hey guys, im, finally done the car. its been 2 years and alot of time and money as im sure you all know exactly what i mean.
so ive had the car running for a few months now but was wating for the body shop to finish all the odds and ends. i had problems at first with fouling plugs but thats all figured out now.
so i just got the car back from a local high performance garage( they actually did the alot of the slp contracts and built alot of the lt4 motors) called ZEKES. so i brought the car there to get tuned and dynoed.
1st- car was making 406rwtq @ 4800rpm then dropped off. (belt slip?)
2nd-changed 2.65 pulley to 2.75 pulley. this time made 476rwtq @3500rpm compared to 380rwtq of first runs. then fell down to original torque curve.
3rd-we noticed the tensioner was jamming so we replaced it with a new one and did another pull. this was the same as the first.

conclusion: in all of the dyno runs the car wouldnt make power past 4800 rpm. A/F was around 11.0 which i know is a little rich but it is a street tune from Ed Wright at FASTCHIPS. so what do you guys think.

-is this still a belt slip problem
-is this a valve spring problem (trickflow 1.460 dual spring from assembled heads)
-any other ideas

also what would cause the huge jump in the 2nd dyno run?

anything would be great guys, im from montreal and the car season has almost come and gone again and i just really want to enjoy the car before i have to store it in october fro the winter. thanks

 

Forget it. I see you in fact from Montreal.

Should check out http://www.mfba.com/forums/. Some highly modded cars. We get togeher once a month at Hooters on the south shore. First Monday of the month.

Zeke's has a crap reputation from the guys.
I've been supercharged for 10 years. First with a 383 and now a 355.

Hard to comment but don't OBD2 LT1s have a preoblem of cutting fuel when the MAF maxes out?? There is a way to cheat the PCm but no clue how as I have an OBD1.

 

-Belt slip will cause boost drop- how many psi is it making?
-Doubt the valve springs are at fault at only 4600rpm
-11.0 is too rich. How many degrees of timing are you running? What is target AFR? If WOT timing is too retarded its going to be down on power and rich. A scanmaster datalog would help out.

INCREASE in blower pulley size and making more power definatly an issue. The belt may be too stretched or slipping. While you will make less boost on the bigger blower pulley, you have a little more belt wrap to keep it from slip. What belt are you running?

I'm in the process of working out bugs as well (for the past 5 months), and being my daily driver it kinda sucks.

 

im not to sure on the exact belt size but its tight. i bought 2 and kept the smaller much harder one to install ( 2 people). i was thinking of buying a set of cog pulleys to see if that helps but dont want to drop the cash on a test. if i knew of a performance shop in the US that could dyno tune the car i would trailer it there and have it done. is there anyone around who specializes in lt1 dyno tunning. im pretty sure its not belt slip causing the problem and i think the valve springs are strong enough as well. could it just be a bad tune. they had the car at zekes and they contacted Ed Wright and tried to re-tune it but still made no pwer past 4800rpm. i also had a tune from pcm4less that i could send back to him with the graph from the dyno and ask him to try to re-tune it.

 

Come on out to the next meet and you can ask the guys questions on Zeke's and their famous email tunes. I know of a 355 S-trim car that didn't last a season with their "tune".

I get me work done by a place in St Jean and do my own tuning and will be going in a few weeks to dyno tune the car.
I help out the other Lt1 guys and have had Lt1 edit since 1999-2000. PM me. I might be able to help. You should get TTS datamaster and do some logging.

It is tough to say what the problem is but if it won't do anything over 4000ish RPM it might be the MAF/OBD2 broblem. From what I know when the MAF maxes out it shuts down the injectors. 11-1 AFR is safe and rich, not optimal but shouldn't kill 100's of HP. There is a way around it. Do a search.

 

ya, i wasnt to happy that they gave the car back to me the way it was. i guess its becuase they didnt build the motor. some of the guys there are great. but one only seems to want to sell parts that i know i dont need. he really didnt think the dual intake pump setup was good and that i should change all my fuel lines to support 500rwhp. then i told him that my setup should be pushing over600rwhp and he kinda laughed at me. so i really want to get this problem fixed asap and bring the car back there to dyno it to shut him up. so after talking to the guys from PCMFORLESS im buying a cog belt setup from a member here as they are having the same problem with a customers car and belt slip is the issue. so ill start there and then they said i could send back the pcm with a dyno graph and they would retune it for me.

i see that youre not that far from where i live in chateauguay. would you be interested in coming to my place and seeing if theres something you could do to the tune before i install the cogs to see if belt slip isnt the problem. i would gladly pay you for your services. send me a pm if youre interested. thanks

 

Instead of the cog set-up get a spring tensioner. Dual pumps and stock lines will get you far. Get a good tune in your computer.

 

isnt the tensioner that comes with the kit a spring tensioner. if not where can i get one.
for the tune, i have to mailorder tunes one from ED WRIGHT @ FASTCHIPS and one from PCMFORLESS. both well know tuners and the same thing happened witheither of the pcm in the car. so maybe this really is a belt splippage issue. makes sense as it would basically be boosted to 4800rpm then the belt slips and power will drop off almost becoming naturally aspirated right. so hopefully my cogs get here this week and i should know by the weekend if all goes well.

 

DO you have a larger crank pulley? If not thats one way around going with a smaller driven pulley. It will balance out the loss from the larger driven pulley.

 

What intake pipe to the supercharger are you running? If its the stock one, junk it and build a solid one. When I had the T-Trim on my 383, 6psi was max I could ever get out of it, I built a solid tube and the boost jumped to 14psi.

 

Rockers too tight.

Rich

 

-im using the larger of the 2 pulleys that i have 2.75, which is still pretty small

-im running a front mount intecooler and have all soild piping so cant be that

-rockers were adjusted by my buddy a 25year mechanic. they were nice and slack when we installed them but i guess i could check.

-i just had an idea. i have a 4'' flexible hose as my inlet tube for the supercharger,is is possible that its colapsing at higher rpm? i guess i could jack the cars rear up and put her in gear and rev her up with the inlet tube off and see if i loose boost. would this be worth trying?

thanks for all the replies guys, really appreciate it. keep them coming

 

Yes, yes, yes. Get a solid pipe. I run a brad brand. There was a custom hard pipe for a T trim for sale a while back. Search the sale forum.

 

Collapsing intake is a definite possibility,

Rich

 

Take the intake tube off and do a dyno pull- if you suddenly don't drop off I would say that is prol your culprit. The flexible hoses aren't very reliable IMO. Many people have swapped them out for hard tubing and gained PSI.