Go Back   Corvette Forum > C3 Corvettes, 1968 - 1982 > C3 Tech/Performance
Sign in using an external account
Register Forgot Password?
Register Search Today's Posts Mark Forums Read FAQ Vendor Directory
Search
C3 Tech/Performance
V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette Sponsored by
VBP

Welcome to Corvetteforum.com!
Welcome to Corvetteforum.com.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join Corvetteforum.com today!


Corvette Store
 
 
C7 Parts & Accessories
C6 Parts & Accessories
C5 Parts & Accessories
C4 Parts & Accessories
C3 Parts & Accessories
C2 Parts & Accessories
C1 Parts & Accessories
Wheels & Tires
Sponsored Ads
 
 
Vendor Directory
  
Reply
 
 
 
 
Thread Tools Search this Thread
Old 10-05-2010, 10:58 PM   #1
1968-72 Corvette PR
Junior Member
 
1968-72 Corvette PR's Avatar
 
Member Since: Jul 2010
Location: Dorado Puerto Rico
Default True hp of 1970 LT1, and more about LT1.

Hi to all.

All of us C3 Corvette knowers know that the 1970 LT1 is rated at 370hp, and that the LS5 of that same year is rated at 390hp.

I believe that the 370hp rating of the LT1 is a factory lie, another case of an engine being underrated by the factory, and that the true hp of the LT1 is closer to 400hp. If this is the case, then the LT1 is probably a bit more powerful than the LS5. Is there any fact to this ? Do any of you know ?

Another thing. Of the 1287 LT1 Corvettes of 1970, only 25 were built with the race-ready ZR1 package. Was the LT1 in the ZR1 any different from the normal LT1 ? Did the ZR1 have a little bit more hp than the normal LT1 ?

Also, did the LT1 have L88 components ?

Wanting to know.

Best regards,


José, from Puerto Rico
1968-72 Corvette PR is offline   Reply With Quote
Old 10-05-2010, 11:22 PM   #2
Roughrider
CF Senior Member
 
Roughrider's Avatar
 
Member Since: Mar 2007
Location: Frederick Maryland
Send a message via MSN to Roughrider Send a message via Yahoo to Roughrider
Default

The LT-1 in the ZR-1 package was the same engine. The ZR-1 package included other performance goodies...primarily chassis mods compared the standard car.
No way the LT-1 had L88 components...LT-1 was small block...the L88 was a big block. About the only things that could interchange were the oil filters, thermostat and maybe a few sensors. Though the distributors could fit one another they were calibrated differently.

Horsepower ratings were often the subject of subterfuge back then. Not so much that the car makers absolutely lied about them but played games with ratings in other ways. For example, say Chevrolet gave a particular engine a rating of 350 hp at 4000 rpm's, that tells the insurance companies it may not be a super power engine. What they don't say or advertise is the same engine puts out 425 hp at 5500 rpm's (just making numbers up...may not be realistic but simply for example).

That's how Chevrolet got away with rating the L88 at 430hp...it was true for the hp/rpm they advertised. It could actually put out over 500hp at a higher rpm. They simply did that to discourage street drivers from buying the car as it was for dedicated racers. They preferred to sell the 435hp L71 to street guys so gave it a higher hp rating plus a few creature comforts they deleted with the L88 cars.

All kind of reasons why car makers play with advertised hp ratings.
Roughrider is offline   Reply With Quote
Old 10-06-2010, 12:02 AM   #3
MN-Brent
CF Senior Member
 
MN-Brent's Avatar
 
Member Since: Apr 2001
Location: Minneapolis, Mn USA
Default

wiki:
LT-1
Years: 1970–1972
The LT-1 was the ultimate 350 cu in (5.7 L) V8, becoming available in 1970. It used solid lifters, 11:1 compression, a high-performance camshaft, and a 780 CFM Holley four-barrel carburetor on a special aluminum intake with ramhorn exhaust manifolds and a low-restriction exhaust to produce a factory rated 370 hp (276 kW) (the NHRA rated it at 425 hp for classification purposes) and 380 lb·ft (515 N·m). Redline was 6500 rpm but power fell off significantly past 6200 rpm.

The LT-1 was available on the Corvette and Camaro Z28.

Power was down in 1971 to 330 hp (246 kW) and 360 lb·ft (488 N·m) with 9:1 compression, and again in 1972 (the last year of the LT-1, now rated using net, rather than gross, measurement) to 255 hp (190 kW) and 280 lb·ft (380 N·m).
MN-Brent is offline   Reply With Quote
Old 10-06-2010, 08:35 AM   #4
7T1vette
CF Senior Member
 
7T1vette's Avatar
 
Member Since: Jan 2006
Location: Crossville TN
Default

The LT-1 engine was a potent small block machine...but it didn't have the flat/constant torque level that the big block engine had. But, since the BB was heavier, an LT-1 car and a 400hp BB car were probably evenly matched. Some folks liked high-revving cars; some liked raw torque. What you bought depended on what you liked. Oh....the BB engine was a little more than half the option cost of the LT-1. It was more expensive to get that much power out of a small block engine.
7T1vette is offline   Reply With Quote
Old 10-06-2010, 09:17 AM   #5
Timsride
CF Senior Member
 
Timsride's Avatar
 
Member Since: May 2008
Location: Stratford Ontario
Default

The LT1 in the 70 Z28 camaro was down 10 HP from the vette. The only difference being the carb on the camaro, if I remember corectly it was a 750 Holley.
Timsride is offline   Reply With Quote
Old 10-06-2010, 11:13 AM   #6
Les
CF Senior Member
 
Les's Avatar
 
Member Since: Dec 1999
Location: Sierra Foothills CA
Default

Quote:
Originally Posted by Timsride View Post
The LT1 in the 70 Z28 camaro was down 10 HP from the vette. The only difference being the carb on the camaro, if I remember corectly it was a 750 Holley.
The Z28 carb was also 780 cfm. The Z28 had a single crossflow muffler instead of two mufflers like the Vette. I've never seen that identified as the reason for the 360 HP rating but it may have been. I have seen it written that the Vette got the higher rating to keep the Vette as the "top dog", although I don't know for a fact if that's the case.
__________________
08 Jetstream Blue Z06 w/ Comp Grey wheels & 2LZ- and LeMans Blue 69 coupe, original 427(now 439), L88 hood, forged alum. pistons(9.5 comp), Barry Grant Holley DP, Edel. Perf. RPM Airgap intake, Edel. Perf. alum. heads, Ultradyne solid flat tappet cam(243/251 @.050,.586/.601 lift) Jet Hot coated Hedman headers, mandrel 2 1/2" exh. w/ Dynomax Ultraflos & X pipe, TH400 w/ B&M cooler, Continental 2600 RPM stall TC, 3.55 gears, QA1 adjust. shocks, MT ET Street Radials, 1/4 mile in 11.37 @ 119.7 MPH
Les is offline   Reply With Quote
Old 10-06-2010, 01:16 PM   #7
10caipirinhas
CF Senior Member
 
Member Since: Nov 2009
Default

It was over rated IMHO by about 25-30 HP.

Hot Rod did a couple of dyno tests of OEM small block GM, Mopar and Ford engines in a rather long and detailed magazine article not too long ago (within 5-7 years IIRC) and the LT1 was down on HP (it actually produced around 340-350 at the flywheel) whereas the 302 was well over 300. The Ford's were all under rated and produced in excess of their factory ratings due to their excellent flowing cylinder heads.

The article was posted here on this site, and while I did search for it I could no longer find it, even though I read it within the last year. Perhaps someone else will post it.

FWIW the state of tune of each engine will have affected the outcome and any competent tuner could have easily regained probably 10% more in each of these engines with tweaking. This test was just a snapshot in time on a particular day.

Last edited by 10caipirinhas; 10-06-2010 at 01:18 PM.
10caipirinhas is offline   Reply With Quote
Old 10-06-2010, 01:54 PM   #8
Lt1er
CF Senior Member
 
Lt1er's Avatar
 
Member Since: Dec 1999
Location: Reno nevada
Default

Quote:
Originally Posted by 1968-72 Corvette PR View Post
Hi to all.

All of us C3 Corvette owers know that the 1970 LT1 is rated at 370hp,
I believe that the 370hp rating of the LT1 is a factory lie, another case of an engine being underrated by the factory, and that the true hp of the LT1 is closer to 400hp. . Is there any fact to this ? Do any of you know ?

Wanting to know.

Best regards,


José, from Puerto Rico
As a proud owner of a Lt1 I can tell you that it was over rated at 370 hp. It has been said that factory rating were without ACC attached. So no belts on the front of the motor. The motor was held back by a low lift cam and head technology of the time period for production cars. I have a modern solid cam, higher lift, ported and polished heads....., and balanced motor that puts out a true 400 hp at the crank. It is a vast improvement over the factory "LT1" I have no problem revving it up to 7000 rpm. The best thing you can do for a LT1 is to throw away the cam and springs
Lt1er is offline   Reply With Quote
Old 10-06-2010, 02:54 PM   #9
SteveG75
CF Senior Member
 
SteveG75's Avatar
 
Member Since: Jun 2000
Location: Lusby MD
Default

Quote:
Originally Posted by 1968-72 Corvette PR View Post
All of us C3 Corvette knowers know that the 1970 LT1 is rated at 370hp, and that the LS5 of that same year is rated at 390hp.

I believe that the 370hp rating of the LT1 is a factory lie, another case of an engine being underrated by the factory, and that the true hp of the LT1 is closer to 400hp. If this is the case, then the LT1 is probably a bit more powerful than the LS5. Is there any fact to this ? Do any of you know ?
Well, if GM underrated the LT-1, what makes you think that they didn't underate the LS-5? So, even if the LT-1 made 400 hp, and I am not saying it did, that what prevents GM from selling an LS-5 that made 420 hp?
SteveG75 is offline   Reply With Quote
Old 10-06-2010, 04:04 PM   #10
z10kl
CF Senior Member
 
z10kl's Avatar
 
Member Since: Feb 2007
Location: Denver nc
Default

Quote:
Originally Posted by Les View Post
The Z28 carb was also 780 cfm. The Z28 had a single crossflow muffler instead of two mufflers like the Vette. I've never seen that identified as the reason for the 360 HP rating but it may have been. I have seen it written that the Vette got the higher rating to keep the Vette as the "top dog", although I don't know for a fact if that's the case.
The Vette had better flowing exhaust manifolds and transistorised ignition.
z10kl is offline   Reply With Quote
Old 10-07-2010, 01:38 PM   #11
jb78L-82
CF Senior Member
 
jb78L-82's Avatar
 
Member Since: Oct 2007
Default

As mentioned above, the HP ratings of all engines prior to 1972 were GROSS HP figures versus NET HP ratings beginning in 1972. Gross HP ratings were done on an engine stand, with zero accessories hooked up (no water pump, alternator, power steering pump, AC compressor, and an open exhaust (probably not even ram horns) with no exhaust system at all and were measured at the flywheel. Net HP ratings include all of the above installed and hooked up as well as any emissions hardware, and a completely stock exhaust system including the pipes, OEM ramhorn manifolds, and mufflers-thus the giant HP drop starting in 1972. A 1971 LT-1 rated at 330 HP Gross is really no different than a 1972 LT-1 rated at 255 HP NET-they are essentially the same engine just rated differently. With these differences in mind, it is not surprising that a genuine 400 HP SB today would feel MUCH more powerful than a LT-1 rated at 370/350/330 Gross HP. A 1970 370 HP LT-1 probably actually made about 310-325 NET HP. Hope that helps!
jb78L-82 is offline   Reply With Quote
Old 10-07-2010, 04:03 PM   #12
garage-ghost
CF Senior Member
 
garage-ghost's Avatar
 
Member Since: Aug 2004
Location: www.Z16.org North/West Pennsylvania
Default

I had my 72 on a Mustang Dyno, (stingy with HP); a couple of years ago, just to see if GM did under rate them. The results were 260HP @ 5500 RPM I wouldn’t let them go higher even after they begged, saying “it was still climbing real nice”. I was afraid of breaking something. I have never had it over 5000 so letting them go to 5500 was a real heart stopper.
garage-ghost is offline   Reply With Quote
Old 10-07-2010, 09:10 PM   #13
dmayhew
CF Senior Member
 
Member Since: Oct 2007
Location: Brown Summit North Carolina
Default

[QUOTE=1968-72 Corvette PR;1575535448]Hi to all.

LT1 is closer to 400hp. If this is the case, then the LT1 is probably a bit more powerful than the LS5. Is there any fact to this ? Do any of you know ?



If you concede that the LT-1 under rated , then would it not make sense that the LS5 was also underrated?

The 390 HP could have been closer to 425??

I think the HP game was marketing magic

Who cares in the end, If the LS5's and LT-1's were kicking the crap out of mustangs on the street then that is what counted in the real world
dmayhew is offline   Reply With Quote
Old 10-08-2010, 10:21 PM   #14
Solid LT1
CF Senior Member
 
Solid LT1's Avatar
 
Member Since: Dec 2003
Location: Fremont CA
Default

LT-1 SAE tests were supoosedly performed with 30-30 Z28 cam where the real LT-1 cam is a little smaller on the intake (same exhaust.) My wife's LT-1 is only 370HP just like it says on the plate "bone stock" yeah that's the ticket
Solid LT1 is offline   Reply With Quote
Old 10-08-2010, 11:32 PM   #15
Gale Banks 80'
CF Senior Member
 
Member Since: Nov 2008
Default

Lets keep in mind that the LT-1 is the 70-73 and the LT1 is the 1990-96 Engine. Chev High Performace Magazine did a Test on the two of them in the last 6 months or so. It was wild how the two of them were very close in HP being 20 Years apart. The LT-1 had a bigger Cam but the new LT1 had many modern improvements. They both made about 350 HP at the Flywheel with Dyno Headers.
Gale Banks 80' is offline   Reply With Quote
Old 10-09-2010, 07:36 AM   #16
HamadUP
CF Senior Member
St. Jude Donor '08
Support Corvetteforum!
 
HamadUP's Avatar
 
Member Since: Jan 2003
Location: Doha
Default

The Car & Driver magazine tested a LS5 with a TH400 and 3.08 and loaded with many heavy options, it passed the 1/4 mile in 14.2 @ 100.33 MPH, and Motor Trend mag. tested a '70 LT-1 with 4 sp. and 4.11 rear and it passed the 1/4 mile in 14.36 @ 101.69 MPH.
HamadUP is offline   Reply With Quote
Old 10-09-2010, 08:40 AM   #17
jb78L-82
CF Senior Member
 
jb78L-82's Avatar
 
Member Since: Oct 2007
Default

Quote:
Originally Posted by Gale Banks 80' View Post
Lets keep in mind that the LT-1 is the 70-73 and the LT1 is the 1990-96 Engine. Chev High Performace Magazine did a Test on the two of them in the last 6 months or so. It was wild how the two of them were very close in HP being 20 Years apart. The LT-1 had a bigger Cam but the new LT1 had many modern improvements. They both made about 350 HP at the Flywheel with Dyno Headers.
That would certainly match up with my estimate above of Gross versus net horsepower for a 1970 370 HP LT-1. GM rated that motor with 370 GROSS HP with zero accessories and no exhaust. Add back the accessories with no exhaust 340-350 Gross HP at the flywheel. All accessories with a full stock exhaust about 300-310 NET HP, much less to the rear wheels after drivetrain losses which are greater 40 years ago than today. Again, there really is not much debate on this issue since the 1971 GROSS rated 330 HP LT-1 is the exact same LT-1 as the 1972 255 NET rated LT-1. Same engine, 75 HP difference between the GROSS and NET ratings. Hope that helps!

Also, the 1/4 mile times tell the real story about the actual HP of the 1970/71 LT-1's with a 14.3 sec time with 4.11 gears and a car that weighted about 3,200 lbs or less. Those times along with the weight, and 4.11 gears indicate a true NET HP of probably under 300 HP (more like 290-295 HP). As a comparison, a 78/79 L-82 4 speed with 3.70 gears which is a couple of hundred pounds heavier than the early 70 C3's with a 225 HP NET rated engine (L-82) would do high 14's in the 1/4 mile according to magazine articles at that time.

I think that the 70/71 LT-1's are possibly the best small blocks put in the C3's, but there is a tendency to over exaggerate the actual HP and performance of these SB's versus the many others that were offered over the years. Were they better, most certainly. Is a 71 LT-1 330 HP/350 HP, (not the 370 HP) much faster than the 74 L-82 4 speed rated at 250 HP, NO.

Last edited by jb78L-82; 10-09-2010 at 08:46 AM.
jb78L-82 is offline   Reply With Quote
Old 08-29-2013, 01:34 PM   #18
stuartc53
CF Member
 
Member Since: Aug 2013
Default

Quote:
Originally Posted by Lt1er View Post
As a proud owner of a Lt1 I can tell you that it was over rated at 370 hp. It has been said that factory rating were without ACC attached. So no belts on the front of the motor. The motor was held back by a low lift cam and head technology of the time period for production cars. I have a modern solid cam, higher lift, ported and polished heads....., and balanced motor that puts out a true 400 hp at the crank. It is a vast improvement over the factory "LT1" I have no problem revving it up to 7000 rpm. The best thing you can do for a LT1 is to throw away the cam and springs
I have an original 70 LT1 that came with Lunati cam with 502 lift when I bought it. I was gonna change it back to make it original, but after reading your post, I am thinking twice. What cam do you have in your LT1? Thank you
stuartc53 is offline   Reply With Quote
Old 08-29-2013, 03:50 PM   #19
Easy Mike
CF Senior Member
Cruise-In II Veteran
Support Corvetteforum!
 
Easy Mike's Avatar
 
Member Since: Jun 2000
Default

Quote:
Originally Posted by 1968-72 Corvette PR View Post
...I believe that the 370hp rating of the LT1 is a factory lie...
Okay.

Quote:
...did the LT1 have L88 components?...
No. The LT-1 is a small block. The L-88 is a big block.

Quote:
...Wanting to know...
Buy a copy.
Click the image to open in full size.

This is also good.
Click the image to open in full size.

Easy Mike is offline   Reply With Quote
Old 08-29-2013, 03:58 PM   #20
Mike Ward
CF Senior Member
 
Mike Ward's Avatar
 
Member Since: Jul 2001
Location: about an hour away from Paul74 in Ontariariario
Default

More dead in the grave threads being dug up for no apparent reason?
Mike Ward is offline   Reply With Quote
Old 08-29-2013, 03:58 PM
 
Go Back   Corvette Forum > C3 Corvettes, 1968 - 1982 > C3 Tech/Performance
Reload this Page True hp of 1970 LT1, and more about LT1.
 
 
 
Reply

Tags
1970, 1971, c3, cammed, carburetor, corvette, crossflow, holley, lt1, lt1corvete, lt1hp, muffler, numbers, performance, photos, starter


Thread Tools Search this Thread
Search this Thread:

Click for Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
1971 Corvette LS6. 1968-72 Corvette PR C3 General 4 10-17-2013 04:55 PM
Ontario Orange 1/24 scale Maisto 1970 Corvette 1968-72 Corvette PR Die Casts & Collectibles 0 01-01-2013 06:14 PM
L46 350cid engine 1968-72 Corvette PR C3 Tech/Performance 6 12-29-2012 10:05 AM
Test pilot message. 1968-72 Corvette PR Intros 20 08-09-2010 10:59 PM
Great National Day Of Corvettes - Arecibo, Puerto Rico c3dreamer Southeast 23 08-05-2006 01:59 PM


All times are GMT -4. The time now is 03:55 PM.


Emails & Password Backup