BUILDING our Hemi six has turned out to be a bigger job than we thought. Initially it was just supposed to be a re-sleeve and slap-together job to repower my Valiant wagon, but like any build, it’s easy for things to get out of hand.
So we’ve sleeved our block, and then bored, honed and aligned it. In part three we ported the head and gave it some shiny new Ferrea valves. Now it’s time to finish throwing it all together and see how it goes on the dyno.
We finished off our Hemi’s cast-iron head by kitting it out with beehive valve springs and retainers from our friends at Crow Cams, shaving the rocker pedestals down a tad to suit the ARP rocker studs, and fitting a set of Comp Cams 1.72-ratio roller-tipped rockers. We could have gone full roller rockers at four times the cost, but these Comp Cams units are tough, and at just over $200, they’re cheap.
The balancing and machining was handled way back in part two, which made slotting it all together child’s play.
There’s nothing exotic in the bottom end at all. The crank and rods are standard, and they’re held in place with ARP bolts from Precision International, from whom we also sourced the 40thou-oversize cast pistons. The block and head were decked significantly to yield 10.6:1 compression, and the head was given a tickle to help it flow a bit better. With a custom Crow Cam hydraulic bumpstick slid inside, and the sump, sideplate and rocker cover bolted on, she was almost ready to hit the dyno.
The finishing touches were a set of Pacemaker headers, a Redline 4bbl intake and a 470 Holley from Automotive Performance Distributors. But it wasn’t all smooth sailing; check out the captions to see what we went through.
With the bare block all machined and ready Johnny starts with the bearings and rear main seal. Getting the rope rear main seal seated correctly is a time-consuming task, but necessary. Johnny likes them tight enough that you can’t turn the crank by hand
When we started our aim was to hit 300hp with a hydraulic cam and a single 4bbl carby, and with a bit of trial and error we hit that mark. Our best was 305.5hp at 5400rpm and 323.4lb-ft at 4800rpm, with over 300lb-ft available from 3700rpm to 5300rpm. She’s a torque monster!
So that’s it for our Hemi six; we’ve done what we set out to do: rescued a block headed for the junkyard and turned it into something worthy. Now it’s time to drop it into my VG Valiant wagon and get ready for some summer cruising. We might even hit the strip for a bit of fun, just to see what it’ll run.
In the engine room Johnny assembles the bottom end while his son Jay looks on. He like to use the Warren and Brown deflecting beam toque wrench for his engine builds
Ignore the degree wheel – Crow Cams ground us up a custom hydraulic bumpstick with 233@.050 duration and 0.599in lift
We also used Crow Cams lifters, timing chain, valve springs, retainers, locks and pushrods
To tighten up rod bolts properly, you don’t rely on torque figures. Rod-bolt stretch is the way to go; this gives the bolt the correct clamping force. For our bolts ARP recommends 0.006 to 0.0065in stretch
If Hemi sixes have a weak link, it’s the oil pump. The boys rebuilt the stock pump using a JP kit and pressed on the Crow Cams-supplied oil pump gear
Hemi sixes can have either of two different oil pump gears, and most cam-grinders will supply the right gear to suit the cam they just sold you. The new gear is simply pressed into place
After the oil pump and pick-up were fitted it was time to seal it all up. A little extra care spent here can save you a lot of drama down the track; nobody likes a weeping motor
To get 10.6:1 compression, Johnny set the Hemi up so the pistons were sitting 0.010thou above deck-height at TDC. More compression means more power, but we’ll need to run our Hemi on 98-octane to prevent detonation
The rocker posts were machined down 0.320in to suit a set of ARP 7/16in screw-in studs. All our ARP bolts came from Precision International; they carry a full range of ARP fasteners
Shaving the angled rocker pedestals down meant the mounting holes in the factory guideplates needed to be opened up, as they were now closer together. Changing just one thing in an engine can have an effect on many others
It was so cold the day we painted the Hemi that the boys stoked up the wood-fire to help the paint dry. We went for Hemi Orange on our six-pot rather than the factory blue hue that most of them left the factory with
The last piece of the puzzle before the rocker cover went on was the Comp Cams rockers. Normally for big-block Chevs, these 1.72:1 rockers are a good fit with the ARP studs, Ferrea valves and Crow Cams valve springs
Johnny uses Brad Penn ‘break-in’ oil for all the engines on the dyno, and after seeing it in action we reckon it’s pretty good too. With extra zinc, it’s got all the stuff that new engines need
First time on the dyno for our Hemi six. We went with the Redline 4bbl intake, a 470cfm vacuum-secondary Holley and Pacemaker extractors, in the interests of streetability. The Redline air filter is a nice finishing touch
Automotive Performance Distributors get these 470cfm Holleys made specifically for the Australian market. They feature a single fuel inlet and quick-change vacuum springs, as well as a secondary metering block for easy jet changes. Perfect for Ford, Holden and Chrysler sixes and small-cube V8s
Pacemaker headers come in three pieces, which makes them lots of fun to fit, and they come with this Y-piece. The headers are great, but we discovered the Y-piece choked the exhaust and cost us 10hp – we threw it away
With the Redline intake the engine made excellent low-down torque, especially below 3500rpm, but seemed to nose over at 4200rpm
We found the Redline 4bbl intake liked a 2in spacer, and the best we saw with the 470cfm Holley was 271hp at 5400rpm and 307lb-ft at 4100rpm
If you’re going to find a problem, it’s better to find it on the dyno rather than the car. Water in the oil is never a good sign - we discovered our mildly ported head had some porosity issues
The boys pressure-tested the head and found a couple of the head bolt recesses were leaking water. Rather than starting again from scratch, they machined the offending area and sealed the leak by pressed in some custom inserts (along with high-grade sealant) – problem solved
When the Hemi went back together we elected to use head studs rather than the old head bolts; just an extra piece of insurance. This was the only change to the core engine from the initial build
The engine was pulled down and cleaned out while the boys sealed the head. Although we didn’t originally plan to do it, we had so many requests from readers to test the Aussiespeed AS0265 4bbl intake we just had to try it
The Aussiespeed intake uses slightly longer runners and a divided plenum when compared to the Redline intake
Side-by-side the Redline is a smoother-looking casting and bolts straight on, while the Aussiespeed intake required some grinding to fit
With the Aussiespeed AS0265 we ran through all the combos, and with the same carby and two-inch spacer combo as the Redline intake it made 286hp at 5400rpm. Then we stepped it up with a 650DP Holley, and after jetting changes it made 296hp at 5600rpm and 313lb-ft at 4600rpm
Every manifold combo we tested seemed to like a two-inch spacer, so we tried a few different types, and believe it or not the basic open spacer on the left made the best power on our Hemi six set-up
Dyno testing is a long and laborious process, but Johnny loves it. He’s there at all hours testing new combos and builds everything from 80-year-old flathead four-pots through to 1800hp blown methanol monsters
After hitting 296hp with the AS0265, Aussiespeed sent out the latest version of their long-runner intake
The long runner intake is still under development, but the longer intake runners seemed to work well, especially with the flat inset bolted into the plenum
Best run overall was 305.5hp and 323.4lb-ft with the long-runner intake, but the hollow at the top of the curve shows there’s still more work to be done. We reckon the finished product will be a screamer
Here's the three best runs from each intake. Being such a long engine it’s really hard to get an even fuel/air distribution across the ports. The Redline intake showed some distribution issues, so we didn’t run the 650DP on it, but even with the little 470cfm Holley it still managed to show 271hp and good low-down torque, which would make it an excellent street intake. All things being equal, the Aussiespeed AS0265 showed an extra 15hp over the Redline, with the 650DP yielding an extra 10hp again to show a total of 296hp and a long, flat torque curve. But to get over the 300hp mark we had to try the Aussiespeed long-runner intake. It also showed some distribution issues (exactly opposite to those in the Redline), but you can’t argue with the power. To show the true horsepower potential of this motor we could have tried a set of triple Webers, but they were way outside our budget for this engine.
We would like to thank the following businesses for helping this engine come together, with particular attention to the team at Powerhouse Engines (Johnny, Brian, Chook & Trev). We would use and recommend all of these businesses again.
Automotive Performance Distributors (APD)
Victorian Performance Wholesale (VPW)