Harrop supercharger

[bolus]

I admit I dont know the whole story there and I was going by what he said in the post with the graph " the only thing that has changed is the cams"  I also hate how the search on the forum is terrible and if you ask for help everyone yells at you to go search.  Even the GM build book doesn't say what the advantage is. 

I remember doing a lot more research last year when I was building my engnie I couldn't find anything that justified the extra $400-500 bucks for cams in an engine that was already over budget.  There is more bang for the buck elsewhere.  Just like the porting.  Even my engine builder said spent the money on the turbo side of things

But if you know different it would be a good time to mention it now since Norm has his engine a part. 

[Speedytec]

This is what he says under those graphs:

colors, cams, date that it was done. street numbers, not OMG dyno numbers.
red - gmr - 7/5/08
green - 272 - 2/10/08
blue - stock - 10/27/07

red was 11.6 afr. 20 degree's of timing
green was 12.0 afr 24 degree's.
blue was 12.4 25 degree's of timing.

im aware of the torque differences. there is a reason behind it. timing has a part of it, but the bigger part of it is compression ratio.

5* less timing and 0.8 more fuel for the GMR's. That's why their power is lower. He later explained that the lower dynamic compression is from the increased valve overlap of the GMR's. Therefore GM used/could use 10:1 pistons in their 300HP build.

[bolus]

even Compcams fails to have a dyno of their cams in an ecotec.  Not the best sales tactic to not even say what they do. 

[Speedytec]

For info, he has switched back to stock cams and is now making his power with a Harrop SC.
Apparently too much trouble with the lash adjusters for the GMR's.

To me that is a bit of the lazy way to make power. For an Atom you don't really need more torque I think, but a nice smooth (high) revving engine with excellent throttle control.
My view => Lightened rotating assembly (flywheel, balancer delete), good flowing head with uprated valves/cam, a good header+exhaust off course and an efficient intercooled SC to feed all this...

[bolus]

The balance shaft delete wasn't worth it for me or Darth who did it.  We might have got a little more power but the vibrations weren't worth it in the Atom.  I had an exhaust mount already break and Darth had some trouble too,  besides the fact that I get carpel tunnel symptoms from holding the sterring wheel now. 

[Speedytec]

People here who did this reported not much change in engine vibrations, but probably the LSJ is a bit less flexible (solid?) mounted in an Atom... 

[Heywood-Yablowme]

Vibration is your enemy

[bolus]

[quote="Speedytec"]
People here who did this reported not much change in engine vibrations, but probably the LSJ is a bit less flexible (solid?) mounted in an Atom... 
[/quote]

The engine is solid mounted to the frame and the frame is solid mounted to your ass

[Kempo]

[quote="bolus"]
[quote="Speedytec"]
People here who did this reported not much change in engine vibrations, but probably the LSJ is a bit less flexible (solid?) mounted in an Atom... 
[/quote]

The engine is solid mounted to the frame and the frame is solid mounted to your ass
[/quote]

that was funny bolus.

[atomaker]

Anyone attempting to boost S/C Atom 2 Ecotec output above 300 HP at the C/shaft, with or without water injection, needs to be warned about stock piston durability concerns.  This is via GM Motorsports.  The K20 Honda engine may be capable of it; the Ecotec isn't, for any prolonged period.

[bolus]

Some of the cobalt guys have put their stock engines through crazy HP without blowing up though I know those guys aren't seeing track time other than the drag strip.  But those guys have stock engines doing 400+ wheel HP and surviving.  Amazing!

As I posted in my turbo build here are the recommended upgrades from GM Racing based on power level.  If norm get's those pistons in there he should be fine until 400 hp

http://bolus.shackspace.com/atom/turbo/build_order.jpg
[img width=570 height=600]http://bolus.shackspace.com/atom/turbo/build_order.jpg[/img]

[Heywood-Yablowme]

K20 pistons are no better than LSJ pistons. Both cast. Both of modern design. Both very close to same piston speed/same rpm.

Both engines would need piston upgrades if constantly subjected to 300+ hp. like track days.

[bolus]

any updates Norm?  you going to be able to get new pistons in there?

[NormLarson]

Yes, new forged pistons.  Good call on them, thanks!

I tried to call and get a status today, but, it was to late in the day.  I will update the status shortly.  Last I checked he was busy routing the accumulator, oil cooler, etc.  He is doing all braided stainless, so, it will be very functional and blingy.  Can't wait ...

[NormLarson]

Here is a picture of the Harrop in the chassis.  I am told that it actually fits well.  Now it has to come back off so the pistons can go in ...