Northstar rebuild: Will style (Page 29/119)
Will FEB 10, 10:01 AM
Ok, just kinda thinking...

0.0055 from shank stretch
0.0023 from rod bearing clearance
0.001 from piston pin to rod clearance
0.001 from piston pin to piston clearance

0.0098

Because the bores are larger than the journals, there's room for the bores to oblong by (bearing clearance)*Pi/2... or 0.0036 if using 0.0023 bearing clearance as recommended by Alan Johnson. The corresponding number for the small end of the rod is 0.0015

That gets to 0.0149

Things that still require looking at:
Piston stretch
Crank stretch (main bearing clearance?)
Rod bolt stretch beyond what happens during installation
Stretch of the "big end" beyond simple oblonging of the bore

[This message has been edited by Will (edited 02-10-2006).]

Will APR 21, 09:41 AM
Ok... I took the block back from Mauzy's shop. He does great work, but it's a VERY busy time of year for him and he wouldn't be able to get to the block for a month or more. He also doesn't have any experience with engines with the N* style bottom end.
After installing time serts in the main bolt holes, I took the block to Justice Racing Engines in Frederick, MD. This shop has done a LOT of very high level import drag racing work, including the Enfantis' Supra engines. In addition, he has the tooling and experience to deal with engines that have the lower crank case style bottom end. Besides the Northstar, this includes Honda F & K series and Toyota 1ZZ and 2ZZ engines, among others. Justice is also a CP Pistons distributor, which Mauzy currently is not.

I didn't get the whole kit to install the main bolt time serts. I bought the installation mandrel ($50 for a glorified bolt!!!) from Kent-Moore and did the rest on a mill. A friend and I set up the block on a large 90 degree plate and supported the far end with a machinist's jack. We drilled the holes out with a 13/32 drill to full depth, about 1.230 (the depth to which GM drilled them originally). Then we counterbored with 1/2" end mill to a depth of 0.250-0.255. This depth is important as the inserts MUST be installed to sufficient depth both for strength and not to restrict oil flow to the main bearings. The final mill operation was tapping 10x1.5-STI to prep the holes. I ran the inserts in by hand along with a generous helping of Loctite maximum strength retaining compound.

Once Justice decks the block and provides me with a deck height, I'll finish my quench math and tell CP what compression height I want on the pistons and then that particular ball will be rolling.
ryan.hess JUL 27, 07:08 PM
Can't let this go do-do...

You need to create a short, concise thread of the things you learned, the things needed, etc... 8 pages is a bit much to go through to find out that you need to use xxx with yyy or explosions happen.

And you need to do some more math.
Will JUL 30, 12:13 AM
CP pistons are on the way. Total Seal Diamond Finish rings will be coming with. The pistons will include pins, which will be 2.25" long vice the stock 2.48" long. I still would have liked to have ceramic aluminum pins, but Hank the Crank was having "problems" last I checked.

I built a spreadsheet to look at quench numbers, but I kept on getting unexpectedly small numbers, so I decided that I didn't have enough info to calculate that directly.

However, I have been told that a 350 with 4340 rods and comparable quality pistons can run as little as 0.032 quench to 7200 RPM.

With a 3.48" stroke and 5.700" rods, the piston acceleration at TDC at 7200 RPM is...

R = 5.700"
T = 1.740"
S = 120 RPS

a(t) = 754t
da(t)/dt = 754
(da(t)/dt)2 = 568,489

A(t)|t=0 = -1,291,128 in/sec2
= 3,362 g's.

With 6.000" rods, this would be 3,322 g's (~1% difference).

At 7200 RPM, the Northstar pistons experience 3,130 g's.

So if the pistons weighed the same, The Northstar should experience the same rod stretch at 7640 as the 350 does at 7200.

HOWEVER, the pistons do not weigh the same. CP has given me estimates of the Northstar piston weights. I need to call them back and get a number for a comparable 350 piston and do a bit more arithmetic.

However, in the mean time I've decided to go for 0.035 quench. I'm going to set the pistons up at 0.005 in the hole and use an 0.030 MLS gasket (stockers are around 0.065 compressed(!)). If I decide I can get away with it, I may drop to a 0.027 gasket.

The CP pistons will be fit at 0.003 bore clearance, while the Ross pistons required 0.0045 bore clearance. That should give a clue about the difference in engineering between those to brands.


Concision is for Cliff Notes.

[This message has been edited by Will (edited 07-30-2006).]

ryan.hess JUL 30, 01:58 AM
is stock quench 0.065?
Erik JUL 30, 03:32 AM
nitpicker ..why not shoot for at least 8,500 rpms? ..I know, its a N* and it has its limitations ..Will, not long ago I seen several IRL "N*" engines on ebay that went for about 8 grand ..sure its some cash but still ..if you can come up with a combo that isn't going to cost an arm, leg, and several 88 GT Ttops to finance please do share the specs ..I've always thought the N* was the ultimate Fiero swap short of a 355 Ferrari engine
Will JUL 30, 08:53 AM
When I get the piston weights from CP (basically, when I get around to calling), I'll have better estimates. Suffice it to say that a 3.670" bore piston will be lighter than a 4.000" bore piston and I'll gain RPM capacity over a 350 that way.

I don't know the stock piston/deck dimension. I know the LS1's are a little bit OUT of the hole from the factory. Not sure if the stock N*'s are zero deck or out of the hole.
ryan.hess JUL 30, 10:22 AM
Cline was saying that a shorter quench would lead to faster carbon buildup and make it more prone to carbon rap. That doesn't make much sense to me, because it seems like with less squish, it would create more airforce on the carbon to shoot it out into the center of the cylinder.... But at any rate, I guess you'll have to do your italian tuneups regularly...

And I won't accept less than 10krpm from you. The stock parts can go to 8500 for a dyno run or two...

[This message has been edited by ryan.hess (edited 07-30-2006).]

Will JUL 30, 12:28 PM
With a hard breakin and good ring seal, I don't see that carbon would be an issue as long as the engine is tuned well.

Why don't 350's have problems with tight quench?
Will AUG 21, 12:10 PM
I'll do a couple of 3-2 upshifts to demonstrate 10,000 RPM capability from the assembly.

Write me a 7730 program with the limiter at 10.5...

After discussion with CP, a 350 piston of comparable design to mine would weigh about 18% more. The difference in bore cross section is 19%, further indication of how well the CP pistons are optimised.

Ok, so with the same weight pistons, a Northstar can spin to 7600 with the same quench as a 350 has at 7200. The fact that the pistons weigh 18% less means that there will be 18% less stress on the rod from piston acceleration. This won't mean an 18% reduction in rod stress... because there are things like the pin and the weight of the small end of the rod to consider... but I'll fudge it and say that there is a 10% reduction in rod stress from 18% reduction in piston weight.

Rod stress goes up as the square of RPM, so the RPM increase would be the square root of 1.10, or about 1.05. This multiplied by the previously mentioned 7640 gives just a touch over 8,000.

So I ought to be safe with 0.032 quench at 8,000 RPM. 0.035 quench should be good for 8300-8400.