Okay, educate me...

[CLABORN1960]

Thinking more about horsepower and fast cars and what I ultimately want led me to this question.

What is the crucial difference between my car (93 LT1) and say a new C6 (or a LT4 or a C5) in terms of what does an extra 100 hp get you? Here is what I mean, yes its quicker, but does the extra horses mean it will top out at 200mph and my car 150? Or just that it gets to the top end quicker? Or what?

Additionally what is the difference between say a LT1 and a LT4? Does more horsepower mean higher top speed? If all the top speeds are similar, then what is the point of having more hp?

Thanks for taking the time to answer the question....

 

[UB2 SLOW]

This is not really a quick answer. As an example, you need about 500hp to hit 200mph. Why? This is due to drag. The faster you go the more drag you encounter so the more hp you need to go faster. The shape of the car is the biggest issue when it comes to drag. If two cars weigh the same and have the same hp but one is a brick and the other is not, then the non-brick car will require less hp to go faster. Then you have gearing to worry about also.

 

[CLABORN1960]

This is not really a quick answer. As an example, you need about 500hp to hit 200mph. Why? This is due to drag. The faster you go the more drag you encounter so the more hp you need to go faster. The shape of the car is the biggest issue when it comes to drag. If two cars weigh the same and have the same hp but one is a brick and the other is not, then the non-brick car will require less hp to go faster. Then you have gearing to worry about also.

So a bone stock 94 vette, compared to a bone stock 04 vette, the newer vette gets to the top speed faster? Is that all? how about a stock 94 vette, compared to a modified 94 vette... the outcome is what?

 

[1995 RedVette]

There are several parts to your question.

1) you can make anycar go fast as long as you have enough money

2) What determines how "fast" a car is its hp output combined with its gearing and coeffecient of drag (Cd). This is why a 67 435HP car will top out at some where between 130 -145MPH depending on the final drive ratio and a 2004 will run 180MPH with only 350HP

3) The other defining factor between say the 1994 and 2004 vettes is how "Quick" the car is. Quick = acceleration. Again depending on drive ratios, the 2004 could run identical E.T's, or be .5 to .8 second faster through the quarter mile.

4) Another thing effecting acceleration is the suspension set up. The C4 is notoriously stiff, meaning that there is little weight transfer upon sudden acceleration. The C5's are set up to allow more transfer to the rear suspension upon acceleration, thus increasing traction, 60 ft times, and allowing a more spirited launch.

As for the difference between an LT1 and LT4. The LT4 has a higher lift and duration cam than does the LT1. It also has 1.7:1 rocker raito as apposed to 1.6:1m thus making better use of the increased lift from the new cam. The valve springs are also different to tolerate the increased lift. The output of the LT4 is conservatively listed as 330 HP, however, from dyno figures I've seen posted here on CAC, it is probably closer to 350HP at the flywheel.

Brett

 

[CLABORN1960]

There are several parts to your question.

1) you can make anycar go fast as long as you have enough money

2) What determines how "fast" a car is its hp output combined with its gearing and coeffecient of drag (Cd). This is why a 67 435HP car will top out at some where between 130 -145MPH depending on the final drive ratio and a 2004 will run 180MPH with only 350HP

3) The other defining factor between say the 1994 and 2004 vettes is how "Quick" the car is. Quick = acceleration. Again depending on drive ratios, the 2004 could run identical E.T's, or be .5 to .8 second faster through the quarter mile.

4) Another thing effecting acceleration is the suspension set up. The C4 is notoriously stiff, meaning that there is little weight transfer upon sudden acceleration. The C5's are set up to allow more transfer to the rear suspension upon acceleration, thus increasing traction, 60 ft times, and allowing a more spirited launch.

As for the difference between an LT1 and LT4. The LT4 has a higher lift and duration cam than does the LT1. It also has 1.7:1 rocker raito as apposed to 1.6:1m thus making better use of the increased lift from the new cam. The valve springs are also different to tolerate the increased lift. The output of the LT4 is conservatively listed as 330 HP, however, from dyno figures I've seen posted here on CAC, it is probably closer to 350HP at the flywheel.

Brett

So if for example I modify my 93 and add 50 to 100 horses, it may make no difference? If the gearing were difference would it? I thought the wrong gearing will decrease the top end.... I was also under the impression that more hp would translate into higher top end and a quicker car.... or if I modify my 93, say get 450 hp, add a supercharger, that would be a waste?

 

[toby]

http://vettenet.org/torquehp.html

An excellent theoretical and practical description of the issue.

Toby

 

[Vettelt193]

So if for example I modify my 93 and add 50 to 100 horses, it may make no difference? If the gearing were difference would it? I thought the wrong gearing will decrease the top end.... I was also under the impression that more hp would translate into higher top end and a quicker car.... or if I modify my 93, say get 450 hp, add a supercharger, that would be a waste?

Horsepower is the ability to make torque at a given RPM.

If your '93 is a 6-speed, you may increase your top-end by adding HP, because you may be able to use 6th gear. The stock 6 speed has top end rated in 5th gear... People that really go for top end on our cars tend to move the ratio higher in number (from 3.55 to 4:10). Although, on just about any other car, that would slow you down on top end, to make you quicker at the bottom end.... we can have the added benefit of both quicker and faster because of the unusable 6th gear with stock HP.


Normally, if you add power, you can count on quickness... but to get more top-end, it is far more complex than just HP. The only way to get more speed is to rev higher RPM's, or change the gearing to get the wheels turning faster....

 

[CLABORN1960]

thanks for the link to the article that was quite helpful.... things are slowly coming into focus.....

 

[1995 RedVette]

So if for example I modify my 93 and add 50 to 100 horses, it may make no difference? If the gearing were difference would it? I thought the wrong gearing will decrease the top end.... I was also under the impression that more hp would translate into higher top end and a quicker car.... or if I modify my 93, say get 450 hp, add a supercharger, that would be a waste?

Yes and No.

Case 1
Assuming that your car is an automatic (final transmission ratio of .70:1) and its top speed is redline limited, then adding hp will only get you to your top speed quicker, because to go faster with that setup you would have to increase RPM to make the car go faster. However, if you reduced your final drive ratio from 3.42:1 to a 3.07:1 then your car will be traveling faster at the same 6000 RPM redline because the half shafts will be spinning roughtly 11% faster.


Case 2
Assuming that you have a 6 speed with a 5th grear ratio of .86:1 and a 6th gear ratio of .50:1 then you have some room to experiment. In a Vett's stock configuration the engine produces enough torque to hold somewhere in the neiborhood of 130mph in 6th gear, however redline limits 5th gear to 160mph. By increaseing you hp then you may have enough hp to increase your top speed by using more of 6th gears potential. To make thing more complicated, you could deepen the rear gears to something like a 3.93 or higher and possibly come to some equilibrium between the very high (low numerical number) gear ratio that 6th gear provides, hp, and rear gearing to use all of 6th gear about the time you runn out of torque.


It does get complicated, but it comes down to mechanical advantage, drag, and hp. The higher the gear (lower numerical value) the more torque is required to spin that assembly at a given RPM. That added with the physical drag of the car dictates a lot of hp and some very low gears (high numerical value) to use all of potential that .50:1 can provide.

Brett

 

[CLABORN1960]

Yes I have an automatic......

 

[toby]

For those of us driving on the street, the great thing about the LT4 (and, to a slightly lesser extent, the LT1), is not just that they make a lot of torque, but that they make the same high torque across a very wide range of engine speeds (i.e., a practically flat torque curve from 2000-4500 RPM in the LT4). So, anytime you put your foot down in that range, you get the same pressed-into-the-leather feeling. If you look at something like a BMW M3, which produces a similar max hp to the LT1 and LT4, the M3's max torque is lower (mid 260 ft-lb range), and the torque curve is "peakier" (not flat). By producing a little torque at high rpm the M3 can make decent hp, but if the M3 is at an rpm off its torque peak, the torque (and hp) are way down. This difference in "peakiness" between the C4 and the M3 doesn't show up in published 0-60 times or at the drag strip (where the engines can be kept near their power peaks all the time by sidestepping the clutch at high-rpm launch, and powershifting thereafter), but it surely does matter in real-world driving where we (at least *I*) don't rev to redline before sidestepping the clutch, or downshift two gears just to pass an 18-wheeler on a twisty 2-lane. In my world, that flat and wide LT4 torque curve just keeps the power coming in a never-ending rush whenever I ask for it. As long as I'm in 4th or 5th gear at highway speeds, the Green Monster flies around traffic with just a touch of the accelerator. C4s, LT4s, and V-8s forever!

See dyno sheet for bone stock LT4 at: http://temp.corvetteforum.net/c4/gsragtop//gs951dyno2.jpg

Toby

 

[JEFNLSA]

For those of us driving on the street, the great thing about the LT4 (and, to a slightly lesser extent, the LT1), is not just that they make a lot of torque, but that they make the same high torque across a very wide range of engine speeds (i.e., a practically flat torque curve from 2000-4500 RPM in the LT4). So, anytime you put your foot down in that range, you get the same pressed-into-the-leather feeling. If you look at something like a BMW M3, which produces a similar max hp to the LT1 and LT4, the M3's max torque is lower (mid 260 ft-lb range), and the torque curve is "peakier" (not flat). By producing a little torque at high rpm the M3 can make decent hp, but if the M3 is at an rpm off its torque peak, the torque (and hp) are way down. This difference in "peakiness" between the C4 and the M3 doesn't show up in published 0-60 times or at the drag strip (where the engines can be kept near their power peaks all the time by sidestepping the clutch at high-rpm launch, and powershifting thereafter), but it surely does matter in real-world driving where we (at least *I*) don't rev to redline before sidestepping the clutch, or downshift two gears just to pass an 18-wheeler on a twisty 2-lane. In my world, that flat and wide LT4 torque curve just keeps the power coming in a never-ending rush whenever I ask for it. As long as I'm in 4th or 5th gear at highway speeds, the Green Monster flies around traffic with just a touch of the accelerator. C4s, LT4s, and V-8s forever!

See dyno sheet for bone stock LT4 at: http://temp.corvetteforum.net/c4/gsragtop//gs951dyno2.jpg

Toby

I hear ya
Good analogy.

 

[UB2 SLOW]

There is allot of good information here. The bottom line is you need to set a goal in what you want to do. Then work your package to reach that goal. The worst thing you can do is just start buying parts and slapping them on the car without a goal or a process. Why? You may actually lose power if you dont do it in a good seqeunce. For example, you dont want to do just a intake, heads and cam without first getting some good exhaust. Why? Because you are not going to get much benefit of the increased air flow into the engine without first being able to get the air out of the engine.
You also dont want to have 500hp without being able to put it to the ground. So you need to consider suspension, gears and tires. If you start spending money for modifications and you are not happy with the results, then you are going to get discouraged. If you are going to mod your car for speed, you have to have paitience and a goal as to what you want to accomplish.

 

[DRTH VTR]

2) What determines how "fast" a car is its hp output combined with its gearing and coeffecient of drag (Cd). This is why a 67 435HP car will top out at some where between 130 -145MPH depending on the final drive ratio and a 2004 will run 180MPH with only 350HP

That 435HP in 1967 was measured as 'gross', while the 350HP in 2004 is 'net'. There is a substantial difference in how that is measured. The actual output of those two engines rated under the same conditions would not be that different. I suspect that the big block car would have more torque at lower RPM, but would have difficulty breathing at higher RPM with resultant drop in torque and horsepower. I think that the change in HP ratings from gross to net was about 1972 or 1973.

 

[tomtom72]

Hi, May I ask a question, not trying to hi-jack, in the same vein? How does the top end of a ZR-1 turn out to be above 160mph with about the same hp & torque #'s as a LT4 or LT1? Are the tranny & rear ratios different? I mean 350 hp vs 375 hp doesn't seem like alot? I mean I thought the hp requirement went up in a geometric progression at some point in the speed vs drag equation? I would think that the drag #'s on all C4's are about the same? Or is the engine design of DOHC/4V that better at flat, broad torque curves? Sorry for intruding, Tom.

 

[1995 RedVette]

Perhaps I should have used another example, my point was, despite the power of the 60's big block engines, they were geared such that they ran out of RPM before they ran out of torque to push the car faster. With late model setups, overdrive, 6 speeds, etc the package can attain greater speeds despite the differential in HP and torque.

Brett

 

[Vettelt193]

Hi, May I ask a question, not trying to hi-jack, in the same vein? How does the top end of a ZR-1 turn out to be above 160mph with about the same hp & torque #'s as a LT4 or LT1? Are the tranny & rear ratios different? I mean 350 hp vs 375 hp doesn't seem like alot? I mean I thought the hp requirement went up in a geometric progression at some point in the speed vs drag equation? I would think that the drag #'s on all C4's are about the same? Or is the engine design of DOHC/4V that better at flat, broad torque curves? Sorry for intruding, Tom.

The LT5 has a bigger power band. (i.e. revs higher) So, even if a LT4 has the same amount of power, the Z can out rev it on the top end and 'use its gears better'. Basically, if you have 2 engines with the same HP, but one can rev an extra 2,000 RPM's, the one that can rev higher should be able to go a bit faster.

 

[CLABORN1960]

There is allot of good information here. The bottom line is you need to set a goal in what you want to do. Then work your package to reach that goal. The worst thing you can do is just start buying parts and slapping them on the car without a goal or a process. Why? You may actually lose power if you dont do it in a good seqeunce. For example, you dont want to do just a intake, heads and cam without first getting some good exhaust. Why? Because you are not going to get much benefit of the increased air flow into the engine without first being able to get air out of the engine.
You also dont want to have 500hp on without being able to put it to the ground. So you need to consider suspension, gears and tires. If you start spending money for modifications and you are not happy with the results, then you are going to get discouraged. If you are going to mod your car for speed, you have to have paitience and a goal as to what you want to accomplish.

Very true. There are two things I have learned thus far about modifying my car, one it has to be done in the context of modifying the whole system and not one component of that system. Secondly, modification has to be done with the end result in mind.

I know that I want a daily driver which will limit how radical the modifications are. I also know that I want as much power as I can get and still not sacrifice the drivability. So far it seems like having about 400hp (Doug Rippie has a package 390hp/375ft.lb. torque) will satisfy my need for speed. I also know that I will have to change the rear end gears (right now they are totally stock, which is 2.59 for my car), also the exhaust, brakes, and suspension components, oh and get a chip burned to deal with the changes....

That would cover the complete system would it not?

 

[tomtom72]

Thanks! So the object of modding a motor should be to make power over as wide an rpm range as possible with an eye to reliability and then gear the car to use that power? No that don't make sense. If you mod your motor you have to keep in mind what the rpm limit is and only do those mods that will work within the rpm limit? With EEC systems that sounds like it could get complicated quickly? Forgive me, I am new to the world of EEC. The last vette I had was a 72 so this EEC stuff is beyond my knowledge at the present. Thanks for answering! Tom

 

[UB2 SLOW]

Very true. There are two things I have learned thus far about modifying my car, one it has to be done in the context of modifying the whole system and not one component of that system. Secondly, modification has to be done with the end result in mind.

I know that I want a daily driver which will limit how radical the modifications are. I also know that I want as much power as I can get and still not sacrifice the drivability. So far it seems like having about 400hp (Doug Rippie has a package 390hp/375ft.lb. torque) will satisfy my need for speed. I also know that I will have to change the rear end gears (right now they are totally stock, which is 2.59 for my car), also the exhaust, brakes, and suspension components, oh and get a chip burned to deal with the changes....

That would cover the complete system would it not?

You will want to have to get a shift kit also to allow quicker and firmer shifts so you dont lose as much power through the tranny. Brakes are often over looked when people start to mod. I always say "Its more important to stop fast than to go fast." With out know what DR has on their engine its hard to say what else you might need. You could post a breakdown of the engine he is selling and see if anyone else see's something you might want to add.