Ok i posted about a week ago w/ my dyno #'s and such. After going threw the car again, i cannot figure out why i'm so down on power. I mean i'd expect to make much more power than i'm showing. The peak rwhp was 398 @ 5300 rpm, and 421 ft/lbs rwtq @ 4,xxx rpm. It made over 400 ft/lbs of torque from about 3k - 5k rpms, but i'd think my car would make more hp up top, and on the dyno sheet it claims to fall off at around 6k rpm. The airfuel is rather suspicious down low, w/ it ranging from 14.5 in the low rpms (1800-2800) to 12.9 - 13.5 in the higher rpms (4-6k). i thought that maybe it was possible that w/ the comp r lifters they were truly preloaded down too much and hurting power, or possibly that they are too loose? (somewhat noisy) and causing valve float at higher rpms. I'm using the k motion k-800 valvesprings w/ titanium retainers, comp pro mag 1.6's. I was thinkin also maybe that i was not making full compression on some or all of my cylinders? what would be the total compression (psi) that i should read at each cylinder w/ 12:1 compression on a 396. The cam in the car is a GM 847 camshaft, w/ comp r lifters, fully forged bottom end, 6" eagle hbeam rods, srp pistons, stage 2 ported heads w/ 2.00/1.56 valves. slp cai, dynatech long tubes, 3" true dual w/ xpipe and bullet mufflers, 4.10 gear. Lucas 42.5 lb/hr injectors/walbro fuel pump. I'm sorry for such a long post, i'm just really confused and very aggrevated at my new combo, i mean the car runs great, sounds really strong, but just i am really disapointed as to the #'s it put down for what it is? ANY HELP WOULD BE AMAZING!

thanks,
Nick

 

I guess the obvious question is...have you had it dyno tuned? or have had the PCM reprogrammed?
You have a nice set-up there. I also think you should've gone with a custom ground cam, perhaps bigger than what you got there. You can also look at what your flow numbers were. And of course, you can check the easy things related to that, like the O2 sensors.

 

yes it has been dyno tuned that was w/ the dyno run. It was tuned by Finish Line Performance in Naperville, IL. The heads are good heads, not anything too extreme, i'd say w/ flow #'s around 265-270 @ 600". What exactly should i be looking at the o2's for? like what readings are good? and what about other sensors.. i know that i was pulling timing due to the lt1 km, but i replaced it w/ a lt4 km and it seemed to fix all of that. I just dont really understand what is holding my car back from making power up top, in my opinion i'd think im not getting full powerband out of that 847 camshaft. The specs on that are 234/242 575/595 @112.

 

No idea man, was this thru a 12 bolt?
Your head flow numbers do not look very impressive so that might be part of the problem, what are some of the mid lift numbers? Also, are you runing colder plugs gapped at .035 instead of stock?
Marcin

 

no that was thru the stock 10 bolt w/ gm motive 4.10's and a mac girdle. as far as plugs im using bosch platinums gapped at .035. I gotta go find the flow sheet, i have no idea as to where i put it. How much would the stock throttle body be holding me back? Also how would i be able to tell if the rockers are possibly adjusted to tight?, or maybe if they are loose and i'm getting valve float.

 

What size throttle body do you have? On a 396 I'd definatly use a 58mm or even a monoblade.

-Tony

 

i currently still have the stock throttle body, could this equate to the car falling on its face after 6100 rpm? about the cylinder heads, i looked around and cannot find the flow sheet, i want to say that i remember seeing 276 @600, and as far as porting these heads are really really ported, some of the intake runners have matterial added to them. and they're currently set up w/ manley raceflo 2.00/1.56 valves, k-motion k-800 valvesprings, titanium retainers, 10degree locks, 1.6 rr's comp pro mags.

 

id prolly try at least a 52mm TB...

 

nah, go right up to the 58mm or the AS&M monoblade tb.

also, is the intake manifold ported?

the intake is the main restriction that seem to limit everyone to the 400ish rwhp range.

 

i know the intake was port matched to my old cylinder heads, what exactly should i do to the intake to produce more power? and does anybody have a 58mm TB for sale, i desperately need one ha!

 

Get rid of those plat plugs! TR6 or Autolite 103's for starters. Had a friend w/ plat's in his 383 and the car ran good but decided to change em' out after I and a few others recommended it. Totally different car. Will gain your hp back? No but those plat plugs aren't helping your cause either esp w/ the CR. Just like the rest said around here get a 58mm tb. I know alot of people say a stk tb can support 400-500 hp but how many do you see around here using a stk tb on their heads and cam cars around here let alone a stroker?

Hope you get it running right.

 

ok sweet, so say i get a fully ported intake also matched to a 58mm tb, and a holley 58 mm tb, change the plugs. what kind of numbers should i be expecting. maybe i just have really high expectations, or i dunno but i was disapointed w/ what my car put down.

thanks,

Nick

--- where can i buy some autolite 103's or tr6's?

 

PM sent regarding TB.

 

What kind of dyno did you run the car on, Dynojet or Mustang?
Mustang dynos always show lower hp & tq than Dynojet.