35 Cafe Racer w 502's - which heads to go with?
 

Hi everyone,

I have been a silent reader and admirer of the knowledge in this forum for quite some time. Greetings from Germany!

I bought my 1987 Cigarette Cafe Racer 35 a few years ago (it already had the Gen V/VI 502s) and restored it to my liking. After three seasons of having a blast with it, one of the roller rockers failed. That was the trigger to pull the valve covers and dig deeper.
Upon inspection, we found that the issue went deeper: the stock iron heads were completely worn out (valve guides/seats are done).

So, instead of just fixing the broken rocker and sinking money into refurbishing the old iron, I figured this is the right time to let the project "snowball" a bit and upgrade to aluminum heads to save ~200 lbs off the stern and pick up efficiency. I reached a decision point regarding the new setup and could really use a "sanity check" from the OSO experts.

The Boat Setup:

• Hull: 1987 Cigarette Cafe Racer 35.
• Drives: Converted from old TRS to sturdy Mercury Racing XR drives.
• Balance: We structurally modified the engine compartment and moved the engines forward to optimize the center of gravity (CG).
• Cooling: Full 2-circuit closed cooling system (antifreeze in block & heads).
• Use Case: Typical offshore chop, cruising 3500-4000, WOT blasts limited to ~5200-5400 RPM.

(See attached pictures of the boat below)

The Proposed "High-Torque" Recipe – Do you agree?
My goal is a rock-solid 550 HP per side with massive low/mid-range torque to get this heavy girl out of the hole.

1. Cylinder Heads: The "AFR vs. Edelbrock" Decision
I spent a lot of time debating between AFR Heads and the Edelbrock Marine RPM #61459.

• The Dilemma: I know the AFRs are the flow kings with their CNC porting. Under normal circumstances, they would be the undisputed choice.
• Why I lean towards Edelbrock: My decision came down to the combustion chamber size. The Edelbrocks come with 110cc chambers, whereas most OTS AFRs or stock replacements are ~118cc.
• My Theory: Using the 110cc heads allows me to bump my compression from a lazy ~8.75:1 to a crisp 9.5:1 utilizing my existing pistons. I believe that for my heavy hull and RPM limit (<5500), the gains in thermal efficiency and torque from the compression bump outweigh the superior high-rpm flow numbers of the AFR heads.
• Plan: I am buying them as BARE castings and having my local engine builder install Edelbrock Inconel exhaust valves (#9744) and quality stainless intakes to ensure they survive the marine duty cycle.

2. Valvetrain:

• Cam: Custom Hydraulic Roller (specs roughly similar to a Voodoo marine grind).
• Springs: Howards Cams Dual Springs (140lbs seat pressure) – custom fitted to the specialized heads.
• Rockers: Harland Sharp Rollers.

3. Intake Manifold:

• Edelbrock RPM Air-Gap #7561 (Oval Port).
• Since I run closed cooling, the automotive Air-Gap should survive the bilge environment just fine while keeping the charge cool.

My Questions to you:

1. Sanity Check: Does my logic on choosing the 110cc Edelbrocks (Compression) over the AFRs (Flow) hold up for a heavy offshore boat application?
2. Oval Ports: Am I right in assuming that for a <5500 RPM setup, the velocity of the Oval Ports will beat the Rectangular Ports in real-world drivability and hole shot?
3. Prop Selection: With the engines moved forward and the added power, I expect to need more bow lift. I was thinking of starting testing with Bravo 1 FS props. Any other recommendations (Maximus / Hydromotive Quad IV) known to work well on a Cafe Racer with this balance?

Thanks a lot for reading and for your input!

Stefan
https://cimg0.ibsrv.net/gimg/www.off...6af1d000c0.jpg
https://cimg1.ibsrv.net/gimg/www.off...4a2ce1ea6c.jpg
https://cimg2.ibsrv.net/gimg/www.off...27c4234705.jpg
https://cimg3.ibsrv.net/gimg/www.off...8da00735c1.jpg
https://cimg6.ibsrv.net/gimg/www.off...7e2d92eed0.jpg
https://cimg8.ibsrv.net/gimg/www.off...d03cb96e2f.jpg
https://cimg1.ibsrv.net/gimg/www.off...07038a924b.jpg
https://cimg4.ibsrv.net/gimg/www.off...55f7f7d178.jpg

Nice job on the restoration! It sounds like you’re on the right track with the motor upgrades🍻

Nice clean Cig.

A couple thoughts.

You started the whole project bevaise of a broken rolloer rocker. (Curious what brand/model?) Going with a better quality rocker would be advisable. What is the over the nose spring pressures? Roughly what are the cam details? Lots of marine Voodoo grinds.

AFR has BBC heads with smaller chambers. Flotek and Promaxx also have their 290cc int runner heads with 110cc chambers. Flotek heads come with powdered seats. These would be great for a marine app...vs the hard ductile iron seats in AFRs etc.

TRS drive setup...you had the Merctrans or Borg Warner Trans? When re-fit with Bravos, you kept the engines in the same location?? Or now moving them forward with the re-power?

The Flotek heads can be had bare. I would suggest Ferrea Extreme Duty exh valves. Their version of inconel.

Either way, you may need to get rockers that minimize your roller contact on the stem.

Edelbrock heads have never been 'perfromers' compared to far better options.

On your oval port thoughts...yes...marine 454s and a bit larger make up to 585hp with Peanut Port Iron heads around 5800 rpm. The velocity in tje ports would be up there. I measure my PP heads at 208cc intakes.

The rec port GM heads on Marine at 454 are very lazy dogs. Certainly at your proposed RPM.

keep in mind that most if not all after market aluminum heads have raised exhaust ports and can cause exhaust alignment issues.........nice resto

agree, the big clunky Gil exhaust might hit each other with raised exhaust ports.

brodix racerite cylinder heads have standard height exhaust ports . FYI

as far as i'm informed, the edelbrocks don't have raised ports, so this might be another point for them.

the big question remains - better flow or higher compression? I haven't found any afr/brodix/... heads for the 502 so far, which have 110cc.

https://www.airflowresearch.com/265c...nder-head/p603

109 to 112. The 265, 290 and 300 are all in that range and can be flat milled or angle milled to reduce further.

What gasket thickness and quench height did you use to calculate?

This 298cc 2.3” valve Brodix head would be my favorite option for a 502. It’s got a 115cc chamber though. So it would have to be flat milled around .0250in. You’ll also need to pay attention to piston to valve clearance, most modern bbc heads are 24* now instead of 26* of the original.

• Angle Milling:
.0066 in Per cc

• Flat Milling:
.0050 in Per cc
https://cimg5.ibsrv.net/gimg/www.off...80e53540fe.png

https://brodix.com/heads-2/big-block...block-series24

They also sell 26* bb2 heads. And they are usually cheaper. On a 502 a 270-300cc runner will be the best all around performer for torque.

I think targeting compression ratio and quench first is a good idea. It’s worth at least 4% more power guaranteed. All of the aftermarket heads will flow enough to make 600hp or more with a healthy cam.

If you only want 550hp and the most torque, get the compression ratio as high as you’re comfortable with, run a 265-270cc runner head, and keep the cam LSA tight, like 110 degrees. The performer rpm manifold is perfect.

https://www.airflowresearch.com/290c...nder-head/p598

AFR 290s have 112cc chambers.

The 3/8" raised exh ports...raise them at a 45° angle when mounted on the block.

265cc BBC heads would be a great choice too.

Why were those gigantic holes cut in the transom