3100 bottom end rebuild

[blackbombshell95]

Before I do my top end swap(3100/3100), i am GOING to have my shortblock rebuilt. I got a quote for $1075 locally with a 7 year 75k mile warranty.

And while i am getting the lowerend torn apart
I want to know what all can I do to prepare my car for 6-15 psi(not sure how far I will go). Knifeedge crankshaft(what does this do) And custom pistons.
Which place do you guys recommend for the best bang for the buck custom Pistons. I want to lower my compression.

To be honest, I don't know what a good compression ratio for boost is? Maybe just the same as the TGP's?
Note: with the engine put back together, the car won't have boost for a few months. Lack of funds are sure to come. How would car run made for boost with lower compression with no boost?


I pretty got all the parts I need for my topend swap. Some of you saw my old thread of my top end swap progress http://www.60degreev6.com/index.php?...ewtopic&t=5903


Any info is greatly appreciated

[SappySE107]

RE: 3100 bottom end rebuild

Actually, the 9.6:1 3100 pistons work extremely well with boost. Mick explained the quench characterstics a long time ago, perhaps when we were on GMF. Anyway, I would stick with that, even custom forged with the same design. Otherwise, yeah, ross, je, wiseco, or anyone else could make you some lower compression pistons.

Knife edging the crank reduces drag from the crank spinning around. A windage tray is used on the 3100s already so you should be good there. Having a crank scraper made up would be great, as would converting to the newer mains and cross bolted aluminum pan. Its not a direct swap for the pan but Im sure it can be done. I still have yet to put my block on the stand and take the pan off the 3100 I have here to see how much work is involved.

[blackbombshell95]

RE: 3100 bottom end rebuild

Actually, the 9.6:1 3100 pistons work extremely well with boost. Mick explained the quench characterstics a long time ago, perhaps when we were on GMF. Anyway, I would stick with that, even custom forged with the same design. Otherwise, yeah, ross, je, wiseco, or anyone else could make you some lower compression pistons.

Thats good to know. Thanks for the info Ben.

And If i'm understanding my pistons correctly, they have a big lip on them. And I hear anything over a 50shot of nitrious will waste my motor? Which was another reason why I wanted to go forged. I don't know how well the lip of the piston and nitrious get along together. It would be interesting to know why.
I plan to do a 50 shot maybe even a 75 shot of WET. Would you still recommend Forged Pistons?

[blackbombshell95]

RE: 3100 bottom end rebuild

Knife edging the crank reduces drag from the crank spinning around. A windage tray is used on the 3100s already so you should be good there. Having a crank scraper made up would be great, as would converting to the newer mains and cross bolted aluminum pan

What is a crank scraper? What benefits might i see from that and from converting to the newer main bearings?

[SappySE107]

RE: 3100 bottom end rebuild

You can run a 200 shot as long as your tuning and fuel are in order. The 50 shot is for a dry setup probably. I know people have ran 100+ without problem but they have done it well...not slapping it in and calling it good.

The crank scraper is like a more advanced windage tray in the way it helps the motor. The scraper will help keep the oil off the crank. The newer main bearings are larger, new metal (though i forget what year they improved them originally) and works with the aluminum pans. The cross bolted pan helps structurally, sort of like a girdle only not as good. Still, better than nothing. I honestly don't know if your stock motor has this setup. I went from a gen 2 to DOHC and haven't played with the gen 3s nearly as much as I would like to.

[geoffinbc]

Balance, balance, balance. The single most important part of your engine rebuild if you are going to push this thing. They should be spin testing the crank for proper results.

[SappySE107]

RE: 3100 bottom end rebuild

http://www.crank-scrapers.com/

That should explain quite a bit for you.

[bszopi]

RE: 3100 bottom end rebuild

That?s a fairly good explanation of cylinder quench, although it can apply to most any head type with the proper piston design.
The basic idea is to use a dished piston, with an optimized distance of around .030 for piston/head clearance. The abilty to obtain this distance on a non-splayed valve head would be the determining factor for its application there.

When GM finally caught on to the fact that optimized cylinder quench was critical to good engine design, they were able to increase the cr of the 3.1 60V6 from 8.9 to 9.6 using the same fuel octane rating. The result of this along with many other significant improvements, was the GEN III 60V6.
The reason they were able to acheve such a drastic increase in static cr, is the increase in detonation threshold that quench optimization provides. Detonation threshold also happens to be the primary factor used in determining gasoline octane ratings.

The design of the forged pistons I use is based directly on the GEN III 3100 SFI design (i.e. same compressed height, etc), with an increased dish volume to lower the cr from 9.6:1 to around 9.0:1. Since the optimized quench distance is retained, this is actually the equivalent of an 8.3:1 cr if one were using the non-optimized 3.1 Vin T piston design.

Successful turbo charging of an application that uses iron heads with a "higher than stock" cr forged piston, would really depend on weather the piston incorporates an optimized quench design. If not then I would say that one would be much better off using a nitrous oxide system as a power adder.

In any event, the stock Fiero engine management system does not include ESC control via knock sensor. The lack of a knock sensor eventually results in "several thousand pieces of piston" when significant boost is applied, since "precise tuning" is quite hard to achieve without one.
The 85 Fiero V6 ECM included ESC control / knock sensor options, which might be an alternative if one could also obtain a 2-bar version of the $24a code.
I have yet to see what would be considered as an acceptable 2-bar conversion of this code (IMO), although some claim to have accomplished it, (i.e buyer beware).

Other forced induction Fiero V6 engine managment alternatives, such as the relatively inexpensive swap to the 1227748 PCM loaded with modified $58 code (4.3 90V6 Sycone /Typhoon, 2-bar, HEI Distributor, speed density) will typically offer "very" acceptable results.

[bszopi]

RE: 3100 bottom end rebuild

Other quench info from a very reliable source...

http://www.theoldone.com/archive/quench-area.htm

http://www.theoldone.com/articles/The%5FSoft%5FHead%5F1999/

I could probably list just about every archive and article on that site, but that will give some good reading.

[blackbombshell95]

RE: 3100 bottom end rebuild

You can run a 200 shot as long as your tuning and fuel are in order. The 50 shot is for a dry setup probably. I know people have ran 100+ without problem but they have done it well...not slapping it in and calling it good.

So its all about tuning. not about the pistons?

I'm just thinking of getting the newer style 3100 bottom end. hmm.

[blackbombshell95]

RE: 3100 bottom end rebuild

Balance, balance, balance. The single most important part of your engine rebuild if you are going to push this thing. They should be spin testing the crank for proper results.

'

I will note that down

[blackbombshell95]

RE: 3100 bottom end rebuild

When I get some time i will read those articles brad