HELP! Do I buy these 3.3 turbo 8.5-1 coated pistons and trick rods?

[adomakin]

Im building a 400hp 3.3 turbo and i need some pistons. I was going to buy a set of 7.5-1 je's then these came up- (description below)


"I have a set of custom JE pistons for a 97mm 3.3 turbo. They are 8.5-1 pistons. THis jump in compression will give your car 6% more hp just from the compression. Not to mention a lighter and stronger piston than stock. They have been thermal barrier coated on the top and dry filmed on the side this was an additional 250 dollars on top of the 1000 for the pistons and pins. These pistons have 400 miles on them and are like new. The rods are ready to handle some real power. They are shot peened They were ran for 400 break in miles then removed as we are stepping up the combo a ton. They have been dry film coated to reduce oil clingage. This coating makes the rods very very slick as well as black in appearance. This coating cost over 100 dollars. EBS resized the rods for ARP rod bolts which were 250 dollars. Then we put good guides in them not the original replacements."



Is 8.5-1 too much? Do I need them trick rods? Will it DEFINATELY make the engine a stronger unit if I choose to boost more in future? I was going to boost to 1bar with no compression increase, then I started learing about how the comp increase will get rid of some lag AND i wont have to run as much boost?


What do I do? Sorry about all the questions but....I need some good advice!



ANdy, UK

[beepbeep]

A bit on a high side but it would work...you can boost maybe 0.7 with this setup and rev a lot. Twin-plugging would help a lot.

Frankly, that would make some very tractable motor...but forget megalomaniac boost plans as 911 combustion chambers are crappy and don't tolerate lot's of boost before knock occurs.

With other words: it will make motor more tractable and rev-happy but also cap it's ultimate HP potential.

[adomakin]

cheers beep, do you think this setup would work well with sc cams?

am i limiting myself in overall horsepower if i increase comp? I thought that by running a stronger rod would allow me to boost some more?

[adomakin]

i wasnt really looking to rev it out too hard either and was thinking of using a rev limiter to control things a bit.

[beepbeep]

Yes, you are capping your ultimate HP potential and boost you can use by using higher C/R pistons.

Stronger rod will support more boost but 8.5 C/R won't. But strong and light pistons and rods will allow you to rev more which in turn will allow you to use hotter cams which will in turn allow you to smear torque-curve higher up in revband which in turn provides horsepower. Still with me?

SC cams would be too mild with those rev-happy P&C's ... I would recomend GT2 EVO grind or similar.

[beepbeep]

If you twin-plug the heads, use GT2 EVO cams, EFI and boost just enough (my guesstimate is about 0.7 bar) you could be making some serious power (around 400+ -ish) with very nice driveability.

[adomakin]

still with you! so i am effectively relying LESS on boost and MORE on revs

[adomakin]

i was hoping to get my 400 horses from a k27 highflow, sc cams and a 1bar spring. I can see the sense in the spec you just mentioned but my budget aint goona cope with the twin plugs and efi. Hmmmmm.......
how about 7.5-1 with the sc cams, high flow and 1bar spring? too much boost?

[beepbeep]

Your ultimate boost has mostly with C/R, twin-plugging and IC-efficiency (and combustion-chamber shape, and fuel octane etc. etc. ) to do.

With EFI, you can boost less and still get same power or boost the same and get more power.

First thing to ditch would be CIS, in my case. check out Tony's Megasqirt, it would work quite nice together with Carrera plenum.

So possible combo for you could be something like this:

Carrera crank, 8.5:1 trick rods and pistons, Carrera intake, Tony's Megasquirt, Carrera (or SC) single-plugged heads, hi-flo K27 and hot cams (as hotter than SC)...it would bring you to approx 400 hp w/o too much fuss and rev to high heavens with little lag.

There are people turbocharging their US Carreras which have little lower C/R than Euro models and it supposedly works fine with 0.5 to 0.7 boost.

[beepbeep]

Oh, and one more thing:

Forget building hot turbocharged 911 motor "on budget". There is no such thing. I would rather recommend waiting until you have the means than experimenting with mix of hot (high flow K27, trick rods/pistons) and not-so-hot parts (CIS).

You either do it right or you do it wrong and then find out and are forced to do it right later with 30% markup

[adomakin]

wise words beep, i see where your coming from!

[adomakin]

beep, going back to something i said earlier, do you think 7.5-1 and 1bar is too much?

[beepbeep]

Originally posted by adomakin
beep, going back to something i said earlier, do you think 7.5-1 and 1bar is too much?

Hmmmmm....it's on ragged edge. Single-plugged 7.0:1 930 engines tolerate 1-bar barely.

[adomakin]

really? do you think id be better off with 7.5 and .7 or 7 and 1bar?

[beepbeep]

You shouldn't focus solely on boost. There are things about reliability and driveability.

If you have the means, 7.5:1 would be optimal. If you are on the budget, set of used 7.0:1 930 P&C's will tolerate wide range of boost and octane ratings and are probably cheaper.

1 bar is probably possible with 7.5:1, but margins will be smaller.

[adomakin]

i need to replace three of my standard 930 pistons and thought that it would be a good time to buy a set of 7.5-1 je pistons and take advantage of the ability to "spec" my compression. i assume that i would HAVE to run on high octane if i use 7.5-1

[350HP930]

While I agree wholeheartedly with beep about the CR and boost issues I would disagree with his opinions about the CIS and twin plugging.

If you address the fueling issues and clean it up a bit the CIS can flow well over 400 HP worth of air and the detonation issues you will have with a highly compressed 930 motor will not magically go away with twin plugging.

Twin plugging is good at taking care of flame front propagation issues on high dome pistons but 930 pistons are practically flat top pistons.

[adomakin]

cheers 350. what would you rather run, more comp and less boost or less comp and more boost? and do you think that they are a worthwhile buy for a street engine? do i really need to be revving highly or am i worrying about this so called "terrible" lag too much?

[350HP930]

Personally I am going for a slight bump to 7.5:1 compression.

I would also recommend adding a knock sensor/timing controller box to the car if you are going to push the limits.

Detonation will quickly destroy any HO turbo motor. I can attest to how well my motor did after years of abuse since it never had to deal with bad detonation.

For additional info you might want to check the link in my sig.

[beepbeep]

Originally posted by 350HP930
While I agree wholeheartedly with beep about the CR and boost issues I would disagree with his opinions about the CIS and twin plugging.

If you address the fueling issues and clean it up a bit the CIS can flow well over 400 HP worth of air and the detonation issues you will have with a highly compressed 930 motor will not magically go away with twin plugging.

Twin plugging is good at taking care of flame front propagation issues on high dome pistons but 930 pistons are practically flat top pistons.

Twin-plugging will speed up flame front propagation troughout the combustion chamber (and 911 has notoriously inneficient one) which means you can run more ignition advance which means that combustion will spend more of it's time pushing down on piston which ultimatly yields more power which means you can lower the boost which means you can run higher C/R which means less lag and better low-end response.

CIS sucks. Period. Especially 930 CIS which can flow loads of fuel but it doesn't help as it's plunger chokes the airflow. It's not just matter of providing the fuel, it's also about providing enough air into the engine.

With no CIS and twin plugging, you can use less boost and less advance and get same power as OEM 930, or you can bump C/R or use same boost to bring you more power.

I mean, you can get 500HP from a carbs if you try hard enough but it's deep in area of diminishing returns.