Need some help with new motor
10-31-2008, 12:43 AM
#1
Instructor
Thread Starter
Member Since: Sep 2005
Location: St. Louis MO
Posts: 173
Likes: 0
Received 0 Likes
on
0 Posts
Need some help with new motor
I bought a new crate engine for my 1984 vette, its a a 383 stroker, I lost the paper work, and heres what I remember:
4 bolt main
forged domed pistons
hydrolic roller cam
new 64cc elderbrock aluminum heads
10 to 1 compression
my question is, what determines the RPM limit of a car, the stock motor was like 5000. normally shifting gears at 4200 or so.
Is the 4200 rpms going to be the limit of the new motor or can it go higher? if so how high?
4 bolt main
forged domed pistons
hydrolic roller cam
new 64cc elderbrock aluminum heads
10 to 1 compression
my question is, what determines the RPM limit of a car, the stock motor was like 5000. normally shifting gears at 4200 or so.
Is the 4200 rpms going to be the limit of the new motor or can it go higher? if so how high?
10-31-2008, 01:17 AM
#2
Melting Slicks
Is it a turnkey crate?
I'm assuming its the zz from GM less the intake.
If your bolting your stock CFI on it you will be limited and restricted.
Your gonna need to do some mods to the intake if you want to get its full potential.
I'm assuming its the zz from GM less the intake.
If your bolting your stock CFI on it you will be limited and restricted.
Your gonna need to do some mods to the intake if you want to get its full potential.
10-31-2008, 06:29 AM
#3
Burning Brakes
The RPM is "limited" - meaning the torque peak is past and the available power has run up against the connected load to the point where the rpm will not climb any further - by the mechanical horsepower limitations of the motor.
In real world terms it means breathing, and the foundation for that is the camshaft. All of the rest of the stuff - heads, intake, exhaust etc. can't Add more breathing than the cam is capable of but they can, and do, certainly Limit it.
Think of the motor as an air pump. It sucks air In, and blows it Out. As a pump it has an efficiency curve: as the RPM's climb higher the ability of the pump to move it's entire theoretical displacement of air (100% Mechanical efficiency) becomes reduced - and the ideal straight line representing air flow vs. rpm becomes a curved line instead. This is One reason (probably the Simplest reason) to explain why the Torque curve looks like it does, falling off after some peak value, as the rpm climbs.
The combination of Camshaft, heads and etc. will determine where that torque peak happens, and how fast it falls off beyond that peak. Whatever the actual torque Numbers are, the balancing of that torque against the Load (vehicle weight, mechanical friction losses, aero drag, etc.) will determine the point where the thing just will not go any faster - it ran out of "horsepower".
In the real world you also do have to consider the mechanical Strength of the motor assembly - crank, rods, pistons, valves/springs, etc. All of it has to be able to reliably handle the sustained loadings being applied (it doesn't blow up, in other words).
Rev limiters ("add-on", sort of, usually in the ignition system, although Could be in the fuel system on an injected motor) are there to make sure that the rpm of the motor stays down within the mechanical strength limits of the assembly. Particularly in low load situations (lower gears) the Load isn't great enough to prevent the motor from reaching an RPM higher than the components can withstand.
Now - there is NO "rev limiter" in your '84 vette. Nothing in the chip that limits the RPM by shutting off the fuel, or the spark. There is a fuel cutoff, set at some (editable, probably) Speed - I don't know what this is for an '84, but it's probably well out of reach anyhow.
However - like QWS said - the crossram intake setup for the '84, or a TPI setup, will severely limit the airflow possible through the motor (there's that mechanical efficiency thing again), and the Practical RPM limit - and where the torque peak is - is going to be not much different than the Old motor had. A stock exhaust setup, with convertor, will be the same problem.
More displacement, more compression, etc. will mean bigger torque numbers from almost zero RPM (compared to the Old motor). It'll Pull much harder at Any rpm. Up to where it "runs out of breath", and with the same airflow restrictions on the intake and exhaust sides of the pump that "out of breath" rpm isn't going to change much...
In real world terms it means breathing, and the foundation for that is the camshaft. All of the rest of the stuff - heads, intake, exhaust etc. can't Add more breathing than the cam is capable of but they can, and do, certainly Limit it.
Think of the motor as an air pump. It sucks air In, and blows it Out. As a pump it has an efficiency curve: as the RPM's climb higher the ability of the pump to move it's entire theoretical displacement of air (100% Mechanical efficiency) becomes reduced - and the ideal straight line representing air flow vs. rpm becomes a curved line instead. This is One reason (probably the Simplest reason) to explain why the Torque curve looks like it does, falling off after some peak value, as the rpm climbs.
The combination of Camshaft, heads and etc. will determine where that torque peak happens, and how fast it falls off beyond that peak. Whatever the actual torque Numbers are, the balancing of that torque against the Load (vehicle weight, mechanical friction losses, aero drag, etc.) will determine the point where the thing just will not go any faster - it ran out of "horsepower".
In the real world you also do have to consider the mechanical Strength of the motor assembly - crank, rods, pistons, valves/springs, etc. All of it has to be able to reliably handle the sustained loadings being applied (it doesn't blow up, in other words).
Rev limiters ("add-on", sort of, usually in the ignition system, although Could be in the fuel system on an injected motor) are there to make sure that the rpm of the motor stays down within the mechanical strength limits of the assembly. Particularly in low load situations (lower gears) the Load isn't great enough to prevent the motor from reaching an RPM higher than the components can withstand.
Now - there is NO "rev limiter" in your '84 vette. Nothing in the chip that limits the RPM by shutting off the fuel, or the spark. There is a fuel cutoff, set at some (editable, probably) Speed - I don't know what this is for an '84, but it's probably well out of reach anyhow.
However - like QWS said - the crossram intake setup for the '84, or a TPI setup, will severely limit the airflow possible through the motor (there's that mechanical efficiency thing again), and the Practical RPM limit - and where the torque peak is - is going to be not much different than the Old motor had. A stock exhaust setup, with convertor, will be the same problem.
More displacement, more compression, etc. will mean bigger torque numbers from almost zero RPM (compared to the Old motor). It'll Pull much harder at Any rpm. Up to where it "runs out of breath", and with the same airflow restrictions on the intake and exhaust sides of the pump that "out of breath" rpm isn't going to change much...
10-31-2008, 11:13 AM
#4
Burning Brakes
my question is, what determines the RPM limit of a car, the stock motor was like 5000. normally shifting gears at 4200 or so.
Is the 4200 rpms going to be the limit of the new motor or can it go higher? if so how high?
The TPI runners and intake manifold is the major restriction to higher RPM's. The long tubes produce awsome low end torque, but restrict air flow volume above about 4200.
Most hi revving engines have excellent breathing and are restricted by the valve springs holding the followers to the cam lobe, valve float. I am talking about engines that rev higher than about 6,000. Hydraulic roller cams can rev to around 6,000 I think, so the after market FI induction is still the major limiter, like around 5500-5800 for a typical hi-perf street engine. The cam lobe is important too, but most after market perfomance cams can run easily at 5500+ level.
Is the 4200 rpms going to be the limit of the new motor or can it go higher? if so how high?
The TPI runners and intake manifold is the major restriction to higher RPM's. The long tubes produce awsome low end torque, but restrict air flow volume above about 4200.
Most hi revving engines have excellent breathing and are restricted by the valve springs holding the followers to the cam lobe, valve float. I am talking about engines that rev higher than about 6,000. Hydraulic roller cams can rev to around 6,000 I think, so the after market FI induction is still the major limiter, like around 5500-5800 for a typical hi-perf street engine. The cam lobe is important too, but most after market perfomance cams can run easily at 5500+ level.
10-31-2008, 04:00 PM
#5
Le Mans Master
Short answer:
Bottom end/valvetrain: Determines how high the motor can rev repeatably without loosing it.
Induction system/cam/etc: Determines how high the motor will still be building power.
Which answer are you looking for?
Bottom end/valvetrain: Determines how high the motor can rev repeatably without loosing it.
Induction system/cam/etc: Determines how high the motor will still be building power.
Which answer are you looking for?
11-17-2008, 09:07 PM
#6
Instructor
Thread Starter
Member Since: Sep 2005
Location: St. Louis MO
Posts: 173
Likes: 0
Received 0 Likes
on
0 Posts
I think I asked the wrong question...let me see if I can rephrase it.
The stock engine, ecu, and transmission is setup so that it redlines at 4500, and the transmission usually shifts around 4200 at WOT.
The new crate engine is able to rev up to about 6500 rpms (as long as there is enough air etc...)
The transmission is still shifting at 4200 rpms.
the new engine is cable of 6500 minus the 4200 rpms it is using, means that there are about 1300 rpms per gear that I am missing out on.
(I would actully like the transmission to shift at about 5500-5800 rpms.)
What controls when the transmission shifts? internal parts? the ECU?
Also I would like instructions to do an EGR delete. I capped the egr port on the intake, and siliconed it shut to make sure there was no air link in it. I then capped the tube on the rear of the front Throttle body.
To do an egr delete do I need reprogram the ECU as well?
Sorry guys, I decided to get this project car for a learning experiance, and boy have I learned a ton..
Nothing worse then getting a 383 stroker, with a 350 non-externally balanced flex plate, a brand new motor that leaks coolant from the bottom of a head, and an oil leak..
Next time, im building the engine my self.. I spent the extra money to have a "pro" put it togather so I wouldn't have to deal with the aggravation of leaks.. oh, and the place that put it together was a well known trusted shop in town that many people refered me to.
The stock engine, ecu, and transmission is setup so that it redlines at 4500, and the transmission usually shifts around 4200 at WOT.
The new crate engine is able to rev up to about 6500 rpms (as long as there is enough air etc...)
The transmission is still shifting at 4200 rpms.
the new engine is cable of 6500 minus the 4200 rpms it is using, means that there are about 1300 rpms per gear that I am missing out on.
(I would actully like the transmission to shift at about 5500-5800 rpms.)
What controls when the transmission shifts? internal parts? the ECU?
Also I would like instructions to do an EGR delete. I capped the egr port on the intake, and siliconed it shut to make sure there was no air link in it. I then capped the tube on the rear of the front Throttle body.
To do an egr delete do I need reprogram the ECU as well?
Sorry guys, I decided to get this project car for a learning experiance, and boy have I learned a ton..
Nothing worse then getting a 383 stroker, with a 350 non-externally balanced flex plate, a brand new motor that leaks coolant from the bottom of a head, and an oil leak..
Next time, im building the engine my self.. I spent the extra money to have a "pro" put it togather so I wouldn't have to deal with the aggravation of leaks.. oh, and the place that put it together was a well known trusted shop in town that many people refered me to.