'74 LS-4 454

[Tom Lawrence]

I am purchasing a 1974 Vette with the optional 454 big block. Why was there such a drop in horsepower in the 70's model vette's as opposed to the 60's. I've looked at specs for 60's models and the engines are pushing 390 to 400+ horses. The LS4 is rated at 270. What happened?

[Tom Freeman]

Re: '74 LS-4 454

Tom, I am also the owner of a newly purchased LS4 (see post below). What happened, emissions, rating systems, and insurance companies. In 70 and before the engines were rated on a gross HP system, dynoed without any accessories, no mufflers, no alternator, etc, etc. In 72 they used net ratings, which had all accessories and mufflers in place. Also in prep for unleaded gas, they started dropping the compression ratios in 72. This resulted in the 72 LS5 454 having 270 HP, the 73 LS4 454 having 275 HP, and the last 454, the 74 LS5, having 270 HP. (In 71 the low compression 454, 8.5:1, was rated at 365. I would guess this to basicly the the same as the 72-74 454s.) Also during this time the Vette was starting to change from a fire breathing monster to the later crusers of the late 70's. I will not even think of what the insurance companies did to these cars back then.

Any way, hope you enjoy your new car.

tom...

[Tom Freeman]

Re: '74 LS-4 454

Tom, I am also the owner of a newly purchased LS4 (see post below). What happened, emissions, rating systems, and insurance companies. In 70 and before the engines were rated on a gross HP system, dynoed without any accessories, no mufflers, no alternator, etc, etc. In 72 they used net ratings, which had all accessories and mufflers in place. Also in prep for unleaded gas, they started dropping the compression ratios in 72. This resulted in the 72 LS5 454 having 270 HP, the 73 LS4 454 having 275 HP, and the last 454, the 74 LS5, having 270 HP. (In 71 the low compression 454, 8.5:1, was rated at 365. I would guess this to basicly the the same as the 72-74 454s.) Also during this time the Vette was starting to change from a fire breathing monster to the later crusers of the late 70's. I will not even think of what the insurance companies did to these cars back then.

Any way, hope you enjoy your new car.

tom...

[Patrick H.]

Re: '74 LS-4 454

Tom,

The big change occurred in 1972 when GM changed the rating from "gross" to "net" horsepower, resulting in about a 20 to 25% "decrease" in power. At the same time, in 1971 the compression ratios were decreased from 10.5:1 or 11:1 to 8.5:1 or 9:1 in order to allow engines to run on the lower octane unleaded fuel. Both of these resulted in horsepower loss.

Another way to measure the change would be to look at the torque values, which did not change as much and might reflect more accurately the true decrease in power.

Hope this helps.

Patrick Hulst

[Patrick H.]

Re: '74 LS-4 454

Tom,

The big change occurred in 1972 when GM changed the rating from "gross" to "net" horsepower, resulting in about a 20 to 25% "decrease" in power. At the same time, in 1971 the compression ratios were decreased from 10.5:1 or 11:1 to 8.5:1 or 9:1 in order to allow engines to run on the lower octane unleaded fuel. Both of these resulted in horsepower loss.

Another way to measure the change would be to look at the torque values, which did not change as much and might reflect more accurately the true decrease in power.

Hope this helps.

Patrick Hulst