4L80E (and 383 stroker) project

[storm9c1]

Hey all, I am re-powering my '69 flatbed.

I have a freshly built 383 stroker with a forged crank, internally balanced (and thus a 2-piece rear main seal). This crank has a 3.58" bolt pattern for the flexplate. I am mating it with a 4L80E. Problem is, the 4L80E was mainly designed for 1-piece rear main seal cranks with the 3" bolt pattern.

My torque converter is a 11.5" bolt circle (and a 6-bolt).

Anyone have any suggestions on what flexplate to use? I've been searching for weeks, came up empty so far.

Anyone else do this and what flex plate did you use?

Another option would be for me to re-drill holes in an existing flexplate (ie: a 3-bolt re-drilled for 6-bolt), but I really would rather avoid that. And also I would like to avoid a custom converter as well since I like the 6-bolt. This is going into a 1-ton truck that will see 12,000 lbs of towing.

[clinebarger]

I dont think anyone makes a 2-Piece seal flexplate with the dual(6) 11.5" converter bolt pattern.
The Dual 11.5" pattern is a 1-piece/4L80E only thing.
I whould redrill a new SFI approved flexplate

[ripdog28]

Email or Call Jake...

940-458-5564
jake@jakesperformance.com

This is his site.

He is the trans king.. Knows a lot about doing this kind of trans set up and can get you the parts needed.

[storm9c1]

Originally Posted by ripdog28

Email or Call Jake...

940-458-5564
jake@jakesperformance.com

This is his site.

He is the trans king.. Knows a lot about doing this kind of trans set up and can get you the parts needed.

Thanks. Email sent. Local guys keep telling me to use 3 bolts. But my converter has 6 bolts and I really really want to use all 6 bolts. Most think I am crazy for wanting to over-engineer stuff. But a project like this is all about the details. And that's the way I roll.

[storm9c1]

OK, Jake wasn't able to help me with the flexplate. But I may buy some other parts off of him.

Oddly, just doing some hit-and-miss searching on various automotive websites, I found a flexplate for a the 292ci (6 cyl motor) that appears to have the 6-bolt setup. Does anyone know if the crank hub is the same on the 6cyl as a 2-piece SBC V8? And why the heck would they offer a 6-bolt torque converter (assuming TH400HD which a 6-bolt should have the same pattern as a 4L80E) behind the 6cyl and not the V8? This is driving me nuts.

[ripdog28]

You know most flex plates only use 3 bolts. I have a 10in 3500 stall verter and only using 3 bolts.

[storm9c1]

Originally Posted by ripdog28

You know most flex plates only use 3 bolts. I have a 10in 3500 stall verter and only using 3 bolts.

Sure. But since my brand new torque converter is a 6-bolt, it seems silly to let a flexplate hold me back from doing it right (which if I knew it would be this hard to find a flexplate, I would have made a different decision on the converter). My truck sees 12,000 pounds towing various classic cars, so I purposely want to overengineer as much as I can. The easy way out here is to use 3 bolts. But I never take the easy way out. Story of my life. LOL.

[Captainfab]

The Mark IV 454's that were backed with the TH475 (motorhomes) had all 6 holes in the 11.50 bolt circle since the TH475 used a 6 bolt converter. But that doesn't help you with an internally balanced 383, just a little FYI.


If it were me, I would carefully elongate the other 3 holes that are for the 10.750 bolt circle out to the 11.5 circle. As long as you maintain the width of the hole, I don't see a problem. The stock holes typically aren't that tight with the bolt. In fact some I've seen were actually an oval hole from the factory.

[storm9c1]

Originally Posted by Captainfab

The Mark IV 454's that were backed with the TH475 (motorhomes) had all 6 holes in the 11.50 bolt circle since the TH475 used a 6 bolt converter. But that doesn't help you with an internally balanced 383, just a little FYI.


If it were me, I would carefully elongate the other 3 holes that are for the 10.750 bolt circle out to the 11.5 circle. As long as you maintain the width of the hole, I don't see a problem. The stock holes typically aren't that tight with the bolt. In fact some I've seen were actually an oval hole from the factory.

Yes, I researched both of these points (I was also searching for a flexplate for the TH475 aka TH400HD). Struck out there too.

I may go the re-drill route on the "dual pattern" flexplate.

My latest lead though is that a 292 I6 was offered in a late 70's C30 and came with a 6-bolt flexplate. And it's also my understanding that the 292 is the same crank pattern as a SBC and also uses the same bellhousing for the TH400. Which also tells me that it's compatible with a SBC. It's also not weighted, another good thing. So I am going to head to my local Advance and pick up one of these flexplates for $41 and see how it lines up. If it looks as strong as my other flexplate, and it bolts up, that's good for me. Anyone have any objections or comments about this plan? I know the 292 was a torque monster down low which explains the 6-bolt mount. And most of the research I've done tells me that the crank bolt pattern and bellhousing spacing was relatively universal between 6cyl and 8cyl engines until '86. I am hoping that someone comes along and says "yeah, I've done that and it definitely works." Otherwise I guess I'm the guinea pig and will report back here with my definitive findings.

Boy, who would have thunk that I would have ran into these troubles with an engine swap...a $41 flexplate is holding up a several thousand dollar project. That never happens, huh.

[Captainfab]

As far as I know the 292 I6 flexplate will bolt up to a small block. It seems like I've heard that they use 2 dowel pins instead of 1. And yes to the 292 having the same bellhousing pattern as a small block or big block. Please do let us know how this works out. I'm kind of surprised that you were able to find a flexplate for a 292.

[storm9c1]

Well the parts from Advance came in.




The flexplate is correct! A 6-bolt. Finally. However, the bolt holes for the crank are larger than my other flexplate. Is this an issue or will the crank hub keep it properly centered? It also came with 3 new dowel pins, none of which fit THIS flexplate or crank. Nor do I even think I need them since it appears to be neutral balanced. Why did they send them if they don't even fit?

Does anyone know what the spacer is for at the top center of the pic? Never seen one of those before. Center hub size is same. Bolt pattern is same, so it's not an adapter. Could it just be a reinforcement? Haven't tried to bolt up the converter. Perhaps it's for the nose of the converter? Not sure.

Also pictured is the "Nippon Denso" (AKA "mini") style starter. Also from Advance. This is for a 8.1L 2003 Yukon/Silverado. Notice the offset (L) shaped bolt pattern. This perfectly matches the mount pattern for a SBC. It will bolt right up. And it's a 168 tooth gear pattern. Lifetime warranty FTW as well. $118. Much cheaper than those aftermarket "mini starters". Yet the same thing. I've used starter swaps like this in other applications and these starters last forever. I may cross post this pic in the "mini starter" thread.

Flexplate is Advance PN 04376, starter is Advance PN 17420. This flexplate is a CRITICAL part for anyone doing a 4L80E swap with a 6-bolt converter into a truck with a 2-piece rear-main seal crank. This has taken me weeks to dig up. And not one trans shop that I called had any idea about this flexplate (or flywheel for those who call it that).

[Super73]

My guess is the part in the upper left is a spacer. I know 4L80E's with a factory flexplate behind an LS motor require one becuase the crank is physically shorter than the Gen 1 SBC's. You may need it, you may not. Put the flexplate on the crank and bolt the starter up before putting the trans in to see if things line up correctly. If the trans needs to come back out, you will have saved yourself some time.

[storm9c1]

Originally Posted by Super73

My guess is the part in the upper left is a spacer. I know 4L80E's with a factory flexplate behind an LS motor require one becuase the crank is physically shorter than the Gen 1 SBC's. You may need it, you may not. Put the flexplate on the crank and bolt the starter up before putting the trans in to see if things line up correctly. If the trans needs to come back out, you will have saved yourself some time.

That was my initial thought. But that's the interesting thing here. This flexplate was ordered as a stock part for a 1978 C30 with a TH400 and 6cyl 292. And if I cross this flexplate PN in just about every parts database, it lists for the 73-79 straight-6 292 and a few other V6s applications to 1989. If this is really a spacer for the LS, it would show up as a cross for those applications as well. The 4L80E or the LS wasn't even invented yet. Plus it doesn't look like one of the LS spacers anyways. Nor is the center circle for the hub the right diameter for LS. So the question is, did older motors need such a thing? These oddities drive me nuts. I'm thinking not needed for my V8, but the good news is that I will be test fitting the transmission OUT of the truck just to be safe.

Even though the metal looks as beefy as my other flexplates, I hope it holds up to my stroker/4L80E setup. I'm still dumbfounded as to why GM used 6-bolt converters on the 292 application and not the SB. I did find one for a BB application, but it was weighted and the weight looks hard to grind off.

Should I worry about any of this stuff?

[BigDan3131]

Have you mated that convertor to the tranny? Does it fit like its supposed to? What trans did that convertor come from? Have you asked companies like Art Carr and TCI or B&M about your swap?

[Super73]

Maybe it is a spacer for the I6?

[storm9c1]

Originally Posted by BigDan3131

Have you mated that convertor to the tranny? Does it fit like its supposed to? What trans did that convertor come from? Have you asked companies like Art Carr and TCI or B&M about your swap?

A local pro shop that I've used for years put together this setup for me, trans and converter. And he knew what engine I was mating it with. He even asked me the cam specs and how much weight I expect to pull so he can get the right converter. He did not give me a choice of a 3-bolt or 6-bolt converter. He knows my truck, and he said 6-bolt converter for my type of towing. Period. But he struck out regarding the flexplate, as does everyone else it seems until I found this 292 version. I have everything else I need, the Baumann controller, TPS, cooler, lines, VSS, Cable-X box for the speedo, I mean I did my homework here, and I didn't skimp out on anything along the way.

Regarding this issue, I checked with TCI, B&M and Jakes Performance (Jake deals with 4L80E swaps). In fact, I ordered the Baumann TCU from Jake.

My problem is that I have a weird setup. I have a forged crank, fully internally balanced, with a 2-piece rear seal (which the engine builder claimed that the 1-piece forged cranks were on backorder for months). So there has been a comedy of errors here...all focused at this flexplate. I have an engine that's ready to jump, a fresh transmission and all of the goodies. And a darn $41 flexplate in the way. I could have dropped a modern LS motor in my truck like everyone else does who wants the 4L80E, but honestly, a carb motor belongs in there. And more importantly, I have a hydraulic pump pulley setup that is custom made for a SBC that runs the tilt bed. I didn't want to mess with that setup. So an iron-headed 383 stroker, built for torque and towing plus a fresh 4L80E seemed like a good choice for this application. And would swap right in. Or so I thought.

I digress. If all else fails, I can still elongate/re-drill the other flexplate I have (for 6-bolt) or run 3-bolts. But darn it, I wanted to solve this. And I wanted to share my findings. I'm stubborn like that. Here's hoping that the 292 flexplate doesn't let me down.

[Captainfab]

Thank you for your research in finding these parts, and sharing the results with us here.

I don't know for certain, but my guess is that ring is a reinforcement that goes between the flexplate and the bolts. As long as the center of the flexplate fits your 383 crank snuggly, and if the dowel pin in your 383's crank will fit one of the 3 holes in the flexplate, you should be fine.

You might start a thread over in the '73-'87 section to see if anyone over there is familar with the 292's backed with the TH400.

[storm9c1]

Originally Posted by Super73

Maybe it is a spacer for the I6?

I was hoping someone could confirm/deny that. As far as I know, there isn't a spacer needed for the I6. The crank hub and offset is the same as a SBC.

The only thing I could think of is there were a few V6 models that this fit. Maybe one of the V6's needed the spacer. I wish I knew... Any other theories out there????????

I'm probably going to ignore that spacer and the dowel pins that don't fit and just bolt it up like any other flexplate for a SBC. There appears to be no difference in offset than my other SBC flexplates. And the thickness in metal is the same as other stock flexplates for various SBC and BBC applications. The cut and welds are also the same (single sided welds for the gear). I have another aftermarket flexplate that is welded on both sides, but my understanding is that all stock flexplates are only welded on one side. So apples to apples so far.

I guess I won't know if apples are really apples until I shatter the dang thing towing 12,000 lbs uphill at 60 MPH? Hrrrmmmmm.

[storm9c1]

Originally Posted by Captainfab

Thank you for your research in finding these parts, and sharing the results with us here.

I don't know for certain, but my guess is that ring is a reinforcement that goes between the flexplate and the bolts. As long as the center of the flexplate fits your 383 crank snuggly, and if the dowel pin in your 383's crank will fit one of the 3 holes in the flexplate, you should be fine.

You might start a thread over in the '73-'87 section to see if anyone over there is familar with the 292's backed with the TH400.

OK, good suggestion. I was thinking the same thing on the reinforcement. If it clears the converter, I may just use it that way anyways (I'd have to get longer crank hub bolts though). That's an awful beefy setup to be behind an I6.

Oddly, my 383 forged crank does not have a dowel pin. My guess is because it is internally balanced and doesn't need a weighted flexplate (and thus not clocked)? That little detail has puzzled me since I embarked on this journey. But the I6 flexplate bolts up regardless.

[Captainfab]

Those 292's do develop some torque. Not quite like a BBC, but they do, do OK. My '63 C60 has the 292, and I've rolled at 30,000# with truck and trailer.

[storm9c1]

Originally Posted by Captainfab

Those 292's do develop some torque. Not quite like a BBC, but they do, do OK. My '63 C60 has the 292, and I've rolled at 30,000# with truck and trailer.

Maybe I should have swapped in a 292 instead.
Great motor actually. Certainly underrated. 30,000#? That makes me feel a little better. However, that's most likely with a manual trans, thus no flexplate. This flexplate does belong in other C30s, which all are spec'd to tow 10K to 12K usually (esp the duallies). So perhaps I'll be OK.

With the money I've spent, I could have also gone with a BBC for just a few dimes more. But as I mentioned, I needed to go with a SBC to minimize pain in several other areas.

[BigDan3131]

Could you possibly sell of everything as a pkg deal and get a th400? My thinking is if you could because I know you want the OD feature, get the th400 and then buy a factory rebuilt Gear Vendors Overdrive unit. Instead of just have 3 plus OD it would turn the th400 into a 6 speed of sorts.

[D13]

292 uses 3 dowel pins, align reamed. It is designed to use larger bolts, needed in HD truck manual trans applications. IIRC in a manual trans the plate retains the pins (they don't go thru it). Since the cranks are the same the auto trans application that came later takes the plate, pins, and big bolts too. Many were used in C30/40/50/60 trucks so they were designed to be very used for a lot of loaded work, and you don't want empty holes in the crank flange when lugging all the time.
The plate also acts as a reinforcement that sandwiches the flex plate to the flange (goes between the flex plate and the bolt heads). This helps prevent cracking (spreads the bolt loads out). As you can tell by time you get all the bolts and pins in there's not a lot of metal left at the flange. The combo should be neutral balance.

Reading the LS swap threads they usually need to add a spacer to get the flex place back to an 'old style' converter. But if your 4L80E is pre-LS then it should be set up for SBC flex place position which is the same as the L6 position. I'd measure the block to mounting distance, and then the plate pad to converter pad clearance once it was in.

I'm assuming it's a 168 tooth flex plate to match the 168 tooth starter you show.

There is no 'net' hole on the flex plate? Then the alignment must be in the crank pilot. Be sure to lube it, and make sure your converter has enough snout to clear the bolt heads. I'd be real tempted to check and correct it's run out after I snugged it up to the plate. IIRC the 6-bot converters used big bolts with fairly tall stand offs and may have had long snouts.

As a curiosity, how about a flex plate from a 350 powered C40/50 w/auto trans? Those also should have used the hd TH400 converter (pretty sure that's where the 6 bolt single pattern comes from).
Anyway, keep us updated!


Inquiring minds want to see the result!

[storm9c1]

OK, here is the update you asked for. But not quite the update you are thinking...

I didn't like the fact that the flexplate (I6 version) needed 1/2" bolts, yet my crank was the typical SBC which takes 7/16". So I went back hunting. The problem I originally had is that websites typically need a make/model/year. I know Summit is nice because you can do extensive searches based on engine, which I tried, but did not find ANY flexplates for TH400HD (6-bolt). Nor Jegs. And LMC truck doesn't have pictures of their flexplates.

I learned that ATP made this I6 flexplate that I got, so I decided to see who is this ATP company. Well it turns out they are Dorman. Gee, imagine that. All run-of-the-mill parts stores roads usually lead to Dorman. But that's where it became sweet. Dorman has a nice website where they have pictures of EVERY flexplate they stock. So I browsed through pages and pages of flexplates, stopping at the ones that met my specifications (6-bolt converter, no weights). I found two more flexplates that look more appropriate:

Dorman/ATP #04321: '69 Corvette 5.7L
Dorman/ATP #04327: '79 C30 5.7L w/ TH400HD

I ordered both.



A picture speaks 1000 words. The one at the top is the I6 flexplate plus reinforcement plate, plus dowels. The one on the left is the '79 C30 truck flexplate. The one on the right is the '69 Vette flexplate. And my 4L80E converter is all the way on the right.

I was afraid that the converter holes would be different between the truck and Vette flexplate, which is why I ordered both. And they are different. The truck flexplate has wider, ovalish holes. Looks like it would be easier to service (more forgiving to change) on the truck. The Vette flexplate has perfectly round holes. The metal looks to be the same thickness, but the website says that the truck Flexplate weighs .2 pounds more, which equates to more metal in my book. Also, surprisingly, the truck flexplate has a "Made in America" stamp on it whereas the Vette flexplate has a "Made in Mexico" stamp on it. Needless to say, the Vette flexplate and the I6 flexplate will be going back to the store. We have a winner. I'll be keeping the one on the left, "Made in America" FTW.

Now here is the final question, do I need a reinforcement plate for the SBC truck flexplate? Or is that reinforcement plate only appropriate for the I6 which takes 1/2" bolts and thus has less metal around the hub assembly?

And yes, I mounted the converter to the flexplate with the reinforcement plate plus the bolts, and as long as I use ARP bolts with no lock washers, I have clearance. But barely. Cheap bolts that need lock washers will not fit. This will be a non-issue if I don't need the plate. Either way I will be using the ARP bolts. On the converter side, I thought it was the standard 3/8" bolts, but actually it's a metric bolt, probably because 4L80E is modern and GM seems to like metric these days. I can't remember the metric size off the top of my head, but it's very very close to 3/8". And they fit in the flexplate with a little extra play...just enough but not too much. One hole in the flexplate is smaller which fits the bolt tightly, combine that with the crank hub and converter snout, and I think the flexplate and converter will center itself.

Oh and to answer your question, it's an early 4L80E designed for the typical SBC setup...NOT LS. Actually, from what I read, the 4L80E in general was never made for the LS series. The mating and offset correction for the LS series comes with the flexplate and adapter special for that setup. Not the case for me. Which is why I even dared to swap in a 4L80E. And which is why I got the older style 4L80E with the front cooler lines and immediately had it rebuilt and beefed up. I figured it would be an easy setup (mechanically). Too bad this flexplate fiasco kicked my butt.

Oh, and to answer someone else's question -- I have a TH400 in there now. That's the whole point of this -- I want to ditch it. With gusto. It's a good trans and did quite alot of work for me over the years. But with the 383 stroker, I really need an overdrive. I purposely want a computer controlled transmission so I can tune it exactly how I want it without needing to turn a wrench or drop a pan. I do this already with my LT1/4L60E cars. I'm used to it. I regret not going with a fuel injection setup for the 383, so perhaps someday down the road I may look into that too if the Holley 670 Street Avenger gives me too much grief. The engine builder recommended against any FI setup, but most old school folks do. And he claimed that the Street Avenger is the best streetable carb for this engine (though I consider that advice to be dubious). I kinda wanted to keep the soul of the truck old school as well anyways. So it will have a carb for now.

Speaking of which, I haven't even gotten into the wiring that I will need to do for the 4L80E. I got a Baumann TCU and wiring harness. We'll see how that goes. Eventually I will be starting a new thread in the project area when the actual engine/trans swap begins. I intended for this thread to be the primer for the project but it got moved here (sorry for posting it in the wrong place originally).

[Captainfab]

Again thank you for sharing the results of your research. It looks like you finally found just what you were looking for. I am sure it will help someone in the future.

I don't see why you would necessarily need a reinforcement plate, but it may not hurt considering your useage.