Coop

Tom, what an inspiration you are! Keep up the good work my friend. All of us enjoy reading about your experiences and professional advice. Thank you!

Brainz

Thanks, as always, for sharing. Glad you're ok and the car is on the mend.

It's actually pretty remarkable how little frame damage there is in the rear - - I'm not repair specialist, but it looks like that should pull out.

Best wishes in getting it back on the road/track.

voodoo

lcrain

What bad luck! I feel certain that the car will emerge better than before the hit, given everything else you have done to the car!

Tom@TPC Racing

Thank you, Gents! We have repaired Cups cars that were in far more severe incidents and they turn out to win races and championship. So no doubt on the repair quality. It feels a bit personal taking a hit on my own street car but that's the accepted risk that goes along with this activity. With some parts, labor time, and love it'll be better than before. Looking forward to share the progress. Only regret I have is shoulda bought track insurance.

Tom@TPC Racing

There's so much to be done that it can become overwhelming when I think about the entire scope of the repair and how many nights and weekends it'll take. The best way for me to stay in-tune to the process is just to start somewhere and get the repair process in motion- So my engine bracket(aka engine carrier) is bent from the impact so I need to replace it. I thought it'll be neat to use a RSR-style bracket. This RSR-style bracket is from Demon Speed Motorsports(shown in image below) made for a 997 Cup. According to DSM this is more durable than the factory Cup bracket. In my application I probably won't notice the difference because I'll be using semi-solid engine mounts instead of the all-metal fully-solid engine mounts that come on Cup and RSR. I want to do it anyway just to be different and I think its cool.


The DSM RSR-style engine bracket on top of image.
OEM 997 GT3 street car engine bracket on bottom of image.



One of the differences between street car and race car bracket is that the street car version has square openings that line up to the square "step" of the street car engine mount. Street cars use M12 fasteners.
The race car version doesn't use square openings, just round holes and M10 bolts.




Doing a test fit of bolt holes here by using same height spacers to bolt the two brackets up(this was necessary because the street car bracket isn't flat). Passed this test...better to find out this way then hustling to bolt it up to the engine.




Slight problem, the race car engine bracket is approximately 25mm wider between the two openings(just FYI, the street car engine mounts don't sit perfectly centered to the square opening, so 3mm deviation on my measurements below on a bracket that's over 800mm in length isn't a deal breaker). No biggie, just have to shorten the bracket slightly and drill another set of holes for the modular end pieces to match the street car bracket opening-to-opening distance. What I think its cool about the modular end pieces is that they are offset differently which may allow me to move the engine forward by a few millimeter, and the "tube" portion for the bolt is lengthy so I can machine them down and tune the height of the engine within the car's body. Moving a few hundred pounds of mass slightly forward and downward...see where I'm going with that.




The Rennline semi-solid engine mount worked good in taking some of the impact to prevent further frame damage. So need to replace the engine mounts too.



I had no problem with Rennline tune-able semi-solid engine mounts. This time I am going the the Stomski Racing tune-able semi-sold engine mounts, they are the only tune-able engine mounts that uses a through-bolt instead of a stud, which I feel is a better pairing to the race car-style engine bracket, being that I tighten the bolts without the square step.




The two brands have engine mounts have different approaches in their design to how the lateral and vertical load is distributed to the tune-able polyurethane inserts.



But of course all street car engine mounts use M12 fasteners. So I'd either have to drill out the race car bracket end pieces to M12 or machine some M10 ID stainless steel bushings for the Stomski Racing engine mounts for my uncommon application. I chose the latter option. Only needed two M10 ID stainless steel bushings but made two extras. Using the same 10.9 grade bolts as OEM to perhaps allowing the bolts to give away in event of an impact rather than the car's frame.








Umm, so let's step back for a moment, I did the machining and ordered the M10 bolts actually prior to receiving the DSM bracket and assumed that the bolt holes were same size as Cup brackets which is 11.8mm(just small enough so that you can't put a M12 bolt thorough it, but using a M10 bolt the clearance allows for easier engine installation with some margin of fit tolerance. Here I am getting too gung-ho before receiving the bracket (and I didn't ask, I just assumed), the bracket arrived and the holes are M12. The engine ain't going to fall out so I'm not changing it now.

Tom@TPC Racing

Forgot, also machined these sick M10 stainless steel load bearing washers for the mounts.

voodoo

dives right in! haha

Coop

This guy s awesome....

Tom@TPC Racing

So I was pretty excited to have a race car style engine bracket on my engine after putting in a total of 7 hours measuring, machining, and fitting(width and offset), but it turns out that this just isn't going to work out when I realized the race car brackets are actually less rigid than the street car brackets. My mind was stuck on the idea and the thinking that "race car parts must be better" and didn't think things through beyond the part itself. I came to realize that the less rigid race car brackets are meant to be used with all-metal solid engine mount and all-metal transmission mounts to provide a more stable triangulated platform than the polyurethane bushing mounts that I am using. Laterally all the brackets are rigid, but longitudinally the race car brackets are very flexible(can easily flex them by hand), I think they rely on the all metal transmission mount to control longitudinally movement, i.e. during hard braking. For my personal preference, I want to keep using polyurethane bushing mounts, so as much as I don't want to back out on a cool mod I have to abandon this one. For those who's thinking about doing this without using solid mounts, learn from my 900-dollar mistake(that's the amount I spent on parts and materials)- Don't do it. Now, does anyone want to buy a race car engine bracket? I have a few.

Brainz

Interesting. I hadn't thought about it until you mentioned it. I get that the race mounting plate is more flexible than stock (in all directions), but even the stock plate looks pretty flexible longitudinally. Does that mean that the transmission mount is doing most of longitudinal bracing? And the rear brace/mounts are for lateral and up/down forces?

I recently swapped my factory 997TT engine mounts for 964RS units and was blown away by the beneficial change in feel (without undue NVH). There's no more pogo and wag in back and I'm happy.

Tom@TPC Racing

The engine mounts, engine bracket, the engine itself, the transmission and transmission mount together makes up the "drivetrain suspension system". The load is distributed between the components of the system. I think having more rigid components is good for high performance usage, but not to such a degree that the rigidity of the components become greater than the engine block that's bolted to, as this could cause the engine block to crack when it becomes the more deformable components in the system during operation at high loads.

It looks to be a common theme that the factory engineers put an effort to stiffening the upper portion of every bracket(both street and race). With each generation of race car the upper portion becomes stiffer(see photos below). I am not a Drivetrain Suspension Engineer, but it appears to me the stiffer the upper portion of the bracket becomes the more load(lateral and longitudinal) is distributed to the engine mounts. It is also a common theme that all the race car brackets are more flex at the lower portion than on the street car brackets; race car bracket don't have the lower ribbing that street car brackets have. Also the race car brackets are made from 2mm thick sheet metal, whereas street car bracket is 4.0mm thick. My opinion on that is likely because street cars came factory equipped with rubber mounts(engine and trans), this allow the rubber mounts to do most if not all the flexing under loads, thus having an overall less flexible (street car)bracket is required to limit the movement of drivetrain after the rubber flex is at peak. In my mind this is a two-stage suspension. Putting a stiffer rubber mount in like you and I did reduced the first stage of movement thus in some mild to medium load situations will subsequentially reduced or eliminate the second stage loading. In the race cars all three mounts(two engine mounts, one trans mount) are solid so during high load some flex at the lower portion of the bracket(where most of the engine's mass is) to allow for a number of tiny movements instead of one big movement that effects the balance of the car is a good things. I think vertical load is more controlled by the engine mounts since the engine end of drivetrain is heavier than the transmission end.

Other thoughts:
1) Street car engines, especially twin turbo are heavier than race engines without AC compressor, without PS pump, without emissions stuff, and lighter weight exhaust so a thinner bracket is more suitable on race cars.
2) Street cars have the additional aluminum adapters that go between the engine mounts and the chassis, these adapter may have additional suspension value or leverage value by raising the engine mount height by 40mm.
3) Something that should be so simple is also so complicated. Damn, why didn't I think of all this when I spent 7 hours and 900 bucks.

Photos:

Street car bracket has 40mm wide mounting pad that was factory designed to for use with rubber mount. Definitely not much flex here.



Street car bracket has 15.6mm rib near the center. The sheet metal is 4mm thick.



997.2 Cup race car bracket. The sheet metal is 2mm thick.



997.2 Cup has 10.5mm upper rib along the width. The lower portion ribbing is 3.5mm.



991 Cup(aka RSR style) has very rigid 24mm boxed upper portion. The lower portion is 2mm thick sheet metal with no ribbing at all.

Brainz

Terrific education and interesting stuff I'd never thought of. Thanks as always for sharing!

AudiOn19s

cause I'm curoius...did you weigh all of them?

Tom@TPC Racing

The OEM 997.1 GT3 bracket(which is same part # as 997.1TT, 997GT2/GT2 RS, 996GT3/GT2/TT) is 4.75 lb.
The OEM 991.1 Cup bracket is also 4.75 lb.
Its neat to see where the OEM engineers increased and decreased the rigidity for the different applications with the other components of the system in consideration.