Should I be making more power?
01-09-2014, 11:29 PM
#1
Should I be making more power? Looking for opinions as to why my car dyno's low. The car is a full weight 98 SS and made 408/393. Tuned at Vengeance so I feel the tune is solid. Best I've managed at the track is 12.6 with a 2.1 60' (the driver is probably the bottle neck). Motor is a forged 347 with Weisco -3.2 pistons and compstar rods. Currently about 2k miles on the motor since the rebuild. The 806 heads were ported by Advance Induction and given the 219cc CNC port program along with a 3 angle valve job. The heads were decked .075 and I used .045 cometic head gaskets to reach a 10.7:1 compression ratio at .040 quench. Advanced Induction expects the heads to make anywhere from 400 to 450 rwhp depending on other supporting mods. The camshaft is a Cam Motion 228/234 595/595 lift - 112 LSA. Other bolt-ons include first generation 1 3/4" SLP headers/Y pipe (no cats) with cutout and dual/dual cat back, Crane 1.7 accelerated lift rockers, LS6 intake, SLP under drive pulley, ported polished throttle body with coolant bypass, SLP Lid, Paper filter, stock MAF with screen, LS7 Clutch, Comp 918's, FTRA, 4.11 10 Bolt. AC Delco Iridium Plugs and new wires along with new fuel filter. Injectors cleaned and refurbed at Fuel Injector Connection. Factory ZR1 wheels up front and replica 17x11's in the rear. 315 nitro DR. The car runs very well and I manage 25mpg's on the highway. All maintenance is up to date. Pop the hood when running and the motor is VERY quiet. No ticking or shaking or anything like that. I've encountered many TR224 cam cars making as much or more HP/TQ than I do with this setup. I had a TR224 and made 355/345 with that cam. Seems that I should be closer to the 430's with this setup. What do you guys think is holding me back at the track and on the dyno? Aside from the drive mod. Does that trap speed align with a 400 HP car?
01-10-2014, 09:45 AM
#3
Dynos are tuning tools, they are not remotely consistent with each other a lot of the time
Also if what I have read is correct your setup is oddball with dished pistons then mill the crap out of the heads to get the compression back up? Milling a bunch hurts flow according to posts I've read here.
Post the trap speed and density altitude and weight of the car as it races. Those 3 things will tell more than a dyno.
Also if what I have read is correct your setup is oddball with dished pistons then mill the crap out of the heads to get the compression back up? Milling a bunch hurts flow according to posts I've read here.
Post the trap speed and density altitude and weight of the car as it races. Those 3 things will tell more than a dyno.
01-10-2014, 10:48 AM
#4
Heads and cam were all installed at the same time. Lifters are Brian Tooley SLR. Car traps at 113-114 (sorry - forgot to post that). Density Altitude: 183. Race weight is about 3800lbs w/ me driving. Trap speeds are consistent from the three track days last summer/fall. I have about 15 runs total all in the 12.6 - 12.8 range. I'm running here locally in GA. The -3.2 piston is a flat top, valve relief style piston, not an actual dished piston. Compression was raised to 10.7:1 via milling. Part of that milling was to offset the additional cc's from the valve reliefs. Understanding that dyno's are inconsistent from one to the next, I made 393/375 on the same setup (different dyno and tune) before Vengeance tuned it. The first pull on the Vengeance dyno was 38X before revising the tune. I have confirmed full throttle voltage at the TPS and the throttle blade is dead on 90° at WOT. Keep you thoughts coming.
01-10-2014, 11:08 AM
#5
Thanks for the update. Sorry for my misunderstanding on the pistons.
Depending on the calculator I am getting 405-430 rwhp with a 3800lb weight. I think you are in the ballpark.
Should run even better if you can get plenty of traction and nail the shifts. Do you know what you were shifting at in relation to your dyno graph peak RPM? Seems a lot of people tend to shift early (sometimes by accident due to the stock tach).
Depending on the calculator I am getting 405-430 rwhp with a 3800lb weight. I think you are in the ballpark.
Should run even better if you can get plenty of traction and nail the shifts. Do you know what you were shifting at in relation to your dyno graph peak RPM? Seems a lot of people tend to shift early (sometimes by accident due to the stock tach).
01-10-2014, 11:18 AM
#6
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You have your dyno sheet? Can you post it. What do you shift at?
I feel as if the traps are low but that could be depending what rpm you shift at. You are getting good gas milage.
I feel as if the traps are low but that could be depending what rpm you shift at. You are getting good gas milage.
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01-10-2014, 11:56 AM
#8
I am probably shifting a little early. Shifting at 6500 per the stock tach. I'm told the stock tach is off on the low side. I reviewed the dyno sheet with a few racers and the suggestion is to shift at 6400-6500. An area where I think I may be losing performance: Wheels - 17x11" ZR1's in rear.
Another area where I suspect I may be losing power is the Crane Accelerated Lift 1.7 rockers. They are floating and properly adjusted IMO but I just don't trust them. Lol. Any one have experience with these rockers?
Another area where I suspect I may be losing power is the Crane Accelerated Lift 1.7 rockers. They are floating and properly adjusted IMO but I just don't trust them. Lol. Any one have experience with these rockers?
Last edited by 98cherrySS; 01-11-2014 at 08:01 AM.
01-10-2014, 02:36 PM
#9
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Your graph looks good I doubt they are hurting you. You would see it in the graph.
I think you could find some power with bigger headers and better intake but I still think you are trapping low.
I think you could find some power with bigger headers and better intake but I still think you are trapping low.
01-10-2014, 06:15 PM
#13
My tuner said there was a discrepancy between my tach and the actual RPM. I've been thinking about a shift light instead of a aftermarket tach. I'll try get one setup before the next trip to the strip. I've been wondering if the intake ports are a little misaligned since decking the heads so dramatically. Advanced induction didn't seem to think so. According to them the .075 mill job is pretty common. FWIW I built the motor for nitrous and gapped the rings accordingly.
01-10-2014, 06:44 PM
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My tuner said there was a discrepancy between my tach and the actual RPM. I've been thinking about a shift light instead of a aftermarket tach. I'll try get one setup before the next trip to the strip. I've been wondering if the intake ports are a little misaligned since decking the heads so dramatically. Advanced induction didn't seem to think so. According to them the .075 mill job is pretty common. FWIW I built the motor for nitrous and gapped the rings accordingly.
01-10-2014, 10:32 PM
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On a side note. If you have any pictures of your heads after they came back from ai I would love to see them. I am thinking about heads next and want to send my 806 heads to ai so I do not have to source valve covers