Compression and Pistons

[cboney2000]

Ok, now I'm hearing that both the L67 rods and pistons are NOT forged, which i thought one or the other was. So basically I dont have any idea where to get a good set of forged rods from or where I could get mine shotpeened and cryo treated. Im getting pistons/rings/wrist pins from Ross, and since a blower would cost near $3000 in the future, I'm going to up the compression to about 10.5, run 93 octane only, and maybe throw a 75 shot on after I learn a lot about nitrous first, since the majority seems to think that high compression and nitrous work well together. The higher compression would add some horsepower too I think, and with a cam from Comp and a set of Supersix heads, I think I should pretty much set to hit the 300 crank HP mark and maybe beat it. I also plan on getting the pacesetter headers, with an electric cutout for use with the nitrous, upgraded fuel injectors (if you know where to get a good set, please let me know, was thinking Lucas..), the Walbro fuel pump, and the Mini AFC with Autotap to tune it all correctly. One other concern was how the transmission with 95000 miles on it will react to nitrous and if I would need to get a newer or stronger one. Thanx!

[ April 28, 2003: Message edited by: cboney2000 ]</p>

[camaro_speedemon]

I thought the L67 rods and pistons WERE forged. If not, that puts a hitch in my supercharger project.

[cboney2000]

Ok, we need to get somebody in here who knows for sure, everybody keeps saying different things about them.

Are either the L67 Pistons and Connecting Rods forged or not?????

[navyblue2000]

correct me if i'm wrong whoever knows, but if i'm not mistaken the rods are forged, the pistons are hypereutectic (sp?)

[Dominic]

I believe we should all assume that they are not and instead go aftermarket.

Ross makes a set of good pistons we can use for under $500 anyways, and I would rather go that route. Rods, well the L67 rods are beefier whether theyre forged or not...

[cboney2000]

Sounds like thats the best plan, here's the big question for me though. Could I get a set of GTP rods (shot peened and cryo'd, anybody know where to get this done?) and a set of FORGED copies of GTP pistons from Ross only with the compression upped to 10.5 for use with nitrous. Basically domed top GTP pistons so that the rods will accept them (those rods dont attach to L36 pistons and wrist pins i heard..) There wouldn't be a supercharger and the nitrous would love the compression, so would the N/A cruising too with 93 octane. :D This sound feasible??

[ April 28, 2003: Message edited by: cboney2000 ]</p>

[BillyCobin]

http://www.bgsoflex.com/crchange.html

# Engine Horsepower (peak) is 200
# Old Compression Ratio is 9.4
# New Compression Ratio is 10.5
Computation Results:
# Computed New Engine HP is 206, a 3 percent change

According to that, you only gain 6 hp, and you will be forced to use 93 octane all the time. To me, it wouldn't be worth it to raise the compression that much. Especially if gas prices sky rockets.

[cboney2000]

I checked that website and I find that it doesnt seem to be anywhere close to accurate. For example, i'm nearly positive that 17:1 compression (i ran it through the formula) would do a little better than 11 HP over stock, and besides the whole idea for raising it wasnt just N/A power/efficiency, its for the 75 shot of nitrous i'll be installing soon enough afterwards.. :D

[viper98885]

I believe that the flat top piston from Ross for the 3.8 will bump your compression to 10.0:1. I know that my Ross flat tops for my 3.4 bumped the compression to 10.0:1. They suggest not going higher than that if you are running on pump gas (92 or 93 octane).
A few things to keep in mind...
1) Flat top pistons are cheaper.

2) A flat top piston will not disrupt airflow coming into the cylinder (this is a big plus)

3) Going with a domed piston in order to bump the compression up a half point really isn't worth it in my opinion. There is a lot of information that goes into the calculations for your compression and the pistons themselves are more expensive. A half point change in compression on my engine would have made very little difference.

4) Ross pistons are COMPLETELY custom. They can make them at any bore size, with any wrist pin hole diameter that you want and the price DOES NOT change. You need to find out the bore of the wrist pin hole on the rod. From there, they can do the wrist pins in either the 4340 material (which is what I got - EXTREMELY STRONG) or with the Tool Steel material.

If you have any questions about Ross pistons, let me know. I just had a set made for my engine as well as a set of forged aluminum rods from Manley. The rods are rated to 750Hp@7500 RPMs. This was a completely custom rod and they are fitting perfect in the crank journals. If anyone would like to look into doing a custom 3.8L forged rod setup from Manley, let me know.

[cboney2000]

How much did it cost you for the set of forged aluminum rods from Manley and what did you have to do to get them?? Very interested if its affordable.

[viper98885]

<blockquote>quote:</font><hr>Originally posted by cboney2000:
How much did it cost you for the set of forged aluminum rods from Manley and what did you have to do to get them?? Very interested if its affordable.<hr></blockquote>

Rods ended up being close to $500.00 shipped. They have a form on their website that is a worksheet for custom rods.


Manley Custom Rod page

[Bliggida]

<blockquote>quote:</font><hr>Originally posted by BillyCobin:
http://www.bgsoflex.com/crchange.html

# Engine Horsepower (peak) is 200
# Old Compression Ratio is 9.4
# New Compression Ratio is 10.5
Computation Results:
# Computed New Engine HP is 206, a 3 percent change

According to that, you only gain 6 hp, and you will be forced to use 93 octane all the time. To me, it wouldn't be worth it to raise the compression that much. Especially if gas prices sky rockets.<hr></blockquote>

Your math is right, but here is what you neglected to realize. The engine these guys are talking about are not stock, they are going to make 300+ Hosrepower. And yes, you said 3 percent but actually for every point in compression you raise expect to gain 4% more power.
At 200HP, and 1 point raised in compression it doesn't seem like it's worth much. But at 400. You are looking at 16 horses, if you go up two points thats 32 more horsepower at 4 points, would be 64 more horsepower!!! Well worth it.

But, you also forgot the fact that these guys are going to be supercharging the engine. Which means they will probably drop the static compression down to near 8 to 8.5:1. So they can run more boost. If you run 8:1 static, and run 10 pounds of boost, your Effective Compression Ratio is going to be 13.44:1

So you figure 200 stock, at 10 pounds the supercharger will probably yeild 50% or better efficiency. So that's at least 300 horsepower, and on top of that you figure in from 9.4 to 13.4 - a 4 point jump in compression. at 300HP that figures to about 48 more horsepower. Well well worth it

So built right, he should be pretty close to a 350 horse V6.

[BillyCobin]

That 300+ horse power is only going to be with a power adder. The ssm powerpak says 200 rwhp, so with 16.5% drivetrain loss, that about 240 at the crank. The highest anyone around has raised their CR is 10.5. So then, without a power adder, and with a cam/heads, you are only looking at a 7 hp increase at the crank for a raise to 10.5.

For a track/weekend car, an extra 14-20 cents a gallon for 7 hp might be worth it. But for a NA everyday driver, it seems like an expensive 7hp.

[Bliggida]

Where are you getting these numbers? Someone is giving you some bad info. 16.5% loss in the driveline? For an automatic or manual? Because really it's about 20% for a RWD automatic, and about 15% for a RWD manual.

Just because no one around here has a serious car doesn't mean you can't do it.

The Powerpack will give you about 235-236 horsepower at the engine. But that's if you follow thier specs. You can make so much power by mixing and matching parts. I for one would not bother looking at the SSPP cam. I figured a 9.44 more horsepower by going only 1 step in compression bringing it to around 245-246 horsepower. Almost 10 horses by just raising one point in compression. If I was going to build an engine and was really serious about the performance I'd go and run 11 to 11.5:1 with means of still driving it on the street.
With a powerpack as your reference point that's 254.88 horsepower an 18.88 gain in horsepower. And all you have to do is run 93 instead of 87. I think that's worth it. Again that's only figured on a normally aspirated engine.

You have cam/heads, and a supercharger if you build it right you should be making about 325 to 350 horsepower at the 9.4:1 effective compression. So by the time you figure in 2 or 3 points raise in compression. All the sudden you are looking at 12-12.5:1 and if you are making 350 horsepower thats an additional 42 more horsepower. And that brings your total to just under 400 at 392. Again, anywhere from 33 to 42 more horsepower (depending on N/A or force inducted) to me is well worth the extra few cents in gas. Especially since you'll still get well over 20 MPG in the car in full drag trim sporting 4.11's or bigger cogs.

[ April 29, 2003: Message edited by: Bliggida ]</p>

[Dominic]

With the right cam, with stock heads, and with proper fueling, timing, no detonation, and no other little problems like compression leakage, on a stock engine, with headers and every other nice little bolt on.

The theoretical best horsepower is ~375hp @ 7000RPM for a 3800-II.

Again, with the *right* cam you can easily achieve 345-360hp.

I'm not saying anymore until I put a dyno sheet on this board though.

And compression is worthwhile if you've done everything else. On a topend engine its worth about 30-40hp with 1.9" intake valves. Stock, no its not worth it at all.

(And this is n/a)

[ April 29, 2003: Message edited by: Dominic ]</p>