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Old 01-22-2011, 07:38 PM   #1
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quick questions 1987 iroc-z tpi 355

okay so i had an engine built for my camaro 355 6'' rod w/ heads, cam, roller rockers etc... I am still having major issues

when driving down the road once the trans shifts into over drive (built 700r4) if im not deep in the throtle the car will buck hard and jerk and it does not feel good at all, if i drop it back to 3ed it does not do it at all, weither im on the gas hard or just a little. Now i do not have a stall in the car yet and i know i have to get one because of the cam, is that the cause of my probs??? Any ideas??


The timing on the 1987 camaro iroc-z tpi 350 is 6..... im at 20 if i go any under 20 it will not idle what so ever... just keeps stalling out. Now at the 20 i have it set at it will kind of idle but once warmed up if it park the idle will go from 600ish to 1500 then back and forth... i am about to loose hope in keeping the tpi intake and just go with a carb but i really want to keep the tpi set up.... any ideas what so ever? this car did not run like this with the stock engine in it...


Fuel lines stock/walbro 255 pump
accell 30lb injectors
stock intake manifolds w/air foil

Dist/ignition is stock as well
Stock program on ecu

headman 3/4 length headers/flowmaster cat back
o2 bung welded in where y pipes meet

PBR Aluminum "bowtie" heads w/ comp cams 1:5 roller rockers
Comp cams mild cam (dont have specs off hand)

bored 60 over/block decked
Scat crank
6'' rods




Any help at all would be great.... does anyone know if someone has a write up for converting to carb from a tpi??? Thanks
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Old 01-23-2011, 07:45 AM   #2
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Re: quick questions 1987 iroc-z tpi 355

I would first double-check your firing order on the engine to make sure it's firing on all eight cylinders. If you've got a decent performance motor with a cam, the misfiring of two cylinders might just make it sound tough enough to fool you. The engine will run and start on only six cylinders. I've done it, and been there.

Double-check that the 18436572 rule applied properly. Trace each and every plug wire from the distributor post to the spark plug.
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Old 01-23-2011, 08:46 PM   #3
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Re: quick questions 1987 iroc-z tpi 355

okay i will do that. its just killing me man... i can not get it right and its doing nothing more than the stock engine did.........there is SOMETHING holding it back....... your spark answer might be a good start... when at idle (when it will idle) if i rev is the is a hard vibration through out the rpms do you think the stock ignition is not enough??? i cant see it being so but its a thought. once i get back to my shop ill check that out and see what i come up with....... anyone else have any input???
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Old 01-24-2011, 06:50 AM   #4
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Re: quick questions 1987 iroc-z tpi 355

The stock ignition should be enough. HEI is pretty good. I seriously think you need to check and make sure the cylinders are firing in the correct order. If you have two of the plug wires swapped around, it'll do just what you are describing. As a guess, just for fun, I am going to guess cylinders # 2 and 4.
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Old 01-24-2011, 06:57 AM   #5
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Re: quick questions 1987 iroc-z tpi 355

Yes, the bucking is from the lack of a stall converter. You NEED a stall converter for that setup.

Also, why in the world are you running the stock manifold and tune? You put some work and money into the long block just to keep the stock stall, intake, ecm.

The TPI is exactly what it is, a tuned port intake. It was tuned to stock specs. It is nowhere near what you want for the long block you have.

You really need to finish out the rest of the stuff for that engine to ever run like it should.

for more help check out www.thirdgen.org
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85 S10: 350/350 combo, Dart 200P Pro1s, 10.5:1, Lunati 40150 244/249 @ 50 .565/.543, Air-Gap, 650 DP
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Old 01-24-2011, 02:10 PM   #6
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Re: quick questions 1987 iroc-z tpi 355

I disagree that this is caused solely by a too-tight stall converter. We don't even know the cam specifications to arrive at that kind of conclusion. About the only thing we can possibly assume that could cause "light-throttle bucking" might be if the engine is going into lean-out because the ECM isn't delivering enough fuel relative to the engine's altered volumetric efficiency. It's a guarantee that the engine will be choking with a stock TPI manifold & runners, and it'll limit you to 5000, 5200 RPM. The 30 lb. injectors are most likely larger than you'll need with the manifold, but if you swap to a stealth ram in the future, the 30 lb injectors will be about right. They'll currently be injecting more fuel per given pulse width than the stock injectors, but if the computer isn't throwing codes, it's probably still able to adjust the block learning modifiers (BLM's) to compensate and get the fueling to go to stoich at light throttle/cruise.

If you are sticking to that stock manifold, what you really want to do is maximize torque. That means a cam with no more than 219 degrees of duration, and a 112 to 114 degree intake centerline. You do that, and you won't have to worry too much about adjusting the stall speed of the converter, since your peak torque should come in below 2400 RPM. Now that said, what kind of cam *did* you put in there?
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Old 01-25-2011, 07:56 PM   #7
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Re: quick questions 1987 iroc-z tpi 355

i really can not tell you what cam is in it, i know its comp cams because the kit i bought was cam, roller rockers, springs, etc, etc but when i bought everything i gave it to the man that built it and im still waiting on it all coming back. its not a huge cam... that car has a 2800 stall in in and the guy said it may or may not be enough of a stall becuase its a hair over stock.

I have not been to the shop yet to re check fireing order but if that does not fix it like you said about it limiting what the engine really can do that im swaping to a edelbrock carb and going to enojoy the power without efi head ache.

I will update this once i go to my car, thursday night!
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Old 01-26-2011, 07:40 AM   #8
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Re: quick questions 1987 iroc-z tpi 355

first you said it was a stock stall. Now you say 2800. Im confused. Does it have a 2800 stall converter in the car when it was "lurching"?

2800 is not a hair over stock. If you did have that converter in it, it is not your problem. I would do like WS6 mentioned.
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85 S10: 350/350 combo, Dart 200P Pro1s, 10.5:1, Lunati 40150 244/249 @ 50 .565/.543, Air-Gap, 650 DP
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Old 01-26-2011, 01:02 PM   #9
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Re: quick questions 1987 iroc-z tpi 355

First of all, there is no such thing as a stall converter. It's a torque converter. When some mentions a higher stall converter, the torque part get dropped and too many pick up "stall converter".

Secondly, the stall rating of the torque converter has nothing to do with anything once the transmission locks up the converter clutch, so having too tight of a converter is a problem but it's not THIS problem.

Third, without some cams specs we can't help too much. You have a converter that changes with every post, a stock tune, and an unknown engine and are asking for help. You really do need to provide more information...

Finally, the vibration you mention in the engine isn't normal. Either you have a mechanical problem, or more likely a misfire condition. The engine should not vibrate off idle, unless you've got a cam with a ton of overlap and it's under 1200rpm or so. But most cams that will pull enough vacuum for a street application will smooth right out just over 1000rpm.
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Old 01-26-2011, 04:34 PM   #10
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Re: quick questions 1987 iroc-z tpi 355

okay to clear things up i am sorry about the post by saying stall insted of tq convert. i had the transmission done well prior to the new engine that was built and it slip'd my mind sorry for that part of confusion.

I will post all my specs as soon as i get everything back including my old heads, etc. I know im shooting in the dark asking for help without specs and im sorry for that.

the man who built the long block had a heart attack right after i got the engine back since then he is home now but i dont want to be too pushy to him to get my things back to me. i will take a trip up there soon and get them my self if i dont have them by this up coming weekend.

When we talked about the build he did say that the cam was a mild application and i would not have any issues as far as is running decent off a stock tune/ transmission/etc. He is known to be the best around my area with fuel injected camaros... I would have the car to him now trying to figure it out but again he had a heart attack and i dont want to be pushy.

I will be checking the fireing order friday 1/30 and make sure its fireing on all 8 just like mentioned before. Reading what everyone here has wrote about the spark issue seems to be a good start to my prob. that would explain why i cant get the timing i need out of it if its only fireing off 6cyl. Anyway thank you everyone who has posted in here. and i will get back to you on specs and failures or success this weekend.
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Old 01-27-2011, 06:29 AM   #11
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Re: quick questions 1987 iroc-z tpi 355

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Originally Posted by Marc 85Z28 View Post
First of all, there is no such thing as a stall converter. It's a torque converter. When some mentions a higher stall converter, the torque part get dropped and too many pick up "stall converter".
No disrespect but arent you pushing it alittle with this? Its not like anyone is going to think of something else when you say a stall converter. They will know exactly what you are talking about. Yes its a torque converter, but do you get aggrevated when people call a carburetor a carb?
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85 S10: 350/350 combo, Dart 200P Pro1s, 10.5:1, Lunati 40150 244/249 @ 50 .565/.543, Air-Gap, 650 DP
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Old 01-27-2011, 07:41 AM   #12
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Re: quick questions 1987 iroc-z tpi 355

Personally, I don't think Marc is being picky here. These tech boards are here for a couple reasons; the first of which is to help each other know what works and what doesn't with these F-cars. The other reason is for education. I have learned VOLUMES from my fellow automotive enthusiasts, including Marc. However, education sometimes requires the educator to point out inaccuracies. Let's just take it as such. You could also have simply said "Yeah, that's what I meant: Torque converter. " If we want to be better, more informed auto enthusiasts, and if we want to sound like we know what we are talking about, we should use the correct terms.

Personally, I am looking forward to hearing more about Cbystrack's Z28 engine specifications, and I'm looking forward to hearing the words "WOW - THANKS! IT's running great!!" when he finally sorts it out.
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Old 01-27-2011, 09:26 AM   #13
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Re: quick questions 1987 iroc-z tpi 355

Alright then.
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85 S10: 350/350 combo, Dart 200P Pro1s, 10.5:1, Lunati 40150 244/249 @ 50 .565/.543, Air-Gap, 650 DP
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Old 01-27-2011, 10:45 AM   #14
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Re: quick questions 1987 iroc-z tpi 355

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No disrespect but arent you pushing it alittle with this?
Probably. But it sure made the point. The guy is here to learn so he can get his car running right. No point in teaching him poor terminology - it will only make matters worse.

Quote:
Yes its a torque converter, but do you get aggrevated when people call a carburetor a carb?
Nope, carb is short for carburetor. But I would get annoyed if someone referred to my wheels as rims.
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Old 01-27-2011, 11:37 AM   #15
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Re: quick questions 1987 iroc-z tpi 355

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But I would get annoyed if someone referred to my wheels as rims.
Ditto
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85 S10: 350/350 combo, Dart 200P Pro1s, 10.5:1, Lunati 40150 244/249 @ 50 .565/.543, Air-Gap, 650 DP
67 Chevelle SS: 396, 4 speed, 3.73, Flowmaster 40s
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