theoretical discussion, bullet proof a boosted LQ1

[brian89gp]

Just to have some fun, how would you go about bullet proofing a LQ1 and at what power level would it fail? Seen a couple turbo LQ1's in Fiero's that are in the 400-450hp range but it is a very small sample size to get any information off of as far as reliability.

Rods/pistons: Probably as strong as you can afford to buy. Stock rod length or change it? Larger wrist pin?

Crank: GM steel 3500/3900 crank, leaving the stock 2.25" crank pin diameter. Anybody in the turbo 3900 crowd manage to break one of these yet?

Block: How much abuse can he stock 2 bolt main block take? Drill for 4 bolt? Girdle? Sleeve it for more displacement?

Heads: How much power before they lift off the block or crack?

Intake: 91-95 or 96-97? Probably not necessarily the best flowing engine anymore but are there any (uncorrectable) limitations that would be hit with not being able to flow enough?

[robertisaar]

the VVT3500 crank is a 3" stroke..... would help out with the rod/stroke ratio and allow for a lot of range on either rod length or piston pin location.

[brian89gp]

Same stroke as the 2.8 crank. Is the gains in rod/stroke ratio worth loosing 0.3L of displacement if you were pushing >15psi? Stock 3.3" stroke and 5.7" rod is already at 1.72 rod/stroke ratio

Was doing some reading and like anything on the internet it is a hotly debated discussion but there is somewhat of a concensus that a higher rod/stroke ratio is less beneficial in a charged engine even so far that the slightly longer dwell at TDC from higher ratio's might actually increase the chance of detonation slightly. For strength of the crank, RPM potential, less angularity of the longer rods, and a different piston pin location might be worth considering.

Stock 3.3" stroke and 5.7" rod = 1.72 rod/stroke ratio
3.0" stroke and a 5.85" rod = 1.95 rod/stroke ratio (rod increased half the length of the stroke decrease)

Calculating redline RPM based on a maximum piston speed of roughly 4000 fpm which is considered a good number to stay under to maintain reliability
3.3 stroke = 7301 rpm
3.0 stroke = 8032 rpm

[Will'sFiero]

There's a turbo TDC build underway on the Fiero Forum right now...
The rest of the build is good reading as well, but here's where he gets started on engine internals: http://www.fiero.nl/forum/Forum3/HTML/000143-10.html

He went with the large journal steel crank and found that the even fire Chevy 4.3 90* V6 with split rod journals also have 2.25" rod journals, and snagged a set of H-beams for that application. He had to narrow the big ends to work in the 60* engine.

As far as rod ratio goes... it's overrated. Stock 1.72 rod ratio is fine.

270 degree grooved main bearings are apparently essential to getting a TDC to live at high RPM. Steven Snyder has these in his engine.

Other than spinning a rod bearing due to lubrication problems, I don't think I've ever heard of anyone blowing up the bottom end of a TDC from power or boost.

[brian89gp]

I've been following that other thread too, quality workmanship.

RE: blowing the bottom end out. I've only heard of a handful of people pushing it, mostly topping out around the 400hp range and a couple around 450hp. What would you do to support 550hp?

[Will'sFiero]

I've been following that other thread too, quality workmanship.

RE: blowing the bottom end out. I've only heard of a handful of people pushing it, mostly topping out around the 400hp range and a couple around 450hp. What would you do to support 550hp?

Re: Rod ratio above... don't go crazy in search of rod length, as that's not a big deal. However, with a stroke that short and 60 degree deck height being what it is, definitely use 6.000" rods. The combination of longer rods and shorter pistons ends up with a lighter reciprocating assembly than stock rod length and taller pistons.

As far as bottom end goes... The big concern for me would be the 2 bolt main caps. At the very least I'd get the main caps doweled and use ARP bolts. The swap to ARP bolts and higher clamp loads requires align-honing the mains, of course.

The next step would be to make a stud girdle.

The bow-tie block used 4 bolt caps on #2 & #3 mains... I don't recall if there's enough thickness in the webbing in the TDC block to add 4 bolt caps, or if the caps are even available, but that would be the last resort.

[ericjon262]

here's another build, supposedly used 4 bolt mains(page 3) as well...

http://realfierotech.com/phpBB/viewtopic.php?f=3&t=15680

recently on the dyno, no numbers posted though...

[brian89gp]

Thank you Will, and thank you for the link ericjon. Gives me some idea's to ponder. It is surprising that a stock bottom end stands up to as much abuse as it does.