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 07-25-2012, 10:59 PM   #1
riverracer au
CF Senior Member
 
riverracer au's Avatar
 
Member Since: Oct 2010
Location: Adelaide, Australia
Default 1970-71 LT1 engines

a mate has just bought a '71 LT1 and we got talking about the engine.
what makes the '70 with 370 hp so special over the '71 with 330hp?
was it the 186 heads, cam, higher compression pistons etc, or what?
or was it the new rating system, but i thought that came in '72?

where can we find a break down/listing of parts that go in a LT1 engine?
ie: cam specs, pistons used etc.

any good engine books on this?

this mite solve/start a bar fight for us...

riverracer au is offline   Reply With Quote
Old 07-25-2012, 11:49 PM   #2
maxler
Junior Member
 
maxler's Avatar
 
Member Since: Mar 2007
Location: Troy MI
Default

In 1971 GM mandated a compression drop on all engines to a max of 9.5 to 1. That is most of the difference from 1970 to 1971. Gm did change rating in 1972 so the HP changed again.
maxler is offline   Reply With Quote
Old 07-26-2012, 01:25 AM   #3
gbvette62
CF Senior Member
 
gbvette62's Avatar
 
Member Since: Oct 2000
Location: Shamong, NJ
Default

The 70 LT-1 has 11-1 pistons, while the 71 has 9.5-1 pistons. GM was preparing for regular un-leaded fuel.
gbvette62 is offline   Reply With Quote
Old 07-26-2012, 01:51 AM   #4
Les
CF Senior Member
 
Les's Avatar
 
Member Since: Dec 1999
Location: Sierra Foothills CA
Default

The 70 LT-1 had 11 to 1 comp. ratio, as stated. The 71 LT-1 actually dropped to a 9 to 1 comp. ratio.
__________________
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 07-26-2012, 01:55 AM   #5
Vette5.5
CF Senior Member
 
Member Since: Sep 2004
Location: Livonia MI
Default

Maybe a little more info on the leaded fuel thing. Adding lead to fuel was a cheap way to bump octane rating. This turned out to be a bad thing coming out of the tail pipe, so was phased out. At first, there was low lead gas, that still allowed a little octane boost, but after a couple years, that was gone too. Todays higher octane fuel, is done through further refinement, yielding less actual fuel, per given crude oil input. It's now considered a more politically correct thing to limit premium octace to 91, in CA and other states, to save maybe 1% crude over doing 93 octane, allowed in other states. No lead's actually a good thing though, as the engines combustion chambers burn much cleaner now.
Vette5.5 is offline   Reply With Quote
Old 07-26-2012, 09:42 AM   #6
Easy Mike
CF Senior Member
Cruise-In II Veteran
Support Corvetteforum!
 
Easy Mike's Avatar
 
Member Since: Jun 2000
Default

Quote:
Originally Posted by riverracer au View Post
...where can we find a break down/listing of parts that go in a LT1 engine?...ie: cam specs, pistons used etc....
Try Google. Tons of information has been published on the LT-1s.

Last edited by Easy Mike; 07-26-2012 at 01:40 PM.
Easy Mike is offline   Reply With Quote
Old 07-26-2012, 12:22 PM   #7
larrywalk
CF Senior Member
 
larrywalk's Avatar
 
Member Since: Oct 2002
Location: Coronado CA
Default

Quote:
Originally Posted by riverracer au View Post
a mate has just bought a '71 LT1 and we got talking about the engine.
what makes the '70 with 370 hp so special over the '71 with 330hp?
was it the 186 heads, cam, higher compression pistons etc, or what?
or was it the new rating system, but i thought that came in '72?

where can we find a break down/listing of parts that go in a LT1 engine?
ie: cam specs, pistons used etc.

any good engine books on this?

this mite solve/start a bar fight for us...

To lower the compression ratio...
Pistons - flat top versus .100" dome
Heads - 76 cc chambers versus 64 cc chambers
larrywalk is offline   Reply With Quote
Old 07-26-2012, 12:32 PM   #8
jb78L-82
CF Senior Member
 
jb78L-82's Avatar
 
Member Since: Oct 2007
Default

1972 was the first year of Net HP ratings, which is the current standard today. Prior to 1972, all the engines were rated at Gross HP which is very misleading since the engine power is measured at the flywheel with no accessories on the engine including water pump, power steering pump, Alternator (not sure about this one), and most importantly an open exhaust (or lack thereof-no OEM exhaust manifolds, exhaust pipes, mufflers etc). The best example of the difference between Gross and net HP ratings on the C3 corvette is the 1971 LT-1 rated at 330 Gross HP an and the 1972 LT-1 which is essentially the same motor as the 71 LT-1 which was rated at 255 Net HP-which is a 75 HP difference between the 2 rating systems on the same engine. For the uninitiated the difference between Gross and Net HP is very confusing and misleading! Hope that helps!
jb78L-82 is online now   Reply With Quote
Old 07-26-2012, 12:41 PM   #9
Mike Ward
CF Senior Member
 
Mike Ward's Avatar
 
Member Since: Jul 2001
Location: about an hour away from Paul74 in Ontariariario
Default

Quote:
Originally Posted by jb78L-82 View Post
1972 was the first year of Net HP ratings, which is the current standard today. Prior to 1972, all the engines were rated at Gross HP which is very misleading since the engine power is measured at the flywheel with no accessories on the engine including water pump, power steering pump, Alternator (not sure about this one), and most importantly an open exhaust (or lack thereof-no OEM exhaust manifolds, exhaust pipes, mufflers etc). The best example of the difference between Gross and net HP ratings on the C3 corvette is the 1971 LT-1 rated at 330 Gross HP an and the 1972 LT-1 which is essentially the same motor as the 71 LT-1 which was rated at 255 Net HP-which is a 75 HP difference between the 2 rating systems on the same engine. For the uninitiated the difference between Gross and Net HP is very confusing and misleading! Hope that helps!
No alternator, no air cleaner, no engine driven smog stuff, no nothing.
Mike Ward is offline   Reply With Quote
Old 07-26-2012, 12:54 PM   #10
riverracer au
CF Senior Member
 
riverracer au's Avatar
 
Member Since: Oct 2010
Location: Adelaide, Australia
Default

thanks for the in-depth info
makes me want to rebuild my piddly underpowered '72 L48 to match earlier specs
maybe a set of '70 186 heads, new manifold and cam to match to keep the stock look
just thinking/rambling....
riverracer au is offline   Reply With Quote
Old 07-26-2012, 04:41 PM   #11
Alan 71
CF Senior Member
 
Alan 71's Avatar
 
Member Since: Sep 2006
Location: Westminster Maryland
Default

Hi,
I believe that Chevrolet did publish the SAE net hp ratings for 71 engines, but the info wasn't widely disseminated.
This chart is from the Corvette News edition that had the 71 introduction info in it.
There are a couple of interesting numbers if you look closely.
Regards,
Alan

Click the image to open in full size.

Click the image to open in full size.
Alan 71 is online now   Reply With Quote
Old 07-26-2012, 09:12 PM   #12
Solid LT1
CF Senior Member
 
Solid LT1's Avatar
 
Member Since: Dec 2003
Location: Fremont CA
Default

186 heads should add 20HP to a later LT-1 motor, combustion chamber shape much better fro making HP. We used to swap 292 "Turbo" heads back in the 70's, these heads really woke up those low compression smog headed motors. My buddies 70 Z28 360HP Camaro went from 14.40's at the drags to 13.90s with this swap (done by 18 year old kids who didn't know much back then.)
Solid LT1 is offline   Reply With Quote
Old 07-26-2012, 10:02 PM   #13
74modified
CF Senior Member
 
74modified's Avatar
 
Member Since: Oct 2008
Location: Mobile Alabama
Default

Quote:
Originally Posted by Vette5.5 View Post
Maybe a little more info on the leaded fuel thing. Adding lead to fuel was a cheap way to bump octane rating. This turned out to be a bad thing coming out of the tail pipe, so was phased out. At first, there was low lead gas, that still allowed a little octane boost, but after a couple years, that was gone too. Todays higher octane fuel, is done through further refinement, yielding less actual fuel, per given crude oil input. It's now considered a more politically correct thing to limit premium octace to 91, in CA and other states, to save maybe 1% crude over doing 93 octane, allowed in other states. No lead's actually a good thing though, as the engines combustion chambers burn much cleaner now.
Not to hijack the thread, but the lead also lubricated the valves, the reason older engines need hardened valve seats installed.
74modified is offline   Reply With Quote
Old 07-26-2012, 10:32 PM   #14
Barry's70LT1
CF Senior Member
 
Barry's70LT1's Avatar
 
Member Since: Oct 2001
Location: Halifax, Nova Scotia, Canada
Default

A little more LT-1 trivia....

- Crankshaft = Forged Steel, Tuff Trided Journals (Base engine = Cast)
- Rods = Shot Peened/Magnafluxed (pink) (Base engine = not)
- Pistons = Forged TRW (Base engine = cast)
- Heads = 2.02 I / 1.6 E with Push rod Guides (Base engine = 1.94 I)
- Intake = High rise Aluminum (Winters Foundry) (Base engine = cast Q-Jet)
- Carb = Holley (Base engine = Q-jet)
- Cam = Solid lifter Hi-Perf (Base engine = Hydraulic Lo-Perf)
Barry's70LT1 is offline   Reply With Quote
Old 07-26-2012, 10:32 PM
 
Go Back   Corvette Forum > C3 Corvettes, 1968 - 1982 > C3 Tech/Performance
Reload this Page 1970-71 LT1 engines
 
 
 
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Forged vs Cast Pistons??? Vet76te C3 Tech/Performance 14 10-10-2013 09:00 AM
LT-1 solid cam - couple of questions 71coupe C3 General 2 09-09-2012 08:40 PM
1971 LT-1 Cam Specs? spdrcr29 C3 Tech/Performance 5 09-20-2011 03:05 PM
340HP 327 Pistons bowtyebob C1 & C2 Corvettes 8 12-18-2009 09:59 PM
Help with piston & rod ID. L Holmes C3 Tech/Performance 12 04-15-2007 09:24 AM



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


All times are GMT -4. The time now is 10:25 AM.


Emails & Password Backup