by mt-engines »

Those 3993820 heads are some killer stock heads when done up.
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Re: What Happens When..............

Post by n2omike »

Those extra wide lobe separations (minimal overlap) worked well with the incredibly restrictive exhaust manifolds, small exhaust systems and restrictive mufflers of the time. Running very much overlap without an extremely free flowing exhaust absolutely kills power, as instead of good VE, all you get is reversion.
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Re: What Happens When..............

Post by F-BIRD'88 »

Also worked well for the engine purpose which will run at part throttle (and less), Most Of The Time.
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Re: What Happens When..............

Post by vortecpro »

BradH wrote: Wed May 12, 2021 11:40 am Not an apples-to-apples comparison, but it might give you an idea of what to expect:

Took a stock "rings & bearings" BBM '70 440 9.0 CR engine w/ a 6-bbl intake, factory stamped 1.5 rockers, 1.75" headers, and 222 @ .050" x .455" (1.5 rocker) on 112 LSA HFT cam

In my E-body Mopar weighing around 3700#s w/ driver it was a 13.2s @ 103 MPH car on sticky street tires

Swapped the stock '906' 2.08/1.74 heads for home-ported '452' 2.14/1.81 iron heads (later generation BBM passenger car heads) which had been milled a bit (probably about .5 CR increase) and put on Crane 1.6 iron rockers while the heads were being changed.

Next time at the track the weather may have been slightly better (figure early spring vs late fall for the previous tests), but the new heads & rockers combo picked up big time... 12.5s @ 109 MPH w/ the rest of the car being the same. Yeah, I was "pleasantly surprised" at that much of an improvement for just those two mods. Oh, it didn't idle totally smooth, but didn't have an excessive lope, either.

So, even w/ the small cam, I still believe there's the potential for noticeable improvements w/ your build.
Excellent post, I think your right. Did I mention the engine will be drag tested in my Chevelle!
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vortecpro
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Re: What Happens When..............

Post by vortecpro »

Some pictures of my build.......
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Re: What Happens When..............

Post by 1980RS »

BradH wrote: Wed May 12, 2021 11:40 am Not an apples-to-apples comparison, but it might give you an idea of what to expect:

Took a stock "rings & bearings" BBM '70 440 9.0 CR engine w/ a 6-bbl intake, factory stamped 1.5 rockers, 1.75" headers, and 222 @ .050" x .455" (1.5 rocker) on 112 LSA HFT cam

In my E-body Mopar weighing around 3700#s w/ driver it was a 13.2s @ 103 MPH car on sticky street tires

Swapped the stock '906' 2.08/1.74 heads for home-ported '452' 2.14/1.81 iron heads (later generation BBM passenger car heads) which had been milled a bit (probably about .5 CR increase) and put on Crane 1.6 iron rockers while the heads were being changed.

Next time at the track the weather may have been slightly better (figure early spring vs late fall for the previous tests), but the new heads & rockers combo picked up big time... 12.5s @ 109 MPH w/ the rest of the car being the same. Yeah, I was "pleasantly surprised" at that much of an improvement for just those two mods. Oh, it didn't idle totally smooth, but didn't have an excessive lope, either.

So, even w/ the small cam, I still believe there's the potential for noticeable improvements w/ your build.
The same thing happened with my 406 last year switching Vortec heads. Mind blowing isn't it.
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Re: What Happens When..............

Post by BradH »

My car had 3.55s and a 2200-stall converter at the time.

Pre parts swap it started falling on its face by 5500; the new heads also had stiffer springs and the engine pulled a few hundred RPM higher after the switch.
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Re: What Happens When..............

Post by rustbucket79 »

Love the idea of the build, expect disappointment from the cam.

I won’t bore you with my story of a personal 350 build decades ago so here is the abridged version.

274 @ .050 cam lost a lobe, but before that the car was a blast to drive. Replace with 1st (maybe 2nd design, who remembers) GM off-road cam, on paper it should have better manners. The car felt like it lost 50 to 75 HP, and it no longer had traction problems pulling away from a stoplight. #-o
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Re: What Happens When..............

Post by F-BIRD'88 »

GM should have made that oval port hi-rise intake in aluminum. I had the 454 cid version of your 427.
1970 LS5 454/390 hp 10.25:1 cr and that same cam.
Came factory in 1970 Canadian built big Pontiacs here.
You could get the 454 or 396 or a 350 sbc. The Pontiac Safari wagon here was a Chev Kingswood Estate wagon in Pontiac sheet metal.. Chev frame all chev drivetrain including HD chev 12 bolt posi rear.
I upgraded it with a GM LS6 "143" 454-450 hp solid cam and valve springs. Headers etc.. Big difference but the stock LS5 454 ran good.
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Re: What Happens When..............

Post by vortecpro »

What do think this will run in my Chevelle?
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Re: What Happens When..............

Post by 1980RS »

vortecpro wrote: Thu May 13, 2021 7:26 am What do think this will run in my Chevelle?
10.93@119mph
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