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Cheap-a$$ long rod + stroker + high CR pistons?
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ideola  



Joined: 01 Oct 2004
Posts: 15510
Location: Woodstock IL

PostPosted: Fri Dec 21, 2012 6:35 am    Post subject: Reply with quote

fiat22turbo wrote:
I wonder if the NA head could be machined with the 931's combustion chamber (or something similar)? Would that be easier for use in a NA application? Just thinking out loud since the heads don't seem that much different other than the combustion chamber, the location of the ports and the spark plugs on the opposite side (hey maybe put a set on either side and run dual plugs!)


I'm not sure why you would want to do that???

In addition to the combustion chamber, you would also need to change the valve seats (which are NLA) and make significant mods to the valve chambers as well, as we've demonstrated the differences there between the NA and 931 heads.

While anything is possible, it hardly seems worthwhile given that 931 heads aren't so hard to come by. The other alternative if you wanted to stick with the NA head is to simply use a different piston set (I've identified several alternatives), eliminating the need to do any machining to the NA head (although extensive porting would be strongly recommended to improve flow).
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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Fri Dec 21, 2012 8:06 am    Post subject: Reply with quote

Well, the thought was then that you could more easily use the NA header and DCOE intake.

I know we've discussed the other differences between the two heads, but the port flow difference isn't enough to get me excited enough to deal with building an engine to use the 931 head. The easier to access spark plugs is a nice touch, but the combustion chamber sucks monkey butt.

As for the valve seats, I guess I would say that one would would likely be using a big-valve set in the first place, which would negate that issue, but it is a major concern (not just for this brain-fart, but for you poor bastards who have to try and rebuild a 931 head and have bad seats!)

The ability to make your own combustion chamber could allow for playing with a twisted wedge or another more modern chamber design instead of just a basic bathtub.

But, since this doesn't follow the CPP-approved list of performance modifications, ignore it and move on.
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ideola  



Joined: 01 Oct 2004
Posts: 15510
Location: Woodstock IL

PostPosted: Fri Dec 21, 2012 8:38 am    Post subject: Reply with quote

fiat22turbo wrote:
Well, the thought was then that you could more easily use the NA header and DCOE intake.
This is no big deal, just drilling out a few holes...not quite the same level of effort as machining a combustion chamber.

fiat22turbo wrote:
The ability to make your own combustion chamber could allow for playing with a twisted wedge or another more modern chamber design instead of just a basic bathtub.
As I understand it, combustion chamber design is quite a black art, and requires significant trial and error (not to mention R&D budget).

fiat22turbo wrote:
As for the valve seats, I guess I would say that one would would likely be using a big-valve set in the first place, which would negate that issue, but it is a major concern
A big valve head is a $2000 investment, any way you slice it. It may not be appealing to everyone, and is certainly not required for this setup...although my advice is to always start with the head before considering the lower end mods.

fiat22turbo wrote:
(but for you poor bastards who have to try and rebuild a 931 head and have bad seats!)
I don't know of anyone who has gotten bad valve seats. I know of someone who welded on a head AFTER the BVK was installed and experienced a subsequent failure, but the seats were not bad.

fiat22turbo wrote:
CPP-approved list of performance modifications
????
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tyfighter123  



Joined: 19 Jan 2010
Posts: 549
Location: Colorado

PostPosted: Fri Dec 21, 2012 2:42 pm    Post subject: Reply with quote

Quote:
fiat22turbo wrote:
(but for you poor bastards who have to try and rebuild a 931 head and have bad seats!)
I don't know of anyone who has gotten bad valve seats. I know of someone who welded on a head AFTER the BVK was installed and experienced a subsequent failure, but the seats were not bad.



The welding was done to close holes found on the California cars heads. The welding was done based on advise given by someone who sells the kits. The holes go from the exhaust chamber and exit on the intake side. A TIG spot weld was done on each hole one at a time on the intake side. The head never got hot enough to where it couldn't be handled by hand. The seat failure was on the intake valve on cylinder 3. After inspection of the head and seats my local machinist said he thought the tolorence between the seats the head was not tight enough and that more than likely each seat had not been measured individually and that was more than likely the cause of failure and not the spot welding.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Fri Dec 21, 2012 4:46 pm    Post subject: Reply with quote

tyfighter123 wrote:
The welding was done based on advise given by someone who sells the kits.
I sold you the kit. I did not advise you to weld the head, although we did discuss the holes in the head, which you discovered after the big valve kit was installed.

tyfighter123 wrote:
After inspection of the head and seats my local machinist said he thought the tolorence between the seats the head was not tight enough and that more than likely each seat had not been measured individually and that was more than likely the cause of failure and not the spot welding.
Everyone is going to have an opinion, especially after the fact. It certainly is possible that the craftsman who did the valve job screwed up.

However, the BVK manufacturer is the one who suggested that the welding could cause the seats to come loose, not me. I've spoken with three other engineers who agreed with the manufacturer, and who also indicated that it is not uncommon at all for newly installed seats to come loose from simple overheating or high temps due to detonation. As I recall, there were a plethora of issues including fuel delivery when that engine was first being started up and run-in.

In any event, this is one example of why I will no longer coordinate services for customers who buy product from Ideola's Garage. There is no way for me to warrant the work of others. Have you contacted the guy who actually did the work yet?
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tyfighter123  



Joined: 19 Jan 2010
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PostPosted: Sat Dec 22, 2012 3:57 am    Post subject: Reply with quote

Dan, we did talk about the holes and I was going use JB weld to plug them and you said if it were you, you would weld them closed. I don't want to cause any problems, especially online. I have not posted my frustrations here because I have not wanted to hurt your business in any way. I also never mentioned anything about who was involved in my post about my engine. So I don't appreciate you using me as an example it adds insult to injury.
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tyfighter123  



Joined: 19 Jan 2010
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PostPosted: Sat Dec 22, 2012 4:10 am    Post subject: Reply with quote

And just to be clear Dan, I don't blame you for anything that happened with my engine. I would like everyone to know that you have been very helpful with getting the project together, and when it did fall apart you were kind enough to give me a spare head to start the re rebuild proccess again! That is why I bought more items from you to start over. I appriciate what you do for these cars and am glad the 924 has someone like you who is passionate about them.
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itbracer85porky  



Joined: 02 Mar 2012
Posts: 43
Location: New Hampshire

PostPosted: Sat Dec 22, 2012 2:14 pm    Post subject: Reply with quote

It really sucks that your motor blew up. Been there, done that with my IT car. Nothing worse then firing up a fresh engine, and that sickly smell of grinding metal and oil. Simple fact of life is that when we gamble and push these little engines, its a mixed bag of results, and sometimes "things just happen". From what I have learned on this board, is that with as much engine building I have done on cars and piston aircraft engines, you are all VERY helpful and smart with these engines. Its much appreciated.
I am still very excited to hear about the results of this build. I am ready to go now (yesterday actually) to buy the parts needed to get mine started. Cant wait to hear the results.
Also, I am going to use my N/A head and CIS, as I think it will work quite well with the stroker crank mods and new pistons, header, cam, scraper, etc (unless one of you has some insight stating otherwise).
I do however, have a 931 head that if someone needs, they are more than welcome to it.
Dan, (Ideola, think thats your name, sorry if I am wrong) if you need a 931 head for some R & D, let me know. Maybe we could work something out when I purchase all the parts. If not, no biggie.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Wed Jan 30, 2013 10:14 am    Post subject: Reply with quote

Last night:


This night:






Plenty of room for the stroker, no chance of interference. If one were willing to forego the cheap approach, one could weld and regrind the journals and add a significant amount more stroke.
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tyfighter123  



Joined: 19 Jan 2010
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PostPosted: Wed Jan 30, 2013 11:10 am    Post subject: Reply with quote

Dan, Looks awesome! Did you just paint the pulley? Also after measuring the stretch on the ARP rod bolts they should be torqued to 55ft/lbs. Is that what you ended up using?
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Fifty50Plus  



Joined: 28 Feb 2008
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PostPosted: Wed Jan 30, 2013 11:14 am    Post subject: Reply with quote

Did I miss something...do you have a 16 valve head to go with the pistons?
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ideola  



Joined: 01 Oct 2004
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PostPosted: Wed Jan 30, 2013 12:59 pm    Post subject: Reply with quote

Ty, I took all of the ferrous parts from this motor and blasted them with glass bead, then had them plated in yellow cad dichromate for corrosion prevention. I am still debating what to do with the alu parts...considering either powder coating or trying a new clearcoat corrosion-proofing product a friend of mine recommended.

The ARP bolts in this motor are not the AR336 bolts for our 924 rods...these are Manley rods that ship with ARP2000 bolts. The torque specs for them are 65 ft lb when torqued with 30 weight break-in oil. I'm using the Brad Penn stuff.

Chuck, no 16V head...I wish!!! The goal with this motor was to come up with a high comp stroker for as little money as possible, so I selected an off-the-shelf piston from a more modern sport compact that obviously has 16V head. These pistons had the ideal quench ring design, and the correct compression height to put the piston almost flush with the deck (1.45mm in the hole, to be precise).

This setup will be using the 931 head, so the shallow dish of this piston combined with the longer rod will give me ~11:1 CR. It will be an interference motor, but I'm used to that with the turbos, so not really a big issue. The valve reliefs should have negligible impact to the overall function of the motor. I tried to find a piston that didn't have them, but they all had a much lower compression height, resulting in a less-than-ideal quench distance. I opted to favor better quench over a flat top design with no valve reliefs, as I believe it will result in a more detonation-resistant configuration.
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the_mad_electrician  



Joined: 16 Nov 2009
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PostPosted: Wed Jan 30, 2013 1:30 pm    Post subject: Reply with quote

What pistons would the N/A use?
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Wed Jan 30, 2013 10:31 pm    Post subject: Reply with quote

the_mad_electrician wrote:
What pistons would the N/A use?

Not sure what you're asking...this will be a normally aspirated build...I'm just using the 931 head because of the superior port design and flow, plus the better quench arrangement.

If you wanted to use an NA head with these rods, there are several different alternative piston choices resulting in various distances "down the hole", I'd have to go back and look at my notes to figure out which would be best. It also depends somewhat on what CR one wanted to achieve...
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the_mad_electrician  



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PostPosted: Wed Jan 30, 2013 11:11 pm    Post subject: Reply with quote

I ment n/a head I just forgot to type head.
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