I just got back from the dyno (the only dynojet in my area) and have finally got some numbers for those who are curious. Also would like some opinions so feel free to comment/criticize... My setup is the comp cams XE230/236 544/555, 1.6rr, stock heads with mild work - flow about 260/170 cfm @550, LT's, Mufflex exhaust all this through a Heavy duty driveshaft and 12-bolt rear.. Peak numbers are in sig (the lower numbers were with a different tune from pcmforless which was slightly richer)

Here's the graph:



The main problems are the HP/TQ curve dip in the mid-RPM range, but the AFR also dips down into the low 11's in that exact range so I think some tuning will fix that easily so the TQ peak will be slightly higher maybe 325ish...
The big problem is that the torque really falls off in the upper RPM's... I was thinking maybe some valvefloat there?? I was going to maybe change the valvesprings to something stiffer that will handle the extreme lobes on my cam. If I could just keep the tq up there in the 5800+ RPM it would REALLY be impressive... Could anything else explain why it falls like a rock past that? It makes good power on top but it would be ALOT better if I could keep the TQ curve flatter.

Any comments would be appreciated.

 

your torque sucks imho... i know not all dynos are the same but i made 277/317 with bolt ons untuned with a misfire

and mine was also on a dynojet

 

What is your current valve springs?

 

CM 612's for the spring.

 

If you look at a lot of dyno curves, you'll see that a cam doesn't raise the TQ #'s that much, with stock heads. My bolt-on LT1(before 1.6 RR's) had 290 rwhp, 322 rwtq, and with stock heads and a cam, I don't expect to get more than 335 rwtq or so. I expect my HP to go up to about 335 rwhp though. What the cam does is extend out the tq curve rather that raise it very much, which raises the HP values.

HP=TQ*RPM/5250

Dan

 

yes but his heads are mildly ported

 

It's true the low-mid range torque (up until about 4000) is dissapointing. To be honest SOTP I thought I had LOST power down low but the dyno shows an improvement. Either way I'm not concerned with that too much (maybe a dyno tune would help though since I'm still on mail-order from pcmforless), I would rather concentrate on making the most out of the top end. Like if I could just help the torque curve a little bit up top I could easily reach 350 RWHP.

 

who ported those heads?

 

Looks like your ported heads are about as good as stock heads. Do you have a dyno graph with an RPM chart instead of MPH chart?

 

LOL it was a local shop here in Montreal 3 years ago and it was his first and only set of LT1 heads... I thought they flowed pretty good on the intake side compared to stock? Exhaust is obviously not much better than stock though.

Speed demon I'll get the hp/tq vs. RPM from the dyno guy soon, but the curves look pretty much the same... the dip in torque occurred somewhere in the mid-range, and peak hp was at about 6300 IIRC to give you an idea. crossover at 5252, obviously.

 

The dip in the tq curve is usually due to the overlap in the cam. I agree with the others that there is plenty of room for improvement, most likely in the heads. If you consider that you're using stockish heads with a mail order tune and going through a 12 bolt, it's not that bad.

 

Better springs and improving the tune might be a good idea.

 

What valvespring do you guys think would work well in the high RPM with this cam? Iwas thinking about running the crane 10308 dual valvespring kit?

 

Beehive springs are recommended, but you can get that Crane kit if you want to save some money.

 

Something is definately not right. Are you sure those heads flow 260? My last 383 made 370 to the tire with heads that flowed 260 and a cam that was 6 degees smaller. I also had restrictive exhaust and an automatic.