Dear Mr

Dear Mr. Coleman,

I am writing to take issue with your assumptions in the SCC June 2000 Sentra SE-R cam article. But before I go into further detail, let me say whom I am. I am not an automotive engineer or any sort of engineer for that matter. I am an auto enthusiast of two years and I have familiarity with the SR20DE engine. I am also a social scientist. I have a vast understanding of the philosophy of science and the “tricks” of statistical analysis. I have done my fair share of studies to know that the research paper’s assumptions have a direct impact on the results of the article itself. The assumptions that you start with, determine to a large extent the results that you get.

I believe that the assumptions that you start with for your testing are flawed and this leads to flawed results. Permit me to explain.

On page 258 of the article you state “We did all the tests on our 91 engine which has the best cams and best head of the bunch. In an attempt to simulate the performance of the later engines, we also tested the stock 98 cams in our 91 head. This may not be exactly representative of the 98 engine’s performance, but it is the best we could do.” What does “may not be exactly representative" mean? Does that mean that the “98 cams in a 91 head” are closely representative or totally not representative? I take it that you mean that they are closely representative, because on page 260 you instruct the reader to look at pages 265, 267, 269, 271, and 273 in order to approximate the power of the tested cams on late model SR20DE engines. “If your SR20-powered steed is newer than that [post-1993], the second two charts are a better approximation of what you should expect.” So your basically telling your readers to extrapolate the results of the aftermarket cams tested in your "98 cams in a 91 engine” to all the post 1993 SR20DE engines.

What you are saying is that the “98 cams in a 91 engine” is close in power output to post 1993 SR20DE engines. But your baseline results for the “98 cams in a 91 head” show 128hp and 124 lb-ft @ 6400 and 4800 rpm respectively. And the 91 SE-R that you tested the cams in had a Hotshot header, advanced timing, HKS cat-back exhaust, and an Injen intake. This car earned you 13-14 hp in a previous Sentra SE-R article. A 128hp @ 6400 rpm from a late model SR20DE does not sound right.

Independent dynamometer testing (http://www.se-r.net/car_info/dyno/index.html) on a 1998 Sentra SE with a K&N drop-in filter produced 123.6 hp @ 6200 rpm and 121.6 ft-lb @ 4800 rpm. Assuming that the K&N filter produces 1-2hp, it is safe to assume that a late model SR20DE stock engine produces around 120-121 hp at the wheels. Am I to understand that a Hotshot header, HKS exhaust, Ingen intake, and 21 degree timing produce only 7-8 hp in a post 1993 SR20DE engine? That is highly unlikely.

Dynamometer runs of post 1993 SR20DE powered vehicles equipped with modifications similar to your 91 SE-R taken from http://www.se-r.net/car_info/dyno/index.html show the following:

A 1996 200SX SE-R with header, exhaust, JWT ECU, and advanced timing produced 138.4 hp @ 6200 rpm and 127.2 lb-ft @ 4800 at the wheels. Granted the car has a JWT ECU. But by your own admission (p. 270) this is only responsible for a slight gain of less than two hp. It also does not have an intake, yet it produces 10 more hp @ 6200 than your “98 cams in a 91 engine.”

A second 1996 200SX SE-R with a CAI, Greddy exhaust, and JWT ECU produced 136.0 hp @ 6000 rpm and 131.2 lb-ft @ 4750 rpm at the wheels. This car does not even have a header, yet it produced 8 more hp @ 6000 rpm than your “98 cams in a 91 engine” did @ 6400 rpm.

A third 1996 200SX SE-R with a Hotshot header, intake, JWT ECU, and an aftermarket muffler produced 140.4 hp @ 6500 rpm and 137.1 ft-lb @ 4600 rpm. Again, this late model SE-R produced 12 more hp @ 6500 than your “98 cams in a 91” set up did @ 6400 rpm.

It is clear from the above that the “98 cams in a 91 engine” that you created does not approximate the power output of late model SR20DE engines.

I know that comparing dynamometer runs is not advised due to variations in temperature, altitude, and dynamometer machine (most of these examples are from a Dynojet machine similar to the one you used). But I do doubt that these variations will produce differences of 8-12hp between dynamometer runs. Moreover, you compare different dynamometer readings in the MR2 vs. Miata article, so I will give myself the same leeway.

The problem is in the assumptions that you started with. You assume that the 91-93 SR20DE engines have the best cams and the best head. While the former is correct, the latter assumption is false. 91-93 SR20DE cams do produce a dynamometer proven 5-6 hp on a late model SR20DE engine. But 98 cams in a 91-93 head reduce the power output of an SR20 engine. This is because Nissan redesigned the 95-99 head and intake to work well with the reduced cam profile of later model SR20 engines. Thus, while Nissan reduced the cam profile they modified the head and intake to keep the power output at or around 140 hp @ 6400 rpm at the flywheel. Evidence for this comes from your July 1997 Project 200SX SE-R article. A Bosch chassis dynamometer found the power of the 1995 200SX SE-R to be 137 hp @ 6700 rpm at the flywheel. This is not far off from Nissan’s claim of 140 hp @ the flywheel for late model SR20DE engines.

I believe that “98 cams in a 91 engine” creates a fake baseline for the power output of a late model SR20 equipped vehicle. This fake baseline, in turn, affects the cam test results. When the aftermarket cams were tested from the fictitious baseline, they seem to create a higher power output than they actually would in a “real” late model SR20DE engine. For example, the JWT S3 cams (the most widely used by SR20DE powered vehicles) produced 25.9 hp @ 7000 rpm from around the 115 hp @ 7000 rpm fictitious baseline. I am pretty certain that had you tested a "real" late model SR20DE powered vehicle with similar modifications to the 91 SE-R, then the power output with the JWT S3 cams would have been around 128-130 hp @ 7000 rpm. The 26 hp @ 7000 rpm gain would have been reduced to about 14-15 hp @ 7000 rpm. The 14-15 hp gain is more in line with what the JWT S3 cams would produce on a late model SR20DE vehicle at 7000 rpm.

I really appreciate the testing that you do for the SR20DE community. Honda dominates the import aftermarket scene. It is refreshing to see Nissan tests in SCC. But I have to believe that SCC erred on this one. In your testing procedure you treated the SR20DE head and intake as a constant and the cams as the variables. In reality, however, both the head/intake and the cams are variables. This means that you cannot put 98 cams in a 91 head and approximate the power output of a late model SR20DE. You need two SR20DE powered vehicles, a 91-93 model and a 94-99 model. If you did not have the resources to include a 94-99 SR20DE powered vehicle, then it would have been appropriate to drop the “98 cams in a 91 head” from the testing procedure. As currently constructed, the article gives a false impression about the power gained from these aftermarket cams on a late model SR20DE vehicle.

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Update:

Recently I had my SE-R power output tested on a dynamometer. The car had the following power modifications:

Place Racing Cold Air Intake
Hotshot G3 header
JWT S3 cams,
Unorthodox Racing 4-pulley set.

Take a look at the dynamometer results here: http://www.geocities.com/n_dahi/dyno.htm

As you can see the maximum power output was 147.1 hp @ around 6300-6400 rpm (third run). Assuming that the maximum base power output of post-1993 SR20DE engines is around 119 hp at the wheels, I gained around 28.1 hp at the wheels from my stock base. That gain came with all the bolt-on power that you can add to an SE-R (except ECU). Had SCC's testing been correct, I should have gained 26 hp from the JWT S3 cams alone. That is clearly not the case. If I accept SCC's testing, then I gained 26 hp from the JWT S3 cams and 2.1 hp from all the other bolt-on modifications. That is simply unreasonable. It is more reasonable to deduce that I gained 12-14 hp from the cams and 11-13 hp from the rest of the bolt-on modifications. 12-14 hp is what most enthusiasts would gain from the JWT S3 cams on a post-1993 SR20DE engine.

It is clear to me that their "98 cams in a 91 SR20DE engine" is not a close approximation to the power output of a "real" post-1993 SR20DE engine.