My Vortec Combo disappoints
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
I'm a little confused, does 260 hp at the rear wheels equate to net or gross hp? Assuming a 20% drivetrain loss 260 hp at the rear wheels should be 325 at the crank or 100 crank hp over stock, or looking at it the other way around, stock L82 225 hp should be 180 at the rear wheels so your 260 rwp should be 80 rwhp over stock. That sounds like quite a dramatic improvement and basically the equivalent of the 330HO GM crate motor you were attempting to clone, but you say you couldn't tell any difference between your stock and modified L82?
Or is it that the rwhp figure they give you is gross, for example that the stock L82 225 net hp is the equivalent of (about) 281 gross hp so your net gain is 325-281 or about 44 hp?
Last edited by Priya; Jan 14, 2013 at 04:55 PM.
Melting Slicks
Joined: Aug 2011
Posts: 3,140
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I've never had the privilege to drive a c5 or c6. Would like to. My ideal of streetable car is will it start with out ether, can I pull away from a stop light from idle with out winding up to 5000 rpm or 3000rpm for that matter & and can I cruise around tone in traffic with out it over heating. I can't call my Yvette a daily driver cause I live in Alaska, but it's definitely my fair weather driver, it and my Harley. I love a Lopey idle which is a sign of poor idle vacuum, but I get and agree with the c5 and c6 being the ls engine series makes a ton of horse power and idles all calm and smooth at 600 rpm. My truck makes 430 horse and idles smooth and nice @ 550 rpm in gear. But that's comparing apples to oranges don't you think.
Advanced
Joined: Oct 2012
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I must admit, I have brought many a thread back to life due to searching for information on something and instead of checking the date I just post my reply/question on the searched thread.
That said, I would sooner someone post on a 10 year old thread when they have a question that pertains to something in that thread than to start a new and possibly redundant thread. my .02
Race Director
Joined: Jan 2000
Posts: 12,399
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From: San Jose CA
A lot of problems in the "just off-idle" zone won't be seen in a WOT dyno pull. A good dyno operator can figure that stuff out by simulating driving the car... with the right datalogging tools, you can figure it out by driving around.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
I'm a little confused, does 260 hp at the rear wheels equate to net or gross hp? Assuming a 20% drivetrain loss 260 hp at the rear wheels should be 325 at the crank or 100 crank hp over stock, or looking at it the other way around, stock L82 225 hp should be 180 at the rear wheels so your 260 rwp should be 80 rwhp over stock. That sounds like quite a dramatic improvement and basically the equivalent of the 330HO GM crate motor you were attempting to clone, but you say you couldn't tell any difference between your stock and modified L82?
There is no magic bullet for translating how much horsepower is lost between the engine and the tire. Some people swear it's a percentage(20%, as an example, would mean that a 300hp car makes 240hp at the wheels), some people think it's a somewhat slippery fixed number(ie, all accessories and drivetrain eat up 70hp; a 300hp net rating would get 230 rwhp in this instance). I'm more inclined to believe the latter.
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
Okay, after thinking about it some more I think I answered my own question regarding "net" vs "gross" rear wheel horsepower. Gross horsepower was a measurement without exhaust system and accessories such as air cleaner, power steering, alternator, or water pump. Net horsepower was a measurement with exhaust and accessories installed. So, when you get a rear wheel horsepower measurement that would be "net" rear wheel horsepower as the measurement is taken with exhaust, air cleaner, water pump, alternator, etc. in place.
So, assuming a 20% drivetrain loss with an automatic trans, 79vetter's 260 rear wheel horsepower dyno measurement should equate to 325 net horsepower or 100 horsepower more than the stock L82. Seems like that should be very noticeable.
79vetter, was your L82 completely stock before you put the Vortec heads, cam, and intake on it?
So, assuming a 20% drivetrain loss with an automatic trans, 79vetter's 260 rear wheel horsepower dyno measurement should equate to 325 net horsepower or 100 horsepower more than the stock L82. Seems like that should be very noticeable.
79vetter, was your L82 completely stock before you put the Vortec heads, cam, and intake on it?
Last edited by Priya; Jan 14, 2013 at 05:48 PM. Reason: posted before reading Shark Racer's response
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
Thanks Shark racer, I'll need to do some more thinking about this.
In re-reading 79vetter's original post I see he has a manual trans and not an automatic so the drivetrain loss on a rear wheel dyno would be less than what I was assuming.
In re-reading 79vetter's original post I see he has a manual trans and not an automatic so the drivetrain loss on a rear wheel dyno would be less than what I was assuming.
Last edited by Priya; Jan 14, 2013 at 05:53 PM.
Safety Car
Joined: Jan 2009
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From: anchorage ak
So what do we think could help Vetter? I mean since thus thread got resurrected and all, what are your ideals toward helping him reach his goals, which seem to be better torque off idle and retain top end horse power. If he went to a lower duration cam like the xe254h or xe262 it would increase off torque idle, but top end would suffer some. I beleave the heads would still need machining to run 1.6's for increased lift(please correct my thinking if I'm wrong) changing heads would be extra costly due to the fact of every thing being set up for vortecs. I do beleave a modern camshaft with less duration would help low end. If ya had machine work done to accommodate additional lift it might help compensate some for reducing duration by running 1.6 rockers. When I did the l48 with the xe262 it would spin the tires but was funnier to drive once I put a 2400 rpm stall converter in. This is what I can think of that might help. Going with less duration you would want to check the dcr. Like Mako suggested changing gear ratio to multiply torque would give ya more bottom end and get ya into the torque range of the cam.
Last edited by bluedawg; Jan 14, 2013 at 09:23 PM.
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Melting Slicks
Joined: Aug 2011
Posts: 3,140
Likes: 262
Work on the carb - pump shot, stuck power piston ??, tighten secondary air valve opening etc ?
Confirm that the cam is installed correctly - not a tooth out (retarded).
Buy a torque cam - something less than the L82 or what he has now, as he is looking for torque off the line I believe ?!
Confirm that the cam is installed correctly - not a tooth out (retarded).
Buy a torque cam - something less than the L82 or what he has now, as he is looking for torque off the line I believe ?!
Last edited by QIK59; Jan 14, 2013 at 09:53 PM.
Safety Car
Joined: Jan 2009
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From: anchorage ak
He could try advancing the cam 4 degrees. Might pick up the low end torque he feels its lacking. Comp cams says that if you have to advance a cam that its the wrong cam. While that might be true, if it got vetter the low end he was looking for it would be better than buying a new cam and if it got him closer then hed know what direction to go. I highly doubt its the carb, although it could be possible for lars to have not gotten something right with the carb, I'd sooner beleave the moons made of cheese or that we have a great president.
Melting Slicks
Joined: Aug 2011
Posts: 3,140
Likes: 262
Just because Lars laid his hands on the carb doesn't mean that there is no reason to confirm or check anything.
That's how people have problems - making assumptions and not checking (and rechecking) things.
But we are all such brainers on here right ??
That's how people have problems - making assumptions and not checking (and rechecking) things.
But we are all such brainers on here right ??
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Well post # 53, 79vetter said he would just leave it alone.
Few yrs back i did some work on a 54 vette for a cousin. Original blue flame six was gone it had a dead stock low compression 350 in it with a 4 speed. He wanted an auto for his wife to drive it so i converted it back to an auto using a turbo 350, no high stall or anything no hot rodding involved. Car was a blast to drive it still had the 4.11s in it that came with from the factory for the little 235 inline six.
Sure a 54 is worlds lighter then a 79 but with the slug engine no converter the 4.11s made it snap to attention. Every stop light was fun lol.
3,650 pound 79 vette with 3.36 gears with a 350 its going to be sluggish.
Few yrs back i did some work on a 54 vette for a cousin. Original blue flame six was gone it had a dead stock low compression 350 in it with a 4 speed. He wanted an auto for his wife to drive it so i converted it back to an auto using a turbo 350, no high stall or anything no hot rodding involved. Car was a blast to drive it still had the 4.11s in it that came with from the factory for the little 235 inline six.
Sure a 54 is worlds lighter then a 79 but with the slug engine no converter the 4.11s made it snap to attention. Every stop light was fun lol.
3,650 pound 79 vette with 3.36 gears with a 350 its going to be sluggish.
Last edited by Little Mouse; Jan 14, 2013 at 11:12 PM.
Melting Slicks
Joined: Aug 2011
Posts: 3,140
Likes: 262
Well post # 53, 79vetter said he would just leave it alone.
Few yrs back i did some work on a 54 vette for a cousin. Original blue flame six was gone it had a dead stock low compression 350 in it with a 4 speed. He wanted an auto for his wife to drive it so i converted it back to an auto using a turbo 350, no high stall or anything no hot rodding involved. Car was a blast to drive it still had the 4.11s in it that came with from the factory for the little 235 inline six.
Sure a 54 is worlds lighter then a 79 but with the slug engine no converter the 4.11s made it snap to attention. Every stop light was fun lol.
3,650 pound 79 vette with 3.36 gears with a 350 its going to be sluggish.
Few yrs back i did some work on a 54 vette for a cousin. Original blue flame six was gone it had a dead stock low compression 350 in it with a 4 speed. He wanted an auto for his wife to drive it so i converted it back to an auto using a turbo 350, no high stall or anything no hot rodding involved. Car was a blast to drive it still had the 4.11s in it that came with from the factory for the little 235 inline six.
Sure a 54 is worlds lighter then a 79 but with the slug engine no converter the 4.11s made it snap to attention. Every stop light was fun lol.
3,650 pound 79 vette with 3.36 gears with a 350 its going to be sluggish.
It would run side by side with the late 70's Vette's LOL
Melting Slicks
Joined: Aug 2011
Posts: 3,140
Likes: 262
Work on the carb - pump shot, stuck power piston ??, tighten secondary air valve opening etc ?
Confirm that the cam is installed correctly - not a tooth out (retarded).
Buy a torque cam - something less than the L82 or what he has now, as he is looking for torque off the line I believe ?!
Confirm that the cam is installed correctly - not a tooth out (retarded).
Buy a torque cam - something less than the L82 or what he has now, as he is looking for torque off the line I believe ?!
My initial suggestion was change the torque converter but yanking out the tranny seems like a lot of work when you haven't first ruled out something simple that may have been overlooked.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
I ordered a new 78 L/82 with 3.70 rear, M21 trans. Lets just say it was a very long way from impressive lol. Part of the problem could have been a 396 and 454 i had already owned by that time. The 396 was in front of 4.11s in a 66 vert. the original 427 it came with was gone. I built the 396 to 375hp specs but i only had a two bolt block to work with. Same car ended up with a large journal 331 had 12.5 pistons in it. You could still buy pump fuel back then. I needed a block from the machine shop " forman no problem $5.00 ", The large journal steel 327 crank same price $5.00. Hey crankshaft grinder how does this crank look . Sure wish i could bring these times back. New base engine C7, $55,000.00, Beam me back scotty.
Last edited by Little Mouse; Jan 15, 2013 at 12:03 AM.
Race Director
Joined: Oct 2000
Posts: 15,053
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From: central FL, near the beach.
The point everyone is missing is gearing, transmission and intended use. A 3.08 rear gear with stock convertor and TH350 car is streetable and fun to drive with a 325 hp engine with XE 262 flat tappet and 9 to 1 compression.
In my car with a 4.11 and a close ratio 6 speed manual a XE262 and 9 to 1 compression is a waste.
525 hp, 10.4 to 1 and a 288 roller is very streetable (street car) and very fun to drive.
600 hp, 11 to 1 and a solid roller with over 300 advertised duration might be very streetable and more fun to drive. With proper gearing it is not doggy off the line at all or miserable to drive in any way. That would compare to a new Supercharged C6 Z06, over 600 hp, 11 to 1 compression, 6 speed manual, very streetable and fun to drive..
Matt Gruber might not like it.................. he might love it and it could very well change his whole prospective.
'
I drove my 61 like that for 4 or 5 years! It was fun, i admit that. But it got 11 mpg.
Still have the 4.11 in my 61 and it now gets 15-19 mpg at cruise. still just as much fun, even more as it doesn't need any warm-up(to drive off gently), even down to 38F. Same 270 magnum cam, just a fully divided dual plane. 1000-6000+ power band. That is my point, i'm not giving up anything, and, as my 72 proves, a 3.08 works great with the 4 holer base gasket. If someone needs more rpm than the 6000 the ex262, or more power,go right ahead with a larger cam, higher stall, steep gear, whatever. Just keep the 2 planes fully divided for more fun and decent mpg at cruise.
The op should be checking that carb base gasket! 4 hole only! No cut down divider! No unused cross passages in the carb base!(plug them) The devil is in the details!
Last edited by Matt Gruber; Jan 15, 2013 at 01:02 AM.
Safety Car
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From: anchorage ak
You'd beat me there to as I let all my equipment warm up to operating temp. I couldn't promise that this prevents any thing or prolongs engine or tranny life, it's just what I do.
Race Director
Joined: Oct 2000
Posts: 15,053
Likes: 79
From: central FL, near the beach.
bluedawg
So how much earlier do you get up, to get to work on time?
Idling just reduces engine life. All those r's and no forward movement.
35-40 mph takes about 10 hp, and the engine can't tell the difference between that and idling.
BUT, with an open base gasket, my 61 would sometimes stall if i tried to drive off gently on a cold start. 4 holer fixed that quirk. And it only needs 1000 rpm for fast idle. Open gasket, it needed 1500-2000 and it would still stall
sometimes, very annoying, even dangerous when pulling out into atlantic ave.
BUT, not ever again, since 2007 when i sealed off the 2 planes, and blocked the extra carb cross passages.
So how much earlier do you get up, to get to work on time?
Idling just reduces engine life. All those r's and no forward movement.
35-40 mph takes about 10 hp, and the engine can't tell the difference between that and idling.
BUT, with an open base gasket, my 61 would sometimes stall if i tried to drive off gently on a cold start. 4 holer fixed that quirk. And it only needs 1000 rpm for fast idle. Open gasket, it needed 1500-2000 and it would still stall
sometimes, very annoying, even dangerous when pulling out into atlantic ave. BUT, not ever again, since 2007 when i sealed off the 2 planes, and blocked the extra carb cross passages.
Last edited by Matt Gruber; Jan 15, 2013 at 06:27 AM.
Safety Car
Joined: Sep 2012
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From: Palm Harbor, Florida
he can probably tear down and rebuild a carb blindfolded better then some of us can do with our eyes open and a manual 
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
When I said a car with good drivability will start readily on a cold day and warmup without stalling without your foot on the gas I was talking about -20, not +38 or +40. You're spoiled.