Intake bolt angle and angle of spacer needed for SBC intake swap

I know I've seen this info covered in one form or another but I figured I'd post it here for visual aid.
As you can see in the picture below, the angle the intake bolts are drilled and tapped on the lt1 heads are 72° when measured from the intake deck (not sure of its technical name) and the intake to head bolts. When paired with an SBC intake that is drilled at 90°, you would need to spot face the intake 17° or have some 17° shims made (107°-90°).


If this is contradictory to anything someone else has found, please feel free to call me on it. I arrived at these numbers by measuring many different ways. For some reason I recall hearing an 18° shim is what's needed but every way I've ran it, its came out to 17°.
http://img.tapatalk.com/d/14/06/07/apure2a8.jpg

http://img.tapatalk.com/d/14/06/07/aje3y3uh.jpgGood visual man. I had a local machine shop make my spacers at 17*. And I mean really, if its 1* off, its prob not really gonna make a dif... haha

Making you silky smooth...

Probably not. But I'm glad they were made 17°. That tells me my numbers must be close!

Good info here for anyone wanting to convert to a SBC intake. Isn't there a difference in bolt pattern as well?

There definitely is. There are bolts in the center that are way off (and most just omit because they don't seal anything on the lt1 heads). The 4 very outer bolts are in the correct location and the next inward bolts from them need moved. @ZOHAN (or anyone else) if you know what that distance is, feel free to chime in. I'll be posting up in a few days the reasons for what I'm drawing up. ;)

Yup, I redrilled my center holes but couldn't get the bolts to fit in past the intake runners (right frickin next to them) so I didnt use the centers. The 4 outer bolts are in the correct location but at least with my intake, redrilling them put the hole right at the outside of the metal. So I used the washer to support as well, can kinda see in the pic above how the intake curves in way before the outside of the washer. The second set of holes front and rear, are about 3/8-7/16 further apart on the LT head. Or if you are having any head work done, you could always have the heads redrilled for the gen1 bolt pattern. I already had my heads mounted when I decided on the single plane

Making you silky smooth...

Or for a nominal fee id build one for someone. Haha

Making you silky smooth...

Quote:

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Originally Posted by firebird_1995

I know I've seen this info covered in one form or another but I figured I'd post it here for visual aid.
As you can see in the picture below, the angle the intake bolts are drilled and tapped on the lt1 heads are 72° when measured from the intake deck (not sure of its technical name) and the intake to head bolts. When paired with an SBC intake that is drilled at 90°, you would need to spot face the intake 17° or have some 17° shims made (107°-90°).


If this is contradictory to anything someone else has found, please feel free to call me on it. I arrived at these numbers by measuring many different ways. For some reason I recall hearing an 18° shim is what's needed but every way I've ran it, its came out to 17°.
http://img.tapatalk.com/d/14/06/07/apure2a8.jpg

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I wanted to thank you for posting this, your info will be usefull for my single plane swap. http://www.forum.uni-hannover.de/ima...lies2/beer.gif

nice it doesnt sound like much of a difference till you see the spacers... damn

great info.
:claps:

I got a super vic jr that I spot faced the bolts to work without the spacers. Sold the motor but still have the intake.

Quote:

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Originally Posted by firebird_1995

I'll be posting up in a few days the reasons for what I'm drawing up. ;)

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? ? ?

To add some information. You can drill and tap the heads to use the std sbc pattern with the exception of the outer 4 bolt holes. At that point you can use unmodified fp1206 gaskets.

Another good reason from drilling the heads to use sbc intake pattern is you can buy gaskets in many different port sizes and gasket thicknesses. Different thickness gaskets can help align ports if needed.

I know of another guy running washers like in post 2. If anybody makes a set, sign me up.

Just got my heads back from being converted to SBC intake bolt pattern and I figured I's share some pics to help show difference for future searches. The difference is not only the spacing but also the bolt angle. The LT1 enters the head at an angle compared to the SBC that enters at 90* to the gasket surface.
Attachment 36618Attachment 36619Attachment 36620

The bolt spacing is also different, the outside (4) line up (but are at the wrong angle). The center 4 need to be drilled/tapped. It's the ones just outside the runners that are tricky because the holes overlap. Here's and SBC gasket over an LT1 gasket:
Attachment 36621

LT1 gasket laying over SBC, notice the holes overlapping outside the outer ports:
Attachment 36622


There's a few ways to make it work, my local shop wanted to use epoxy and king serts to correct the angle and line up the outer (4) holes. This way I can use any SBC intake without any modification needed. As posted previously angled spacers can be made, and people have widened the holes outside the runners to retain use the LT1 hole and then omitted inner bolts. I'm sure all methods work, but here's the way I decided to go. King serts installed in outer four with epoxy sealing the LT1 holes and new holes drilled/tapped in the center.

Attachment 36623

Hope this helps explain the difference for those looking into converting to SBC intake in the future!

I plugged the 4 middle bolt holes with brass all thread, filled smooth, then used a jig to get the correct 90 degree angle. drilled standard SBC bolt pattern and drove on. I'll try to get pictures.

my first attempt I drilled the manifold used bushings washers bla bla bla , looked like Jethro :facepalm: had built it

took my heads to a wheel repair shop and had all center 8 holes welded up then with a jig i made i used a drill press and redrilled and tapped the holes for SBC bolt pattern.

http://ltxtech.com/forums/showthread...TERBIRD/page46

post #457


cost me $40 at the rim shop and about 3 hours to drill and tap the heads going very slow