Blower spacer bolt length?

[Scott]

I have a supercharger spacer kit from my old Hellcat.
Will I need longer bolts to put it on my new Redeye?

 

[BULL]

Depends on if you were ok with the bolts that are too short in the first place...

 

[Scott]

Depends on if you were ok with the bolts that are too short in the first place...

What do you mean by that? Is there a better fitting length for the spacer kit?

 

[BULL]

The OE bolts have the correct and optimal thread engagement.

If you add a 10mm spacer, but only increase the bolt length by 5mm, now the thread engagement has been reduced by 5mm.

Of note, the thread is aluminum, so engagement is even more important.

I and some other members chased a variety of options, but none were any better, or were very expensive (very).

The option I'm currently, slowly, chasing is welding the correct length shank to an OE bolt head, using two sets of OE bolts, cut to the correct length. I have the bolts, I just haven't gotten around to doing it.

 

[coolblue]

The OE bolts have the correct and optimal thread engagement.

If you add a 10mm spacer, but only increase the bolt length by 5mm, now the thread engagement has been reduced by 5mm.

Of note, the thread is aluminum, so engagement is even more important.

I and some other members chased a variety of options, but none were any better, or were very expensive (very).

The option I'm currently, slowly, chasing is welding the correct length shank to an OE bolt head, using two sets of OE bolts, cut to the correct length. I have the bolts, I just haven't gotten around to doing it.

I have never heard of that. I have made many, many custom length bolts over the years for different purposes but I always bought an overlength bolt, cut to length desired, then used the proper die to cut the threads.(always an argument of superiority of rolled threads v.s. cut threads) I would never trust a welded on head for a stress related component. Unless you are an absolute expert and used a tig then maybe but I personally wouldn't trust it. I was a nut (pun) for this kinda stuff for a while and actually bought a fastener book that explained all sorts of fastener's grades, materials and purposes including aviation apps. I even experimented with "grade 9" hardware and stressed to failure just to see if they were indeed stronger. Again, I just would not trust it. Just my .02.

 

[Scott]

The OE bolts have the correct and optimal thread engagement.

If you add a 10mm spacer, but only increase the bolt length by 5mm, now the thread engagement has been reduced by 5mm.

Of note, the thread is aluminum, so engagement is even more important.

I and some other members chased a variety of options, but none were any better, or were very expensive (very).

The option I'm currently, slowly, chasing is welding the correct length shank to an OE bolt head, using two sets of OE bolts, cut to the correct length. I have the bolts, I just haven't gotten around to doing it.

Is there enough material there to counter bore the lid deeper to help?

 

[BULL]

Is there enough material there to counter bore the lid deeper to help?

I would not do that myself, and certainly not the 5mm needed increase, but to be honest, I haven't specifically checked.

Just as a reminder, while I believe this is a legitimate concern, the flip side of this same coin is that I don't know of anybody that has solved it, so that means that everybody that is running the spacers is running with this "issue", and I also haven't heard of anybody RIPPING out the threads in the aluminum heads...


My profession is mechanical engineering, so I tend to be a bit "sensitive" to things like this...

 

[Scott]

I have never heard of that. I have made many, many custom length bolts over the years for different purposes but I always bought an overlength bolt, cut to length desired, then used the proper die to cut the threads.(always an argument of superiority of rolled threads v.s. cut threads) I would never trust a welded on head for a stress related component. Unless you are an absolute expert and used a tig then maybe but I personally wouldn't trust it. I was a nut (pun) for this kinda stuff for a while and actually bought a fastener book that explained all sorts of fastener's grades, materials and purposes including aviation apps. I even experimented with "grade 9" hardware and stressed to failure just to see if they were indeed stronger. Again, I just would not trust it. Just my .02.

I would not do that myself, and certainly not the 5mm needed increase, but to be honest, I haven't specifically checked.

Just as a reminder, while I believe this is a legitimate concern, the flip side of this same coin is that I don't know of anybody that has solved it, so that means that everybody that is running the spacers is running with this "issue", and I also haven't heard of anybody RIPPING out the threads in the aluminum heads...


My profession is mechanical engineering, so I tend to be a bit "sensitive" to things like this...

Someone needs to contact APR to have them make a correct bolt or stud with nut on top.
Or order/source chrome Molly thread rod and make our own.

 

[Diboblo]

So, what is the optimum target length, for the bolts... and grade?

Bob
Riverside, California

 

[BULL]

So, what is the optimum target length, for the bolts... and grade?

Bob
Riverside, California

I'll have to get back to you on that,. I have notes somewhere.

What makes it a challenge is the combination of the non-standard length, flange-head hex drive, and zinc plating.

Cutting down a black-oxide SHCS results in a bolt that corrodes and due to the reduced head diameter, digs into the face of the S/C lid. It also requires that you run a die up the shank because that length bolt is only partially threaded.

 

[Mike L.]

Has anyone contacted Forced Induction about this?

 

[BULL]

Has anyone contacted Forced Induction about this?

Yes, he does not see this as a problem.

 

[motorhead]

Yes, he does not see this as a problem.

Typical vendor.

 

[Diboblo]

Yes, he does not see this as a problem.

This is why I haven't purchased a set.

Way back in the olden days, I ran 10mm spacers on my 6.1L Charger. First thing I did was go out and get longer intake bolts. That huge aluminum intake was heavy and I didn't want to going anywhere, or any air leaks.

After I get my supercharger replaced, I'll look more into this situation and keep an eye on this thread, for more info.

Bob
Riverside, California

 

[BULL]

To be clear, there are longer bolts provided with the kit, but they are only 5mm longer, whereas the spacers are 10mm thick...

The issue is what is available off of the shelf in "commodity" lengths, versus a custom order for what would be a very expensive bolt.

 

[Mike L.]

Is there a better gasket available without the weakness? I'd be in for that. I won't install my spacers untill a better bolt is available.

 

[BULL]

Is there a better gasket available without the weakness? I'd be in for that. I won't install my spacers untill a better bolt is available.

Near as I know, this is the ONLY spacer available...

 

[BULL]

FYI:

Stock bolt length - M8 * 195mm with 15mm thread engagement

Spacer thickness - 10mm
Supplied bolt length with spacer kit - 200mm (with ~10mm thread engagement)

 

[Magnified]

Has anyone had the "supplied" bolts fail? I am a big one for over-engineering any solution (the elevator principle) but I would have to suspect (or hope) that they would have done some destruction testing on this set up before marketing it. If not, there could be a potential case there for design defect...

 

[BULL]

Has anyone had the "supplied" bolts fail? I am a big one for over-engineering any solution (the elevator principle) but I would have to suspect (or hope) that they would have done some destruction testing on this set up before marketing it. If not, there could be a potential case there for design defect...

View attachment 11233

If there have been failures, I'm not aware of them. But, clearly, there is MUCH I'm not aware of...