Engine swap rule proposal

[ttweed]

As mentioned in other rules threads, the current engine swap modification point penalties are not proportional to overall power to weight changes across the entire Porsche lineup, but rather an absolute value based on the total Horsepower change multiplied by a fixed factor. The same 100 HP upgrade in a 2000 lb. early 911 or 914 is obviously not the equivalent of a 100 HP upgrade to a 3,000 lb. late-model 911 or Boxster, yet they are penalized the same amount.

Since we are going to a new classification system based on Power to Weight ratios, this is a perfect opportunity to correct this disparity and make stock engine swap upgrade penalties proportional to their effect on PW ratio, rather than on the total amount of HP involved. I am making this proposal here for discussion purposes, but will submit some form of it to the Rules Committee after revision for comments/suggestions that might be offered.

Existing rule:

J. Engine horsepower increase:
In cases where entire engines and associated engine components are replaced with a factory engine of higher horsepower, and no modifications are made to this engine, entrants may take the following points instead of Section III Parts D through I.
Points shall also be taken according to this formula for engines that have additional horsepower from modifications not otherwise listed, such as the X-50 option.
Increase in horse power multiplied by 2.2 = total points.
For sums ending in more than a whole number, round to the next highest whole number.

Example:
179 hp (911SC) to 247 hp (964 3.6L) motor = 68 hp
68 x 2.2 = 149.6, rounded to 150 points.

Proposed new rule:

J. Engine horsepower increase:
In cases where entire engines and associated engine components are replaced with a factory engine of higher horsepower, and no modifications are made to this engine, entrants may take the following points instead of Section III Parts D through I.
Points shall also be taken according to this formula for engines that have additional horsepower from modifications not otherwise listed, such as the X-50 option.
Penalty points are determined by calculating the difference in power to weight ratio achieved by the engine substitution according to the following formula:
[4000 / (W / ModifiedHP)] - [4000 / (W / StockHP)]

"StockHP" is defined as the Horse power of the factory engine original to the base car as listed in the chart in Section XVIII Appendix C. "W" equals the weight for the base car as listed in the same chart. "ModifiedHP" is the Horse power for the replacement engine as listed in the chart for the donor car.

Example:
172 hp (1983 911SC) changed to 247 HP (1993 964 3.6L) motor = 75 HP upgrade

[4000 / (2552 / 247)] - [4000 / (2552 / 172)]
resolved as:
(4000 / 10.33) - (4000 / 14.84)
or
(387 - 270) = 117 point HP modification penalty

While writing this post, I just noticed that the 911SC engine is listed in the Appendix C chart as 172 HP instead of the 179 that is commonly assigned by the factory for the 3.0 L engine. Anybody know why this is? Typo? Any insight, Tom B.? I am leaving it that way for my example, even though the rulebook deems it 179 HP in it's example, which contradicts the chart.

TT

[rshon]

A good way to check your proposal would be to take a model with two different engine sizes, like a Cayman and a Cayman S, and see if your formula puts a Cayman with a Cayman S engine in/close to the same class as the same year Cayman S. I have forwarded examples of this kind of comparison to Tom Brown, including a 2004 996 with a GT3 engine vs a 2004 GT3, and under the current rules, the base model with the upgraded engine always comes out with more points than the "S" or the GT3, even without the attendant suspension, brake, driveline, and aero mods...

[Cajundaddy]

+1
Yes Tom I think this is a better approach that could be tested with common engine swap data and will give good results. 911sc+3.6L, Boxster 2.7-3.4, Cay 2.7-3.4 are all pretty easy to calculate points and get good results.

[Greg Phillips]

I think the 172 vs 179/180 is the difference between DIN (PS or pferdstarke German horses) and SAE or American horses.

I have not looked hard at the charts to see if they are consistently using one measure. I guess the new rule should specify which.

Since the new rules have the power to weigh ratio as their underpinnings and major factor, we should try utilize the formulas as much as feasible, specifically when we are working directly with weight or power changes.

I will also throw out another concept out for perusal and consideration. Using DynoJet measured rear wheel horsepower, as an option for engine modification points.

Some of the older cars have swapped motors for cost or convenience rather than ultimate power. Using a newer engine and putting carbs on it rather than trying to get the stock CIS injection to work. They can't use the stock swap rule, and the points for modification may be greater than their real power output.
If they wanted to have their car tested on a DynoJet (for consistency), they could use that RWHP number multiplied by 1.19 (to account for the 16% driveline loss) in their PW calculation and take points based on the difference between the stock and new motor. They would have the option of choosing whichever system worked out best.

Greg

[ttweed]

I think the 172 vs 179/180 is the difference between DIN (PS or pferdstarke German horses) and SAE or American horses.

Porsche has always quoted HP in DIN, no? I think all the other numbers in the chart are DIN--why would we have SAE numbers for the SC? All the other HP numbers in the chart that I am familiar with for the early 911 models are all in DIN HP. We should definitely have a look at this and be consistent.

Since the new rules have the power to weigh ratio as their underpinnings and major factor, we should try utilize the formulas as much as feasible, specifically when we are working directly with weight or power changes.

I will also throw out another concept out for perusal and consideration. Using DynoJet measured rear wheel horsepower, as an option for engine modification points.

I think this is a good idea. People with custom motors have always been hammered under our rules by taking all the individual mod points compared with doing an engine swap with a stock engine of known HP. Giving them a choice to use dyno data would be fairer.

TT

[Greg Phillips]

Porsche has always quoted HP in DIN, no? I think all the other numbers in the chart are DIN--why would we have SAE numbers for the SC? All the other HP numbers in the chart that I am familiar with for the early 911 models are all in DIN HP. We should definitely have a look at this and be consistent.

TT

I just looked at my 1989 928 owner's manual and the horsepower was listed as 315 SAE net-horepower SAE J 1349, or 235 kW at 6000 rpm Appendix C=316 hp
Curb weight was 3505 pounds 1590 kg. Appendix C=3525 #

Top speed was listed at 168 mph, that has held up well
0-60 = 5.7 seconds, that is about what the V6 Mustang, Camaro and Hyundai Genesis run
1/4 mile= 14.2 just ahead of a Audi A4 3.2 and MB CL350 sport

Greg

[ttweed]

I just looked at my 1989 928 owner's manual and the horsepower was listed as 315 SAE net-horepower SAE

That's 'cause the 928 is actually a German Corvette, so they had to use American horsepower in it.

TT

[Mark Garriott]

My next step was to try to toss in non-stock engine changes, using dyno data. After all, horsepower is horsepower. Why shouldn't a that be allowed?

There is one really small nitpick with this proposal. Weight and horsepower changes should be done simultaneously -- i.e. sections J and X should be merged -- maybe title it "Modification to Power/Weight Ratio".

The progressive upward curve of the 4000/PW formula means that the final total is more than the sum of the parts. For a 10 lbs/hp car, losing 1 lbs/hp is worth 45 points, but losing 2 lbs/hp is worth 100 points. The first pound or horsepower is 45 points, the next pound or horsepower is 55 points. Calculating weight changes separate from power changes is like taking the 1st step twice.

However, from a practical standpoint, it doesn't matter much, since the practical difference would be 5 points or less.