Blue Printing a Motor - What can you get?

[Ron Earp]

Quite a lot.

Shown below are the most recent engine dyno plots of my 260Z race engine. Now bear in mind the SCCA Improved Touring class I race in has very little in the way of engine modifications.

• 0.5 compression increase (basically to account for head milling)
• 0.040 overbore max
• Exhaust is free
• Port matching allowed only 1" into port
• No "non-stock" combustion chamber work, valve jobs, etc.

Stock cam must be used. Stock carbs must be used. Stock rods, crank, pistons, etc. Lots of attention is paid to getting good parts, ring selection, and small details.

The 1974 260Z engine was rated at 138 net hp or 163 gross hp. In the US this engine was used for only one year, supplanted in 1975 by the 280Z and preceeded in 1973 by the 240Z.

My current race engine I built myself and is in my car now. It ended up right at 168 rear wheel hp, or around 193 flywheel hp with a 15% correction. Still going strong.

Shown below is the dyno plot of the motor I just had built for me by a local Z engine builder, Sam Neave. I wanted to find out if the motor I built was any count and if I was missing out on something. His motor is also around 193 flywheel hp but it has an improved torque curve compared with my engine. A bit broader and flatter. I think much of that is that Sam knowing what he's doing with the carb tuning and having the engine on a dyno to do 20+ pulls while futzing with needles, weights, oil dampening, and so on.



Anyhow, I just wanted to illustrate what can be done with a lot of attention to detail. These old 260Z motors were dogs on the street, not much power at all and rated as mentioned at 138 net hp. Raising that up to 194 net hp with no real aftermarket additions is pretty good, about a 30% improvement. Not bad at all.

I'm sure this isn't news to the engine savvy folks on this board. But I have posted such results on the Z boards, including the point about using the stock flat top 260Z carbs that everyone thinks are boat anchors, and I basically get told I'm lying. Lots of folks don't believe you can get these sort of results without using a non-stock cam, webers, or a lot of compression on a stock Z motor. Doesn't have to be done.

The 280Zs in my class race at a higher weight but they generally make 10-12 more hp and a bit more torque. The 240Zs race at a slightly lower weight and the best of those will make somewhat similar hp (better carbs) but less torque. In the end a fairly even match up.

[Neal]

Good stuff!

[Jeff Young]

Very true. HP in our racing world comes 1 hp at a time, via attention to detail.

Ron's got a dyno plot for my car (a TR8 with a 3.5 liter Rover V8) somewhere. 173 whp, 198 wtq.

Stock, net at the crank it was 138 whp, and 165 wtq.

15% conversion factor, and I'm looking at 198 crank hp and 227 crank torque. Greater than 40% improvement.