LT1 to LT4 kit conversion: Wouldja do it again?
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
LT1 to LT4 kit conversion: Wouldja do it again?
Forgive me, but I'm relatively new to this board, and no doubt this question has been sliced and diced a zillion times 
. So let me ask it this way...
Preface: I'm looking for 425 to 450 hp while maintaining that phenominally flat torque curve the LT1 is famous for. I'm intrigued by the GM Direct LT1 to LT4 conversion kit including heads, intake, 1.6 roller rockers, and the Hot Cam. So Q: For those who have made this conversion, (not to exclude anyone with knowledge on this, ya understand ;-) is this going to get me there, or should I throw in a 383 stroker to "help make it so", i.e., help keep the torque curve flat?
Thanks in advance. This is quite a board y'all have here!!!
P.
. So let me ask it this way...Preface: I'm looking for 425 to 450 hp while maintaining that phenominally flat torque curve the LT1 is famous for. I'm intrigued by the GM Direct LT1 to LT4 conversion kit including heads, intake, 1.6 roller rockers, and the Hot Cam. So Q: For those who have made this conversion, (not to exclude anyone with knowledge on this, ya understand ;-) is this going to get me there, or should I throw in a 383 stroker to "help make it so", i.e., help keep the torque curve flat?
Thanks in advance. This is quite a board y'all have here!!!
P.
Melting Slicks
Joined: Dec 2004
Posts: 2,137
Likes: 5
From: Howard PA
Personally, I'd do the stroker. If you do the conversion you're still stuck with the LT1 crank. A forged stroker will be stonger and offer some piece of mind. Buy your own heads, there's better heads out there than the LT4s.
However a 383 build might not be cheaper than just doing the conversion.
Spend the money, do it the way you know in your heart is the way it should be done.
However a 383 build might not be cheaper than just doing the conversion.
Spend the money, do it the way you know in your heart is the way it should be done.
Safety Car
Joined: Jun 2004
Posts: 4,197
Likes: 0
From: lafayette co
Originally Posted by Paul Workman
Preface: I'm looking for 425 to 450 hp while maintaining that phenominally flat torque curve the LT1 is famous for.
I don't think that conversion kit will get you anywhere close to that RW horsepower.
I've got an LT4 that I have modded pretty heavily. I'm not even making 400 RWHP.
See my sig. for my mods.
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
Originally Posted by boulderlt4
Is that RW or flywheel?
I don't think that conversion kit will get you anywhere close to that RW horsepower.
I've got an LT4 that I have modded pretty heavily. I'm not even making 400 RWHP.
See my sig. for my mods.
I don't think that conversion kit will get you anywhere close to that RW horsepower.
I've got an LT4 that I have modded pretty heavily. I'm not even making 400 RWHP.
See my sig. for my mods.
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
Um, yeah. I was wondering about that. Not as much of a lift as one might hope. Gross to gross, using 12% for a manual would amount to a 45ish hp gain. As ALLT4 said, maybe I should do what's in my heart and do the stroker at the same time to get an "net" closer to the 425-450ish.
Thanks for the info.
P.
Thanks for the info.
P.
Melting Slicks
Joined: Apr 2000
Posts: 3,490
Likes: 2
From: Oviedo FL
It would be 95 more gross hp than you have now (330), but I can tell you that 425 figure is with long tubes and a few other bolt ons (exhaust, 52 mm tb, etc). I remember the article in Corvette Fever from about 6 years ago that had MORE Performance testing this kit. And you can forget the 12% loss and figure it to be around 15 - 17%, which would put this somewhere around 350 - 360 rwhp.
Mike
Mike
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
Originally Posted by luvmy92
It would be 95 more gross hp than you have now (330), but I can tell you that 425 figure is with long tubes and a few other bolt ons (exhaust, 52 mm tb, etc). I remember the article in Corvette Fever from about 6 years ago that had MORE Performance testing this kit. And you can forget the 12% loss and figure it to be around 15 - 17%, which would put this somewhere around 350 - 360 rwhp.
Mike
Mike
Gross, net, RW... The trouble with standards is there are so many to choose from!! LOL!
The efficiency of the manual xmission is slightly better than the auto, according to some articles. 15-17%, oft quoted on this board kinda lumps them together. I guess that is OK, as long as we're all on the same page when comparing the result of this or that modification. Long tubes, 'eh? I wonder if they would be legal in IL?
Thanks for the clarification, Mike.
P.
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Race Director
Joined: Dec 2002
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From: SCMR Rat Pack'r Charter Member..Great Bend KS
Originally Posted by steve9899
The 425 advertised for the conversion is gross not net.
Sounds like very enthusiastic advertising to me.
The answer to Paul's original question is that you will need a thoroughly-massaged 383 to reach 425-450hp.
Larry
code5coupe.
Race Director
Joined: Jan 2005
Posts: 10,641
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From: Slidell Louisiana
Originally Posted by rocco16
How does a "converted" LT4 make 425hp when an original LT4 only makes 330hp?
Sounds like very enthusiastic advertising to me.
The answer to Paul's original question is that you will need a thoroughly-massaged 383 to reach 425-450hp.
Larry
code5coupe.
Sounds like very enthusiastic advertising to me.
The answer to Paul's original question is that you will need a thoroughly-massaged 383 to reach 425-450hp.
Larry
code5coupe.
So the difference between a stock LT4 and the oft quoted 425HP LT4 is the HotCam, Long tube headers, better exhaust, high flow cats, and a tune.
So it is not a cheap install and I bet to actually see those numbers you will need to have the heads ported.
Mike
Safety Car
Joined: Apr 2003
Posts: 3,793
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From: VA
Originally Posted by rocco16
The answer to Paul's original question is that you will need a thoroughly-massaged 383 to reach 425-450hp.
Melting Slicks
Joined: May 2002
Posts: 2,670
Likes: 4
From: Severna Park MD
Originally Posted by aboatguy
No one ever reads the small print that 425CHP LT4 had the HotCam, LT headers, high flow cats and a tune.
So the difference between a stock LT4 and the oft quoted 425HP LT4 is the HotCam, Long tube headers, better exhaust, high flow cats, and a tune.
So it is not a cheap install and I bet to actually see those numbers you will need to have the heads ported.
Mike
So the difference between a stock LT4 and the oft quoted 425HP LT4 is the HotCam, Long tube headers, better exhaust, high flow cats, and a tune.
So it is not a cheap install and I bet to actually see those numbers you will need to have the heads ported.
Mike
But you don't get there with just the GM parts of the package added to a stock LT1.
Melting Slicks
Joined: Jul 2004
Posts: 2,695
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From: Chicago Illinois
Originally Posted by steve9899
More than one person here needs to go do a web search and learn the difference between gross and net HP. Stock LT4 has 330 net not gross.
(And they are considered by most to be underrated at 330.)
(And they are considered by most to be underrated at 330.)
Melting Slicks
Joined: May 2002
Posts: 2,670
Likes: 4
From: Severna Park MD
Originally Posted by bobmic93
Ha ding ding, your wrong. Lt4 has 330 gross and maybe 300 net. Lt1 has 300 gross and maybe 270 net. Come on guy!
Gross HP was the standard used in the 60s and 70s. The manufacturers ran the tests in dyno rooms with engines that had no in car accessories. That was Gross. The engines were run as they would in a dragster. So a 1965 327/350 HP does not compare to today's standards.
Net SAE is again run in an engine dyno room but the engine has the normal accessories that would be attached in a car. Like power robbing power steering and A/C.
The switch from gross to net was long ago.
What you are referring to is that manufacturer's ratings are always done in an engine dyno room. Referred to as crank HP or flywheel HP because that's where the dyno load is attached.
What we do is put our cars on dyno rollers, so the engine is in the car, and the connection to the dyno load is through the rear wheels. After the losses of the transmission, crank shaft, rear end, wheel bearings, etc. Not a direct drive between the crank and the dyno. This is rear wheel HP. The conversion is an approximation. (There is a formula but we use 15% fro stick and 18 % for auto commonly).
Last edited by FELNGR8; Jun 23, 2005 at 10:21 PM.
Melting Slicks
Joined: Jul 2004
Posts: 2,695
Likes: 0
From: Chicago Illinois
[QUOTE=FELNGR8]Not true. Steve is correct.
Gross HP was the standard used in the 60s and 70s. The manufacturers ran the tests in dyno rooms with engines that had no in car accessories. That was Gross. The engines were run as they would in a dragster. So a 1965 327/350 HP does not compare to today's standards.
Net SAE is again run in an engine dyno room but the engine has the normal accessories that would be attached in a car. Like power robbing power steering and A/C.
The switch from gross to net was long ago.
What you are referring to si that manufacturer's ratings are always done in an engine dyno room. Referred to as crank HP or flywheel HP because that's where the dyno load is attached.
What we do is put our cars on dyno rollers, so the engine is is the car, adn the connection to the dyno load is through the rear wheels. AFter the losses of the transmission, crank shaft, rear end, wheel bearings, etc. Not a direct drive between the crank and the dyno. This is rear wheel HP.[/QUOTE) The Lt4 has 330 crank HP stock. Which in todays terms would be gross. What it actually has that really means anything is RWHP. All the deductions are taken out and is whats put to the ground. 300 HP Net.
Gross HP was the standard used in the 60s and 70s. The manufacturers ran the tests in dyno rooms with engines that had no in car accessories. That was Gross. The engines were run as they would in a dragster. So a 1965 327/350 HP does not compare to today's standards.
Net SAE is again run in an engine dyno room but the engine has the normal accessories that would be attached in a car. Like power robbing power steering and A/C.
The switch from gross to net was long ago.
What you are referring to si that manufacturer's ratings are always done in an engine dyno room. Referred to as crank HP or flywheel HP because that's where the dyno load is attached.
What we do is put our cars on dyno rollers, so the engine is is the car, adn the connection to the dyno load is through the rear wheels. AFter the losses of the transmission, crank shaft, rear end, wheel bearings, etc. Not a direct drive between the crank and the dyno. This is rear wheel HP.[/QUOTE) The Lt4 has 330 crank HP stock. Which in todays terms would be gross. What it actually has that really means anything is RWHP. All the deductions are taken out and is whats put to the ground. 300 HP Net.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Originally Posted by bobmic93
The Lt4 has 330 crank HP stock. Which in todays terms would be gross. What it actually has that really means anything is RWHP. All the deductions are taken out and is whats put to the ground. 300 HP Net.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Regardless of terminology, the important thing is that the 425 number is inflated compared to the numbers that car manufacturers publish so you can't compare it to the 330 that the LT4 is advertised as having.
What really matters is RWHP. An LT4 with hot cam and full bolt ons will make in the vicinity of 340 RWHP.
What really matters is RWHP. An LT4 with hot cam and full bolt ons will make in the vicinity of 340 RWHP.
Instructor
Joined: Apr 2000
Posts: 223
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From: Aurora OH
I'm curious. Has anybody actually bought this kit and installed it on an LT1? If so, what else, if anything, did you do to it or add to it and what were the results? Dyno results? SOTP results? Thumbs up? Thumbs down? Thanks.