turbo stroker

[brian89gp]

Starting the brainstorming process to figure out the details of what I am going for (ie, how broke I will be when finished). Hopeing someone can help with the finer details for the ones I have long since forgoten and the ones beyond my understanding. Application is going to be a high boost turbo.

91-95 vs 96-97
-Are there flow rates for both types of heads
-Any block differences between the years, it is just front cover and heads up right?
-What is the combustion chamber volume for each?

Stroker with offset ground 3500 crank, 5.7" SBC rods, custom forged pistons
-Is there enough height in the stock piston design in order to use the stock SBC sized wristpin and also raise the height of the wristpin? (wristpin center would need raised 0.125" roughly right?) Does this put the wristpin into the oil ring?
-Is there enough block height so that the piston isn't pulled too far down at the bottom of the stroke?
-Any clearance issues with the block.
-Looking to use the dished 3.4 iron head pistons or similar design. This would lower the compression and also correct for the slight raise in compression from the stroke increase.

Block
-I am seeing youtube video's with around 420whp on the LQ1 now. Has anybody found the upper end for the bottom end strength?
-Is there enough meat on the block for custom 4 bolt mains?
-Anybody used the 3x00 main caps without using the cross bolting? The caps themselves look stronger.

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[pocket-rocket]

-Anybody used the 3x00 main caps without using the cross bolting? The caps themselves look stronger.

I was going to go this route. I've got all the caps and oil pan to do it, and since it's going to need align bored/honed after I was going to pull a double whammy and ARP the mains as well to err on the safe side. I haven't done a mock up though.

[brian89gp]

I was going to go this route. I've got all the caps and oil pan to do it, and since it's going to need align bored/honed after I was going to pull a double whammy and ARP the mains as well to err on the safe side. I haven't done a mock up though.

http://www.fiero.nl/forum/Forum2/HTML/114542.html
The block could probably be plugged and re-drilled. I would imagine the main caps would still line up with the oil pan just fine.


Found this, answers my question about sufficient compression height with the longer stroke
http://60degreev6.com/forum/showthre...r-Internals%29
In readon about the N* I guess the piston is about at its minimum compression height. Read a few comments that the CR couldn't be lowered much beyond 9.5 due to the lack of material to remove beyond that.

1.250" N*
1.476" LQ1
Decrease the compression height to 1.351 to accomidate the increase stroke. Enough to give a 0.101" dish to lower CR. Hoping for more, this is just guestimating.

3.15" x 0.101" dish should give around 13cc piston volume. Enough to drop it 0.5 to 1.0 :1 CR
http://60degreev6.com/forum/showthre...Piston-specs.?

[brian89gp]

Just found the CR calculator... Why is the CR 8.81 using stock values?

Stock values with 3.557" stroke (+0.250') and 13cc piston dish gives 8.55:1

[Joseph Upson]

I stroked my 3900 to 4.2L using small journal chevy 5.7" H-beam rods, so believe me when I say you must use 6" rods for this process. Part of the reason the large journal cranks and possibly all of the reason they have longer rods than previous, is because a 5.7" rod will cause the #3 & 4 piston to come into contact with the internal crank trigger, OE or aftermarket such as I have, requiring clearance.

If you choose to go external crank trigger and remove the internal ring, you'll need to clearance/adjust the short nozzle side of the oil squirter for those intending to use a stroked crank in a later block equipped with them.

Before tearing my motor down after unknowingly running it extremely lean under boost and burning the rings and valves, my oil pressure dropped and often the oil light blinked on at idle. I thought it was a flaky sensor but upon opening the motor up I found three nozzles had been broken off and the strange thing about it is some how I missed the interference while assembling the motor or it's something that happened during a high rev.

One of the most important history tables in TP5 (AFR) in my definition file was not optimized for boost and I didn't know it could be considering the fuel table wasn't either. When I figured it out after the fact last week and replayed the run that did the motor in I found AFRs as high as 18 at 7 psi.

You can see a snapshot of what I found after extending the AFR history table at this link, I haven't been able to post anymore pics here since the file management system was updated. http://www.fiero.nl/forum/Forum2/HTML/119218.html

The bottom end torque increase was easily noticeable so stroking the motor will definitely be worth it.

[brian89gp]

Thats good to know Joseph. Was planning on using a MS-III with sequential ignition so using an external trigger wheel and removing the inner would not be a problem, though not necessairly my first choice. The 3.4 DOHC block doesn't have oil squirters so problem solved there too.

I've read through your original 3500 turbo build then all the 3900 stuff. Quite an ordeal. I did a similar thing several years ago, just without engine damage. Kept increasing a value a little by little, sensor said one thing when in fact it was the opposite to the extreme.

[brian89gp]

Or would using the 3500 crank as is with the larger rod journals, having the wrist pin raised in the piston, and using 5.9" rods be more beneficial? From roughly 1.72 to 1.78 on the rod/stroke ratio.