Bottom End Upgrade - Opinions?

[Ronin951]

First post

I recently (6 mos. ago) bought an '88 951 as a project. It was non-running and needed (still does) some TLC. I first did the water pump, belts, rollers, etc. I also put in a Vitesse Stage II as a "while I'm in here" (turbo getting replaced). I found the non-start problem was a failed fuel pump and she cranked right up. Then I was finally able to get some accurate compression numbers. Heh, thinking back it seems I went about things completely backwards. Anyways, the numbers were low and the subsequent leakdown showed serious blowby in #4 cylinder. I took the head off and sure enough. Pretty ugly. So that's where I sit now.

Now that I'm in another "while I'm in there" situation, I'm a little unsure about the bottom end upgrades. What I'm looking for is anyones experience with these. I understand that reliability is compromised whenever upgrading, so I don't want to go too far over the deep end. Well yes I do *want*, but I'd like to get at least 30k miles out of it.

Below is what I'm thinking. The application is mostly street with some DE and maybe autox. I'd like to build it out myself and not get an out of the box engine.

- 2.5 Liter stock block
- Performance crank (Knive edge, drilled, etc). LR and SFR are current candidates.
- Wiseco Pistons (LR has some that work with stock blocks)
- Stock rods
- Aluminum flywheel
- Performance clutch (Stage 2 Spec)

Questions:

Can I get away with using stock pistons & rods with performance crank?
Can I get away with sticking with stock rods?
Is a "performance" crank prone to breakage?
What's everyones luck been with LR vs SFR cranks? SFR's are $200 cheaper.
Overall potential issues?
Could my money be better spent in other places?

Sorry for all the questions. To me these are some important decisions and I want to get it right the first time!

Thanks in advance.

Matt

[924RACR]

Crank scrapers are inexpensive, and I've been very happy with the results from installing mine... crank-scrapers.com I think...

[JivenJim]

Hey Matt,

Conrad's on taking on a turbo project. Lots to work with there and lot of potential fun.

Sounds like you are on the right track. Here's my 2 cents.

Lightened either Crank or flywheel and you will have to learn how to down shift all over again and hill to toe blip it on the way down. (both and your a beginner again learning to drive a new higher power but VERY touchy beast) But as a perk you will see good results accelerating with less energy going in to the rotating mass. (ie less engine to wheel HP loss) If I had to choose New Flywheel or lighten, knifed Crank I would take the Crank work. But now I'm also going for both.

The Knife edge is what I'm having done right now to reduce oil foaming and reduce risk of Rod Bearing Failure. (also run oil full or just above) Either Lindsey or SFR will get you good stuff. Lindsey Racing might be a bit quicker if that matters.

Would definitely add a Crank Breather / collector tank see Lindsey.
Would Add the Crank Scraper and Windage Tray system 924Racer mentioned. I did. <http://www.crank-scrapers.com>

Stock Connecting Rods and Pistons shouldn't be over stressed by upgraded Crank or flywheel. However if you add more than about 100Hp I would seriously consider some Carillo or Pauter Connecting Rods and new Wrist Pins.

Stage II Clutch is a good mixed use level.
Lindsey has some nice Turbo Pistons to but I don't think that will gain you much unless you really up the boost and go with a modified CAM profile.
Would Replace the Rod/main bearings, and Piston Rings, and all the Seals and Gaskets you can handle. Do it while its apart unless you know it's been done recent.

993TT Blow off valve
and new Chip.

Look at the Lindsey 340HP Turbo Kit and what they recommend.

Sounds like fun stuff. Keep us posted.

Jim

[Ronin951]

Thanks for the input guys. Jim, I am most concerned about the weight of the stock rods and pistons on the machined crank. I'm thinking the reduction of crank mass might cause an imbalance, with the crank being the weakest link. I’ll dig up some formulas I ran across and call my engineer buddy

As for flywheel vs. crank vs flywheel and crank. Tough call. The good think is a thief won’t make it far!

[JivenJim]

I would be curious to see this formula. I thought that the balance shafts were matched to compensate for the Pistons and Connecting Rods, while the Crank itself was symmetrically balanced about its center shaft. I too would enjoy learning if someone cares to share?

When I compared some 968 Connecting Rod Weights. The Stock Turbo's look alot heavier.

1994 968 stock Connecting Rod (forged) 721 Grams
Mid 90's Carrillo H Beam (forged) 715 Grams
Current Carrillo's 669 or 674 Grams
1 gram = .0022 Pounds
So you compare the removal of maybe .1 pound per connecting Rod Verses about 4-6 lbs lightened per Crank balance lobe and that weight seems insignificant. Even with angular changes in Momentum I would still think it's not a big issue. But I don't know. Aftermarket are probably stronger thoe.

I didn't see one weight listed for any Piston I looked at, but would think they could be alot lighter aftermarket.

Let us know what you come up with.

[ae1969]

If you have had the pleasure of comparing our cranks to other applications. Our crank is plenty fine. I would not bothered doing much to it except crossdrilling.....

I run a stock bottom end with no probs. Running +300rwhp with no issues whatsoever.

If I were you I would look at a short block with Darton Mid sleeves.... (Chris White)...

I run a KEP pressure plate, cup disc and fidanza wheel. Heavy but works fine in day to day driving.

If you run 300-350 you will have no problems with a stock bottom end.

[Ronin951]

Originally posted by JivenJim
I would be curious to see this formula. I thought that the balance shafts were matched to compensate for the Pistons and Connecting Rods, while the Crank itself was symmetrically balanced about its center shaft. I too would enjoy learning if someone cares to share?

Here's what I dug up. I didn't mean to duplicate a thread

Knifedging a crankshaft?