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New Engine Slow Acceleration

mrmatt417

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mrmatt417 Enthusiast

mrmatt417

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All:

 

I have a 1992 GMC Sierra K1500 4X4. When I bought it it had bad main bearings in it and I had to replace the engine. I decide to beef up the engine and replaced the 350 with a brand new 383 Stroker. It look great, sounds great at idle or parked, but when I drive it the acceleration is really sluggish. I have to stick my foot in it pretty hard and it just feels like the power is not getting to the wheels. After it gets into 2nd, 3rd, and 4th gear it seems more responsive. It is the same gearing and transmission as the 350 which even with bad bearing seemed stronger. There also is a bad vibration in first gear as it seems to be struggling along.

 

Any thoughts? I have now put a lot of money into this thing and am disappointed that the results are not very strong.

 

Thanks for any help you can give.

 

-Matt

ColoradoSkiCountry Senior Enthusiast

ColoradoSkiCountry

Posted
Posted

What's your axle ratio? That has alot to do with it..

 

 

All:

 

I have a 1992 GMC Sierra K1500 4X4. When I bought it it had bad main bearings in it and I had to replace the engine. I decide to beef up the engine and replaced the 350 with a brand new 383 Stroker. It look great, sounds great at idle or parked, but when I drive it the acceleration is really sluggish. I have to stick my foot in it pretty hard and it just feels like the power is not getting to the wheels. After it gets into 2nd, 3rd, and 4th gear it seems more responsive. It is the same gearing and transmission as the 350 which even with bad bearing seemed stronger. There also is a bad vibration in first gear as it seems to be struggling along.

 

Any thoughts? I have now put a lot of money into this thing and am disappointed that the results are not very strong.

 

Thanks for any help you can give.

 

-Matt

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
What's your axle ratio? That has alot to do with it..

 

He didn't swap out the gears...just a 350 for a 383...it should get up and go like a scaled cat

 

I would be looking into a new trans man...sorry.

Either your 1st gear is slipping or your Torque converter is shot. A built 700R4 is the way to go here...A stocker will not hold up to a 383 for very long...and an old worn out stocker definitely wont.

mrmatt417 Enthusiast

mrmatt417

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Its a new torque converter so I think its good. its the old transmission the stock 700R4. I was thinking about replacing it anyway, so maybe thats the route to go. I agree this think rolls 417 HP and should be screaming...but it just isnt getting into the wheels.

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
Its a new torque converter so I think its good. its the old transmission the stock 700R4. I was thinking about replacing it anyway, so maybe thats the route to go. I agree this think rolls 417 HP and should be screaming...but it just isnt getting into the wheels.

Yeah, I think your 1st gear may be slipping...............

 

 

Wait....Dont these trucks have a TV cable...did you set it up properly??

Cant remember if they do or not.

mrmatt417 Enthusiast

mrmatt417

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I didnt do the engine swap I had a shop do it that does racing engines. I will have to ask them. Good question though.

 

 

Its a new torque converter so I think its good. its the old transmission the stock 700R4. I was thinking about replacing it anyway, so maybe thats the route to go. I agree this think rolls 417 HP and should be screaming...but it just isnt getting into the wheels.

Yeah, I think your 1st gear may be slipping...............

 

 

Wait....Dont these trucks have a TV cable...did you set it up properly??

Cant remember if they do or not.

 

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
Its a new torque converter so I think its good. its the old transmission the stock 700R4. I was thinking about replacing it anyway, so maybe thats the route to go. I agree this think rolls 417 HP and should be screaming...but it just isnt getting into the wheels.

 

It may have 417hp but what is the torque curve like? HP is not what gets it moving so you can pretty much ignore that number. If the cam is too "hot" you will not have any low end, and with the weight of the truck, it just will not pull out of the hole. Once going it will be ok, but down low it will just plain suck. Years ago (like 30 of them) I put a cam that worked great in my buddies Nova (not the exact cam, the same part number I mean) in my boss's van. The thing was a dog. Both had stock 350s in them of the same year. Same gears, same trans, only difference was the extra ton in weight.

mrmatt417 Enthusiast

mrmatt417

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The engine was built just for the high, low end torque. The torque is 421 and the manufacturor matched the cam just to get that low end thrust. In fact they knickname the engine the "neckbreaker" because of it. They Dyno tested at over 350 lbs of torque at 3000 rpms at start. They matched this engine just for the 4X4 application when I ordered it. So I have to feel it is somewhere after the engine....torque converter, transmission, TV cable...I dont know.

 

Anyother thoughts?

 

-Matt

 

PS

I really appreciate all the comments. It is very helpful for me as I work through this. This is a HUGE project for me and the advice I will get her will be invaluable.

 

 

 

Its a new torque converter so I think its good. its the old transmission the stock 700R4. I was thinking about replacing it anyway, so maybe thats the route to go. I agree this think rolls 417 HP and should be screaming...but it just isnt getting into the wheels.

 

It may have 417hp but what is the torque curve like? HP is not what gets it moving so you can pretty much ignore that number. If the cam is too "hot" you will not have any low end, and with the weight of the truck, it just will not pull out of the hole. Once going it will be ok, but down low it will just plain suck. Years ago (like 30 of them) I put a cam that worked great in my buddies Nova (not the exact cam, the same part number I mean) in my boss's van. The thing was a dog. Both had stock 350s in them of the same year. Same gears, same trans, only difference was the extra ton in weight.

 

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
Its a new torque converter so I think its good. its the old transmission the stock 700R4. I was thinking about replacing it anyway, so maybe thats the route to go. I agree this think rolls 417 HP and should be screaming...but it just isnt getting into the wheels.

 

It may have 417hp but what is the torque curve like? HP is not what gets it moving so you can pretty much ignore that number. If the cam is too "hot" you will not have any low end, and with the weight of the truck, it just will not pull out of the hole. Once going it will be ok, but down low it will just plain suck. Years ago (like 30 of them) I put a cam that worked great in my buddies Nova (not the exact cam, the same part number I mean) in my boss's van. The thing was a dog. Both had stock 350s in them of the same year. Same gears, same trans, only difference was the extra ton in weight.

 

Again...this is a 383...not a 350...its going to give you more low end torque than you know what to do with due to the stroke being so much longer...even with a higher RPM cam, it will still pull at least as well as a stock 350...but likely much harder.

These engines are made for low end torque.

Badass69 Senior Enthusiast

Badass69

Posted
Posted

Just out of curiousity what is fueling this 383? Did you switch the truck to carb or are you trying to run it with the stock TBI? If it's TBI tuning is probably most of your problem along with it not getting anywhere near the fuel it needs. For that kind of power with TBI you probably need around 30 psi or more on the stock 350 injectors and a 454's base would become a benefit at that point. I am assuming these dyno numbers you have were derived with a 4 barrel carb of some sorts.....

mrmatt417 Enthusiast

mrmatt417

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Went complete old school 4 barrel carb. No TBI.

 

Just out of curiousity what is fueling this 383? Did you switch the truck to carb or are you trying to run it with the stock TBI? If it's TBI tuning is probably most of your problem along with it not getting anywhere near the fuel it needs. For that kind of power with TBI you probably need around 30 psi or more on the stock 350 injectors and a 454's base would become a benefit at that point. I am assuming these dyno numbers you have were derived with a 4 barrel carb of some sorts.....
Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
Again...this is a 383...not a 350...its going to give you more low end torque than you know what to do with due to the stroke being so much longer...even with a higher RPM cam, it will still pull at least as well as a stock 350...but likely much harder.

These engines are made for low end torque.

 

Actually my mentioning the 350 was in relation to my experiences to relate a message, not his engine. And while a "stock" large displacement engine will genterate an equally large torque number at a low rpm, the "wilder" the cam, the higher the torque peak rpm and thus the lower the torque at the lower rpm. It is very easy to kill the bottom end power of a large cubic inch engine with a camshaft.

 

To the OP: I don't think 350 lb/ft of torque at 3k is all that impressive. A stock 350 (I know, you have a 383) should give you that at a lower rpm. Should a 383 not give you 400 lb/ft minimum? If you are running the stock stall speed converter, do you know that the torque number is at the stall speed of the converter? Do you by chance have a dyno sheet for this engine? Does the shop have a chassis dyno they can run the truck on? If they did not dyno this actual engine, it is possible they have something wrong in the assy (incorrectly packaged part for example).

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
Again...this is a 383...not a 350...its going to give you more low end torque than you know what to do with due to the stroke being so much longer...even with a higher RPM cam, it will still pull at least as well as a stock 350...but likely much harder.

These engines are made for low end torque.

 

Actually my mentioning the 350 was in relation to my experiences to relate a message, not his engine. And while a "stock" large displacement engine will genterate an equally large torque number at a low rpm, the "wilder" the cam, the higher the torque peak rpm and thus the lower the torque at the lower rpm. It is very easy to kill the bottom end power of a large cubic inch engine with a camshaft.

 

To the OP: I don't think 350 lb/ft of torque at 3k is all that impressive. A stock 350 (I know, you have a 383) should give you that at a lower rpm. Should a 383 not give you 400 lb/ft minimum? If you are running the stock stall speed converter, do you know that the torque number is at the stall speed of the converter? Do you by chance have a dyno sheet for this engine? Does the shop have a chassis dyno they can run the truck on? If they did not dyno this actual engine, it is possible they have something wrong in the assy (incorrectly packaged part for example).

 

A stock 350 will not give you 350ft-lbs ever...they're rated at like 275-300 ft-lbs max..and in stock form are built more for mid range operation.

 

A 383 usually has a smooth torque curve starting at 300ft-lbs @1000 rpm...peaking at about 425 at about 4500RPM and dropping back to 300 at around 6000-6500 rpm.

If it has a little less aggressive cam... the torque will move up the band a little...but it will still pump out a minimum of 200-225 at 1000 rpm...almost the max that a stock 350 produces.

A mildly worked over 350 with a street cam will bump out about 325ft-lbs at about 4K

Badass69 Senior Enthusiast

Badass69

Posted
Posted
A stock 350 will not give you 350ft-lbs ever...they're rated at like 275-300 ft-lbs max..and in stock form are built more for mid range operation.

 

A 383 usually has a smooth torque curve starting at 300ft-lbs @1000 rpm...peaking at about 425 at about 4500RPM and dropping back to 300 at around 6000-6500 rpm.

If it has a little less aggressive cam... the torque will move up the band a little...but it will still pump out a minimum of 200-225 at 1000 rpm...almost the max that a stock 350 produces.

A mildly worked over 350 with a street cam will bump out about 325ft-lbs at about 4K

 

Not trying to fight but this isn't even close to accurate. Oh yes a stock 350 can easily give you 350 lb ft, or more.... at a low low rpm. We aren`t talking the over head flowing under displaced LS series engines GM uses now that need 4000 rpm plus to actually accomplish anything. The old TBI 350's were 300 lb ft at 2800 rpm. The Vortec 350's and even the iron headed LT1's in the B bodies made 330 lb ft of it, the LT1 at only 2400 rpm and then the Vortec about the same. TPI 350`s from early 90`s Camaro`s made an honest 345 lb ft at only 3200 rpm....... dead stock

 

Torque( and then the horsepower calculation) is a function of camshaft, cylinder head and intake flow characteristics( and lots more really), not just engine displacement. You can easily build a 350 cubic inch Gen 1 that produces over 400 lb ft at a reasonable low rpm without breaking a sweat. At the same time you can build a 383 that will rev to 7500 rpm plus all day long. Bore and stroke have their affects but it's the package that counts the most. 4.6 Fords as an example are nearly a square engine at basically a 3.5" bore and stroke. Even the 5.0 the new Stangs will run are at 3.63" bore and 3.65" stroke. What does this matter? That 5.0 is a rev happy beast that pulls all the way to 7 grand, not some low rpm torquer, even though the stroke is actually larger than the bore size. It's the cylinder heads, intake and cams you can thank for that. The afformentioned LT1 or Vortec 350's easily would surpass the OP's 383's torque dyno numbers at the same 3000 rpm with nothing more than a custom tune.

 

So with that aside what stall speed of convertor are you running? 350 lb ft at 3000 is decent torque but probably should have at least a 3000 convertor behind it to take advantage of it. What can you flash the convertor too? By that I mean what rpm will the engine rev to when you stomp on it?

 

This engine probably is lazy at low rpm. How about some engine specs? What cam, what heads, what intake, carb and headers? Let's start with that. If it truly was some torque monster I would expect that number at 3000 to be close to your peak, not still building. You have a heavy truck that wants torque.

 

 

This is assuming the carb and timing are setup properly too.......

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