After doing a bit of research I really can't get a clear answer.
Do you lose HP and TQ when you go from a stock 346 to a forged 346? I went from a H/C setup to a forged pistons, rods, and the same H/C setup. My compression with the stock block and the 5.3 heads was 11:1:1. The Ross pistons that I went to were said to have the compression of 10:8:1 with stock 5.7 heads so if I used the 5.3 heads with 59cc and the 10:8:1 compression pistons what would my compression be? I seem to have lost about 35 rwhp and 30rwtq ft lbs.

Gilbert

 

Its really hard to say. Most forged aftermarket parts are going to be a little heavier than stock, but that souldnt result in 30hp loss at all. The lower compression you are running can account for as much as 10hp I would think in that setup. Give the details of the parts you used...floating piston pins? aftermarket rockers? aftermarket lifters...?

 

Heavier? My forged rotating assembly is considerably lighter than the stock components. Also, he's not saying he has lower compression. He stated that the new pistons have an advertised CR of 10.8 with 5.7 heads. If this is true, the pistons must be domed 6 cc's. 5.3 heads with 59cc chambers would result in around 12:1 compression.

What is your combo (head work, cam, etc)? Has the car been tuned? Have you scanned and logged any data? It's hard to determine what's going on without readings. If your CR is really that high, you may be getting a lot of knock retard.

 

Stock rockers, factory lifters, yes on the pins and SSMAN66 is correct on my compression. My compression is higher now than with the stock block. The heads are Patriots stage 2 5.3's with 59cc instead of the 61.xx offered off the shelf 2.02 intake 1.57 exhaust valves, G5X2 cam 232/240 595/609 on 112lsa. No I haven't scanned it yet I plan on doing so Wednesday before I get it retuned.

Gilbert

 

I would think you'd gain with a the forged set up if the correct parts are selected and it's tuned correctly. It's possible to lighten things up with the aftermarket parts. Likewise, the rings should be file fitted, floating wrist pins, custom pistons etc all should help make a little more or at least equal to the stock set up.

Sounds like something isn't right. Is your tranny slipping any?

 

Its a M6 with Spec 3 clutch, no. I will scan to make sure everything looks good. I just made this post because a guy i work with said ithappened with every 302 he built.

Gilbert

 

I would hope that he didn't build your 346 then.

I think it's a safe bet that your tune is way off due to the new heads/compression.

 

If you're running 12:1, I hope you plan on running a race gas mix. You'd have to lower your timing quite a bit to allow you to run pump gas, and that would cost you power.

 

No he didn't. I guess I will have a better idea tomorrow. There is obviously a few more factors that I am not thinking about. I will meet with Jayson from MTI tomorow and see what he has to say.

Gilbert

 

12:1 compression does not require race gas. Look at his cam specs - 232/240 on a 112. There should be enough overlap in that grind to bleed of quite a bit of cylinder pressure.

It's hard to say without seeing some readings, but I think your tune will need some help with the new setup.

 

Compression might be too high for the current tune.

 

Big cams only bleed off cylinder pressure at low engine speeds...up high they increase it...obviously since it adds power. Thats a decent sized cam for an LS1, but still isnt very big as far as BIG cams go for a motor that size. I still think thats a bit much compression to run timing in the high 20s with pump gas. I've seen several times cars running high 11s:1 with big cams burn their motors up with aggressive timing.

 

The scanning and tunning didn't do much. Pre forged I dynoed 416rwhp after forged and after todays retune the car did 396 rwhp. still a loss of 20rwhp. The conditions were different but the correction factor was also adjusted. My timing is 25* and I will be using 104 with an independant fuel sytem for the wet kit while I keep 93 in the fuel tank. The only thing that looked out of the ordinary was a spike in the a/f ratio ( I was looking at data that Jayson had on a Tech 2) He suggested I change my bank 1 (driver side) O2 sensor because it only showed 489 mv and he said the norm was 880-920 mv. Anybody please feel free to correct me if I said something out of context. I understood that an O2 sensor was showing an electrical problem. Other than that I am stumped.

Gilbert

 

That o2 would definitely ba able to kill those 20 hp...swap it out.

 

I swapped it out when I got home. I am still doubtful of that being the problem.

Gilbert

 

how many miles on new motor versus old one? The reason i say this is because a broken in motor will make more power usually. When my friend first got his 04 ZO6 I would actually beat him exspecially if he ran his hard and then we raced after a few thousand miles on his motor he pulled me harder and harder.

 

You have a problem with the hone job or rings or something like ignition or valve float etc. Posth the graphs before and after. The forged stuff won't reduce your hp.

 

1k on the new one 39k on the old stock block. That has crossed my mind but really didn't believe it. I really could care less about dyno numbers as long as at the track everything was the same but I my Et has gone up by about .3-.5 in the 1/4.

Gilbert