[TAQuest]

I bought a 1967 Firebird 400 convertible out of an estate. The deceased owner had the drivetrain build mostly done. I finished the body and now I'm going to tune the engine for the street. I have a thick notebook of all the parts used.

It has a 1975 400 block.

Edelbrock 60599 Heads 72 cc

Edelbrock Cam
Duration at 0.006" Lift: Intake: 278° Exhaust: 288°
Duration at 0.050" Lift: Intake: 204° Exhaust: 214°
Lift at Cam: Intake: 0.280" Exhaust: 0.295"
Lift at Valve: Intake: 0.420" Exhaust: 0.442"
Timing at 0.050" lift: Open Close
Intake: 3° ATDC 27° ABDC
Exhaust: 42° BBDC 8° BTDC
Centerlines: Lobe Separation - 110° Intake Centerline - 105°


COMP Cams Aluminum Roller Rocker Arms

Rocker Arm Ratio:
1.5

Rocker Arm Style:
Full roller

Stud Size:
7/16 in.

Rocker Arm Material:
Aluminum

Slot Width (in):
0.562 in.

Maximum Spring Diameter (in):
1.500 in.

Rocker Arm Finish:
Red anodized



Edelbrock Performer Intake Manifold

Edelbrock 1411 Carb

Doug's Headers

Super Muncie 4 Speed

3:36 Rear Gears Posi

Funtional Ram Air

I just finished a compression test.

On both #1 and #2, cold and dry, 215 psi.

What can I expect for street performance?

What octane am I going to need to use?

Any suggestions on tuning are greatly appreciated.

Thanks!

[pastry_chef]

Cranking PSI is too high.
I'd swap the cam, intake and carb.

[TAQuest]

Originally Posted by pastry_chef

Cranking PSI is too high.
I'd swap the cam, intake and carb.

Thanks Chef.
I thought the pressure was high too. Had to get another gage just to make sure.
Is that about 11:1?
Must have been decked?
Why the cam, intake and carb swap?
What would you swap to?
Thanks again for your help.

[pastry_chef]

Originally Posted by TAQuest

Why the cam, intake and carb swap?
What would you swap to?

A larger cam will better use the heads and help manage your compression.
I'm partial to solid cams but for a hydraulic flat, maybe a Voodoo 703. Assuming you are around 400 cubes.
As Steve said, the Performer intake is limiting. RPM is much better.

[TAQuest]

Originally Posted by pastry_chef

A larger cam will better use the heads and help manage your compression.
I'm partial to solid cams but for a hydraulic flat, maybe a Voodoo 703. Assuming you are around 400 cubes.
As Steve said, the Performer intake is limiting. RPM is much better.

The cam swap sounds interesting. As Steelcity mentioned, the RPM might be a problem with clearance on the ram air.

I drove it last summer. It would pull good up until about 5000K and then it just runs out of pull. It's just not as quick and fast as it should be. All the parts in the build check out. Compression test shows good compression. I'm going to look a little closer at the timing and the distributor.

[wbnapier]

My cold and dry compression is between 185 and 215 on all 8 cylinders.

It is a 1970 455, #48 heads, and a '65 intake. Unknown bore, stroke, and cam, specs with timing at 12 initial and 32 total.

I need to run 91 octane with a 16 oz. bottle of boostane. Even with this, I may have issues on hot days. Without the boostane, the engine diesels when turned off.

[TAQuest]

Originally Posted by wbnapier

My cold and dry compression is between 185 and 215 on all 8 cylinders.

It is a 1970 455, #48 heads, and a '65 intake. Unknown bore, stroke, and cam, specs with timing at 12 initial and 32 total.

I need to run 91 octane with a 16 oz. bottle of boostane. Even with this, I may have issues on hot days. Without the boostane, the engine diesels when turned off.

So the 215 PSI is workable. Thanks.

[tom s]

My 455 with 48s and dished pistons for 9.5 CR and as I remember pumped 180s run fine on 91 at 36 degrees total.FWIW,Tom

[steve25]

The question comes down to does the block still have the 1975 stock Pistons with the chamfer around its OD, if it does then you will have no isuue with compression being too high as you will be lucky to have 9.2 to 1 .

[TAQuest]

Originally Posted by steve25

The question comes down to does the block still have the 1975 stock Pistons with the chamfer around its OD, if it does then you will have no isuue with compression being too high as you will be lucky to have 9.2 to 1 .

Thanks Steve.
The test showed 215 psi. Probably not 9:2:1 correct?
The receipts show that they used TRP forged pistons. Everything is new on this build, except the block.

[Stan Weiss]

My guess would be about 10.75:1 CR

Stan

[TAQuest]

Originally Posted by Stan Weiss

My guess would be about 10.75:1 CR

Stan

Great info. Thanks Stan.

[Stan Weiss]

Originally Posted by Stan Weiss

My guess would be about 10.75:1 CR

Stan

That was just a guess on my part, but why I said 10.75

Head Gasket Thickness = 0.028"

Head Gasket Bore = 4.160"

Combustion Chamber Volume = 72 cc's

Dome Volume = -7 cc's

Zero Deck

CR = 10.752

Stan

[TAQuest]

Originally Posted by Stan Weiss

That was just a guess on my part, but why I said 10.75

Head Gasket Thickness = 0.028"

Head Gasket Bore = 4.160"

Combustion Chamber Volume = 72 cc's

Dome Volume = -7 cc's

Zero Deck

CR = 10.752

Stan

Was this correct? With L2262FSTD pistons? With standard block?

[Stan Weiss]

That was just a guess on my part, but why I said 10.75

Head Gasket Thickness = 0.028" * * *

Head Gasket Bore = 4.160" * * *

Combustion Chamber Volume = 72 cc's

Dome Volume = -7 cc's

Zero Deck * * *

CR = 10.752 <<<<< This is just calculated from above

Stan

Originally Posted by TAQuest

Was this correct? With L2262FSTD pistons? With standard block?

These items were just guesses * * *. Would you have any idea what would be closer to the real numbers?

Stan

[TAQuest]

Originally Posted by Stan Weiss

These items were just guesses * * *. Would you have any idea what would be closer to the real numbers?

Stan

What if it was not decked, what would it be?

[TAQuest]

So it's set up like a ram air IV?

[STEELCITYFIREBIRD]

That cam is the Eddy Perfomer.
https://www.summitracing.com/parts/e...7/make/pontiac
Are you sure you have Full battery voltage to the Dizzy.
Appropriate spark plugs?

[STEELCITYFIREBIRD]

Originally Posted by STEELCITYFIREBIRD

That cam is the Eddy Perfomer.
https://www.summitracing.com/parts/e...7/make/pontiac
Are you sure you have Full battery voltage to the Dizzy.
Appropriate spark plugs?

.....Post #34

I'd keep total mechanical timing to 32 or less with that much cylinder pressure... till you sort out problem, less you create much a larger scale problem.

And check timing as Steve25 called out for , and at higher RPM.

Then unplug your tach recheck timing, they can cause odd problems if bad or incompatible with your dizzy.

A vacuum gauge can tell you a lot about the base engine. I'd expect it to be ~18-20+ at idle with that cam and CR..

Careful setting valves,push rod spin is an acquired feel, zero play is a good description.
Some pictures of your valvetrain, close up of valve end/retainers open and closed may show if there is some bad geometry or interference going on.

It's an ignition problem, my best guess with the info so far.

HTH

[Steve C.]

Originally Posted by steve25

"You do not have any issues to look for in regards to the springs on those heads limiting the motors rpm if it will rev passed 3200 out of gear so stop going back and bringing that up."

His current valve springs may not be the specific issue at hand in his situation but once he gets it all sorted out those cheap Edelbrock single coil springs set up 0.250" away from coil bind is NOT optimum ! That was the point. That said, with the tiny cam it will peak out at such a low rpm anyway so no big deal.

Onward.

EDIT: to add NOT optium



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