Topic: engine build: piston question

[95yj4]

I'm thinkin about rebuilding my motor this summer. I remember seeing someone talking about having the cylinders redone to fit chevy pistons(4.00 to 4.12, I think). I was wondering if this is possible or if I would run into problems. Also would anyone know what the stock crank can handle power wise. Thx

[Jeffy]

I know someone on the Mailing list talked about being able to use Chevy pistons since they are a lot more common.

[damon54]

It depends on what you are you doing with your engine.  If you want to supercharge or turbocharge or raise the compression ratio forged pistons for chevrolet are available off of the shelf, while jeep ones have to be custom made.  If you just want a bigger piston then you can go .06 oversize cast or hyperutectic pistons which are approximately 3.94 (stock is approx 3.88) available from silvolite.  If you match the compression height of the piston you should not have any problems with the piston being too tall.  Your Machine shop can bore match the diameter.  I don't know how much it too much though

[95yj4]

Alright well at least it sounds doable, I'll have to do some searching and measuring. But on building the engine for a supercharger, how do you do that? Cause I've heard that its possible to have a forged crank made but its like 2G's and I haven't seen anyone do it. What do you think the stock crank can handle?

[Jeffy]

Alright well at least it sounds doable, I'll have to do some searching and measuring. But on building the engine for a supercharger, how do you do that? Cause I've heard that its possible to have a forged crank made but its like 2G's and I haven't seen anyone do it. What do you think the stock crank can handle?

How much pressure are you looking at using?  Generally speaking a stock engine should be able to take 6-9psi without any problems.

[damon54]

Go to www.hesco.us and ask on the forums page.  The sell a supercharger kit for the 2.5.  I think 5lbs of boost is around 2k and 10lbs is around 3k.  They should be able to tell you what you need to change and what you can leave stock.

[Jeffy]

Go to www.hesco.us and ask on the forums page.  The sell a supercharger kit for the 2.5.  I think 5lbs of boost is around 2k and 10lbs is around 3k.  They should be able to tell you what you need to change and what you can leave stock.

Interesting they finally came out with a SC kit but it's nothing like what they were saying it would be.     They are using a Rotax SC.  It's a Centrifugal not a Roots/screw...  Funny they should say it works will ALL grades of fuel, too.  That's a pretty bolt statement.  I wonder if it will actually run with 87 and have no detonation problems.  Since it'a a centrifugal, at lower speeds, it shouldn't run boost but hitting boost when 87 can't be good.

The kit was supposed to be CARB legal but it doesn't look like it is either.  They deleted their old threads which said they were supposed to have it around $1600 too.  I'm a bit disappointed.

[wrangler387]

To build for supercharger all you would really need to do is forged pistons/rods and arp type studs. The crank should be good for more then you'll be throwing at it. One day i'll probably blow up my 2.5 testing the limits. Just remember there's isn't a set psi a motor can handle, rather a set power output. Since different sized turbos/superchargers will put out more power from less psi etc...

[95yj4]

Oh I know that it doesnt go by psi for what an engine handle. But I really want to try and get 200 torque out of it . Cause from what people are normally doing (60 over, undersize journals, knife crank, head work....ect.), the most power I can see coming from that work is around 180 torque. I really dont have the time or space to do a swap and I dont really see the point in buying a supercharger if I could spend some extra money and make it push the same N/A. If I were to do a super, I'd be rebuilding the engine too, just cause I wouldnt trust it. So 6g for super and engine build, or less then half that for an N/A pushin close to the same numbers.

[Jeffy]

Oh I know that it doesnt go by psi for what an engine handle. But I really want to try and get 200 torque out of it . Cause from what people are normally doing (60 over, undersize journals, knife crank, head work....ect.), the most power I can see coming from that work is around 180 torque. I really dont have the time or space to do a swap and I dont really see the point in buying a supercharger if I could spend some extra money and make it push the same N/A. If I were to do a super, I'd be rebuilding the engine too, just cause I wouldnt trust it. So 6g for super and engine build, or less then half that for an N/A pushin close to the same numbers.

Well, going with a what Mopar has done in the past you should be able to see anywhere from 173-203hp with a Stage III Mopar Performance, N/A build.  That doesn't include headers, larger valves or a bore, ignition upgrade, roller rockers, etc...  I think with all that you could have around 200lbs-ft and still run pump gas. You'd probably want to ditch the stock computer and run an aftermarket unit.  Then you could play around with fuel curves easier.  For that amount of work a SC would probably be an easier path.  Do some mild work on the head and internals would help beaf up the engine a bit for a more aggressive tune.

[95yj4]

Well I was plannin to do all that but all I could really see comin from it was 180 torque. Will the Stage 3 cam work with my auto without problems, wouldnt I have to change the torque convertor? Were could I get one? And I havent seen an aftermarket chip anywhere. Thanx for the help so far.

[wrangler387]

stock block can hold 200 ft-lbs of torque. i dont have any doubts in that. (assuming it is tuned right obviously). i'm looking to push about 200 to 225 ft-lbs in a few months. I'm finaly working on my set-up again.

[95yj4]

What are u planning on doin to yours?

[wrangler387]

same thing i've been talking about for probably a year now lol... I'm going to be putting a DSM 14b turbo on mine. I'm hoping to be up and running with it next month. Nothing to fantastic, shoudl provide me with some good low/mid power.