Hot Rod Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
32 Posts
Discussion Starter #1
I have searched for threads on using main bearing spacers to use small journal cranks in medium journal SBC blocks, but cannot find any comments on how reliable the motor will be using these main bearing spacers.

Do you sacrifice reliability at high rpm's using bearing spacers? I want to use a 283 crank in a 4 bolt 350 block and be able rev safely to 7000-7500 rpm's.

I plan on using the original type Z-28 pistons (on 70 or 72cc heads) and the original solid lifter Z-28 Duntov 30-30 cam. I figure if I use larger chamber aluminum heads I will get about 10.3 to 10.5 c.r. and be able to use 93 octane pump gas.

For those of you who wonder why a 302, the motor is going in a 1972 Porsche 914. This was the mid-engine Porsche that used the engine from the Squareback VW. The stock transmission cannot take a lot of torque at low rpm's so I need an engine that makes power at the top end. The car weighs 2000 lbs and is geared low for the air cooled 4 banger that came in it. With the SBC and radiator it will weigh about 2300-2400 lbs.
 

·
Registered
Joined
·
32 Posts
Discussion Starter #3
Nope. Even though the engine for the 914 was designed by VW, the transmission, and suspension are from early Porsche 911's If you want to upgrade the tranny, you move up to later 911 transmissions. The problem with that is, other than the initial expense of the transmission, because the 911 was rear engined and the 914 is mid-engined, you have to flip the ring gear otherwise you have five reverse gears and one forward. You also have to fabricate or purchase ($$$) a new shift linkage and shifter. You GM/Ford/Chrysler guys don't know how good you have it on parts prices. Porsche parts are outrageous.

The standard 914 tranny is good for about 325 ft. lbs. of torque. If you don't do burnouts and slam the shifts at full throttle, the tranny will hold up. Besides, I have a good spare transmission as a backup.

You are on the right track with the VW Bus thinking though. A common upgrade for the 914 is to use bus CV joints and axles in V8 conversions.

Waiting to hear from you engine builders out there regarding the bearing spacers.
 

·
Registered
Joined
·
32 Posts
Discussion Starter #4
Bump.

Anyone out there with experience using main bearing spacers? How about you guys with strokers?
 

·
Registered
Joined
·
32 Posts

·
Registered
Joined
·
379 Posts
i know how old this thread is but ive been doing alot of research and this question never got ansered id like to know.
 

·
Registered
Joined
·
32 Posts
Discussion Starter #9
Boy howdy, does this post bring back memories! A week after I posted this in 2004 Hurricane Ivan flooded my house and garage with 4 feet of salt water. I had the Porsche 914 up on jack stands with the old motor ready to pull out, so I couldn't move it ahead of the storm. Needless to say it was covered in salt water (as was the perfect spare transmission) and had to be scrapped. And the worst part is that I was in the process of shopping for a collector car insurance policy for it when it was flooded. :(

I have since moved on to other interests, but I am still curious about the bearing spacers.
 

·
bentwings
Joined
·
2,583 Posts
Well the top fuel and funnycar motors come with replacable inserts so I think they would be ok in a SBC. If you smoke a bearing you just replace the inserts and have the block line honed. many even have several sets of inserts pre honed. Replace like bearings.
 

·
WFO
Joined
·
5,030 Posts
There are two ways to approach the deal. One is by using steel spacers fitted by honing to the block. These steel spacers are designed to use standard type inserts.

The other way is to use "spacer bearings" which are just that- thick bearings that are used as a 1-piece affair to fit the small 2.3" crank into a 2.45" or 2.45" into a 2.65" crankcase.

I suppose honing could be skipped as long as everything measured out OK, but I cannot say one way or the other from practical experience.

The cooling of the journal will be hampered by either method- worse by far, I would think, would be the extra gap caused by the steel spacer scheme. But that said, there should not be so much heat created at the journal to cause a problem in the first place, as long as the bearing clearance is correct and the journals and bearing bores are true and there is sufficient oil flow to lube and cool.

This is a case where the correct bearing crush would need to be confirmed and not taken for granted
 

·
Registered
Joined
·
379 Posts
cool thanx guys- i love this forum its so informitive and everyone is for the most part very willing to be helpfull etc. ive been on alot of the other forums and there is so many jerks- how do you all keep it so modded?
 

·
Registered
Joined
·
2,354 Posts
Blight, I think it is because of the people we have here. For the most part, people want to learn something and there are plenty of sharp guys that are willing to share their knowledge. Continued discussions are to further clarify and broaden the shared knowledge and experience. HR.com is the classic ARMY WAY of teaching: Subject Material is repeated over and over, around and around, up and down, until it finally clicks with all the troops.

Trees
 

·
Registered
Joined
·
43 Posts
While I have not had personal experience with the spacers. I can tell you about an engine of a guy I sand drag with.

He has some "interesting" ideas about things and always likes to be different. A few years back he built a 400 block with a (get this) 283 crank and rods that are mile long.

This was build with the idea of revving it to the moon, and he does. He is using a Lenco transmission and I'm not even going to repeat the RPM he says he is leaving at, because it sounds like B.S.

I can tell you that is pushing the limits of what a pushrod engine should turn and it sound like a big die grinder running at full tilt (8 into one collector headers).

He has ran this engine for three years straight (including this year) and it has not suffered any catastrophic failure yet.

Whatever he did to fit the crank in that block seems to be working just fine. Like I said, it's not from my own personal experience, so take it for what it's worth. I would not have a problem giving it a try myself, and I might some day.
 
1 - 14 of 14 Posts
Top