joemoia

In advance of this weekend's Petit Le Mans I have tried to put together a list the weight/displacement/restictor sizes for all the cars competing in the GT2 class. I have also identified and included competition adjustments to the ACO specs that have been issued by IMSA. IMSA has issued several competition adjustments for GT2 cars over the season and I may have missed one applicable to the class. Waivers aren't published so there may be additional adjustments to specific cars that are not listed below. I've tried to be as accurate as possible, but if someone sees an error, please post so I can correct the data.

For restrictors, "increase" "larger" means more air allowed; "reduce" "smaller" means less air allowed



Ferrari F430GT
min. weight - 1145KG
eng type/displ. - 4.0L 4V/cyl DOHC V8
restrictors (2) - 27.4 mm
max wheel width - 12"
notes:
1. F430GT is running at ACO specs


Porsche 911RSR
min. weight - 1245KG (memo #09-14)
eng type/displ. - 4.0L 4V/cyl boxer six
restrictors (2) - 28.7 mm (ACO bulletin #06-01)
max wheel width - 14"
notes:
1. memo #09-14 increases min. weight to the ACO spec of 1245kg
2. ACO bulletin #06-01 is listed in 2009 IMSA rules/regulations and specifies 28.7 mm restrictors; the 2009 ACO GT2 specs lists 28.6 mm restrictor size for this weight/displacement. I have assumed the 911 is running with 28.7 mm restrictors.



Riley C6 GT2
min. weight - 1220kg (bulletin #09-03)
eng type/displ - 6.0L 2V/cyl pushrod V8 (LS3)
restrictors (2) - 30.6 mm (bulletin #09-09)
max wheel width - 14"
notes:
1. bulletin #09-03 reduces min. weight from the ACO spec of 1245kg
2. bulletin #09-09 increases restrictor size from 28.6 mm ACO spec for this weight/displacement



P&M C6.R GT2
min. weight - 1245KG
eng type/displ - 6.0L 2V/cyl pushrod V8 (LS7R)
restrictors (2) - 28.6 mm
max wheel width - 14"
notes:
1. the C6.R GT2 is running at ACO specs.



BMW M3
min. weight - 1245kg (bulletin #09-11)
eng type/displ - 4.0L 4V/cyl DOHC V8
restrictors (2) - 29.4 mm (bulletin #09-11)
max wheel width - 14"
notes:
1. bulletin #09-11 increases min. weight to the ACO spec of 1245kg
2. bulletin #09-11 increases restrictor size from 28.6 mm ACO spec for this weight/displacement



Panoz GTLM
min. weight - 1245kg (bulletin #09-11)
eng type/displ - 5.0L 4V/cyl DOHC V8
restrictors (2) - 29.8 mm (bulletin #09-11)
max wheel width - 14"
notes:
1. bulletin #09-11 increases min. weight to the ACO spec of 1245kg
2. bulletin #09-11 increases restrictor size from 28.1 mm ACO spec for this weight/displacement



Doran Ford GT MK7
min. weight - 1220kg (bulletin #09-03)
eng type/displ - 5.0L 4V/cyl DOHC V8
restrictors (2)? - 29.1 mm (bulletin #09-23)
max wheel width - 14"
notes:
1. bulletin #09-03 reduces min. weight from the ACO spec of 1245kg
2. I have assumed the Ford GT has dual restrictors but am not sure. The ACO spec restrictor size for 1245kg/5.0L displ is 28.1 mm. IMSA bulletin #09-23 states the following:"Doran Ford GT-R: may utilize the restrictor for the weight category 2 above the declared weight class." I have interpreted this language to mean the Ford may use the restrictor size for 1345kg/5.0L which is 29.1 mm. This interpretation may be incorrect.



Viper GT2
weight - 1358kg?
eng type/displ - 8.3L? 2V/cyl pushrod V10
restrictor - unk (bulletin #09-09)
max wheel width - 14"
notes:
1. I could find no specific weight/engine/restrictor data relating to the Viper. AFAIK it has been converted from FIA GT3 specs to run in ALMS GT2, but I couln't find any specific FIA GT3 data either. Above weight/displacement data is for the Comp Coupe as delivered from the MFR.
2. IMSA bulletin #09-09 specified a 10% reduction in restrictor size, but doesn't state an actual diameter.



Summary

The F430GT and the P&M C6.R GT2 are running at the 2009 ACO spec for their weight/displacement

The 911RSR is running at or near (depending on restictor size) the 2009 ACO spec for its weight/displacement

The BMW M3 and the Panoz are running at the 2009 ACO spec weight and are allowed larger (more air) restrictors than the ACO spec by IMSA

The Riley C6 GT2 and the Ford GT are alllowed lower min. weight and larger restrictors than the 2009 ACO spec by IMSA

The Viper is a mystery to me, so if someone has the applicable data please post

SIK02SS

Great info, thanks! LG is running on the Riley with LS3 right?

joemoia

Yes, LGM runs the Riley C6 GT2

LG Motorsports

Hi Guys,

You can note that all the cars with concessions do not run michelins. All of the changes to the restrictors and weight are there to make up for the tire differences.

2mm in restrictor size in a large cu in engine only yields about 20 hp which is the same as taking off 100 pounds but only in acceleration. Adding 20 hp only helps in one direction where the weight helps in cornering and braking also. So I would rather take 100 pounds off rather than 2 mm of restrictor.

So if 100 pounds is worth 1 second per lap on a 2.5 mile track, then 20 hp is only worth .3 sec. (we tested this to confirm).

The tire issue is worth about 2 full seconds. So you can see why they had to make the changes. BMW would look very bad otherwise. And it would not be that the car or drivers were lacking, just the tire technology and the relative level of investment of the tire companies.

The goal is to have a level competition. The problem is that now they have to balance the performance of the technical aspects of the cars, PLUS the tires to formulate the correct balance of performance.


The free market usually works best.

Thanks

Lou G

PS Joe, Great work

AU N EGL

Give them Hell Lou

joemoia

Thanks Lou,

If you run into your buddy Feinberg ask him what the hell the weight/displacement/restrictor specs are for his Viper, inquiring minds want to know! (I'd also like to get confirmation on the number and size of the restrictor(s) on the Ford)

Good luck to the entire LGM team for Saturday's race hopefully you can run well enough and get enough sponsor exposure to get the funding to make it to Laguna.

Oh, and look out for Bibendum, after your recent comments I think he's out to get you