SBC Mayhem Heads: Straub’s 18° Double Hump Revival
Most cylinder head sales these days come down to a price tag and a shipping ETA. Straub Technologies does not work that way, and the SBC Mayhem heads are a good example of why. Chris Straub has spent 25 years in the performance industry, and his approach starts with knowing what the engine is doing, what the car is for, and what RPM the build will live at before he quotes a part. We spent over an hour with him on the phone, and the conversation went well past the head itself.
This is not a head you bolt on because a spreadsheet told you to. This is a head you build a small block around because you grew up looking at Hot Rod Magazine covers of 461 castings on engine stands, and somewhere along the line, you decided you wanted in on that lineage.
Why The Double Hump Still Matters
The 461 and 462 castings, what most guys just call the fuelie heads or the double humps, sat at the center of small-block Chevy performance for decades. Every cruise night had at least one car running them. Pop a hood at a 70s or 80s street race, and you were probably looking at a set of double humps, shaved a few thousandths, with the obligatory 2.02 intake and 1.60 exhaust swapped in.
Chris said it best when we asked him about that legacy. “When you ask a Chevy guy about his SBC, 8 out of 10 will start with, ‘Well, it had a set of double humps, shaved, and with 2.02 and 1.60.'” That is not nostalgia talking. That is a generation of builders whose identity in this hobby was tied to a specific cylinder head silhouette.
So, when Straub set out to build a real modern 18° head, the decision to wear the double hump on the casting was not a marketing decision. It was respect. “Taking from this heritage, I had our 18° cast with the Camel Humps to bring around the next revolution of SB dominance,” Chris told us.
What The 18° Valve Angle Actually Does
Stock SBC heads run a 23° valve angle. The Mayhem drops the valves to 18° and shifts them to a 40/60 location in the chamber. On paper, that reads like a small change. In the cylinder, it rewrites how air gets where it needs to go.
Tilting the valves toward vertical unshrouds the intake side. The cylinder wall stops blocking airflow as the valve cracks open. So instead of the port curving down toward a steeply angled seat, the air takes a straighter shot at the chamber. More CFM at every lift point, better swirl, less flow separation. The chamber fills the way you want it to, not the way mass production used to dictate.
Bigger valves come with the territory. The Mayhem ships with a 2.15″ intake and 1.60″ exhaust, both larger than what a stock 23° head can swallow without serious bowl work. Chris broke it down for us on why valve size scales with RPM: “As demand, piston speed, goes up, the larger the valve you need. For example, a 4.155 by 4-inch stroke SBC 434 to make peak power at 7000 RPM needs a 2.125-inch intake valve.” The Mayhem sits past that mark right out of the box.
How Do The SBC Mayhem Heads Flow?
Numbers tell part of the story. As-cast, the 237cc Mayhem 18X starts at 140 CFM on the intake at .200 lift and climbs from there. By .400 lift, the intake pulls 258 CFM, and at .500 it jumps to 297. The port keeps gaining all the way through .800 lift, where it reaches 330 CFM. The exhaust follows the same pattern, from 116 CFM at .200 up through 247 CFM at .800.
Step up to the CNC ported version with the 265cc intake runner, and the curve climbs higher. Intake flow hits 349 CFM at .900 lift, while the exhaust pulls 264 CFM. For context, a well-ported 23° head with a comparable runner volume can hang at peak. While it might match the number on the bench, it loses ground in the mid-lift range where street engines actually live. That mid-lift advantage is what makes the Mayhem feel awake under a real street cam.
Hydraulic Roller Or Solid Roller: Where Is The Line?
Straub sells the Mayhem as a complete package, and the hardware decision came across as a builder conversation rather than a sales pitch. Chris told us exactly where each version belongs.
The hydraulic roller version runs the Morel street lifter. Chris was direct about the ceiling: “The hydraulic roller package uses the Morel street lifter, which is limited to a max of .375-inch lobe lift or .600-inch valve lift.” For a street 427 spinning to 6,500 RPM, that limit is not really a limit. It is the right answer. Daily drivers, weekend cruisers, and the guys who hit a few track days a year all live happily under .600 lift.
The solid roller is for the guy who wants to feed the head everything it can take. Once you start asking for valve lift past .600 to fully open those 2.15″ intakes, the hydraulic platform runs out of road. Chris put it the way only a head guy can: “Since lift is the ability to make HP, as RPM goes up, you’re going to need more lift. Here is where the solid roller package gives the customer the power he wants.”
So the line is real. While a stout street car living under 6,500 RPM leaves nothing on the table with the hydraulic setup, the build that sees the far side of 7,000 RPM regularly is the one that earns its keep on the solid roller side.
What Short Block Works With The SBC Mayhem Heads?
The Mayhem 18X is built around a 4.060″ minimum bore, which puts the entry-level combo right around 400 cubic inches and scales up from there. Chris walked us through the RPM windows by stroke. A 3.875″ or 4″ stroke combination supports street use to 6,500 RPM, as-cast. Drop down to a 3.75″ stroke and the head will hang in to 7,300 RPM. Go full racer with a 3.48″ stroke inside a 4.155″ bore for a 377-inch screamer, and the head will support that combination to 8,200 RPM.
That spread is what makes the SBC Mayhem heads such a flexible piece. The same casting feeds a torque-monster 427 street car and a high-revving 377 race build, because Chris and his team sized the port for airflow demand across the whole window. The 3.48″ stroke combination is the modern version of what the original Chevy 302 SBC was doing back in the day. Smaller displacement, more RPM, more head than the cubes really need on paper.
Rocker Arms, Manifolds, And A Sleeper Build Worth Thinking About
Harland Sharp builds the rockers for the Mayhem package with a proprietary geometry that accounts for the longer valves. The order sheet calls for four of each offset rocker on the intake side and eight on-center rockers for the exhaust. Part numbers are 11600-150R, 11600-150L, and 11600-1. We have written about PROFORM rocker arms for small block Chevys before, and the geometry conversation lines up directly with what Straub did here.
For induction, the package ships with a two-piece single plane manifold that takes either a 4150 or 4500 series carb. We asked about a dual plane option. Chris was direct: “With a head like this, it is designed to make HP, which requires a single plane.”
Header fitment is where Chris dropped one of our favorite lines of the conversation. The head uses a standard 23° header bolt pattern, so stock GM or Stahl-style headers both bolt on without drama. While we were talking through exhaust options, Chris hit us with this: “Hell, for the ultimate sleeper, a set of ported ram horn manifolds could be used for the stock-appearing look.” A 427 cubic inch small block flowing 330 CFM through a set of 18° heads, hiding under a pair of factory cast iron manifolds.
The Kind Of Guy Behind The Head
We spent real time talking about the industry, not just the heads. Chris told us straight up that he will point a customer toward another manufacturer if he thinks it fits the build better. Straub’s whole approach is to keep pricing where real builders can reach it and to give people honest answers, even when the honest answer is “this is not the right head for your combo.”
When we asked who carried the Mayhem project from concept through casting and dyno validation, Chris did not single himself out. “It takes a great team, and this head has been a team effort from development to marketing. Everyone at Straub is responsible.” Cylinder head shops are not always team-first operations, but the ones that are tend to build product you can trust.
Who Should Run The Mayhem 18X?
That means 400 cubic inches or larger with serious cam and intake plans, a builder who wants real cylinder head airflow without paying full custom-shop money, and an owner who appreciates that the casting wears the same silhouette that built small block Chevy’s reputation in the first place.
If your build is going to live under 6,500 RPM on a stock-style 350, this is more head than the combination needs. If your build is pushing past 600 horsepower on a 4.060 bore or larger, the Mayhem gives you flow numbers, valve sizing, and an RPM ceiling that most off-the-shelf small block heads cannot match. Chris kept the heritage front and center on this one without giving up the engineering behind it.
The double hump never really left this hobby. With the Mayhem 18X, it just got an 18° valve angle, a serious port, and a flow bench’s worth of homework behind it. For the full spec sheet and ordering, head over to the Mayhem head package page at Straub Technologies. If you want the conversation that goes with it, give Chris a call.
