Any news on ITB weights???

[Chip42]

If you have a dyno plot and some build info that would REALLY help us as the gross-net conversion is not straight math but car dependent.

[Gary L]

SAE gross v. net is a big issue. We are working off of net numbers, so if we encounter an SAE gross rating we'll have to discount it. There are some means to do that but it can be tricky especially when you throw in some ratings that are DIN.

(emphasis mine)

If you have the DIN rating for a US market engine, you should be golden IMO, and most European makes published the DIN ratings alongside SAE gross numbers for the four years in question ('68 thru '71 MY). The conversion factor is well established, and basically amounts to a 1% reduction (1.0142 I believe) of the DIN rating to come up with SAE net. Beats the Hell out of making a WAG based on a "discounted" SAE gross number. Yes... I realize this does nothing for US makes, but I'd bet you can find DIN numbers for most European/Japanese cars, including the car in question here (Opel GT).

[quadzjr]

When I was looking for a cool RWD car for IT I looked at the opel. From what I found none of the GT cars that I was able to locate had the 100 hp engine. All had the 80 something hp engine. Maybe I did not search well enough but it correlates to what wiki says.

"Opel reduced the compression ratio of the 1.9 L engine used in the US and output fell to 83 hp (SAE). "

[Gary L]

When I was looking for a cool RWD car for IT I looked at the opel. From what I found none of the GT cars that I was able to locate had the 100 hp engine. All had the 80 something hp engine. Maybe I did not search well enough but it correlates to what wiki says.

"Opel reduced the compression ratio of the 1.9 L engine used in the US and output fell to 83 hp (SAE). "

Two points:

You left off a couple of words of the quote, specifically - "In 1971....".

So if the Wiki is correct, there were high compression engines imported prior to 1971. Since the listing in the ITCS covers 1968 thru 1973, the process would begin by using the higher hp engine as the starting point. This primarily due to the legal update/backdate of the long block and induction system made available by the rules.

[quadzjr]

One of the many problems with fixing ITB. Did the car come with the 102 and the 83 in teh states? are the same motor sans compression? what CR is the what?

Run through the process it would result in a big difference.

102 hp= 102*1.25*17 = 2170
83 hp = 83*1.25*17 = 1765

car factory weighed right aroudn 2k lbs.. not sure if the lower number can be achieved.

[Chip42]

IF the car came with the earlier, higher CR engine, then only the earlier, high CR HP number is used. then again, it's SAE Gross HP so the equations above don't work regardless.

[Gary L]

A quick look with Google revealed the following:

http://www.carfolio.com/specificatio...car/?car=71588

and

http://www.automobile-catalog.com/ma...gt_j/1971.html

Don't have a clue where those two websites came up with the numbers, but assuming it was copied from something official, the early high CR (9.5:1) motor apparently had 89 DIN hp. I also found references to "90 PS" for that motor in European Opel forums, etc.

So our (USA) 102 SAE gross hp motor was more than likely around 88 or 89 SAE net hp, dropping to 83 SAE net hp in 1971 or 72 when they lowered the compression ratio. Assuming no other major changes, a 5 or 6 hp drop makes a lot more sense than the apparent 19 hp drop from 102 to 83... the latter being an instance of apples vs oranges, so to speak.

[Jimopel]

Thank all of you!This was a great learning adventure.
The numbers you are looking at are right as published,but after some checking I see how hard it is to classify a car!Turns out same high cr engine in Germany has 90 hp,when translated to us it comes out to about 88 hp.
This makes me feel better as my race engine doesn't make more than 95hp ,so now I'm seeing real vs advertised .Thanks again everyone hope to see some of you on the track this spring.Jim

[AE86ITA]

The wait is over for some of us Toyota Corollas, FX-16 and Nissan Sentra 1.6L B13
http://scca.cdn.racersites.com/prod/...TB%2014-02.pdf


Race On