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4 Posts
Discussion Starter #1
Hello All,
I am currently in the process of planning an engine build for a 1978 Pontiac Trans Am. This build will be for a street/strip application. The focus is on low-end RPM torque (as it should be :D). Trying to get all of the numbers to agree with each other so the engine doesn't self destruct. I have a few questions though. The design in its current state is as follows:

IA II Standard Deck Block
-Bore Diameter: 4.35"
-Main Journal: 3.00"
-Deck Height: 10.240"

Eagle Forged 4340 Steel Crankshafts 440043506800
-Stroke Distance: 4.35"
-Main Journal: 3.00"
-Rod Journal: 2.200"
-Material: 4340 Forged Steel

Eagle H-Beam Connecting Rods 66353D2000
-Length: 6.635"
-Rod Journal: 2.200"
-Pin Diameter: 0.990"
-Material: 4340 Forged Steel

Ross Racing Custom Piston Set
-Piston Diameter: 4.35"
-Compression Height: 1.430"
-Type: Reversed Dome
-Valve Reliefs: 2

Cometic MLS Head Gaskets C5846-040
-Compressed Thickness: 0.040"
-Gasket Bore Diameter: 4.380"

These parts lead to an engine with:
1:1 Bore to Stroke Ratio
1.52:1 Rod to Stroke Ratio
0.00" Deck Clearance
0.040" Quench Height
517.19ci (8.475L) Displacement

Here is the first actual question:
I have found conflicting answers to this online and need to know, is a bore-to-stroke ratio of 1:1 too low for a street/strip application?

On a side note, I am leaning towards using a rebuilt/strengthened TH200-4R transmission. Yes, this is all a little bit pricey, but I plan on stretching this out over time and enjoying it. Right now, I am having trouble deciding between two options for cylinder heads, and finding applicable camshaft. The two cylinder heads I am considering are the following:

Edelbrock Performer RPM Cylinder Heads 60539
-Chamber Volume: 72cc
-Chamber Shape: Heart
-Material: Aluminum
This leads to a Compression Ratio of 10.56

Edelbrock Performer RPM Cylinder Heads 60609
-Chamber Volume: 87cc
-Chamber Shape: Heart
-Material: Aluminum
This leads to a Compression Ratio of 9.42

Here is the first second question:
With a deck clearance of 0", aluminum heads with polished heart-shaped combustion chambers, reversed-dome pistons (instead of dished pistons so that the quench area is maintained) with two valve reliefs, and a gasket thickness of 0.040" for a proper quench distance, can this engine run 87 octane pump gas with a compression ratio of 10.56?

Here is the camshaft I have been considering:

Howards Cams 4/7 Swap Camshafts 414145-10
-Intake Duration @ .050: 219
-Exhaust Duration @ .050: 229
-Intake Valve Lift @ 1.6:1 Rocker Ratio: 0.560"
-Exhaust Valve Lift @ 1.6:1 Rocker Ratio: 0.555"

Here is the third actual question:
Is the above camshaft the best selection for a large displacement, low RPM, high torque, street/strip application as I have designed so far, and if not, what camshaft would you recommend instead?

Once all of this is sorted out, I'm hoping to start researching options for a proper intake, carburetor, and stall converter.


4 Posts
Discussion Starter #2
Bumping this.

Since I last posted, I've made changes to this design.

IA II engine block
4.4" bore
4.35" stroke
6.8" connecting rod
1.265" compression height
0.00" deck height
4.41" gasket diameter
0.040" compressed gasket thickness
0.040" quench height
529.2ci displacement
Ported aluminum heads
Polished heart-shaped chamber
Reversed-dome piston
1.01:1 bore/stroke ratio
1.56:1 rod/stroke ratio
9.6:1 - 10.7:1 compression ratio (depending on head and piston dish volume)
2.11" intake valve diameter
1.66" exhaust valve diameter
0.630" intake valve lift (1.8:1 rocker ratio)
0.520" exhaust valve lift (1.5:1 rocker ratio)
219 intake duration @ .050
229 exhaust duration @ .050
Hydraulic-roller camshaft
200-4R transmission
3.73:1 rear gear ratio
17" x 9" rear wheels
285/40/17 tires

I assume that 10.77:1 is too high for 87 octane. I can go with the 87 cc heads and then just reduce the amount of dish in the piston design as I'm going with Ross custom pistons. This will put me at around 10.0 - 10.3 CR.


1. Is an intake lift of 0.630" too much or too little? (The engine will have a displacement of 529.2, intake valve diameter of 2.11", and will need plenty of air/fuel mixture. This Wallace Racing calculator indicates I would need an intake lift of 0.750")

2. Is a stall of 1800 rpm a good choice? (The camshaft is rated for 1800 - 6000 rpm. I'm going for a street/strip build)

4,168 Posts
10.7:1 on 87 octane is a stretch in most every motor unless you have an extremely efficient chamber. I'm not familiar with yours, but are you really concerned about purchasing premium gas? Seems like quite a build to have a concern between 87 and 93 octane.

4 Posts
Discussion Starter #5
but are you really concerned about purchasing premium gas?
My main concern is that with the size of the engine, it'll be sucking large amounts of gasoline. I'm hoping to keep those costs down if I can, but if need be, I can buy the higher rating.

The chamber will be heart-shaped and polished. With the deck height at 0.00" and a quench of 0.040", I have a little leeway, I just wasn't sure where it would get too risky.
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