[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.

[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.

[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 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.

[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.

[TAQuest]

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

[STEELCITYFIREBIRD]

Edit, those are the performer RPM round port ex heads. You should have the 7157 (RA4) cam in it.

[Navy Horn 16]

Put premium gas in that thing and send it. I'll bet it hauls ass.

If you want to be on the safe side, go to the airport and get some 100LL and mix a few gallons into your premium.

[steve25]

Let me get this straight here, where talking about a 400 and not a 455?

There are several wild cards here, such as what Pistons, have the 72 cc heads been milled and what is the deck clearance, these all need to be answered.

If you do indeed have 215 psi then even with the Aluminum heads and 91 octane your gonna be close with having detonation or not and may need to step up to a bigger Cam.

[steve25]

Also that performer Intake is strangling those heads!

[STEELCITYFIREBIRD]

What is a "Super Muncie 4 Speed"...first gear ratio any how.... what ever it is?
Those birds are pretty light.
Look into the performer RPM top end kit for correct components.

[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.

[shaker455]

Originally Posted by 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!

No mention of pistons used but I don't think the CR is the culprit .
Most likely the cam is this deal.
cylinder pressure is too great and will detonate.
Suggest a more modern cam like Lunati VooDoo series...703 cam is a good place to start.

[STEELCITYFIREBIRD]

How is hood clearance on first gen birds with an RPM?

[Stan Weiss]

While it is old school I would look at an "068" installed on the factory ICL. While I am sure there are better more modern cams, they may need a change in springs or maybe have piston to valve clearance problems.

Stan