Twins with Twins, Anyone?

kidturbo

kidturbo

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Well today was a was full learnings. First, LB7 fuel pressure relief valve has smaller thread diameter than LBZ/LMM. Why didn't someone mention that?? You guys are slipping...

Second and speaking of slipping, realized my powder coat guy lost 12 of the coppers off my injectors. So price to coat them just doubled.

But we did manage to get the CP3 back in its hole, and inspected all the pistons with a bore scope. So not a totally wasted day at least.

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juddski88

juddski88

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Figured you were putting that into some slick manifold you had made...otherwise we would have said something..our expectations at this point are pretty high! Even a lb7 manifold would work with some custom lines.
 
PureHybrid

PureHybrid

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Ah man, should've gone for the Keenserts haha.

Is that the first time you installed those injectors since the solenoids were clocked?
 
JoshH

JoshH

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Are those SoCal billet hold downs and stud kit? They're supposed to torque to 32 ft lbs.
 
kidturbo

kidturbo

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PS. All the others held 55lbs, so I enquired with someone I figured had ran into the issue before. Mark said throw the torque wrench away.. LOL

Now I'm searching for 3D 24mm deep helicoils rather than these 12mm shorties from Advance.

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kidturbo

kidturbo

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Did a quick experiment to see the holding strength of a std 12mm long helicoil since nobody in town has the longer 3D versions. Results were pretty impressive actually.

Chalked up a 1" chunck of 6061 alum in the vice and drilled, tapped, and coiled it for the 8x1.25mm bolt. Took a stock hold down bolt, couple shims, and began torquing it down.

Learned 2 things. A helicoil is stronger than ya think, and factory GM 8mm hold down bolt will begin to twist off at about 65ft lbs of torque. After 2 twisted bolts, helicoil threads are still looking good..

Science!!
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MarkBroviak

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Told ya! Anytime you put a steel helicoil in an aluminum piece it is way stronger than the original aluminum threads because of the addition surface area with a stronger material to handle the load. Unfortunately the stock hold-downs torque spec is just that, for stock. You increase the cylinder pressure and the injector is able to move and you end up torching a copper washer and possibly wrecking the head and the injector because of it. Some people have gotten lucky but a lot have had to learn this lesson the hard way over the years and I lost count years ago on the dyno seeing injectors being lifted when making good power. Good news for you Ken is it isn't a horribly difficult fix just more time and money.
 
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kidturbo

kidturbo

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Yeah nothing worth crying over. But it will sure make ya say bad words when the torque wrench goes from 45lbs to 35lbs in a quarter turn..

If starting with bare heads I'd probably helicoil or cert all those holes just for good measure. Get the 24mm helicoils and that should give ya a full depth on the threads.

Also I would cut these 2 tabs pictured off the top side edge of lower valve covers. With the hold down studs in place, ya can't get the valve cover off without either pulling the studs again, or pulling the fuel rails. Just a little heads up for those who like the quick and easy valvetrain inspection options..

Thanks for all the input on this one
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JoshH

JoshH

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kidturbo said:
Someone tell Socal they have a typo on their packaging then... Clearly states "Torque To 55ftlbs" on the package cover. 🤔
Click to expand...
LB7 (which has a much larger size bolt) does torque to 55, but all other generations call should torque to 32. I'm not sure why they put that on the package because those numbers I listed are straight off their website.
 
kidturbo

kidturbo

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JoshH said:
LB7 (which has a much larger size bolt) does torque to 55, but all other generations call should torque to 32. I'm not sure why they put that on the package because those numbers I listed are straight off their website.
Click to expand...
Relayed the discrepancy to Lorenzo. Says mine must have been custom packaged with 55ft lbs at Marks request... 🤔 >>Not.

He did say their current stock reflects the correct spec of 32Ft Lbs for LLY/LBZ/LMM. But funny thing, my helper just did his engine last month, and recalls his package said 55 also. So check your specs before ya wrench. Cause bolt size maters.
 
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