PARTKE

Can anyone tell me what the actual horsepower of a 70 lt1?

leadfoot4

The "advertised" HP rating for the 1970 LT-1 was 370.

kenba

At the flywheel.

BKbroiler

That is 370 GROSS HP. Since 1971 all cars are rated in net HP. That 370 gross figure might be 330 net HP.

redrdstr72

Actually, I think 1972 was when the change from GROSS to NET HP was made. In any event, it was surely the beginning of the steep downward slope to very low performance across the industry.

Gordonm

70 HP was 370 gross. 11:1 compression.
71 HP was 330HP gross 9:1 compression
72 was 255 HP net 9:1 compression

leadfoot4

Correct. 1971 was the year that the change in compression ratio (lowered, to work on low lead/unleaded fuel) was put in place, with net HP the following year. I could be wrong, but I think the LT-1 went from 370 HP, to 330 HP, then finally to 270HP, before it was dropped from the line up.

Sir Keith

Yes, but I believe 330hp for the '71 was gross hp whilst 270hp for the '72 was net hp; which is to say, they were a lot closer in hp than 330 vs. 270 would suggest.

BKbroiler

Yep, you're right. Those were depressing times for us motorheads - not only was the actual power level going down (compression ratio decrease) but the way it was advertised (gross vs net) producing lower numbers also.

Gordonm

HP for 72 was listed at 255 HP. The 71 and 72 LT-1 motors were almost identical. So on paper it looks like the 72 was much less but in reality they were side by side in performance.

Page from the 1972 Corvette brochure that introduced the now-standard security system. (Image courtesy of GM Media.) The base engine, designated ZQ-3, was rated at a conservative 200 brake horsepower. The LT-1 was rated at 255 horsepower and the LS-5 was rated only slightly higher at 270 horsepower.

Barry's70LT1

Here is an actual Dyno, recently done, on a used 1970 LT-1 engine.

Dirty Dalton

Enough. 😁

leigh1322

With headers, on an engine stand
Less in the car, especially if you have factory manifolds on it.

bb62

1972 was the year that ONLY Net HP was first reported. In 1971, Chevrolet released BOTH Gross and Net HP. The following were the released power levels:

LS6 - 425HP Gross, 325HP Net
LS5 - 365HP Gross, 270HP Net
LT1 - 330HP Gross, 275HP Net
L48 - 270HP Gross, 210HP Net

Given that the small blocks exhibited a 55-60 HP loss from Gross to Net, that loss was likely in the range for the 70 LT1 as well. The 370 HP 1970 LT1 could have been as high as about 310 HP - HOWEVER - when the 1992 LT1 was released, Chevrolet Engineering called that year's 300HP LT1 the MOST POWERFUL LT1 produced by Chevrolet. This means that the 1970 LT1 likely was in the 290 to 295 range at the flywheel.

Stev-o

My good friend just bought a '71 Z/28 which has the LT1 motor. What a great car/motor!

I am on the lookout for an LT1 motor now for my '70.

C3 4ME

about 10 years or so ago, Super Chevy did a real world dyno test of many of the famed high hp engines and it was interesting to say the least. I remember as an example, my 79 L-82 didn't fare too badly against the earlier famed engines. I'm pretty sure they did an LT-1, so you might google it and see what you can dig up, if nothing else, for conversation's sake.

leigh1322

I just found those dyno runs online here:
DZ302, L76. LT1 (70&71), L79, L46, L82

Spoiler alert! All 345-360HP except L82 at 313

http://www.superchevy.com/how-to/eng...k-dyno-testing
http://www.superchevy.com/how-to/pro...-block-testing
http://www.caribbean-joe.net/vette/sbtest-4.htm

Jebbysan

Yep...like I have said before, the LT-1 simply will not make its advertised number......it can't, the heads are done. Bolt a Dart 180 head to this engine with zero other changes and it will make 425 horsepower.
The low compression 9:1 LT-1 makes almost the same power as the high compression one because the open chamber unshrouds the intake valve.
It is interesting to note that the 65' 375 horse 327 actually did make 375 horses because of the tunnel ram runners in the plenum.

Jebby

L-46man

With no water pump, no alternator, no air cleaner, open header exhaust, perfect octane matched fuel at 65°F and 50% humidity. With max vacuum and mechanical advance. With 'reference oil'....on a dyno stand.

leadfoot4

Very true, however, pretty much ALL of GM's engines were rated like that, so it's pretty much an "apples to apples" comparison....except where they were playing with the advertised horsepower of the really high output engines, and they wanted to placate the insurance companies.