Engine pitching on my 818S track car

[Dave 53]

I think my engine has excessive pitch under hard braking.

I just discovered my right-side timing belt cover is all busted up on my 818S. I think it got busted up from the engine smashing into the radiator hose/pipe that runs between the cover and a frame rail the fire wall is riveted to. The clearance for the hose/pipe between the timing cover and frame rail is millimeters. As the engine slides forward under hard braking, it's crushing the hose/pipe between the timing cover and frame rail and the cover is the weak link. No indication that anything was rubbing on the actual cam pully.

I drove the car several thousand miles before it was track worthy without a problem and this is a new development since I started tracking the car, so I suspect this is related due to constant hard braking at the track.

Is this a problem for 818R's? What are you R guys doing?

The Subaru WRX donor car had a pitch stop arm that got deleted on the 818. Guess it was there for a reason. Has anyone fabricated a pitch stop arm on an 818?

I have OEM Subaru motor mounts which I suspect are as soft as one can find and were designed to be use with a pitch stop arm. I have found several after-market mounts from OEM, Group N to solid. Is there a solution in motor mounts? Will solid mounts lead to failures somewhere else down the road? I can live with (and might even like) vibration.

Does the coolant hose/pipe need to be rerouted? Maybe cut out the hard pipe section so that crushable hose runs between the cover and frame? But then I'd worry about the hose chaffing.

I made a temporary repair with Gorilla tape and a new cover has been ordered. I'm thinking about covering the new cover in Gorilla tape to keep bits from chunking off if the new cover breaks as the current one did. Is there some other tape product better suited for the job?

I'm willing to bet it also broke the mounting tabs for the rear cover (between the heads and cam pully). There is a little bit of slop when I jiggle the cover. But, I think I'll leave it alone. First, it's a pain to replace the rear cover which involves removing the cam pullies and second, if something has to give, maybe a little bit of flexibility in the cover isn't a bad thing.

Do I need to stop tracking the car until a solution is installed? Scheduled (and paid for) Thunderhill next weekend.

Hoping better motor mounts will fix this - that's the easiest solution.

Standing by for forum wisdom. Hoping you tell me to have fun next weekend and give me a good review on one of the several motor mounts available.

[Rob T]

I am not having that issue. Not sure kind of motor mounts Chad installed on the car, but there seems to be plenty of clearance and now damage. I was just under the car doing a full inspection on Thursday. Sorry I'm not more help. Rob

[J R Jones]

Dave, the problem you describe is a dynamic experienced with FWD powertrains, likely worse for longitudinal engines cantilevered ahead of (low) mounts.
The torque or pitch reaction link is the solution, although I have seen that Honda J series V6 uses a snubber high on the front of the engine.
The pitch or torque reaction is worse with engine braking, especially in lower gears or hard downshifts as the decel load goes into the engine, not the brakes.

A rubber snubber may be easier than fabricating a frame mount for the OEM link.
jim

[Hobby Racer]

Get stiffer motor AND transmission mounts. Group N work well. Do NOT get solid mounts, you'll rattle every nut and bolt loose!

I have Group N motor mounts and a very stiff transmission mount and have had no issues. I also probably have the least clearance between the frame and front engine cover of any 818!

[Bob_n_Cincy]

Watch my oil fill cap with OEM mounts.

I went with the mounts from Megan Racing.

https://meganracing.com/mrs-su-0940

[Dave 53]

Watch my oil fill cap with OEM mounts.

I went with the mounts from Megan Racing.

https://meganracing.com/mrs-su-0940

Yep... I can see how my timing cover got smashed. And not just because of hard braking. Looks like gear shifts or just jumping on and off the throttle throws the motor forward. Very helpful video!

Just ordered some Cusco mounts. They seem to get good reviews on the Subaru forums. Some comment that they might be too extreme for a strict street car, but my build is track first, street second. Also, only positive reviews of Group N mounts.

Maybe OEM mounts are okay for an 818 that is never auto crossed or tracked. I didn't bash in my timing cover until I took it on the track. But, maybe since the 818 deletes the motor pitch stop link, all 818's would be better off with Group N mounts. If you've auto crossed or tracked your 818 with OEM mounts, I'd suggest inspecting your timing cover. Might need to pull off the MAF section of your air intake to get a good view (give your MAF sensor a squirt of MAF cleaner while you got it off).

[J R Jones]

Get stiffer motor AND transmission mounts. Group N work well. Do NOT get solid mounts, you'll rattle every nut and bolt loose!

I have Group N motor mounts and a very stiff transmission mount and have had no issues. I also probably have the least clearance between the frame and front engine cover of any 818!

No issues? Not even ring gear or chain tensioner issues? I have heard of such things happening.
jim

[lance corsi]

I’ve read some good articles about downshifting to slow the vehicle. It generally induces more wear on the transmission, where brakes would normally be the ideal way to scrub off speed. Trans rebuild vs brake replacement. Obviously this would depend upon the circumstances.

[J R Jones]

I’ve read some good articles about downshifting to slow the vehicle. It generally induces more wear on the transmission, where brakes would normally be the ideal way to scrub off speed. Trans rebuild vs brake replacement. Obviously this would depend upon the circumstances.

Lance, Bob n Cincy's autocross video is startling. The engine may lift on acceleration more than it surges forward on deceleration. It looks like a bobble head doll.
Obviously the Subaru design is compromised, I will have to address that before any running. Another incentive to engineer the Honda V6 fitment now.
jim

[GoDadGo]

Dave,

Could you possibly rework your existing mounts with something stiffer?
I used this stuff to repair/replace some steering rack bushing on a couple of occasions.

https://www.energysuspensionparts.com/diymmi

My brother had an Avalanche and a Suburban that the rack bushings wore out over time.
I couldn't just replace the bushing so I used this stuff since the racks were still good.

Steve

[GoDadGo]

On a similar note, could you use sway bar links to create limiting straps on the front of the engine?.. A couple of pieces of angle brackets bolted to the block and/or heads linking the assembly to the frame could create a viable solution.

https://www.energysuspensionparts.co...-end-links.asp

When I was a kid we used this little trick on my 1971 Plymouth that kept tearing the drivers side motor mount... A little fabrication and a little welding solved that issue thanks to the fellow I was working for (Ken Short @ Ken's Racing Services) when I was a high school student.

NOTE:.. My job as a 15-17 year old kid was to clean up the shop, pick up the tools, before taking out the trash.

[Dave 53]

The simplest solution seemed to replace the OEM mounts with a more robust / stiffer mount than the OEM mounts.

Just got done installing Cusco motor and tranny mounts. Movement with these mounts is going to be measured in millimeters, not inches like with the OEM mounts. I can't imagine I will bust up any more timing belt covers with these mounts.

Left motor mount installation was easy. Right required taking off the lateral bolt on chassis brace to be able to raise the motor enough otherwise the turbo was bumping into it. Tranny mount was fairly easy since my rear bumper cut out is open.

New vibration is minimal. Nothing that would catch your attention if you took a ride. It's probably placebo effect, but the car does feel "tighter".

[Bob_n_Cincy]

The reason the engine bounces around so much in the 818 is 2 fold.
1. The 818 does not use the pitch stop (dog bone) that the WRX has.
2. The 818 two-wheel drive has twice as much torque on the motor and transmission mount compared to the 4 wheel drive WRX.
A few builders have incorporated the pitch stop but most have switched to the stiffer group N motor and transmission mounts.

[J R Jones]

The reason the engine bounces around so much in the 818 is 2 fold.
1. The 818 does not use the pitch stop (dog bone) that the WRX has.
2. The 818 two-wheel drive has twice as much torque on the motor and transmission mount compared to the 4 wheel drive WRX.
A few builders have incorporated the pitch stop but most have switched to the stiffer group N motor and transmission mounts.

My son has installed a supercharged Lexus V8 in his Supra that had the 2JZ inline six. It was convenient to use the six cylinder mounts but I convinced him to rework the chassis for the V8 mounts. It functions just like the Lexus, duh.
Engine types have unique vibration characteristics, flat 4, flat 6, inline 4, inline 6, V6, V8, ect. They are engineered to be soft to match isolation requirements and stiff for control/restraint purposes and fail-safe for safety.
I did engine/drive mount development with Lord in Erie PA. It is a complex challenge involving number of mounts, material amount, durometer, shape, position and mount angle.
The mounts must resolve vibration isolation and displacement in the three axis' plus dynamic pitch and roll. The cost and data collection required is staggering.
Eliminating system components and substituting materials is risky and consequential. Imagine your system having to pass safety and durability tests.
In the case of torque (and power) it all originates in the engine and is restrained exclusively by the mounts. It is distributed to two or four tire contact patches, with corresponding traction.

Measuring engine torque on a dyno can be done with a load cell on the shaft behind the crankshaft OR it can be positioned between the dyno stand and engine mount. The torque load is the same on the shaft as the twisting moment on the mount. Then the equation Horsepower = Torque x RPM / 5,252 is calculated for power. Done that too.
jim