why is the L98 hp so much lower than many smaller engines (ie. BMW 4.6L has 315hp)
09-27-2016, 08:01 AM
#1
why is the L98 hp so much lower than many smaller engines (ie. BMW 4.6L has 315hp)
I was showing my 90 vert to a buddy the other day. He was admiring it including the engine. He asked me what size the engine was and the HP. When I first told him it is a 5.7L he said "oh, it must have like 330+ hp". When I told him it had 245hp, he didn't believe me. Part of the reason is that he had a BMW with a 4.6L which had 315HP. He assumed the bigger the engine size, the higher the HP.
Not being a mechanical guy, I couldn't really explain why a bigger engine has such low HP.
Would appreciate if someone could provide me a general understanding.
Not being a mechanical guy, I couldn't really explain why a bigger engine has such low HP.
Would appreciate if someone could provide me a general understanding.
09-27-2016, 08:13 AM
#2
Burning Brakes
As simply put as possible, the design of the engine is to create high torque at low rpm. That is almost exclusively due to the long intake runners, camshaft, and intake manifold design. The cylinder heads are designed to compliment that and also the exhaust. Back in 1985 when it was introduced, emissions and mileage were paramount, and this design was ahead of its time.
Soooo. if tou start to modify it to make more power (which you can) you basically have to change the exhaust and the top half of the engine. you can make 450+ hp on a stock bottom end.
That being said, it's a really fun engine to drive around on a daily basis, with great gas mileage and TONS of low end torque. Car pulls really hard from light ot light, it just peaks around 4500 rpms.
Soooo. if tou start to modify it to make more power (which you can) you basically have to change the exhaust and the top half of the engine. you can make 450+ hp on a stock bottom end.
That being said, it's a really fun engine to drive around on a daily basis, with great gas mileage and TONS of low end torque. Car pulls really hard from light ot light, it just peaks around 4500 rpms.
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09-27-2016, 08:40 AM
#3
As simply put as possible, the design of the engine is to create high torque at low rpm. That is almost exclusively due to the long intake runners, camshaft, and intake manifold design. The cylinder heads are designed to compliment that and also the exhaust. Back in 1985 when it was introduced, emissions and mileage were paramount, and this design was ahead of its time.
Soooo. if tou start to modify it to make more power (which you can) you basically have to change the exhaust and the top half of the engine. you can make 450+ hp on a stock bottom end.
That being said, it's a really fun engine to drive around on a daily basis, with great gas mileage and TONS of low end torque. Car pulls really hard from light ot light, it just peaks around 4500 rpms.
Soooo. if tou start to modify it to make more power (which you can) you basically have to change the exhaust and the top half of the engine. you can make 450+ hp on a stock bottom end.
That being said, it's a really fun engine to drive around on a daily basis, with great gas mileage and TONS of low end torque. Car pulls really hard from light ot light, it just peaks around 4500 rpms.
09-27-2016, 09:11 AM
#4
As simply put as possible, the design of the engine is to create high torque at low rpm. That is almost exclusively due to the long intake runners, camshaft, and intake manifold design. The cylinder heads are designed to compliment that and also the exhaust. Back in 1985 when it was introduced, emissions and mileage were paramount, and this design was ahead of its time.
Soooo. if tou start to modify it to make more power (which you can) you basically have to change the exhaust and the top half of the engine. you can make 450+ hp on a stock bottom end.
That being said, it's a really fun engine to drive around on a daily basis, with great gas mileage and TONS of low end torque. Car pulls really hard from light ot light, it just peaks around 4500 rpms.
Soooo. if tou start to modify it to make more power (which you can) you basically have to change the exhaust and the top half of the engine. you can make 450+ hp on a stock bottom end.
That being said, it's a really fun engine to drive around on a daily basis, with great gas mileage and TONS of low end torque. Car pulls really hard from light ot light, it just peaks around 4500 rpms.
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Frankio C4vetti (02-16-2020)
09-27-2016, 09:20 AM
#5
HP = Torque * RPM / 5252
That's the formula for figuring out horsepower. Our small blocks usually peak below 5k rpms, which is why we have torque numbers that are higher than horsepower numbers. However, if we build the engines (or if GM did) by moving the band higher to peak at 7k rpms then we would have a totally different car. Yes the horsepower would be much higher but you would usually sacrifice bottom end torque (which is the most fun) that you would normally be using while driving around on the street. For the application of a street driven sports car the torque band of a corvette is right where it needs to be (1-3k rpm). Moving the band higher by changing out some of the components that affect it (cam LSA, cam valve's timing, intake manifold design, runner length, etc, pretty much just what cadmaniac said).
Now, engines after 1972 where hit tremedously hard by emissions. In 1970 you had a 300 hp 350ci. In 1972 you had the same 350ci but 200hp! The engine's power never really started recovering until the late 80s. The advent of the C4 had it's focus on handling rather than power with the 84 being able to take over 1g of lateral force when tuned, and around .95g with the stock Z51 package. The handling of those cars beat most cars nowadays, and these cars are over 30 years old.
Also, the cats and the stock exhaust manifold/headers/ram horns also gave a lot of backpressure which is bad for trying to produce power as it limits scavenging and pushes back on the exhaust trying to escape from the cylinders. Then you have the endless debate on whether or not EGR hampers performance (don't think it really does much IMHO). Smog era tech hampers performance all around.
That's the formula for figuring out horsepower. Our small blocks usually peak below 5k rpms, which is why we have torque numbers that are higher than horsepower numbers. However, if we build the engines (or if GM did) by moving the band higher to peak at 7k rpms then we would have a totally different car. Yes the horsepower would be much higher but you would usually sacrifice bottom end torque (which is the most fun) that you would normally be using while driving around on the street. For the application of a street driven sports car the torque band of a corvette is right where it needs to be (1-3k rpm). Moving the band higher by changing out some of the components that affect it (cam LSA, cam valve's timing, intake manifold design, runner length, etc, pretty much just what cadmaniac said).
Now, engines after 1972 where hit tremedously hard by emissions. In 1970 you had a 300 hp 350ci. In 1972 you had the same 350ci but 200hp! The engine's power never really started recovering until the late 80s. The advent of the C4 had it's focus on handling rather than power with the 84 being able to take over 1g of lateral force when tuned, and around .95g with the stock Z51 package. The handling of those cars beat most cars nowadays, and these cars are over 30 years old.
Also, the cats and the stock exhaust manifold/headers/ram horns also gave a lot of backpressure which is bad for trying to produce power as it limits scavenging and pushes back on the exhaust trying to escape from the cylinders. Then you have the endless debate on whether or not EGR hampers performance (don't think it really does much IMHO). Smog era tech hampers performance all around.
09-27-2016, 09:42 AM
#6
thank you. that it explains it for me thanks.
HP = Torque * RPM / 5252
That's the formula for figuring out horsepower. Our small blocks usually peak below 5k rpms, which is why we have torque numbers that are higher than horsepower numbers. However, if we build the engines (or if GM did) by moving the band higher to peak at 7k rpms then we would have a totally different car. Yes the horsepower would be much higher but you would usually sacrifice bottom end torque (which is the most fun) that you would normally be using while driving around on the street. For the application of a street driven sports car the torque band of a corvette is right where it needs to be (1-3k rpm). Moving the band higher by changing out some of the components that affect it (cam LSA, cam valve's timing, intake manifold design, runner length, etc, pretty much just what cadmaniac said).
Now, engines after 1972 where hit tremedously hard by emissions. In 1970 you had a 300 hp 350ci. In 1972 you had the same 350ci but 200hp! The engine's power never really started recovering until the late 80s. The advent of the C4 had it's focus on handling rather than power with the 84 being able to take over 1g of lateral force when tuned, and around .95g with the stock Z51 package. The handling of those cars beat most cars nowadays, and these cars are over 30 years old.
Also, the cats and the stock exhaust manifold/headers/ram horns also gave a lot of backpressure which is bad for trying to produce power as it limits scavenging and pushes back on the exhaust trying to escape from the cylinders. Then you have the endless debate on whether or not EGR hampers performance (don't think it really does much IMHO). Smog era tech hampers performance all around.
That's the formula for figuring out horsepower. Our small blocks usually peak below 5k rpms, which is why we have torque numbers that are higher than horsepower numbers. However, if we build the engines (or if GM did) by moving the band higher to peak at 7k rpms then we would have a totally different car. Yes the horsepower would be much higher but you would usually sacrifice bottom end torque (which is the most fun) that you would normally be using while driving around on the street. For the application of a street driven sports car the torque band of a corvette is right where it needs to be (1-3k rpm). Moving the band higher by changing out some of the components that affect it (cam LSA, cam valve's timing, intake manifold design, runner length, etc, pretty much just what cadmaniac said).
Now, engines after 1972 where hit tremedously hard by emissions. In 1970 you had a 300 hp 350ci. In 1972 you had the same 350ci but 200hp! The engine's power never really started recovering until the late 80s. The advent of the C4 had it's focus on handling rather than power with the 84 being able to take over 1g of lateral force when tuned, and around .95g with the stock Z51 package. The handling of those cars beat most cars nowadays, and these cars are over 30 years old.
Also, the cats and the stock exhaust manifold/headers/ram horns also gave a lot of backpressure which is bad for trying to produce power as it limits scavenging and pushes back on the exhaust trying to escape from the cylinders. Then you have the endless debate on whether or not EGR hampers performance (don't think it really does much IMHO). Smog era tech hampers performance all around.
09-27-2016, 11:19 AM
#8
True, accessories will take out a bunch but not enough to account for that. If we went to 1971 which I believe was 270hp, that one year change to 72 just shows how much was drawn back due to regulations. But then again, GM could've understated the HP as they have done in other years.
09-27-2016, 11:33 AM
#9
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As has been stated, its the intake/exhaust design that limits the power that the bottom end can otherwise make for its 5.7L displacement. An engine is a big air pump, if you go snorkeling with a straw, you'll see why the L98 doesn't make the top end power.
However the length of the intake runners moves the peak of the port (air) velocity curve going into the engine to a lower RPM, which translates as torque. Port velocity = torque. That is why it makes so much of its power off the line. If you shorten the runners, you move the peak upwards, which moves the torque peak upwards, and using the formula given above, you increase the HP numbers. This is basically what they did with the LT1 engine in 1992.
Modern engines use the same principles but the manufacturers use different tricks to keep the powerband broad and fairly flat without costing MPG.
However the length of the intake runners moves the peak of the port (air) velocity curve going into the engine to a lower RPM, which translates as torque. Port velocity = torque. That is why it makes so much of its power off the line. If you shorten the runners, you move the peak upwards, which moves the torque peak upwards, and using the formula given above, you increase the HP numbers. This is basically what they did with the LT1 engine in 1992.
Modern engines use the same principles but the manufacturers use different tricks to keep the powerband broad and fairly flat without costing MPG.
09-27-2016, 01:35 PM
#10
Agreed with all posted about the design of the intake system above since I had that set up for a while with the 85;
This is old technology; what kind of power were BMW's making in 1990?
i have an inline 6 cylinder BMW that makes 300 hp, but it is an 08 and turbo car.
This is old technology; what kind of power were BMW's making in 1990?
i have an inline 6 cylinder BMW that makes 300 hp, but it is an 08 and turbo car.
Last edited by 856SPEED; 09-27-2016 at 02:00 PM.
09-27-2016, 04:04 PM
#11
Team Owner
Pro Mechanic
208hp, wast the big, bad engine from BMW in '90, I believe. 3.4L Inline 6
OP: you can tell your buddy this: his 4.6L* has 4 valve/cylinder heads, and that is where the majority of the flow/advantage is that allows the 4.6L to produce more power than the much older Corvette engine. On the other hand, your buddies 4.6L V8 is physically as big, or likely even bigger than the Corvette engine. Although the SBC gives up some power/swept volume of it's cylinders, it compensates by being very space efficient and light weight for it's power.
An apples to apples comparison that illustrates this point fairly well is the '90 L98 compared to the '90 LT5 (ZR-1 engine) which had the same 5.7L displacement, but 4 valves/cylinder like the BMW. The L98 make the 245hp you stated, the LT5 makes 375-405hp...but is physically much larger and also heavier in spite of all aluminum construction.
*BMW only made a 4.6 V8 from '02-'03, so this engine is 12-13 years newer than the '90 L98, which was near the end of it's life cycle.
OP: you can tell your buddy this: his 4.6L* has 4 valve/cylinder heads, and that is where the majority of the flow/advantage is that allows the 4.6L to produce more power than the much older Corvette engine. On the other hand, your buddies 4.6L V8 is physically as big, or likely even bigger than the Corvette engine. Although the SBC gives up some power/swept volume of it's cylinders, it compensates by being very space efficient and light weight for it's power.
An apples to apples comparison that illustrates this point fairly well is the '90 L98 compared to the '90 LT5 (ZR-1 engine) which had the same 5.7L displacement, but 4 valves/cylinder like the BMW. The L98 make the 245hp you stated, the LT5 makes 375-405hp...but is physically much larger and also heavier in spite of all aluminum construction.
*BMW only made a 4.6 V8 from '02-'03, so this engine is 12-13 years newer than the '90 L98, which was near the end of it's life cycle.
Last edited by Tom400CFI; 09-27-2016 at 04:14 PM.
09-27-2016, 04:18 PM
#12
Melting Slicks
I've owned L98, LT1, LT4, LS1 etc. The L98 is flat fun on the street. The only engine that really truly beat it, just from a fun experience, is the LT4 which took the best parts of the L98 (low end torque) and combined it with an even better LT1 peak.
One of my current cars is a BMW E93 M3. 414 HP at 8300 RPM. 295 lb-ft of torque at 3900 RPM. The old L98 made 350 lb-ft at 3200 RPM. I can tell ya that when revving the crap out of the M3 on curvy roads it is awesome. But getting moving stop light to stop light type driving it just doesn't have the same fun factor of the low end torque. Vice versa the L98 seems to fall flat in the upper RPM and leaves you wanting for more.
One of my current cars is a BMW E93 M3. 414 HP at 8300 RPM. 295 lb-ft of torque at 3900 RPM. The old L98 made 350 lb-ft at 3200 RPM. I can tell ya that when revving the crap out of the M3 on curvy roads it is awesome. But getting moving stop light to stop light type driving it just doesn't have the same fun factor of the low end torque. Vice versa the L98 seems to fall flat in the upper RPM and leaves you wanting for more.
09-28-2016, 04:46 AM
#13
- it's all about the torque. I've always said, "...don't let a L98 guy get the jump on you off the line - you'll play hell catching him!" it's torque and how fast you build it, and i'm pretty sure the L98 builds torque, at lower RPMs, at faster rate than most. 
my 1985 L98 is rated at 330 lbs torque at 3200 RPM, the LT-1, 340 at 4000. only 5 pounds more at 800 higher rpm's. how much driving do i do between 3200 and 4000 RPM's? not much! on the street, I probably do 99% of my driving below 3200 RPM, so i'll take more torque at lower RPM's, over HP any day. remember the old saying, "horsepower sells cars, torque wins races!" horsepower is for bragging rights, and unless you're tracking your car, high horsepower numbers is about "as worthless as ***** on a bishop!" - (just my 2-cents --
)
Last edited by Joe C; 09-28-2016 at 05:25 AM.
09-28-2016, 05:52 AM
#14
Melting Slicks
Why are c3's even lower, yes I know why just saying.
09-28-2016, 11:31 AM
#15
- it's all about the torque. I've always said, "...don't let a L98 guy get the jump on you off the line - you'll play hell catching him!" it's torque and how fast you build it, and i'm pretty sure the L98 builds torque, at lower RPMs, at faster rate than most. my 1985 L98 is rated at 330 lbs torque at 3200 RPM, the LT-1, 340 at 4000. only 5 pounds more at 800 higher rpm's. how much driving do i do between 3200 and 4000 RPM's? not much! on the street, I probably do 99% of my driving below 3200 RPM, so i'll take more torque at lower RPM's, over HP any day. remember the old saying, "horsepower sells cars, torque wins races!" horsepower is for bragging rights, and unless you're tracking your car, high horsepower numbers is about "as worthless as ***** on a bishop!" - (just my 2-cents --
)i agree and here is another example.
my 87 has 10 more hp than my 85. but my 85 will take it off the line and the 87 will never catch up. its marginal, but its true. and i can only think that its because the stock torque converter on the 85 is a 2050 vs stock on the 87 is 1400.
So that 85 lets the engine rev up a bit higher which puts more torque to the ground faster.
im not an expert on this but im thinking that is the situation.
the other thing i have noticed is that the 87 will only get to 5k before it shifts.
the 85 will get to 5.5k
admittedly there are other factors possibly going on here due to mileage and wear on the vehicles but the torque converter i am told makes a significant difference.
09-28-2016, 01:33 PM
#16
At the end of the day your comparing performance of a 30yr old car to a modern day car. It was fast in its day... now it only has to look fast... and as was said earlier it says corvette on the back... that's good enough for me
09-28-2016, 02:36 PM
#17
Melting Slicks
Good answers here. This discussion reminds me of the T-shirt that says "my Harley makes more torque at idle than your Honda at redline." lol
No question that the L98 has a fatter torque curve than the LT1, especially at lower RPMs.
I think the only engines that have big torque across the board and also produce big power at high RPMs are either big-displacement (LS7/427) or turbocharged.
NA formula 1 engines produce insane horsepower from tiny engines, but they have hardly any torque.
No question that the L98 has a fatter torque curve than the LT1, especially at lower RPMs.
I think the only engines that have big torque across the board and also produce big power at high RPMs are either big-displacement (LS7/427) or turbocharged.
NA formula 1 engines produce insane horsepower from tiny engines, but they have hardly any torque.
Last edited by DGXR; 09-28-2016 at 02:42 PM.
09-28-2016, 02:59 PM
#18
Team Owner
Pro Mechanic
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Frankio C4vetti (02-16-2020)
09-28-2016, 03:01 PM
#19
Safety Car
Lets not get too bogged down on HP vs TQ. HP is a unit of measure that determines how much work can be done. Simply put, the higher the HP over the RPM range that you use the engine the more work that can be done. (In the case of a car the higher the acceleration)
When you are accelerating at WOT you don't care about how much torque you have at some RPM, what you care about is how much HP you have over the RPM that the car is shifting at (which if you really think about it means you have the highest torque and HP available at the wheels which is what is actually accelerating the car). When you are not at WOT then you are choosing not to accelerate at the maximum rate, this means high TQ at low RPM does not mean much except you do not have to downshift as much to hit max acceleration.
Food for thought, plot out the torque at the rear wheels Vs speed of L98 vette vs the torque at the rear wheels vs speed of a 2002 Z06 and you will quickly figure out why the Z06 runs 2 seconds quicker in the 1/4 mile, even through the torque of the engines is similar but the Z06 peaks at higher RPM (higher HP).
When you are accelerating at WOT you don't care about how much torque you have at some RPM, what you care about is how much HP you have over the RPM that the car is shifting at (which if you really think about it means you have the highest torque and HP available at the wheels which is what is actually accelerating the car). When you are not at WOT then you are choosing not to accelerate at the maximum rate, this means high TQ at low RPM does not mean much except you do not have to downshift as much to hit max acceleration.
Food for thought, plot out the torque at the rear wheels Vs speed of L98 vette vs the torque at the rear wheels vs speed of a 2002 Z06 and you will quickly figure out why the Z06 runs 2 seconds quicker in the 1/4 mile, even through the torque of the engines is similar but the Z06 peaks at higher RPM (higher HP).
Last edited by bjankuski; 09-28-2016 at 03:08 PM.
09-28-2016, 03:09 PM
#20
Melting Slicks
That is an interesting graphic. I've never driven an L98 Vette, only what people on CF have said about it being a torque monster... and it looks like I should learn to shut my mouth... sometimes.
Anyway, it sure doesn't feel like my stock 1995 LT1 has 300 ft-lb of torque at 1000 rpm.
Anyway, it sure doesn't feel like my stock 1995 LT1 has 300 ft-lb of torque at 1000 rpm.