increase in compression/increase in HP

I recently rebuilt my 72 Daytona motor; Carobu engineering, in Costa Mesa, CA did the work.

Stock Daytona motor is supposed to put out 352 Hp. They had measured one at 330 or so before rebuilding.

Stock compression ratio is around 9:1. I had them put in 10:1 pistons. They also ported the heads a little, added optical ignition. Car is a Euro, which has VERY NICE tuned headers.

My engine put out 415 Hp on the engine dyno. This is without air cleaner. When they added the air cleaner, they had to rejet the carbs, and the motor put out 395 Hp. That's a pretty nice bump over stock. I believe the first five race Daytonas were putting out about 425 Hp.

I have been told that at least on my engine, the best thing you can do to increase Hp is to go to higher compression.

Good luck.

 

Most of you hp is most likely from the porting and although you didn't mention it, I'm guessing a cam change.

Bumping the compression helps keep the low end strong with longer duration cams and or better flowing heads, but by itself doesn’t do an awful lot…I have to look the formula up, but it’s an exponential decay relationship I think, so going from 9 to 10 does a fraction of what 8 to 9 does which does a fraction of 7 to 8, ect. The main thing is keeping the cylinder pressure up when the cylinder is not filling well at low rpm.

 

Increasing compression is a good method for increasing power across the board...but it also increases heat generation. BTW, a higher octane fuel will be necessary unless the car already takes 91.

 

The power gain from a compression increase depends on where you make peak power. And I think US Daytona's were even less than 9:1.
If peak power is at 6000rpm, you might gain 25hp. With a peak at 7000, you may gain 40hp. A lot of variables, but higher compression is definitely good all around.

 

I've never found that to be true and is not supported by any theory I am aware of either.

 

Just the basic HP equation. The higher the rpms with the same amount of torque, more horsepower is made.

 

I have to disagree with such a low figure. 5-10bhp at the flywheel with a drastic change in compression from 8.8:1 to 10.25:1 has yielded excellent results. My reasons are experiences with another Italian engine, but a very cut and dry result was netted.

I rebuilt a Maserati Merak ss engine a few years ago which was dyno'd at the rear wheels at 179rwbhp only months prior to rebuild and in excellent condition. The engine is rated in stock form @ 220bhp at the flywheel by the factory with 9:1 compression. This engine in prior rebuild state had approx 30k miles on it until it dropped a valve, hence the rebuild. The only modification added to this engine were 10:1 custom Ross racing pistons and all rotating components were balanced. The Ross pistons were considerably lighter than stock. End result was 197rwbhp once jets were mated with the new setup for performance. Drivetrain loss with the Citroen gearbox on the Merak ss is about 15%. Not a bad increase once it was tuned correctly.

I am not well versed with the Bosch injection system used on the 2 valve cars, so I do not know how easily tuned it is for such modifications. I bet if 10.25:1 pistons were used in an early carb car with early carb cams, 15-20bhp at the flywheel would be easily attainable with correct tuning. The only difference between the carb motor I just described and the LM engine would be the P6 cams. Carobu made 277bhp at the flywheel with P6 cams and 10.5:1 cpr

 

Compression ratio is not in the hp equation.

It's in the thermal efficency equation, which does not contain rpm. Compression ratio is not in the hp equation. It's in the thermal efficiency equation, which does not contain rpm.

 

how about main and rod bearings at about $400 a set each?

 

mill the heads for higher compression. polish and relieve the manifolds and heads. fire trench the pistons. balance all moving parts.

 

If you are rebuilding, use new pistons for increasing cr and avoid milling the heads. Both JE and Wiseco have done pistons for Ferraris.

Agree with port and polish, but recommend someone with a flow bench do it. If the car is driven on the street, would max flow to point of max velocity. I've heard just a good multi angle valve job makes a big difference as well.

You biggest flow restriction to max hp is your injection system, which in naturally aspirated form will peak out at delivering about 270 hp or so if everything else optimized. There is a lot bantered about regarding larger throttle bodies & plenum opening, but I'm not sure and never saw really good numbers.

While increasing CR may not affect top output as much as you might hope, I believe you will really feel it in the lower rpm range where these cars need it.

Fchatter Pogibm (?) did a similar work up on his injected 2v (CR, p&p, etc) and got spectacular results for a 2v. There is precedent.

good luck!

 

replacing the induction system and cams`wii make a pretty big difference on that engine, but can really be done any time...so after the budget recovers

 

From mk e: "Most of you hp is most likely from the porting and although you didn't mention it, I'm guessing a cam change. "


Based on the rebuilder's comments, compression ratio provided most of the Hp change. CAMS were NOT changed.

Heads were flow ported, but little was needed. That is NOT true for US cars; they have a built in restriction in the exhaust ports.

I'm sure that some of the Hp gain was due to their "tuning" of the cam timing, distributors and carburetors.

It is also possible that the Euro cars normally put out MORE than the listed 352 HP.

Whatever the reasons, I am really happy with the car, except for one minor nagging problem.

 

I am very admiring of your Daytona rebuild and Tate has referenced it several times in our many discussions on engine fine tuning. Some of the lessons that your rebuild and others have taught me is that while you CAN do things one at a time, the effect and matching of several measured changes really can work together.With yours, the cr change with tuning the cam timing, adding some head flow and then matching the Weber jetting all were part of a matched set.

I've done mine fairly piecemeal up until now with small changes and have been happy as well. With the current project - 44DCNF carbs, ported head, larger intake valves, 10.5 CR, .400 lift cam and Tubi Euro headers, I am trying for a set piece. Although each change is not anything large by itself, I am hoping they all come together well.

As to etip's rebuild, I would still see if I could find about $2K and do the carb conversion...on a 2v it would be especially easy and a bolt on affair. Between the Webers and and cr increase, just the change in throttle response ALONE would feel like 100hp although he will probably pick up around 40+ even with stock cams with the cr, porting and Webers. The breathing and response in the lower rpm ranges would really wake up. I've also learned that on the street this is FAR more important than chasing some peaky dyno number to show off.

And then there is that Weber sound thing, NEVER to be underestimated...

Best to all

 

Basic thermodynamics predicts increases in efficiency directly proportional to compression ratio. This means, all else assumed the same, torque and power will scale directly with the increase in compression ratio. So, an increase in compression ratio from 10:1 to 11:1 should yield a 10% increase in torque and hp. Mathmatically, assuming 200 hp at 10:1, should result in 220 hp at 11:1 The resulting power=11/10(200)=220 hp (similarly with torque) if I have my math right.

This assumes, of course, that the engine is not flow limited over the rpm range, 0-7700 rpm and that one has not entered into the region of detonation. If this is the case, benefits will be realized up to the point of the flow limit or be impeaded by detonation.

This also means that fuel consumption will be reduced for a given power output by 10%. Increasing compression ratio is the single most efficient way to improve engine performance provided one can satisfy the octane requirements. You never get anything for free.

Bill

 

This is all true to a point though, as any increase in compression ratio slows down the speed at which the flame front travels.
At high compression ratios sometime it is necessary to use 2 spark plugs per cylinder to offset the problem.