Engine Performance

engines

#1

I like the art of very efficient naturally aspirated engines. I had a friend who had a 1975 Audi Fox and I rebuilt that engine with dual side draft Weber 40DCOE carbs, a full race Crane camshaft and a high flow exhaust to go from 78 horsepower to 200 horsepower at 8,000 RPM which is pretty close to the theoretical maximum for an engine that size. The Crane cam had the same lift and duration as the one used in the original Chrysler 426 Hemi and required relieving the cylinder head to clear the cam lobes. At the time I also had a 1980 Mazda RX-7 that I had equipped with a Rayjay aircraft turbocharger and water and methanol injection which produced 375 horsepower and a top speed of about 195 MPH. I’m really not a fan of turbos though. I like really high revving naturally aspirated engines. I guess it has to do with watching that movie, “Grand Prix” when I was a kid. There’s just something about the instant throttle response of a naturally aspirated engine, as well as that wild sound when it’s running at 7,000 RPM or more. My current car is a rather pedestrian 1992 Mazda Miata with no mods other than tweaking the ignition timing. I once overheated that car driving it flat out on a twisty mountain road. It’s just a delight to drive. It has the limited slip diff and it can actually go offroad and climb mountains. It has nearly perfect neutral handling but you can get it loose if you use the throttle. It has great fuel economy but it’s just fast enough to be fun. It has the old smaller engine that is cammed so hot that the only limit on the horsepower is the rev limiter because it climbs like crazy. If you want to drive it fast you need to keep it between 4,500 and about 7,250 where the rev limiter is about to cut in. There were some bozos who put a MG manifold on that engine with a pair of SU sidedraft carbs and the power kept climbing way past 8,000 RPM or so where their dynamometer couldn’t measure it any more. That little engine is tuned like a mid 1960s Formula One engine. The cams in that thing are incredible. Anyone who claims it doesn’t have any low end is wrong, but when you hit about 3,500 RPM it really starts to kick in and from 4,500 to about 7,250 it just screams. The ratios on the transmission are just about perfect. I’ve driven that car for hours at about 115 MPH which is close to its maximum speed. I cut off the gearshift and put a round knob on it to shorten the stroke. Otherwise the car is completely stock. Most of the exhaust is actually believe it or not three inches. All that for a 1.6 liter four cylinder engine. Other than the rev limiter the main limiting factor on engine performance is the size of the throttle body in the fuel injection which was well demonstrated by those folk who modified one with the MG manifold. They got at least thirty extra horses out of it, though in my opinion it’s a really fun car the way it is and I never considered putting a turbo on it because that would just ruin the experience of driving a highly efficient small displacement car with a really hot set of cams, especially one that handles so nicely. My main complaints about the car were that initially the brake pads were too hard and it would lock up unpredictably in wet weather, and that the gearshift is a little too

notchy and the spring on the fifth gear slot is too weak. This leads to the situation where the gearshift sometimes hangs up going into third and if you’re not careful you can also inadvertently do a two five shift. Otherwise I’ve been driving this car since it was new and intend to keep it as long as I can. It has well over a hundred thousand miles on it but it has been well maintained so it still runs nicely and the engine is still powerful enough to break the rear end loose in a turn. This car is incredibly close to the experience of driving a mid 1960s Formula One car. It’s also very forgiving because it will just tuck back in if you get a little too loose. You can just slightly back off the throttle and it will just get right back in line, and it gives you a lot of warning when you push it too hard. On the other hand my old 1980 RX-7 was a horribly handling car that would swap ends on you in an instant. The rear suspension of that car is possibly the worst thing Mazda have ever built. The engine, however, was awesome. Nasty exhaust emissions, though. It would blow fireballs through the exhaust due to the huge quench area in the combustion chamber which is why they had to use dual spark plugs. On the other hand, the Honda CVCC was a miracle. Plenty of power, but I used to put one of those on an emissions analyzer and it was so clean you could almost breathe the exhaust. It also got great fuel economy. An interesting thing about the CVCC was that it almost never broke a timing belt. Something about that prechamber valve smoothed out the stress on the timing belt.


#2

If you want people to read your post, you have to break it down into paragraphs. As it is, it is just too much of a chore to try to read it.


#3
I agree with VD.  Please make it easier to read.  

One comment did stand out.  I have to say my RX-7 had outstanding handling.  Maybe the difference was tyres or maybe it was differences in our driving experiences.