I'm helping someone with his engine project. Its a low mileage 1973 Cobra Jet short block, dished pistons, originally 8:1 compression. The engine looks fairly good, the owner doesn't want to rebuild the engine, just freshen it up with rings & bearings. He wants to keep the engine looking stock, but pep-up the engine via compression and the camshaft. My first advice was to install TRW flat top pistons, but he wants to use the original dished pistons if possible. His reason is the head and valve train upgrades are expensive enough, without spending extra money on pistons. So I came up with a strategy to work within his limits:

I thought you guys might be interested in this uncommon solution to pepping-up the 1973/1974 Cobra Jet.

He's gonna replace the OEM D3ZE open chamber heads with D1AE quench heads, and mill the D1AE heads about 0.012", to set the chambers at 64cc. This will increase the engine's compression to 9.3:1. Then he'll augment that with a custom camshaft. The cam closes the intake valve 10° earlier than the norm for my projects, at 60° ABDC. The engine will build 7.7:1 dynamic compression with only 9.3:1 static compression. That is the same dynamic compression as an engine with 10:1 static compression, closing the intake valve at 70° ABDC. The camshaft has the same duration specs as the Cobra jet Cam, but 110° LSA. It pushes the overlap to what I consider the limit (for a street engine), and it has a bunch of lift. The overlap is centered very well around TDC, I've explained the benefits of this in the past.

I design cams based on valve events. I seldom spec a cam with 110° LSA, but I know cams with narrow LSA are popular with folks due to the media. So I figured you'd at least be interested in the cam. Reminds me of the cam in the Chevy LS7 corvette engine. Like the title says, its not your grandfather's cobra jet camshaft.

Custom Ground Camshaft via Bullet Cams
Hydraulic roller tappet camshaft
For a Ford 351C street engine
Intake Lobe #HR270/3533 @ 105° mathematic ℄
Exhaust Lobe #HR291/356 @ 115° mathematic ℄
270°/291° duration at 0.006 (advertised)
216°/236° duration at 0.050
Hydraulic intensity = 54°/55°
0.611/0.616 theoretic valve lift (advertised)
0.603/0.607 net valve lift
LSA = 110°
The lobes are asymmetric,
“Max-lift” occurs before the lobes’ mathematic ℄
Seated valve events based upon advertised duration
EVO = 80.5° BBDC
IVO = 30° BTDC
Overlap = 60.5°
EVC = 30.5° ATDC
IVC = 60° ABDC **
**Maximum compression ratio 9.29:1
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Original Post
Sounds interesting George. I hope we get to see some dyno numbers once the engine is done. Thanks for sharing!

Originally posted by garth66:

... I hope we get to see some dyno numbers once the engine is done ...

The owner is doing the work himself, so the engine won't see an engine dyno. He has no plans to put the car on a chassis dyno either, at least not at this time.


Originally posted by ItalFord:

... So what do you think this engines HP and Torque will be ...

The intake valve is reaching max. open about 7° earlier than my typical camshaft. That's a very positive thing. But on the other hand the intake valve is closing 10° earlier than my typical camshaft, good for dynamic compression, not necessarily good for top-end power. Definitely no reversion issues Smiler . With 60° overlap the engine will have a nice Boss 351 kind of burble at idle. The engine should have great low rpm power.

The owner is doing his own head work. he's got them on the bench right now. I told him to blend the seats into the combustion chambers, clean up the valve pockets, round & blend the intake pocket throat without making it any larger. He purchased a set of Manley racing valves for the intake. Afterwards he'll get a 3 angle valve job. The engine is getting a new carburetor, the Duraspark distributor is getting rebuilt and re-curved. He's keeping the Edelbrock Performer intake for now, no budget for another intake, but I advised him to block the manifold's heat passage. If he does a good job with the rings I told him he should expect 425 bhp at the crank, 340 at the rear wheels. Sounds realistic doesn't it? Not bad considering the engine started life making about 260 bhp, the only big changes are compression, cam, and carburetor. Just unfettering the charging rhino.


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Last edited by George P

George, I have read a few posts on this site about cam selection, I am not going to attempt it on my own. How do we get started...you designing a camshaft for my specific project? Do we use this thread, or do I start another?

Cast iron 4V build.

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