Low power in L98?
06-16-2003, 10:36 PM
#1
Low power in L98?
I have an 1989 GTA w/ an L98/ 700R4/ 3.27 gears w/ posi, everything is stock with the exception of a flowmaster cat back, catco cat, K&N cone in place of the original filter canister. The MAF is descreened and ported, and the TB coolant is bypassed. Nothing wild, so I'd expect close to stock times.
Last year I ran a bunch of times at a couple local tracks not known for their track prep work
. Best was a 15.9 all the rest were in the 16s all in the 84-86mph range. I was also having some sever drivablility issues. With an ecm swap (a friend had a TPI iroc that he switched over to carb), the drivability problems vanished. I am waiting to see if my milage has improved (barely in the 20-21mpg all highway @70mph, 15-18mpg mixed city/h-way). Supposedly this motor was a rebuilt motor only about 10k miles before i got the car (another 10k miles). After looking at it, you can see it's painted blue, and there is a badge or plate attatched to the passenger side of the block.
I went to the track last Friday and was expecting some good improvement given how much better it drove. I did run 2 personal best times (out of 4 runs, first runs of the year). However, I only brought the e/ts down to 15.865@86.74 on a 2.350 60'. I know that the 60' would help some with the e/t, but the mph is about 8-10mph off what I understand L98 cars to run.
After all that rambling, my question is this: What would cause a car to run that slow, yet drive just fine? It feels no stronger than my friend's carbed 305 convertable w/ subframes and rollcage.
Last year I ran a bunch of times at a couple local tracks not known for their track prep work
. Best was a 15.9 all the rest were in the 16s all in the 84-86mph range. I was also having some sever drivablility issues. With an ecm swap (a friend had a TPI iroc that he switched over to carb), the drivability problems vanished. I am waiting to see if my milage has improved (barely in the 20-21mpg all highway @70mph, 15-18mpg mixed city/h-way). Supposedly this motor was a rebuilt motor only about 10k miles before i got the car (another 10k miles). After looking at it, you can see it's painted blue, and there is a badge or plate attatched to the passenger side of the block.I went to the track last Friday and was expecting some good improvement given how much better it drove. I did run 2 personal best times (out of 4 runs, first runs of the year). However, I only brought the e/ts down to 15.865@86.74 on a 2.350 60'. I know that the 60' would help some with the e/t, but the mph is about 8-10mph off what I understand L98 cars to run.
After all that rambling, my question is this: What would cause a car to run that slow, yet drive just fine? It feels no stronger than my friend's carbed 305 convertable w/ subframes and rollcage.
06-16-2003, 10:44 PM
#2
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Car: 1989 TransAm GTA
Engine: One sweet modified 355 TPI.
Transmission: The kind that shifts....
Welcome to the wonderful world of, "I don't know why the hell I'm running so slow."
I was at the track a few weeks ago and manged only a best of 15.358 @ 87.34mph w/a 60' of 2.023.
From what I've gathered on my own setup it could be related to a number of things, but that list is huge. So no quick fix.
Timing
Fuel
Plugs/wires/cap/rotor
Perhaps its my MAF burn off relay, or some such.
In any case, the list goes on. Guess its a bump for you, maybe one of the guru's will reply and give us an answer.
I was at the track a few weeks ago and manged only a best of 15.358 @ 87.34mph w/a 60' of 2.023.
From what I've gathered on my own setup it could be related to a number of things, but that list is huge. So no quick fix.
Timing
Fuel
Plugs/wires/cap/rotor
Perhaps its my MAF burn off relay, or some such.
In any case, the list goes on. Guess its a bump for you, maybe one of the guru's will reply and give us an answer.
06-19-2003, 09:45 PM
#5
Thanks for the replys guys, I hope that I can find out the root cause here.
It better not be!!
Looks like thats my next step
Originally posted by FruityOne
Timing - Base is at 7 or 8* (6* is stock, but the engine started to sound different w/ more than that, I'll redo it soon w/ the scanner and see whats going on.) Total advance is at 34* cruising and about 13-15* get pulled under acceleration when the engine is hot, though there was no knock during my runs at the track thanks to the cool down periods.
Fuel - Possible, I'll have to check that, though I did change injectors with no discernable change.
Plugs/wires/cap/rotor - Time to do that again? I did that last fall, time to call up Summit and get some name brand stuff this time.
Perhaps its my MAF burn off relay, or some such. - I believe that that is working ok, it gets commanded on after I shut off the engine, and I can hear a click about 20 seconds later at the same time the scanner shuts off.
Timing - Base is at 7 or 8* (6* is stock, but the engine started to sound different w/ more than that, I'll redo it soon w/ the scanner and see whats going on.) Total advance is at 34* cruising and about 13-15* get pulled under acceleration when the engine is hot, though there was no knock during my runs at the track thanks to the cool down periods.
Fuel - Possible, I'll have to check that, though I did change injectors with no discernable change.
Plugs/wires/cap/rotor - Time to do that again? I did that last fall, time to call up Summit and get some name brand stuff this time.
Perhaps its my MAF burn off relay, or some such. - I believe that that is working ok, it gets commanded on after I shut off the engine, and I can hear a click about 20 seconds later at the same time the scanner shuts off.
1989camarorsrs: maybe its a 305 tpi
D Stroy H8: You need to eliminate all the of the simple questions first. Do a full tune up. Go to the track again.
06-19-2003, 10:08 PM
#6
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Car: 1989 TransAm GTA
Engine: One sweet modified 355 TPI.
Transmission: The kind that shifts....
With the MAF burn off relay I was actually refering to my car. The wires connecting to the MAF burn off plug are stiff, corroded and such. I was thinking that some of my problems may be caused by that.
If your not throwing code 36, then I don't think you'd have a problem with the MAF burn off relay.
If your not throwing code 36, then I don't think you'd have a problem with the MAF burn off relay.
06-19-2003, 10:53 PM
#7
not too long ago i posted about my first time at the track with my 91 L98 Formula. did 15.4 and was wondering the same thing. why it was so slow yet drove fine without no apparent problems. went again last week, did 3 runs with a best now of 14.8@92.5 in warm weather, not stalling the converter and with bad 60 foots.
the more practice i get the better i'll get at launching, shifting, watchin the tach to know when my power dies, etc. i knew this car had to do better the second time around.
like was said before, make sure engine's running in top shape by checking simple stuff first.
the more practice i get the better i'll get at launching, shifting, watchin the tach to know when my power dies, etc. i knew this car had to do better the second time around.
like was said before, make sure engine's running in top shape by checking simple stuff first.
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06-20-2003, 07:22 AM
#8
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Car: 92 T/A VERT
Engine: LB9
Transmission: AUTO
Axle/Gears: 7.5 / 3.42's
Aslo check the casting # on those heads. If its a store bought rebuild it may have the dreaded swirl ports or somthing else just as bad.
06-20-2003, 10:54 AM
#9
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Car: 1991 Z28
Engine: L98
Transmission: 700R4
There is a way to make sure your car came with a L98(check RPO code in glove box).....but then again that doesnt make sure they didnt put a 305 in place of it. The only way to really know is to take the motor apart and look at the bore size
but I dont think you would want to do that to prove a point. Keep practicing and make sure your engine is running in top shape. The first time I went to the track in my car I have now, and granted my strip driving could use some help.....I ran a 15.4. Took the car home, checked timing...was at 10* base??wtf?? Adjusted timing(6*base, 30*adv at 3000rpm), changed plugs, wires, cap, rotor....ran a 14.2@99mph. Im sure there is still more in it, especially with that trap speed.....but keep practicing....even if it's a 305 it should run better than that. Good luck
but I dont think you would want to do that to prove a point. Keep practicing and make sure your engine is running in top shape. The first time I went to the track in my car I have now, and granted my strip driving could use some help.....I ran a 15.4. Took the car home, checked timing...was at 10* base??wtf?? Adjusted timing(6*base, 30*adv at 3000rpm), changed plugs, wires, cap, rotor....ran a 14.2@99mph. Im sure there is still more in it, especially with that trap speed.....but keep practicing....even if it's a 305 it should run better than that. Good luck
06-20-2003, 03:36 PM
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Sounds like a 305, or a POS 350 someone put in just to sale it.
Check the casting number on the block. Driver's side rear. May need to clean off, and use a mirror. Check the casting numbers on the head (under the valve cover). Then you'll have a better idea what you have. Go here with the numbers:
www.mortec.com
Did you get any receipts on the rebuild or other paperwork when you bought the car???
How many miles on the car? Transmission rebuilt or fluid/filter ever changed? Is your posi still working (spin both wheels)?
If the engine needed a rebuild, good chance other mechanical issues need resolving as well. A tune up can't fix a real problem.
Check the casting number on the block. Driver's side rear. May need to clean off, and use a mirror. Check the casting numbers on the head (under the valve cover). Then you'll have a better idea what you have. Go here with the numbers:
www.mortec.com
Did you get any receipts on the rebuild or other paperwork when you bought the car???
How many miles on the car? Transmission rebuilt or fluid/filter ever changed? Is your posi still working (spin both wheels)?
If the engine needed a rebuild, good chance other mechanical issues need resolving as well. A tune up can't fix a real problem.
06-20-2003, 04:55 PM
#11
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Car: 1988 GTA
Engine: 350 TPI
Transmission: TH350
Yeah if I had to take a guess, you got a 305 and some told you it was a 350. The 350 L98 engines can easily break into the 14's and since you have the G92 package (3.27's) it should be even easier. Check your codes and see what you come up with, cuz i got the L98 package with 2.77's and I run low 14's high 13's with ET Streets. It probably doesn't help that your in Michigan either for your time but that shouldn't make that much of a difference. Just my $.02
06-20-2003, 10:50 PM
#13
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Heck guys, even a 305 TPI w/3.27's, would do real low 15's and maybe high 14's...Mi. isn't too high (I think) to make too much worry about corrections on the ET.
Someone else mentioned it, look at the head castings, if they don't end in 083, you didn't get an "L98 rebuild" and more than likely the cam isn't an L98 cam...from any year. Might be able to shine a light through the oil fill hole and get a good peak at the numbers on the heads.
Blue engine? Bah...
Someone else mentioned it, look at the head castings, if they don't end in 083, you didn't get an "L98 rebuild" and more than likely the cam isn't an L98 cam...from any year. Might be able to shine a light through the oil fill hole and get a good peak at the numbers on the heads.
Blue engine? Bah...
06-29-2003, 01:37 PM
#14
Wow, thanks for all the replies guys!
I'll check the casting numbers as soon as possible, its been a crazy last 2 weeks and I haven't had chance to do anything but change my oil. I've often wondered if the rebuilt motor was a 350, though I could more easily see them putting on p.o.s heads and cam before changing the displacement, though thats probably not too hard either
. BTW, the 8th # on the VIN is 8 (L98), but the RPO sticker was long gone by the time I bought her.
As far as Michigan elevation, I don't think that the track is more than a 5 or 600 ft above sea level. I've also run enough times last year, getting all those 16sec slips that I would hope my technique would have gotten over the learning curve by now.
I do have some info from the rebuild, it was done by Capitol City Engines. Says the engine serial # is 58492 if that means anything to anyone and the part # is C3310. No other useful info, just an generic owners manual and warrenty stuff. the customer is listed as Glen's Auto, Westminster MD.
I need to get some $$ from somewhere and get an LS1/ T-56 swap
I'll check the casting numbers as soon as possible, its been a crazy last 2 weeks and I haven't had chance to do anything but change my oil. I've often wondered if the rebuilt motor was a 350, though I could more easily see them putting on p.o.s heads and cam before changing the displacement, though thats probably not too hard either
. BTW, the 8th # on the VIN is 8 (L98), but the RPO sticker was long gone by the time I bought her.As far as Michigan elevation, I don't think that the track is more than a 5 or 600 ft above sea level. I've also run enough times last year, getting all those 16sec slips that I would hope my technique would have gotten over the learning curve by now.
I do have some info from the rebuild, it was done by Capitol City Engines. Says the engine serial # is 58492 if that means anything to anyone and the part # is C3310. No other useful info, just an generic owners manual and warrenty stuff. the customer is listed as Glen's Auto, Westminster MD.
I need to get some $$ from somewhere and get an LS1/ T-56 swap
06-29-2003, 02:19 PM
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Car: 91 Z28
Engine: Forged 383
Transmission: Pro-built 700R4
If you bought the car w/ a rebuilt block that's not factory and you don't know the quality of work of the people that put the engine together, then you should really assume that your engine is possibly a boat anchor. There's so many important things which effects performance when doing a rebuild it's not even funny. If they didn't finish the cylinder walls correctly the rings will never seal, if they used rings without the correct endgap you may be losing major hp to major friction, you could have super low compression due to wrong head gaskets, you may even have a peanut cam, depending on how bad you got screwed. This is an all just an exaggeration, but there are many more little things that may have been overlooked. Definitely check out the shop who did the rebuild immediately.
I'd suggest doing the basic tuneup requirements first. Things like establishing fuel pressure (fuel system), timing, check the plugs, and all your sensors to make sure they're working right. Then I'd do a compression and then a leakdown test. Make sure you search the boards and found out how to perform these tests right or you're wasting your time. Personally, I think there's a good chance your engine is junk, especially if you don't know anythng about the people who put it together. Let me put it this way, I know from my own experience that buying a car with a supposedly rebuilt stock engine is a risky proposition.
I'd suggest doing the basic tuneup requirements first. Things like establishing fuel pressure (fuel system), timing, check the plugs, and all your sensors to make sure they're working right. Then I'd do a compression and then a leakdown test. Make sure you search the boards and found out how to perform these tests right or you're wasting your time. Personally, I think there's a good chance your engine is junk, especially if you don't know anythng about the people who put it together. Let me put it this way, I know from my own experience that buying a car with a supposedly rebuilt stock engine is a risky proposition.
Last edited by camarojoe; 06-29-2003 at 02:21 PM.
07-05-2003, 07:21 PM
#16
Ok guys, I was finally able to get the casting numbers (I believe, they were the only #s I found).
The block #s look promising: GM57LG , would that be GM 5.7L?
The head driver's side head, wasn't about to pull everything off the passenger side too: 14102193.
If someone knows what these are, plese let me know
thanks.
-Steve
The block #s look promising: GM57LG , would that be GM 5.7L?
The head driver's side head, wasn't about to pull everything off the passenger side too: 14102193.
If someone knows what these are, plese let me know
thanks.-Steve
07-05-2003, 07:32 PM
#17
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Car: 89 Iroc
Engine: 383
Transmission: 700R4
Axle/Gears: 3.45
I did a search on this site for '14102193' and found several posts.
Apparently they are the swirl port heads and aren't very good
Apparently they are the swirl port heads and aren't very good
07-05-2003, 08:59 PM
#18
Thanks, i should have figured that one out by myself
. Well, now I know why it sucks so much after 4000rpm, would they also cause major knock when the engine is hot?
Looks like i need to take another look for the engine casting #, or is what i posted above enough to know that its a 350?
Thanks again for the help
Steve
. Well, now I know why it sucks so much after 4000rpm, would they also cause major knock when the engine is hot?Looks like i need to take another look for the engine casting #, or is what i posted above enough to know that its a 350?
Thanks again for the help
Steve
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