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More newb questions re. big bore kits
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rodeking
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PostPosted: Sun Jan 21, 2018 9:29 am    Post subject: More newb questions re. big bore kits Reply with quote

I'm looking at the AA 90.5 cyl/hyper. piston set. It looks like there is a step in the case end. I assume the purpose of that is to maintain the thickest cyl. wall possible as deep as possible
but then it steps down to minimize how much the case has to be opened up? Are these reasonably reliable? What kind of deck height can I expect with these on a stock deck case?
I am considering these with the CB 2280 cheater cam, either stock or mofoco 040 heads, .040 deck height, 8.2 CR for 87 or 89, 1 3/8 header with stock heater boxes, single PICT 34 on stock intake. I know I'll have to screw around with the PICT and probably go to a larger venturi.
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pondervwmike
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PostPosted: Sun Jan 21, 2018 12:30 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

I am kinda a newbie on here as well but I am going to give it my best shot. Laughing

rodeking wrote:
I'm looking at the AA 90.5 cyl/hyper. piston set. It looks like there is a step in the case end. I assume the purpose of that is to maintain the thickest cyl. wall possible as deep as possible
but then it steps down to minimize how much the case has to be opened up?
I assume the same
Are these reasonably reliable?
Yes they are quite reliable for a mild build like yours.
What kind of deck height can I expect with these on a stock deck case?
Stock deck height
I am considering these with the CB 2280 cheater cam, either stock or mofoco 040 heads, .040 deck height, 8.2 CR for 87 or 89, 1 3/8 header with stock heater boxes, single PICT 34 on stock intake. I know I'll have to screw around with the PICT and probably go to a larger venturi.
Lotsa people have done this. Sounds like a good combo to me but then again I am a newbie hopefully some people on here with more knowledge can help you get that 34 pict to work.

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bugguy1967
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PostPosted: Sun Jan 21, 2018 2:06 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

You're not supposed to have an untouched deck when boring for 90.5s. The case gets decked to allow a proper sealing/seating area for the larger cylinders. The cylinders are longer to compensate for this. No one can tell you what your deck height will be. I'll guess around .100" without any decking. You need to mock up a piston/cylinder (preferrably without rings installed) on each side of the engine and measure the differences. They will be different on each side, unless you're really lucky. I've never been lucky in 13 years. I have a new CB 2280 and CB Riosulence lifters for sale. $90 shipped.
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modok
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PostPosted: Sun Jan 21, 2018 2:14 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

No, they aren't longer, all are 112.5
Only the 94 kits in which bore the case to 97.4 mm are longer cylinder.

Expect the deck height to be approx .045-.055
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PostPosted: Sun Jan 21, 2018 2:19 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

Is this a 69mm stroke your thinking? Are you having your case opened for 90.5-92mm cylinders? There are choices 90.5mm 92mm thin and thick bore kits. Good to know exact cylinder length though and what the case deck is. But with shims and various rods lengths, it may be possible to keep the engine width stock.
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rodeking
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PostPosted: Sun Jan 21, 2018 3:26 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

Yes it would be the stock 69 mm crank. I will have the case opened for the 90.5 cylinders. When you say opened for 90.5/92 what does that mean in terms of diameter of the case opening? Do the 90 and 92 mm cylinders use the same diameter case opening and the 92 mm cylinders have a thinner wall? I want the thickest cylinder wall I can get. The reason for the ques. on deck height is because I`m sending the case out and I don't want to have to send it out again if the deck height is too much, I build my engines with tight decks.
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modok
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PostPosted: Sun Jan 21, 2018 3:37 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

Yes current 90.5 and classic 92 cylinders are the same external sizes.

If you want to get the deck right on the first time, you will need to take into account the rods as well, and the case.

Far as variation of the case, new cases vary 2x as much as German cases.
if you pulled a NOS German case out of some time capsule probably it would not be necessary to cut the the deck surface, but today we have the good, the bad and the ugly all out there, can't really predict how it will turn out.
Normal dimensions are
crank center to deck 99.8mm
cylinder length 112.5

Stroke 69mm
Rod length 137mm
pin height 39.5mm

You can do the math, if you get 1.3mm then you did it right. Wink


Last edited by modok on Sun Jan 21, 2018 3:53 pm; edited 1 time in total
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Danwvw
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PostPosted: Sun Jan 21, 2018 3:46 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

Found this thread with the actual case opening sizes posted in it Do I have 90.5 or 92mm?.
90.5's are like stock cylinders in thickness and there are several brands in that size either hypereutectic or forged pistons.
Depending on what your case is if it's a good 8mm stud factory insert case you could open it for 94's then size down to 92's that are made to fit a 94 case they would be (machine in) thick wall cylinders probably have to go with the AA brand to do this though, not sure?

92mm for 94mm opening thickwall.
or
92mm for 92mm opening thickwall. (These will have the super thin bottoms but might be the way to go on a 10mm stud case.)

The 92's make it a 1835cc or 1968cc displacement if going to a 74mm stroke crank which can be done pretty easily with shorter 5.325" rods and everything else stays stock. Probably need better carbs or fuel injection to take advantage of what a 1968cc is capable of especially if running 40mm intake valve heads, but since its a bus, it could be still a pict 34 carburetor with a modified venturi and stock heads opened to fit.
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rodeking
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PostPosted: Mon Jan 22, 2018 8:08 am    Post subject: Re: More newb questions re. big bore kits Reply with quote

Ok now I understand. Yes, I get 1.3 mm dh with those dimensions. I'm going to measure my case when I get back home. It is an AE case with 8 mm studs but no case savers. So I need case savers installed and the spigots bored. I could probably run the original line bore as is but I should probably get a 20 line bore just to make it as close to perfect as possible. I don't want to go over 1776 with a single PICT 34. There are so many configurations possible with these engines it is mind boggling to a newb. So many more than a P-car and at a fraction of the cost. I now understand why there is such a cult following.☺
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pondervwmike
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PostPosted: Mon Jan 22, 2018 8:33 am    Post subject: Re: More newb questions re. big bore kits Reply with quote

Yea I would get a line bore and have the thrust area checked as well.
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rodeking
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PostPosted: Mon Jan 22, 2018 9:22 am    Post subject: Re: More newb questions re. big bore kits Reply with quote

The thrust is ok, the #1saddle width is 0.875 - 0.876 and the std/std bearing is a nice tight fit on the saddle. Whoever had this a part last time set the crank end float but then put the metal gasket in the fw after he set the float so it was .013. This is the o-ring fw. Lifters are all dished and as a result the C20 cam he put in is screwed up. "ULTRA BLUE" everywhere except the one spot where it should be on the cylinder / case surface.
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PostPosted: Mon Jan 22, 2018 5:43 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

rodeking wrote:
It is an AE case with 8 mm studs but no case savers.


I think the 8mm cylinder stud cases all have factory inserts!
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modok
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PostPosted: Mon Jan 22, 2018 6:03 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

That's true. All 8mm stud cases have inserts. And the STD thrust is .866, I checked that today, got a call on it.
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PostPosted: Mon Jan 22, 2018 6:09 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

so..does he know the case will have to be bored if going from a std bore to a big bore kit?? also , they are only as reliable as the builder builds it....
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rodeking
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PostPosted: Mon Jan 22, 2018 7:29 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

Yes, .866 is correct, that is what mine measures, couldn't remember what mine was exactly other than the bearing is a snug fit and it is std thrust width. I thought I measured 8 mm head studs, must be getting confused with the oil pump studs. So what size case savers and studs are best for spigots opened up for 90.5 cylinders? I'm out of town and just trying to put a list together of what I need.
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modok
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PostPosted: Mon Jan 22, 2018 8:07 pm    Post subject: Re: More newb questions re. big bore kits Reply with quote

Any will work. You can convert to 8mm studs using the OE type 12mm OD case savers, OR the most common to use for 10mm studs are 1/2-13 on the outside.
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