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SBF Girdle Modification

General engine tech -- Drag Racing to Circle Track

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frnkeore
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SBF Girdle Modification

Post by frnkeore » Wed Jul 01, 2020 3:48 am

As I've talked about, in these last 3 months, I'm building 306 CI (4.03x3.00) SBF, on a C8 block. It has a neutral balanced, 4340 crank and LW 4340 rods, topped off with SRP, forged piston. I have a fair amount of money, in this short block so, I bought a girdle for it. .600 thick, with ARP studs. The engine will be a dyno mule and will run to 8-8.5K rpm, using different cams, heads and intake.

While looking over the girdle, I saw that it looked like it could be tied into the main bearing bulkheads so, I did some measuring and found out that I was right. I hated to do it at this time in the build as, all the machine work is now done (bored, honed, decked & balanced) but, I had no choice, since the idea came after it was in for the machine work. BTW, it was a LONG wait, I gave the stuff to him in Jan. just got it back, two weeks ago. So, now I have to dissemble, everything and blow all the chips out.

The stand offs are 3/4" CRS, drilled thru & tapped 3/8 x 16, on both ends and are about 2.155 tall (all different lengths), fitted with .005 clearance to the girdle. The idea behind that, is to give the main caps, a little pre-load and then D&T the center bridge of the girdle to add a 1/2x13, set screw and jam nut to support the center of the main cap. Many of the girdles machine the caps and use a thinner girdle. I don't like that and went this direction.

On the main webs, I did a 100% cleanup, with a 3/4 end mill. Both center webs, took about .007 more to clean up that the others and are drilled .50 deep and bottom tapped. I used 1" grade 8 set screws into the block and 1 1/4 grade 8 bolts, from the girdle to the stands. Because the stands are all different lengths, they are numbered to the girdle. The stands are torqued to the bulkheads, that's why I milled the tops 5/8 hex and then the bolts torqued to them both at 35 ft lb. I will only torque the center bolts, to 10 ft lb, to be sure not to distort the main bearing bores. Less if I feel anything turning the crank.

I know it will give extra strength and stability to the bottom end but, I can't say what the percentage might be. I'd be interested in what a mechanical engineer might think it will add.

If this all works out, I'm also building a 332 to put in a car and will do this with the girdle on it, too.

I'd also be interested if anyone else has tried this. I haven't seen it done any place else but, that's not to say that I'm the only one to think off it.

BTW, in part, this came to me through Dan Gurneys main bearing support of the late 60's. He used a bridge, held by the pan rails that applied pressure to the caps. No bolts that I could see to the caps, in the pictures. He placed 2nd at Indy, in '69 and ran the whole season w/o a engine failure (as far as I know), using his arrangement. This with his Gurney/Westlake heads and at least 550 HP, from a 318 CI engine.
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Re: SBF Girdle Modification

Post by BILL-C » Wed Jul 01, 2020 7:05 am

The outer bolts on Boss 302 4 bolt main caps are located approximately in the same spot that you have chosen to mount extra girdle fasteners. Unfortunately, that is where we have seen many crack. Making a girdle that mounts on pan rail and notching the oil pan is a much better idea. The lifter valley brace helps a little in addition to deburring and polishing block.
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Re: SBF Girdle Modification

Post by Kazoom » Wed Jul 01, 2020 7:13 am

girdles are ok and can help with harmonics but the weakest part is the cast iron main caps, if you want best strength stabilizing a stock block, upgrade to billet steel main caps on ALL mains.

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Re: SBF Girdle Modification

Post by apm » Wed Jul 01, 2020 8:06 am

I believe the biggest weakness is how thin the main webs are not the cap, you can bolt a steel cap or a girdle to it but if the web it self is not strong enough it will all come out the bottom as 1 piece, I have had steel caps front to rear from program engineering and a nice girdle and luckily we caught it just as the cracks started (which wasnt long ) we were lucky enough to be able to put the rotating assembly into a Dart block before it made it's way into the asphalt !
I agree that the girdle has some kind of harmonic dampening effect but that I believe is the only benefit , if ita tied into the pain rail somehow then I think you might get some increased strength there.
With all the money, work and time put into a setup like this surely a Dart SHP couldnt cost that much more , unless you run a class where aftermarket blocks aren't allowed

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Re: SBF Girdle Modification

Post by 67satellite » Wed Jul 01, 2020 8:09 am

A similar B.B.M. girdle from about 10 years ago. So far, so good up to 17 lbs. of boost.
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Re: SBF Girdle Modification

Post by gmrocket » Wed Jul 01, 2020 8:25 am

I do something similar but tie the girdle into the pan rails, not the main web bulk heads. the side rails are also trimmed to fit rotating assembly which work as a scraper and are fit tight to the main caps to help stabilize them . my standoff blocks are not tapped, just drilled through, one bolt goes through the girdle, standoff block and then into the support rail, the outer bolt goes through standoff block and into rail. i only set preload about .0015 to .002 as to not distort the girdle. the girdle i use are made from tool steel.

i can remove the whole set up in one piece

i dont think your center bolt is adding anything except maybe some distortion of the main cap bore. done this style many times using stock caps and cranks,none have come apart yet. most are holding together weak late model thin casting blocks with huge windowed webbed blocks. this one is 600hp and has turned 8200
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Re: SBF Girdle Modification

Post by BobbyB » Wed Jul 01, 2020 11:51 am

gmrocket wrote:
Wed Jul 01, 2020 8:25 am
I do something similar but tie the girdle into the pan rails, not the main web bulk heads. the side rails are also trimmed to fit rotating assembly which work as a scraper and are fit tight to the main caps to help stabilize them . my standoff blocks are not tapped, just drilled through, one bolt goes through the girdle, standoff block and then into the support rail, the outer bolt goes through standoff block and into rail. i only set preload about .0015 to .002 as to not distort the girdle. the girdle i use are made from tool steel.

i can remove the whole set up in one piece

i dont think your center bolt is adding anything except maybe some distortion of the main cap bore. done this style many times using stock caps and cranks,none have come apart yet. most are holding together weak late model thin casting blocks with huge windowed webbed blocks. this one is 600hp and has turned 8200
Yours looks very good. Do you have a picture of the oil pan that fits this?

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Re: SBF Girdle Modification

Post by Walter R. Malik » Wed Jul 01, 2020 12:14 pm

frnkeore wrote:
Wed Jul 01, 2020 3:48 am
As I've talked about, in these last 3 months, I'm building 306 CI (4.03x3.00) SBF, on a C8 block. It has a neutral balanced, 4340 crank and LW 4340 rods, topped off with SRP, forged piston. I have a fair amount of money, in this short block so, I bought a girdle for it. .600 thick, with ARP studs. The engine will be a dyno mule and will run to 8-8.5K rpm, using different cams, heads and intake.

While looking over the girdle, I saw that it looked like it could be tied into the main bearing bulkheads so, I did some measuring and found out that I was right. I hated to do it at this time in the build as, all the machine work is now done (bored, honed, decked & balanced) but, I had no choice, since the idea came after it was in for the machine work. BTW, it was a LONG wait, I gave the stuff to him in Jan. just got it back, two weeks ago. So, now I have to dissemble, everything and blow all the chips out.

The stand offs are 3/4" CRS, drilled thru & tapped 3/8 x 16, on both ends and are about 2.155 tall (all different lengths), fitted with .005 clearance to the girdle. The idea behind that, is to give the main caps, a little pre-load and then D&T the center bridge of the girdle to add a 1/2x13, set screw and jam nut to support the center of the main cap. Many of the girdles machine the caps and use a thinner girdle. I don't like that and went this direction.

On the main webs, I did a 100% cleanup, with a 3/4 end mill. Both center webs, took about .007 more to clean up that the others and are drilled .50 deep and bottom tapped. I used 1" grade 8 set screws into the block and 1 1/4 grade 8 bolts, from the girdle to the stands. Because the stands are all different lengths, they are numbered to the girdle. The stands are torqued to the bulkheads, that's why I milled the tops 5/8 hex and then the bolts torqued to them both at 35 ft lb. I will only torque the center bolts, to 10 ft lb, to be sure not to distort the main bearing bores. Less if I feel anything turning the crank.

I know it will give extra strength and stability to the bottom end but, I can't say what the percentage might be. I'd be interested in what a mechanical engineer might think it will add.

If this all works out, I'm also building a 332 to put in a car and will do this with the girdle on it, too.

I'd also be interested if anyone else has tried this. I haven't seen it done any place else but, that's not to say that I'm the only one to think off it.

BTW, in part, this came to me through Dan Gurneys main bearing support of the late 60's. He used a bridge, held by the pan rails that applied pressure to the caps. No bolts that I could see to the caps, in the pictures. He placed 2nd at Indy, in '69 and ran the whole season w/o a engine failure (as far as I know), using his arrangement. This with his Gurney/Westlake heads and at least 550 HP, from a 318 CI engine.
Sounds as if you are attempting to make it do something to help block strength beside tie all the bolts together ...
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Re: SBF Girdle Modification

Post by gmrocket » Wed Jul 01, 2020 12:17 pm

BobbyB wrote:
Wed Jul 01, 2020 11:51 am
gmrocket wrote:
Wed Jul 01, 2020 8:25 am
I do something similar but tie the girdle into the pan rails, not the main web bulk heads. the side rails are also trimmed to fit rotating assembly which work as a scraper and are fit tight to the main caps to help stabilize them . my standoff blocks are not tapped, just drilled through, one bolt goes through the girdle, standoff block and then into the support rail, the outer bolt goes through standoff block and into rail. i only set preload about .0015 to .002 as to not distort the girdle. the girdle i use are made from tool steel.

i can remove the whole set up in one piece

i dont think your center bolt is adding anything except maybe some distortion of the main cap bore. done this style many times using stock caps and cranks,none have come apart yet. most are holding together weak late model thin casting blocks with huge windowed webbed blocks. this one is 600hp and has turned 8200
Yours looks very good. Do you have a picture of the oil pan that fits this?
The side rails are 1/2" thick which are clamped to the block using the original oil pan bolt location holes which were opened up in the block to 3/8" . the original holes in the oil pan were enlarged to slip over the those allen head bolts. so between of the oil pan holes i drilled new holes and drilled/tapped/threaded the support rails for 1/4" original pan bolts.

no gasket are used, the rails are sealed to the block with permatex split block sealer like whats used on motorcycles or two stroke split blocks. because the pan sits 1/2" up off the block, the end gaps around timing cover and rear main cap is filled with permatex the right stuff. never had any leaks

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Re: SBF Girdle Modification

Post by BobbyB » Wed Jul 01, 2020 12:27 pm

gmrocket wrote:
Wed Jul 01, 2020 12:17 pm
BobbyB wrote:
Wed Jul 01, 2020 11:51 am
gmrocket wrote:
Wed Jul 01, 2020 8:25 am
I do something similar but tie the girdle into the pan rails, not the main web bulk heads. the side rails are also trimmed to fit rotating assembly which work as a scraper and are fit tight to the main caps to help stabilize them . my standoff blocks are not tapped, just drilled through, one bolt goes through the girdle, standoff block and then into the support rail, the outer bolt goes through standoff block and into rail. i only set preload about .0015 to .002 as to not distort the girdle. the girdle i use are made from tool steel.

i can remove the whole set up in one piece

i dont think your center bolt is adding anything except maybe some distortion of the main cap bore. done this style many times using stock caps and cranks,none have come apart yet. most are holding together weak late model thin casting blocks with huge windowed webbed blocks. this one is 600hp and has turned 8200
Yours looks very good. Do you have a picture of the oil pan that fits this?
The side rails are 1/2" thick which are clamped to the block using the original oil pan bolt location holes which were opened up in the block to 3/8" . the original holes in the oil pan were enlarged to slip over the those allen head bolts. so between of the oil pan holes i drilled new holes and drilled/tapped/threaded the support rails for 1/4" original pan bolts.

no gasket are used, the rails are sealed to the block with permatex split block sealer like whats used on motorcycles or two stroke split blocks. because the pan sits 1/2" up off the block, the end gaps around timing cover and rear main cap is filled with permatex the right stuff. never had any leaks
Do you know how much weight it adds?

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Re: SBF Girdle Modification

Post by frnkeore » Wed Jul 01, 2020 1:48 pm

Walter R. Malik wrote:
Wed Jul 01, 2020 12:14 pm
Sounds as if you are attempting to make it do something to help block strength beside tie all the bolts together ...
Yes, with as much as the girdle itself, weighs, I thought I'd try to add it's strength to the block and spread the loads over a wider area. Also, with the .005 pre-load having the effect of applying more cap pressure w/o weakening it.

The top of the caps have a slight, 3/4 wide, clean up cut, like the main webs and the set screws are turned flat, to give 100% contact, in effect, adding the bridge of the girdle to the thickness of the cap.

While it remains to be seen how effective this is, it does spread the loads over a much wider area, giving, at least some extra strength to the bottom end, as well as extra torsional rigidity to the block.

I do know that the center bulkheads aren't ideal places but, they do add what ever tensile strength a piece of 1/2 x 3/4 wide piece of cast iron can add x6. Cracking? These block tend to crack at the front main

For me, this was a very inexpensive project. I closed my machine shop and retired in 2007 and other then the purchase of the girdle, the rest of the hardware has cost me about $15.

If these girdles where resigned, you could easily tie the front and rear main caps, into the pan rails, too.

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Re: SBF Girdle Modification

Post by Nefario » Wed Jul 01, 2020 1:54 pm

frnkeore wrote:
Wed Jul 01, 2020 3:48 am
I know it will give extra strength and stability to the bottom end but, I can't say what the percentage might be. I'd be interested in what a mechanical engineer might think it will add. ...... this came to me through Dan Gurneys main bearing support of the late 60's.

Mechanical Engineer here; not professional engine builder so YMMV.

For the few thousandths of distortion the block may experience, your outboard bolts aren't doing much of anything except maybe helping keep the bearing caps aligned. Even at .600 thick, the aspect ratio of the "beam" across the main caps is low. The mounting holes may weaken the block webs. Mounting a heavier structure to the block rails would be preferred.

Applying single point pressure to the center of your bearing caps doesn't seem cool at all and affects the cap bolt stretch that the bearing crush actually "sees". A machined flat on the caps such that the girdle becomes a series of straps across the cap bolts would be more rigid.

Here's a simple Ford girdle more like I'm thinking of:
https://www.ebay.com/itm/Canton-Ford-5- ... 1180595290

Here's a factory engineered Nissan integrated caps/girdle assembly with similar function:
https://www.ebay.com/itm/1992-Nissan-24 ... 2608967442
Dave

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Re: SBF Girdle Modification

Post by frnkeore » Wed Jul 01, 2020 2:57 pm

Dave,
Thank you, very much, for your input.

Yes, I knew when I did this, that it could effect the strength of the main bulk heads but, these engines have a history of failing at the front and 2nd main, at the main bolt holes, not in the outside webs. So, in my opinion, it's kind of a crap shoot.

I would be interested in how much extra force, you think the .005 pre-load might generate on the caps.

What I know about bursting forces, tells me that a strap across doesn't do a lot, to keep the weaker material from failing but, will help to contain the failure. My set screw idea was just to add some contact with the cap, in that area, hoping it would have a positive effect and believeing Gurneys type girdle created pressure at the that point but, noting it was across the whole top. The pressure should be about 100 lb (13 tpi x 10 ft lb - friction), I an cut that in half though. The pre-load should compensate for the all of that, and then some, I think and the ARP studs, should keep the cap tension to at least the stock Ford bolt level.

Overall, I can't see, if no cracks are generated, how it could increase (by some margin) the overall stiffness, by expanding the loads over a larger area.

I'm aware of the Nissan main bearing caps. I have a KA24E engine in my '91 240SX. I think it is a good/better way to do it but, there is nothing available like that, for this application. The one piece casting is a lot more rigid than any bolt together arrangement.

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Re: SBF Girdle Modification

Post by pdq67 » Wed Jul 01, 2020 3:01 pm

I guess that I would make the complete girdle a one piece that included all main caps and then bolt it on. Dowel it and then line bore and hone all main saddles.

Kind a like creating a, "Y"-block.

And to continue, I might add tie bolts up both sides of the outside of the block that would tie a steel deck plate to the bottom end and that would also tie both banks together!

Should be able to hold a grenade!!

Now SBC here, my deck plate would be such that I could install, "LS-", heads to it to modernize the old Gen I block.. (Or whatever heads I wanted to install?)...

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