C4in mesa

I was watching Top Gear some time back and the episode was centered around a drive comparing two older cars. A BMW and a Mercedes I believe ? First a dyno test was done on each car to see where it stood after many years of use. With that said many many variables must be considered for my threads title. Anyway each of these two cars lost around 30-45 horsepower from the factory rated number. I was shocked by this test result. I cant remember if a compression check was part of the test ? This all made me wonder where my 1996 LT4 stands with 101K miles on it ? I just bought the car. I have only driven it once and it has lots of power. Long tube headers with Power Effects mufflers and a open lid with a K&N filter. I know some opinions are that the K&N filter and open lid mean nothing. Anyway lets get some feed back on this one ! I would like to get a compression check done on each cylinder and see if they are all close to specs. The biggest thing I noticed driving this versus my modified 1988 is the gears. I have 2:59 gears and a automatic transmission. Now this car feels so different. I need to get someone to drive one of these cars and see what happens side by side. The 1988 has 20K miles on its engine.

DinoBob

I don't see why the car has to lose much if any horsepower if it is kept in good tune and well maintained.

PLRX

Know a guy who had C6Z06,he drove the hell out of it. He sold it with over 180,000 miles and no issues. He dynoed new, and at around 125,000 miles and had the same RWHP.

WW7

As long as there aren't any issues with the motor there should be very little HP decline... Compression loss / valve leakage, tuning components not kept up to standards, these things can cause HP loss , but if the car is kept in good shape, I would think HP loss should be minimal with 100,000 miles...WW
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Patsgarage

I have to respectfully disagree with you guys, I would think that any engine @ 100k would have let a few horses out of the barn for any number of reasons. As with any machine there will be wear on the internal parts. Good preventive maint can help this, but not eliminate it. Should your car need a rebuild ? No, but it will not make the same power as new. I have owned many very high mileage cars and they ran great, but you can definitely tell that some were down on power.

JD Shredds

There are simply too many variables to conclude how much loss a particular engine will have after 100k+ miles. Some particular engines under certain circumstances might only drop 2% while there are others that could drop a good 20% or more, just as blanket examples.

Speaking of your '88, I was just perusing Craigslist and I check Phoenix along with my search and, lo and behold, I was like, "Hey, that's Dan's!"

crowz

One problem with that test is no one dyno'd the cars new. Who is to say they aren't putting out MORE hp than when they were new.

Ive never really noticed a power loss with mileage even on motors that were burning oil to be honest.

MaxDaemon

I think I'd want a lot bigger sample and some pretty strict controls in place for data gathering (like mileage between oil changes, type of oil, etc) before I took this too seriously. I can see some loss, but 30-45hp seems excessive.

My '84 has 130k miles on it, and I hope I could tell the difference between 205hp and 160hp. In fact, those numbers make it sound like it should be a wheeze bag putting out 145hp at 130k miles.

My wife's Mini is rated around 140hp ..

mlm0

Are they comparing crank hp to rear wheel hp?

C4in mesa

I wish I could remember the name of the Top Gear episode. It was a long drive not a drive on a test track. Each car was put on a dyno to check where the horsepower is compared to the factory numbers. I was shocked by the loss of horsepower but for the average engine it seems to be nothing out of the ordinary. Would a perfect compression number for each cylinder equal little to no loss of horsepower regardless of how many miles ? A C6 Z06 with 180K miles testing the same numbers is very reassuring in Chevy quality given proper maintenance.

ghoastrider1

I read somewhere that todays oil and improved machining on engines have made engines go 200,000 miles without problems. Reduced cyclinder wear ect. There will be HP loss because of wear factors but
its so slight and gradual that who can notice? 35 or 40 HP is a lot to lose but who knows how finely tuned these were to start with. I think over time, a high hp engine putting out near max is going to lose more than the family grocery getter.

DinoBob

The factory numbers are at the crank, net. The dyno is at the wheels. This explains everything.

A common misconception is that SAE net is at the wheels. It is not. It just includes exhaust and accessories.

rocco16

We have a winner. Unless the Top Gear folks pulled the engines out of the cars in question, removed all accessories, and tested them on an engine dynomometer, the numbers they are comparing are tangerines and oranges.

There are several contributors to a high-use engine's drop in output, compression is but one. Cam lobe wear, carbon buildup in ports and on valves, "leaky" plug wires, dirty injectors/carbs/throttle bodies, etc. can affect output.
I'd put the average loss at about 3% in 100K miles.

ex-x-fire

They should test the cars in 0-60 & the 1/4 mile, compare them to test numbers in the old magazines.

QCVette

So lets see some pictures of your new toy!!!!

It sounds nice. I would love to find an LT4.

Klondike

If you have 2.59 gears and an automatic, you don't have an LT4. The LT4 engine came with the the ZF6 transmission and 3.45 gears. Somebody might have put an LT4 engine in that car, but it didn't come with that combo from Bowling Green.

JD Shredds

Ahh, crank vs. at the wheels. Must be it.

Honestly, I've seen bone stock cars with over 100k miles run equal or better 1/4 mile times than when new (tires help, for one).

Pretty sure he was referring to his '88.

cv67

Have an 02 5.3 that at around 120k felt the same as it did new.
Now at 165k I can def feel a difference in power. Probably loss of cyl pressure tired valve springs etc. Still runs good but not like new for sure.

Klondike

DOH !! I really need to read more carefully!

Tom400CFI

Negative. Only if poorly maintained. Well maintained engines do not lose power with miles...certainly not 100,000 miles.



Bingo.

I dyno'ed my stock LT1 at around 150,000 niles and it put down 280 RWHP and 312 RWTQ. That is more than 300 hp and more than 330 tq at the flywheel, so at ~150k miles, it's making more than it's original, factory rating.

Another, more compelling example is my '96 Siverado, which gets the same gas mileage, pulls the same grades at the same speeds in the same gear (empty or towing), as it did 263,000 miles ago. With over a 1/4 million miles, it shows zero signs of power loss.


If your car is losing power at 100,000 miles, you're doing it wrong.


EDITED b/c I had the RWHP wrong. it did 280, not 260..