Why more HP out of 2.7's then 3.0's

[82SC]

Okay may your grizzled old gurus can answer me these questions.

I see guys like Matt Holcomb and crew building monsters out of 2.7 engines...
they are posting numbers in the high 200's...even more then 300 hp sometimes

normally aspirated

obviously time will tell when these get done and dynoed...

but looking at bruce anderson's data my good old 3.0SC with carbs cams exhaust 3.2L upgrade they are struggling to get up to 300hp...(275hp I think)

I thought higher displacement engine would be higher in torque and hp...

it is not that I am comparing engines of different manfacturers...like hondas amazing hp/displacement numbers...aren't these 2.7 and 3.0 theoretically very similar engines???

What gives...

MJ

[Early_S_Man]

MJ,

Smaller cylinders are more efficient ... that has been known for almost 2/3 of a century. As an example ... the flat-8 Porsche F-1 engine of '62 was expanded to its' limit of 2.2 liters for endurance racing, and it put out 275 hp on Weber carbs in the '66-'67 seasons! That is quite a bit more than the 916 DOHC variant of the 901 engine was capable of with six cylinders -- 230 hp at 9000 rpm/2.0 liters ... and that experimental engine was the basis for both the 908 and 917 endurance racing engines.

Back to the 911 ... the peak of efficiency was reached at 2.8 liters in 1972 development for the RSR of '73 with output of 308 hp at 8000 rpm. When enlarged to 3.0 liters, port sizes and conventional butterfly injection throttle bodies became restrictive, and efficiency fell quite a bit -- only 315 hp could be found for the early RSR and IROC engines. It took slide-valve throttle bodies before the final numbers reached 330 hp.

I think the gain of only 7 hp for a displacement gain of 187 cc is the best illustration of the efficiency loss -- when all of the parameters were the same ... exhaust system, induction, cams, and ignition were identical between 2.8 and early 3.0 engines! When earlier 2.5 engines had been around 275 hp, the jump to 2.8 was still very productive ... but the limits in the flow capacity of the 2-valve heads became a barrier as 3.0 liters was reached. Hence, the turbo was the next technology to get past the flow limits of the 2-valve heads. Four-valve heads were tried on the 908 engine as early as 1970 ... and shelved, to be resurrected later for the 935.

------------------
Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[jbailey930]

MJ
an engine builder buddy built a 3litre to 328 hp. He was going for 330 but even with all dyno tricks couldn't get any further. This is was in a Mark Donohoe IROC 911 for the Rennsport club race. I don't know all the goodies but it was the first build I saw with 50mm carbs.
Best
John 79 930
87 951

[juan ruiz]

When i started doing research to beef my 3.2 up i soon find out that as longs as you stay normally aspirated your HP will be limited of course if you spend big time $$$$ thats another story,hard to belive that they got so little hp out of a 3.3,i got 320hp out a 3.2 Turbo of couse.my 0.02
Regards Juan
http://MY88911.homestead.com/newwebpage.html

[911pcars]

Horsepower is nice, but let's not forget that torque is the major difference between a larger and smaller displacement engine, and probably more important in a street-driven vehicle. For example: Compare Honda's S2000 engine and its relatively high HP figures with its low-torque driveability on the road.

Sherwood Lee
http://members.rennlist.org/911pcars

[Bill Verburg]

I second Sherwood Lees observations. Any engine can be tuned in different ways to deliver different power/torque characteristics. The 3 liter flat 6 engines that Porsche made from 76 thru 83 came in the following flavors;

• 930/02 200hp@6000 188lbft@4200
• 930/03 180hp@5500 165lbft@4200
• 930/04 180hp@5500 175lbft@4200
• 930/10 204hp@5900 189lbft@4200
• 930/18 255hp@7000 184lbft@6500

The difference was in cam timing, ignition timing, compression, inlet parameters, exhaust parameters, fuel delivery etc.

Bottom line on older non variable cam timing/lift engines the torque characteristics can be tuned for low rpm, medium rpm or high rpm, but not all 3 at once.

Lower displacement just limits the amount of air moving through the engine thus the maximum torque.

When I bought my 3 liter Carrera (200hp/188lbft)I also drove a 2.7 liter Carrera(210hp/188.4lbft). The 2.7 was tuned for higher rpm use and was not as good on the street(better on the track though). When strictly looking at the #'s this is not immediately obvious.

The beauty of the new computer controlled engines is that almost all of the parameters used for tuning can be controlled and varied dynamicly. So not only is spark timing and fuel delivery varied(as in the older engines), but also cam timing, lift, and duration. An engine thus endowed can be tuned to run optimally through out its rev range, limited only by mechanical and thermal durability.

High hp #'s by themselves are meaningless and must be judged in the context of revs/torque peak/torque revs/vehicle weight/gearing etc.

One last example, a 200hp Porshe 3liter is terrible at towing while a 200hp Chevy in a van is great at that task.

------------------
Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page




[This message has been edited by Bill Verburg (edited 09-28-2001).]