Head sealing and big bore kits

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Edwin Ek
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Head sealing and big bore kits

#1 Post by Edwin Ek » Fri Aug 09, 2019 3:29 pm

What are some guidelines for how big the bore can be before sealing with the heads becomes a consideration. Have there been any advances to allow bigger bores?

I see Willhoit offering 91mm bore setups. How does he do it?

I am interested in a strong street motor that will go many miles and retain compression. My mechanic has expressed caution about this.
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John Brooks
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Re: Head sealing and big bore kits

#2 Post by John Brooks » Fri Aug 09, 2019 3:41 pm

He uses a different head.
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C J Murray
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Re: Head sealing and big bore kits

#3 Post by C J Murray » Fri Aug 09, 2019 4:12 pm

91mm is the largest commonly used. The heads aren't different, just machined to a larger diameter. The limitation is the stud pattern at the case. The cylinders need a minimum thickness to stay round and straight in operation. When the OD of the cylinder base gets to a certain size it finally runs into the studs that are embedded in the case.
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Re: Head sealing and big bore kits

#4 Post by Al Zim » Fri Aug 09, 2019 4:15 pm

The Porsche made a successful street motor that would go many miles and retain compression. It has been know as the Super or C engine. Use a 4 ring 1600CC Mahle or Klobenschmidt piston where the oil control ring is below the piston pin and has a long skirt. the counterbalanced crank is not necessary for 4500 RPM down the freeway. al zim
 

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Re: Head sealing and big bore kits

#5 Post by Edwin Ek » Mon Aug 12, 2019 6:26 pm

Looking at LN's website:

There are 86mm P&C sets sold as "slip-in". I understand that to mean no machining is required for the case or heads. However, there are also 86mm sets (Nickies and Mahle pistons) sold as "slip-in case register". What does that mean? Why is the situation different from the usual?

Thanks for helping a rookie. I am using a NOS 912 case for this build, and I have a hard time contemplating machining it.

The website also shows, for a given bore, 3 different cc ranges. E.g.: 57.5 - 60.5, 60.5 - 63.5, and 63.5 - 66.5. OK, base gasket differences for one range, but 3 ranges for one bore?
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Re: Head sealing and big bore kits

#6 Post by Al Zim » Tue Aug 13, 2019 9:17 am

In my previous post I lauded the Super or C engine as the most versatile 356 engine that Porsche produced. the torque was similar to the S-90/SC and the Zenith carburetors did not wear out around the throttle plates because. The cast iron cylinders and 4 ring pistons with long skirts made the engine long lasting and minimized oil consumption. Do you need to be driving down the freeway or on a curvy road at a high rate of speed in a car that is 55 years old (minimum). Link pins and King pins OK? When did it have an alignment? If you have questions about products for your vehicle you should go to the seller or if possible to the manufacturer to discuss your situation. Finally you should get someone to mentor you on the engine assembly especially the measuring and the torque. My guess is that you do not have these tools and experience to be able to correctly complete your engine. If you have a disaster, it will be expensive. Many individuals post on the list that you should purchase a set of tools and a shop manual and you can do the job. Incorrect! You need precise measuring tools and experience (which is difficult to obtain on line)! As an example: many shops do front end rebuilding, BUT they probably do not have the correct 356 tools to measure the components of the front end to make sure they are within specifications. I have 5 356C cars waiting for me to heal them! al zim
 

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Re: Head sealing and big bore kits

#7 Post by Jacques Lefriant » Tue Aug 13, 2019 10:17 am

Hi Ed
if your case is stock you should not have to machine it unless you go to bigger than 86mm bores. If your crank has the correct stroke and you use stock length rods and cylinder heights and you know the dome volume of the piston then having the volume of the head will enable you to select your base shims/gaskets to achieve the desired CR.
j
 

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Re: Head sealing and big bore kits

#8 Post by Edwin Ek » Tue Aug 13, 2019 12:18 pm

All, thanks for your advice. I am not building my engine, just thinking about the parameters. My mechanic is as experienced as they come. He has been working on these cars since they were new, is factory trained, and has built successful vintage race engines.

Still interested to know what "case register" means.
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Re: Head sealing and big bore kits

#9 Post by Juha Vane » Wed Aug 14, 2019 2:03 am

My understanding is that ”slip-in case register” mean that the cylinders can be used in standard block without machining of
the bore for cylinders in the block. The hole for cylinder in
block is about 90mm. This limit the max cylinder diameter to
86mm.
But I’m known to be wrong...
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Re: Head sealing and big bore kits

#10 Post by GregVandenbussche » Thu Aug 15, 2019 12:07 am

I'm using coper gasket between head and cylinders on my 90mm, it's been working great for the last 8K
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Re: Head sealing and big bore kits

#11 Post by Ron LaDow » Thu Aug 15, 2019 1:02 am

Ed,
Call the guys at LN. Charles is a great guy who has some *real* engineering skills and an uncommon lack of BS in his dealing with others. I'm sure he'll be more than willing to sort out any confusion, and please let us know what you heard.
I'll make this a more general suggestion:
If you read or hear some concern regarding a product from any supplier listed in the 'vendors', please contact them first. Pretty sure that those of us who are listed aren't trying to hide a lot.
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Re: Head sealing and big bore kits

#12 Post by Edwin Ek » Thu Aug 15, 2019 2:35 am

Ron, very sound advice ... I had called once, left a message, and received no response. No worries that, so I thought I'd try here.

I have since called again and talked to a person. I expect to talk to someone knowledgeable tomorrow.
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