The latest and greatest Can-Am car and how Denny Hulme drove it at Mosport.
By Pete Lyons
“Balance,” states Professor Hulme, thumbs tucked comfortably in his Nomex suspenders, “the whole theory of race cars is balance. That’s all there is to it.”
He’s just in from practising Mosport laps. His new Can-Am car, in its first weekend at the front lines, has not been behaving well. The official qualifying times show the Scot Stewart is quicker, but now Denny is confident of holding him off in the race. The McLaren’s tail had been loose, but now he’s put a set of older, inferior tires on the front. Not a sophisticated solution, but it works. Balance.
Out in the sunlit paddock the Kiwis have pushed the long M8F into their roped-off bay and stripped off its bright ochre panels. Its bare metal structure seems a familiar sight. It looks like Lothar Motschenbacher’s ex-factory M8D a few bays away, and really it looks like Roger McCaig’s brand new M8E across the path. The F is in fact a direct progression of the M8 series that have served so well these three years past. Back in the Colnbrook drawing office, we know from the stimulating new USAC and Formula 1 cars, there are plenty of fresh ideas. There are plans for a new Can-Am car which, if built, will be the M20. But probably the F is going to be enough change for this year.
First, the basic car is longer. Three inches have been added to the middle of the tub and now the wheelbase is 98 in., which should have the effect of shifting a fraction of the weight aft and improving braking stability. But the track, which last year went wider in contravention of long-standing McLaren thinking, is narrower again; 60 in. front, 58.8 rear. The suspension geometries are altered, giving modified camber-change curves at both ends and a bit more anti-squat at the rear. The front upright castings are straight off the Indy car and give slightly different geometry as well as being much more rigid. The weight of the rear brakes has been moved inboard next to the transaxle; the intrusion of the l2-in. discs here has forced replacement of the accustomed reversed A-arms with Surtees-style parallel links, which minimize bump-steer.
The transaxle itself is Hewland’s new LG 500 Mk II, distinguishable by its much beefier case and side plates. It follows modifications McLaren made to their own Mk Is last year. The big engines have been giving the hapless internals a bad time; this new case should position them more firmly.
The monocoque’s fuel-tank sides are made of 0.062-in. sheet to try to prevent shunt-punctures. This is pretty heavy stuff and permits the rivets to be recessed aircraft style. It looks neat, but any effect on streamlining must be negligible. The driver’s footwell has been braced with a new hat section hoop, again with the odd collision (fact of Can-Am life) in mind.
Compared with the M8E customer car, the F has a few things made of more exotic materials, magnesium and titanium, and here and there some pieces may be thinner; but the overall weight cannot be very much less. Empty of all liquids the complete car probably scales close to 1550 lb (704kg).
There are two engine options. Gary Knutson, back after two years at Chaparral, builds up normal aluminum-block Chevies displacing 494 cu in. (the 4.44-in. bore of the 430 block with the 4-in. 454 crank) and fits the injection with staggered intake trumpets.
For Mosport he’d developed a torque curve that bulged up to some 600lb-ft and continued to 700 in a straight line over a 1500-rpm band. Peak horsepower reading was about 740, but with Apollo-booster push like that the actual peak seems academic. The drivers were supposed to hold the revs below 7000, but dyno tests have seen these engines running at 7800.
The other option, not used at Mosport, is “the Reynolds motor” with its Vega-type sleeveless block. Partly because of piston-supply problems McLaren has fixed the bore of this at 4.50 in., and in an effort to make it a free-revving unit has elected to use the 427’s 3.75-in. stroke, which gives 480 cu in. The trusty slide rule calculates that with the 4-in. crank, displacement would go out to 512 cu in. It would seem that the 800-bhp Can-Am car is not far away, but whether the current bottom ends could hold it inside for 200 miles is perhaps another thing.
Despite what rulebooks seem to think, the first job of the body is to generate squash. To this end last year’s add-on “fences” have been made integral and run the full length of the body. Air shovelled up from the wedge nose is supposed to stay on top of the body, pressing down as it flows past, and on its way out over the stern the wing throws it upward again. Most of the inlets that used to be let into the top of the body have been relocated to interfere as little as possible with this airflow. The rear body line ducks down more sharply than it did last year to give the wing more room to work in. For what it’s worth in terms of less drag, the side fins are thinner this year, because they no longer carry the full weight of the wing as they did before Bruce McLaren’s crash.
The coolant radiator is still at the front, where the air extracted from it helps generate downforce. A large NACA duct in the left side of the body leads to the doubled-up engine oil coolers; a similar duct in the right flank in early season testing delivered air through three hoses to the rear brakes and the transmission cooler but now merely offers a light breeze to the engine bay. The transaxle cooler is now fed from the only NACA inlet in the top surface, one back under the wing. The rear brake discs have neat little metal fabrications scooping up air from under the engine.
The Goodyear tires are designed especially for Group 7 and don’t work well on anything else. They mount on 15-in. wheels at both ends, the front rims being 11 in. wide and the rears 17. The front “footprint” is about 9½ in. wide, the rear about 14¼, The tire pressures will be set at around 18 psi and the surface compound will run about 180 degrees Fahrenheit. A front wheel and tire, with weights and security bolts fitted, will weigh about 28lb (13kg), a rear wheel about 40lb (18kg).
Every millimeter of the car has been shaped by very careful, very expensive hands. Even a twin parked alongside is slightly different. Both machines will absorb every possible minute, the most painstaking care, the fullest devotion of the swarm of orange-shirted mechanics. After every day of use the cars are stripped for examination. Every critical part, which means nearly every part, is discarded on a strict time schedule and renewed as are cells in the human body.
When the McLaren is clipped together again, it drapes across its wheels with the loose grace of a relaxed athlete. Every line seems to suggest some vaguely evil purpose. The splayed injector horns, tinted light blue, plume from the glistening deck like outrageous irradiated flowers. Says Hulme:
“Shooting up the straight you’re going about 175. Right at the crest of the hill you’ve got to ease up on the pedal. You mustn’t let the nose get too high, or you’ll get air under it and you’ll take off. You mustn’t touch the brakes, either, because you don’t want the tail to get light. You just ease over the hump, sort of float. Then once you’re down you get all over the brakes, get down to third, for turn eight. It’s pretty bumpy through there, the surface is terrible, and I stay over to the inside as I go in. You’ll often find me taking a different line to everybody else. Out at Elkhart, especially.
“Once you get into eight the surface is smooth; in fact it’s one of the few places here where it is smooth. So you can put a reasonable amount of power on early, and get it all on-or off-and-on-early. You’ll find you can put the right front wheel up on the curbing. It doesn’t disturb the car. You want to stay over toward the right of the road to be placed properly for nine. You come off the gas smooth and easy and sort of roll around nine to the left. I can’t seem to get the car right in against the left curb for some reason, it wants to stay a couple of feet out.
“Then you can give it a bit of a squirt if you want to, and get right over to the left; hard braking, get down to second, and then straight across to the apex of ten and out the other side, keeping straight as the road drops off level. You don’t want to give it too much power here, get too far sideways; you could if they’d build up the edge of the road.
I interrupt, saying I suppose another reason not to let the car power slide is that we understand it exaggerates this tire vibration problem everyone’s been having.
“Don’t seem to have that with these tires we’ve got fitted today. Can’t seem to feel it. But you can go out and tell who has it and who hasn’t. You can see it in the marks they lay down coming out of the corners.
“You snatch third past the pits, shoot under the bridge and get set up for one. Don’t get too far over to the edge. Touch the brakes. It seems you could take it faster, but there are bumps all down through the first part and they make the car understeer. You mustn’t toss the car. You must be smooth, let the car just roll in, or you’ll hit the rail like that guy did this morning. It’s a bit like Indy, this turn. You think you need to stay right in the groove but you’ll find you can get away with leaving it to get around traffic.
“When you get the power on the car goes neutral. You can’t actually nail it until you actually get out of the corner. The instant you just crack the throttles you’ve got forty percent of your power. We’ve got lots more horsepower and torque this year, and it’s got just the same holes for the air to go through, and it all happens much more violently.”
I say I remember the number of times last year he asked for a 430 because it was smoother to drive.
“Right. In fact it isn’t until now I realize just how good the 430 was. Another thing about turn one as I think about it, I just now see why it seems slower this year. At the exit out near the rail the surface is bad. It’s always been rough but it’s worse now. You can’t run on it.
“Up toward two, staying in third – in fact you’ll be staying in third all through here until you get to five – you must back off for two at what seems too early. You brake a wee bit and then get right off the brakes and let it roll over the crest. If you let the braking go later and later it disturbs the car too much, because the road drops away from under you. It’s like turn seven at Riverside in that respect. Then there’s a new bump at the apex, a bloody great patch.
“I notice Jackie’s going wide around it and then pinching in tight later on down the hill. This is one of those places I told you about, where I’m apt to take a different line from anyone else. I run across the patch and then let the car go out wide.
“I remember with the high wings a couple years ago it was really keen down through there you could really nail it. You’d come out the bottom like a rocket.
“Going up into three is another of those bumpy places, where you’ve got to be smooth. None of this lock-to-lock business. Coming out it’s like the other corners; you can’t give too much power until you’re really out.
“Then heading into four I give the brakes a wee bit of a pump to make sure the pressure’s up, then steady gas down into the valley, all the way down to the bottom. Then maybe I’ll give it a squeeze right at the bottom, then hard on the brakes and straight down into first gear. It doesn’t seem to matter where you are on the road here, you can be inside or outside. I flick the car in here and give it a big boot and get it sliding up over the crest and heading for the hairpin.”
Pete Revson has been leaning into the conversation, and now he interrupts with a puzzled frown. He can’t make his F do that. If he tries to get its tail out it gives him warning signals. It wants to bite.
“Yeah,” says Denny, “I’ve been seeing that. We must get that sorted out. Mind, last year Dan was getting through there fabulously, much better than me. He’d come rushing right up to me there. I don’t know how he did it. But then he didn’t seem to be as good through the next part, the Moss hairpin.
“Here’s a funny thing. I can tweak the steering hard over long before I get to the hairpin. I can spin it right over to full lock, and it’ll carry straight on for perhaps 20 feet. Then suddenly it digs in and takes me right in to the apex perfectly. Then it’s wide-open throttle and we’re away. It comes out on a lovely power slide, right out to the edge and back toward the middle, tail out all the way. Then just as it begins to get straight you must lift off a wee bit and let the back wheels get locked in.
“Then it’s up through the gears – second, third, fourth and you’re rushing up the straight again.”
Where is this kind of car different from F1?
“Oh, there’s not too much difference really. You use the same line and much the same reference points for braking and so on. This probably brakes a wee bit better, because of the body. In terms of power-to-weight there isn’t really that much difference.
“One thing about driving these cars is you don’t realize you’re going as quickly as you are because of the sound, the low apparent engine speed. An F1 has got ten on it, it’s screaming and roaring, and it really feels like you’re covering the ground.”
I’ve heard that with Can-Am cars the wake turbulence from a preceding vehicle can be troublesome.
“It’s terrible. You want to stay in clear air with these. If you’re overtaking a back marker and you come into a turn behind him, if you stay over toward the inside of his line you’re fine. But gradually he comes in across you, making his apex, and suddenly you’re into his draft. Your car just picks up and moves across the road by yards until you come out the other side. Then it grips again and you’re all right, and you can run by. Out at Riverside, especially. You know the bend in the back straight, before you get to nine? You’re really flying down there, 190 I suppose, and if you get into the bend behind someone your front end goes completely dead and you carry straight on. There’s plenty of roadway there so it’s all right, and you can carry on and be well placed to get underneath him going into nine. But you must be very, very sure not to alter the steering by a fraction while you’re in his draft, because if you did, if you’d put more lock on, once you came out it’d grip again and you’d really go spinning off.
“It’s not just bad in the corners, either. Once last year at Edmonton, you know that long straight past the pits, I got up close behind Motschenbacher, I think it was. Really up close, right on his tail. Suddenly I realized my front wheels were off the ground.”
Quickly, so as not to appear to be overly impressed by a wheel standing Can-Am McLaren, I turn to Revvie. What are his impressions of the M8F?
“It’s definitely a car for a high-speed track. On slow turns there isn’t any down force and the back wants to come out – on mine, anyway. Maybe it’s just my driving, maybe I’m just not used to it yet.
“One Group 7 car can be as different from another as it is from a Trans-Am car, you know. It’s just a matter of how it’s set up. Denny thinks this sudden oversteer thing is because of the engine coming on so strong, but I kind of think it’s chassis problems.
“It’s a car that is very sensitive to changes in things like ride heights. We’ve been playing with my ride heights and spring rates all over the map. My front end was wallowing and pitching around so we went to stiffer springs to hold it up. But now it has a tendency to ‘speedboat’ on the straight.
“Compared with my Lola T220 of last year, the steering is much lighter. I’d say that’s the major difference. And this car seems to do a better job of keeping level. It’s got more front downforce and the aerodynamics are better balanced.”
Suppose that right now Hulme were to start laying down a successor to the M8 series. What areas would he try to improve?
“Well… I suppose possibly we’d be thinking about a suspension system more like the F I car. And we might do some looking into aerodynamics. You see the nose on the Lola that Jackie’s driving; well, we’ve been keeping that in mind for some time, it’s just that they’ve done it before we have. One doesn’t know just what is ideal for us. You could start in with an exhaustive aerodynamics program to find out – or you could whoosh-bonk it! Probably get the same results.”
“Whoosh-bonk” just about describes the race. Stewart’s new Lola, the L&M-supported T260, was taken to Mosport for a private day of testing on Thursday. It proved a valuable advantage for the first day of official qualifying, Friday, for he was fastest at 114.5mph, or I min 17.3sec. This was 0.9 seconds slower than Gurney’s 1970 record but enough to hold off Hulme and Revson at I: 18.0 and I: 18.1. The Gulf-Goodyear-Reynolds McLarens were in their first day on the track and the drivers were confident of doing better the next day. But a combination of factors slowed the track by at least two seconds on Saturday and Stewart retained his pole.
Saturday night the Lola’s engine was replaced, and there was something wrong with the throttle linkage Sunday morning. Stewart found it still sticking on the pace lap, so prudently he let Hulme beat him into the first turn. He had to watch the McLaren pull out a lead of six seconds in the first nine laps. But a back marker, in one fell swoop across his nose, cost Hulme all his advantage and Stewart sneaked by. As soon as he was behind, Denny noticed oil leaking from the Lola’s new Mk II transmission, so he relaxed and sat comfortably in second place waiting for the inevitable. It happened just before one-quarter distance and Jackie pulled off course into a stone quarry. As he walked back to the pits he watched Hulme and Revson run easily to another nose-to-tail Orange Elephant win, just the kind of sight everyone had hoped Stewart could prevent.
Reprint from Road & Track November 1971
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