Plates around bell-housing - racing application

[AydinZ71]

Hi all!

 

Restoring a rusted SCCA vintage race car. Previous owner installed 1/4” thk AL plates around the bellhousing. I didn’t see this in the GCR. I may have just missed it. Should I keep these? I assume they are there to protect your legs if the clutch assembly explodes? 

 

-Aydin 

[clarkspeed]

More common in drag racing but a good safety measure IF the engine is moved back so far that the flywheel is in line with your feet on the pedals. I've never seen that mod before and not sure you can move it back that far.

[AydinZ71]

44 minutes ago, clarkspeed said:

More common in drag racing but a good safety measure IF the engine is moved back so far that the flywheel is in line with your feet on the pedals. I've never seen that mod before and not sure you can move it back that far.

hey thanks a bunch! Il just get rid of them then. The engine mounting points are OEM. Appreciate it!! 

[JMortensen]

I did something similar with 1/4" steel after 3 different machinists looked at my old AZC flywheel. All three picked it up, looked at it for about 5 seconds, then looked at me and said: "That's cool. Do you have a scattershield?" I think the stuff he was selling after the 90s was better designed. Mine had sharp corner cuts right through the pressure plate bolt holes and nothing was radiused.

 

[AydinZ71]

11 hours ago, JMortensen said:

I did something similar with 1/4" steel after 3 different machinists looked at my old AZC flywheel. All three picked it up, looked at it for about 5 seconds, then looked at me and said: "That's cool. Do you have a scattershield?" I think the stuff he was selling after the 90s was better designed. Mine had sharp corner cuts right through the pressure plate bolt holes and nothing was radiused.

 

 

Speaking of flywheels, my local engine shop turns down L-series flywheels to nearly 5lbs! I am tempted since it would be much cheaper than buying new, but honestly I am not confident they have done the engineering or testing to confirm it will hold-up. I saw three leaving their shop on Instagram. Might be OK for the street, but who knows if anyone has ever put one through its paces. it would be quite dramatic if it failed. 

[JMortensen]

Takes 5 lbs off, OK. Turns a 25 lb flywheel down to 5? I don't think so, but I certainly wouldn't run it if they did. If you really want lightweight, get a button clutch that has a smaller diameter multiplate clutch on an automatic flexplate. Here's the dual 7.25" clutch I've got on my LS. IIRC the flexplate and clutch and everything was right around 20lbs.

[calZ]

What's the name of the shop? It would be interesting to look at the pictures on IG. 

[AydinZ71]

Russ_at_steves is the IG name. Steve’s machine shop. Guys, I may have totally read it wrong LOL. @JMortensen you may be totally right about losing 5lbs, not ending up with 5lbs. I attached a screen shot. That’s what happens when you jump to conclusions. It does seem illogical to cut 75% (vs 25%) of the weight just from turning. 

[AydinZ71]

While we are on the topic, any recommendations on lightened flywheels for L-series on the market? Fidanza is thicker AL, and I believe others are selling thinner steel units. 

[JMortensen]

The lightest you can get, I'd go steel if possible, and with the least mass around the edge of the wheel. You see some with holes around the perimeter. That is the way to go, as removing mass from the edge is more important than in the middle. When you go light you do have to be good about not putting too much heat into the flywheel, so if you have bad habits, you'll want to get rid of them before you ruin your new part.

FWIW the AZC one was 12 lbs, I drove with a heavy pressure plate and cammed L28 with 44s in traffic, was easy to drive. I think the crankshaft itself is so long and heavy that the flywheel weight isn't as important. Had a friend with an AL flywheel on his cammed L18 with 44s and Datsun Comp pressure plate (VERY heavy), and that thing was hard to get moving. He got used to it, but I stalled it a lot whenever I drove it.
 

[AydinZ71]

25 minutes ago, JMortensen said:

The lightest you can get, I'd go steel if possible, and with the least mass around the edge of the wheel. You see some with holes around the perimeter. That is the way to go, as removing mass from the edge is more important than in the middle. When you go light you do have to be good about not putting too much heat into the flywheel, so if you have bad habits, you'll want to get rid of them before you ruin your new part.

FWIW the AZC one was 12 lbs, I drove with a heavy pressure plate and cammed L28 with 44s in traffic, was easy to drive. I think the crankshaft itself is so long and heavy that the flywheel weight isn't as important. Had a friend with an AL flywheel on his cammed L18 with 44s and Datsun Comp pressure plate (VERY heavy), and that thing was hard to get moving. He got used to it, but I stalled it a lot whenever I drove it.
 

Your points make total sense from a rotational inertia perspective 👍🏽.

 

I feel like the lightened flywheel is a double-edged sword with a lopey cam (benifit outweighs the drawbacks). I don’t have the experience so I’m just surmising. 

 

on one hand, with a big cam like the one I have (320dur, .500lift) a lighter flywheel may make the lower RPM’s more unstable to maintain on/off throttle. On the other hand, the poor torque in the lower RPM bands will benifit from lower rotational inertia, by reving into the torque band sooner. Although, if you are keeping the rpm’s from dropping too low (consistent downshifting), the unstable lower RPM band becomes Mut. 
 

What are your experiences with that? I’m still working on chassis work so don’t have her running yet. Getting closer every day. 

Edited April 7, 2021 by AydinZ71

[tube80z]

2 hours ago, JMortensen said:

 Had a friend with an AL flywheel on his cammed L18 with 44s and Datsun Comp pressure plate (VERY heavy), and that thing was hard to get moving. He got used to it, but I stalled it a lot whenever I drove it.
 

 

I used to street drive a 10 pound flywheel with no problems.  I personally think it has a lot to do with you set the bite point where the clutch hooks up and this can vary widely between pressure plates.  That requires some fiddling between master and slave cylinder pushrod lengths.  This isn't so much a problem for the inline 6 because they make decent torque off the line.  It also depends on clutch disc material and if it has a sprung clutch hub.   

[JMortensen]

I had a .490/280 cam and wanted to step up to something like you have but ended up LS swapping instead. I love almost everything about the way lightened flywheels work. Revs drop faster so it will shift faster as a result, much easier to heel/toe, engine braking is better, acceleration is better. 2 complaints you'll hear about them is that they make it hard to hold a consistent speed on the freeway, and the trans will probably sound like it has marbles in it at idle in neutral. I never had a problem with the freeway thing at all, and the marbles thing is irritating, but worth it. I've read that it's the gears in the trans rocking back and forth because the flywheel's smoothing of the power strokes is diminished. I had a friend that was really bothered by the noise, and she had the HKS 10 lb flywheel. Seemed a lot more noticeable in her Z than mine, not sure if that was because of engine or trans mounts or different interiors or what. 

[tube80z]

2 hours ago, AydinZ71 said:

Your points make total sense from a rotational inertia perspective 👍🏽.

 

I feel like the lightened flywheel is a double-edged sword with a lopey cam (benifit outweighs the drawbacks). I don’t have the experience so I’m just surmising. 

 

on one hand, with a big cam like the one I have (320dur, .500lift) a lighter flywheel may make the lower RPM’s more unstable to maintain on/off throttle. On the other hand, the poor torque in the lower RPM bands will benifit from lower rotational inertia, by reving into the torque band sooner. Although, if you are keeping the rpm’s from dropping too low (consistent downshifting), the unstable lower RPM band becomes Mut. 
 

What are your experiences with that? I’m still working on chassis work so don’t have her running yet. Getting closer every day. 

 

I guess one question is how low RPM do you plan to drive?  When racing I'd think most of the time you'd be above 2500-3500 on the low end and a light flywheel will be helpful.  

[AydinZ71]

1 hour ago, tube80z said:

 

I guess one question is how low RPM do you plan to drive?  When racing I'd think most of the time you'd be above 2500-3500 on the low end and a light flywheel will be helpful.  

Oh I I’ll likely be driving between 5-7500rpm with this head. Il just need to get used to getting back into that range if I drop off for some reason. This is my first long duration cam so it will take some getting used to. 

[JMortensen]

I think you'll find that all those warnings you heard about not having any bottom end are way overblown. It will be fine, you're going to love it.

[Michael]

To affix aluminum plates to the transmission tunnel, as a completely new feat for me.  Isn't the more common approach a "blowproof" bellhousing?  Something like this: https://www.holley.com/brands/lakewood/products/drivetrain/bellhousings/ .  These are unfortunately very heavy (maybe 40 lbs), but aren't they required by the NHRA?

[AydinZ71]

3 hours ago, Michael said:

To affix aluminum plates to the transmission tunnel, as a completely new feat for me.  Isn't the more common approach a "blowproof" bellhousing?  Something like this: https://www.holley.com/brands/lakewood/products/drivetrain/bellhousings/ .  These are unfortunately very heavy (maybe 40 lbs), but aren't they required by the NHRA?

possibly. I didn’t see anything in the rule book about it for SCCA production or general spec. As someone mentioned, it’s more commonly found in drag racing with dangerous amounts of torque. 

 

 

[Dime Dave]

The SCCA GCR still requires scattershields, it is in Section 9. Your installation is not an unussual way of complying with the rule.

Quote

9.3.40. SCATTERSHIELDS/CHAIN GUARDS
The installation of scattershields or explosion-proof bell housings shall be required on all cars (except Spec Miata, Touring, B-Spec, and Improved Touring) where the failure of the clutch or flywheel could create a hazard to the driver. Chain drive cars shall be fitted with a protective case/shield to retain the chain in case of failure.

 

Minimum material specifications are:

.125 inch SAE 4130 alloy steel

.250 inch mild steel plate

.250 inch aluminum alloy

NHRA or SFI approved flexible shields.

 

Edited September 23, 2021 by Dime Dave

[AydinZ71]

Yeah I absolutely read that! I plan to just put them in. 1/4" AL plates I have. Comes in at a little over a pound, so not the end of the world. Weird that Greg Ira did not install them and he is the EP champ. I spoke to him about this like 6 months ago, and I think he mentioned arguing that the exposure of the bellhousing horizontally to the adjacent pedal area was insufficient to warrant a concern. Most of the bellhousing is just outside the tunnel. 

 

Meh...il just put them in. I just had them sandblasted and repainted anyways