Stock flexplate strength

[Engo]

How strong is a stock flexplate, assuming it is in good condition. Will it hold up behind a 455 making approx 500 hp on motor + 150 hp nitrous plate system, connected to a 10" raceconverter. Car is 69 Bird approx raceweight is 3600 lbs and on drag radials. Engine is shifted at 5800 rpm.

[Engo]

How strong is a stock flexplate, assuming it is in good condition. Will it hold up behind a 455 making approx 500 hp on motor + 150 hp nitrous plate system, connected to a 10" raceconverter. Car is 69 Bird approx raceweight is 3600 lbs and on drag radials. Engine is shifted at 5800 rpm.

[PONTIAC DUDE]

Let's put it this way. You combo's probibly gonna run in the 10's, so NHRA requires a SFI flexplate. Never seen one shatter, but I imagine it has happened. I have noticed that the thicker plates produce less tooth wear on the Pontiacs as mesh is always an inherant problem, fer some reason. Less flex means better cranking contact. I just can't figure why they charge THREE TIMES as much for the same basic configuration & time can't be more once the tooling is done. Someone explain the pricing structure to me as I'm either lame (don't say it, Scott,Gach,David,TM or Dillon) or missing a cost factor somewhere. Later.

[Brian Baker]

OK, Dude, I'll say it, you're lame (LOL). Only kidding, now seriously, the price structure is probably based on the same principle as everything else for Pontiacs in the aftermarket world. Pontiac parts don't sell as much as Chevy, and therefore, will generally be more expensive (depending on what it is).

[Jerry Brock]

I had 2 stock flex plates crack at the center and finally bought a TCI flex plate. I have had no problems since.

[Paul Spotts]

I have seen many stock flex plates crack and never had one on any of my motors. I think PD hit the nail - its starter mesh. most people do not properly shim the starter for proper mesh or use the brace on the front of the factory starters, constanly stressing or flexing the flexplate(kinda oxymoron). I was also wondering how the small blocks have $40 SFI plates while we pay over $100 - so that is one of my goals I'm persueing - made a couple of calls - does seem to be the numbers game.

[PROBRD]

Does anyone make an SFI flexplate that is zero balanced? I screwed up and forgot to send it in when the engine was at the machine shop and the engine got balanced for a zero balance flexplate. I took my stock one and had it zero balanced. I don't think your supposed to go drilling any balance holes in an SFI flexplate. So far I've snuck through tech without it but I would feel better if were SFI approved. What now?


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PROBRD
(probrd1@aol.com)

[Engo]

Thanks for the answers guys. I´m goin to run the stock flexplate this summer and see how it turns out.

[PONTIAC DUDE]

Let me get this right, Opinion wanted on STOCK flexplate. 3 negitives, no positives, 2 questions on price & balance, & your gonna run the stock piece? Why did you even ask if you planned to run it after all the negitive responses with your combination. Just curious,what your reasoning is?

[Triggerman]

I agree with The Dude, I wouldn't run a stock flexplate on a motor developing that much power. I'm sure catastrophic failures are extremely rare...but when they do come apart it is....well.....catastrophic. It makes a serious mess of your car (assuming that if your not buying a flexplate, your also not buying a shield) and could cause personal injury. Having a part like this go away on a run could have serious implications. Could puncture a slick and put you on the roof (boy, I hate that view!). If NHRA requires this, it probably means that someone has been injured pretty bad at some point. As to the balancing question...take the aftermarket flexplate down and have it zero balanced. I've been tech'd by the toughest tracks in FL and I've yet to have a tech crawl under my car to even look for the sticker on the flexplate....much less look for any additional drilled holes. Sorry...didn't mean to get on a rant. TM

[Engo]

Well dude my reasoning goes like this. I do very well know that flexplates, and not just stock ones, sometimes shatters or breaks into pieces. The question was however if a stock flexplate will hold in my specific combo. As you know, every part has a stresslimit and I just wanted know if anyone in this forum knew anything about the stresslimit of a stock flexplate. The price issue of SFI approved aftermarket flexplates for Pontiacs is of course also important but not decisive for me. There are many cars out there running +500 hp 455s with stock flexplates and no problems. But, how much stress will the stock flexplate take?

[PONTIAC DUDE]

Ok, I'll put it like this. You are running a compression engine with roughly TWICE the HP of a STOCK engine, which takes more cranking AMPS, thus creating a load on the flywheel ring gear, that tranfers to the flat plate to the crank flange. The factory unit is very thin in material, PLUS has a bizzion BIG holes drilled in it and puts a hell ava strain on the flywheel bolts. The SFI unit mandated buy ALL RACING organization is thicker to eliminate cracking in the bolt area. What usually happens is the STOCK plate cracks around the flange, from bolt hole to bolt hole, and when your in high speed mode it discinagrates(whatever, spell it like it looks, right Gach?) taking the back of the assembly with it, if not the engine. Look at both flywheels & compare. This is your brain (SFI flywheel)& this is your brain on drugs (stock flywheel) American warped sense of humor. Hahahaha. Hope this post at least sorts out some logic.

[Triggerman]

Engo, I read your post and I get the impression that you are aware of some NHRA certified flexplates that have come apart?? If this is the case I would be interested in knowing the conditions that these failures occured. I was thinking that these units were overdesigned and kinda bulletproof. TM

[Engo]

Triggerman, on a couple of occasions I have seen flexplates came into pieces for other racers(non pontiacs) I don´t know what kind of flexplates all these was but I know for sure that one of the guys had a so called SFI approved flexplate. It was behind a CBB 454 in a all steel heavy Chevelle with slicks and happened just when he left the line.

When choosing the right parts for my race cars I always try to pick only the parts really needed, rather than to just do like everyone else and run into aftermarket madness. If I knew that my car needed a aftermarket flexplate (or whatever part for that reason) I would get it. But if my car can perform as well with a stock (at hand) part I will use that part.

I guess only the engineer that designed the stock flexplate can tell what the stresslimit is.

[Scott Misus]

I have to agree with Engo on this one, and for the very reason that Matt mentioned (no visual inspections are ever done). I can't help thinking that many NHRA safety regulations are passed strictly for the revenue enhancements of favorite NHRA advertisers. The two year seat belt interval comes to mind.

Engo thinks like an engineer: "Who says that the aftermarket parts are any better than the factory ones, which have millions of dollars of R&D behind their development?" I liked his comment regarding the factory engineer. He's exactly correct.

The problem is that small block Chevies, with their inherently crappy designs and inferior materials (cast iron balancers) brought this on and we now have to live with it. Or we can just choose to race in the slower classes.

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[David Holmberg]

Engo, I have seen a flexplate come apart during a run twice, the first time it took off the drivers legs below the knees. The 2nd time was at butlers in 98, the camaro racing in the other lane came back to the pits with dents and holes in his car with one piece going thru the drivers window and nicking his lip and exiting the other window. That was close, I hope you re-think using one.

[This message has been edited by David Holmberg (edited 03-26-2000).]

[Triggerman]

I like how Engo is evaluating the need based on design parameters, (there are lots of areas where this method works really well) I just don't agree with his conclusions for his particular application. However, we all understand that this is his decision to make and results to live with. The advantage of this board is the many opinions to hear so a person can make the decision they feel is sound to them. Scott, I partially agree about the "revenue enhancement" issue...that seat belt ruling has been making me crazy for years. There are a couple of seasons where I had about 30 - 40 passes on my belts...Heck, I know they're not worn out! However, I feel that the vast majority (if not all) of these safety equipment rulings are the result of a racer injury or death. I would encourage anyone to err on the side of caution. The R&D that was done at the factory(as great as those guys were) may not have anticipated the abuse that we place onto these parts while racing. TM

[Engo]

David H: Thanks for your comment. Do you know if the flexplates you saw come into pieces were stock or aftermarket? If not I don´t think your comment is relevant. For safety reason you use shield. I do.

Triggerman: Your comment on the effects of a broken plate such as a punctured slick is well put. I understand your reasoning as "better be safe than sorry" and that I can agree with to a certain limits.

Thanks again all of you guys for your answers.

[Triggerman]

You're quite welcome. The slick flattening comment isn't conjecture....it happened. I didn't drive over anything (pulled the valvestem out of the tube), but could have easily de-aired it that way too. Bad news was it happened in the traps at 137...good news was (besides lots and lots of vibration) car still basically went where I wanted it to. However, I was riding in a car that was virtually irreplaceable...certainly not just a collection of parts that I had no emotional attachment to. Going into the guardrail or onto the roof would have been very ugly. It made me walk around the car later with a new perspective and re-evaluate most every piece of safety equipment on the car. TM

[David Holmberg]

Engo, they were both stock flexplates. I just look at the time and effort to replace one with the cost of a beefier SFI plate. I don't think you will have any problems with your stock one but they were designed for a stock motor to be used in a stock setting. Let us know how quick you go, the combo sounds nice.