View Full Version : question on loss of power
02-27-2008, 09:02 PM
Well I had my car dynoed at speed inc on the 24th of january. Its a h/c/i 98 z28 a4 and put down 368hp/317tq at the wheels. After the first run Larry called me and told me was dropping fuel pressure and so I had them replace the pump with a walbro 255 and they redynoed it. Larry and the guys did an awesome job on the tune and pump install. I'm just wondering why my car is really low on power. When it was tuned the graph is perfectly smooth and a/f dead nuts 13.0 all the way through the rpms. But the thing is the motor was recently rebuilt with crank cut, new bearings and new rings set at .022/.024/and factory for oil ring and only had 200 miles on it for break in. Could that be a reason. Heres a list of mods:
98 short block rebuilt
fly cut pistons
stock mls gasket
patriot stage 2 ls1 heads (2.02/1.57) unmilled
tsp ms3 (237/242 .605/.610 112lsa)
ls2 timing chain
custom true duals with moroso spiral flows
transgo shift kit
fuddle 4400 stall
4.10 gear w/ girdle
lucas 42# injectors
new fuel filter
ngk tr6 gapped .035
I'm really happy with the work that speed inc did on the tune and know it couldnt be tune related as to why the power is down. It should be atleast 400 or so with the current setup. I havent done a compression test on it yet since I really havent had to time too. Just curious as to what other peoples thoughts are.
02-27-2008, 10:04 PM
The only thing I can think is the 4400 stall and 4:10 gear is robbing your power? Does it feel strong?
02-28-2008, 06:30 AM
A4's are not dyno queens, I assume the converter was unlocked
02-28-2008, 08:44 AM
I'm going through the same problem. The A4's with big stalls unlocked will not show huge power.
02-28-2008, 10:26 AM
Did your car pick up anything with the new fuel pump? Also, what valvesprings are you running?
02-28-2008, 03:14 PM
I have almost the exact setup as you same cam, intake, i have prc heads, 3800 stall, 3.73 gears and I put down 410 rwhp 370 rwtq at speed inc's dyno, I'd say something is wrong. THese cams with heads are all over 400 rwhp.
02-28-2008, 05:36 PM
im pretty sure the converter was locked as I've never really had a prob with it locking up. It feals pretty good driving but cant really get on it or end up in a ditch with all the salt on the road and its in semi storage till i buy my new house. Larry called me up and said it was dropping pressure and only did a run up to 5700rpms before leaning out and said it made 372hp but no tq numbers. So I really didnt gain power but reliability. Valve springs are patriot golds that come with the heads. I'll do a compression test and leak down test in the next few days and see what that tells me. I know its not fuel cause pump, injectors, and filter are new and I know its not the tune Cause speed inc does awesome work and the car drives great with no bucking or hesitation and a/f was spot on 13.0 through the entire rpms. I'm curious if anyone has ever had this problem before. Yeah its a big converter and auto arent dyno queens but I think something maybe wrong and cant afford to through parts at it or have a place look at it for a while.
02-29-2008, 06:24 PM
Heres a link to a forum with the dyno graph.
03-01-2008, 07:18 AM
I think you are heading in the right direction with the compression test and leakdown. That is a smooth graph, the torque does not make sense to me. Sorry I can't be of more help.
03-24-2008, 06:11 PM
Well I just got done with a compression test but didnt have time to do a leak down test.
Here are the numbers:
#1 - 160
#2 - 160
#3 - 160
#4 - 160
#5 - 175
#6 - 165
#7 - 175
#8 - 160
So the numbers are a little low but are still with in 10% of the highest to lowest. In 2 weeks I'll have track results on the setup.
03-24-2008, 08:14 PM
Even with the big stall and gears with your mods you should be over 400 easy
03-24-2008, 09:45 PM
I am curious why you did not get your heads milled...a bump in compression would have been a good thing. I bet your dynamic compression is 7.6:1 with that cam and static compression of 10.1:1. I think that is where your torque is and your HP. I can't believe I did not notice that before. This probably not your entire problem but it is a start. This cam only should make at least this much power but ported LS1 heads with no milling did not help you much in my opinion.
03-24-2008, 10:25 PM
I wouldn't worry about it with a convertor that big. Was the converter specced for the motor you are currently running? If you bought it for a stock car, and then put the heads cam in it, it will be sucking a lot of your power due to the mismatch.
03-25-2008, 04:54 AM
Well long story short i bought a t-rex cam and didnt like the way it drove and never got it tuned. Plus ran out of time to get the heads milled to raise static compression. I had the converter when I had the t-rex cam and just staid with it.
03-25-2008, 07:04 AM
I agree the TRex is probably hard to tolerate on a stock displacement auto, the tune would have to be dead on and all the idle trims and such perfect for it to hold idle and not die at every stop light. What kind of power did you make with the TRex? for comparison.
03-27-2008, 05:33 PM
didnt have it tuned with the trex, just put a few miles on it and sold it. Well, i think i may have found my problem. I may have either spun a rod or main bearing. Have to wait a few weeks to survey the damage since I'll be moving into my new house soon. So I'll either need a stock ls1 rotating assembly or a ls1 short block.
03-27-2008, 09:55 PM
Go bigger, I did when I blew a piston...stroker.