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  #31 (permalink)  
Old 12-20-2012, 05:16 PM
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OMG! I feel sorry for the poor car hop girl at the drive in that gets the combo wrong! wrong tomato:cheese ratio with the wrong amount of onion rings.Wont get enough quench with a small rootbeer.Have to watch the compression in order to get the bun at the correct installed height. The roller skate wheels are the wrong diameter causing poorly matched RPM for the distance to the kitchen.

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  #32 (permalink)  
Old 12-20-2012, 06:05 PM
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anybody have the capability to computer simulate the 355 vs 406 combos? I am curious just how much the theoretical numbers would differ and at what revs the action would happen at. So far only one guy has posted about an actual experience w/ a vortec headed 400.. and honestly its sounding pretty good to me. The rest have just said "no gains" or "less rpms than a 355" or "you need change everything" I need to know what 51 cubes would actually change.. when using MY stuff.. lose 500rpms? 1000 rpms? gain 15lbft? 40lbft? help me out here.

clearly there is some other unfinished off topic business goin on here..
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  #33 (permalink)  
Old 12-20-2012, 06:37 PM
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350 vs 400. With the 400, you are looking at an extra 40lb. ft of torque and an extra 40 horsepower, with the same cam as the 350, all of which will occur lower in the RPM range. You can also cam up a step or 2 with the 400 which will handle a larger cam. Peak Hp will be 400-500 rpm lower in the 400. Torque will be good right from idle with the 400. A 350 has to rev up to 2500 to start making good torque. 1 3/4 headers are good for a 400. 1 5/8 headers are probably better suited to a 350 street motor 400 hp or less. 3 in exhaust is a little large. for the 350. 2 1/2 may give better torque on the 350. 3 in exhaust may work fine with the 400.

It is all about hte combination of parts working together. larger exhaust is good for high rpm power - all out racing. smaller headers and exhaust work better for a street driven car. I hope this is helpful.
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  #34 (permalink)  
Old 12-20-2012, 06:48 PM
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Quote:
Originally Posted by cr480r View Post
anybody have the capability to computer simulate the 355 vs 406 combos? I am curious just how much the theoretical numbers would differ and at what revs the action would happen at. So far only one guy has posted about an actual experience w/ a vortec headed 400.. and honestly its sounding pretty good to me. The rest have just said "no gains" or "less rpms than a 355" or "you need change everything" I need to know what 51 cubes would actually change.. when using MY stuff.. lose 500rpms? 1000 rpms? gain 15lbft? 40lbft? help me out here.
clearly there is some other unfinished off topic business goin on here..
OK, this is just my opinion.
L31 heads, as good as they are, are still heads that were designed by engineers to feed a 350 cubic inch engine up to about 5000 rpm's. 350 cubic inches theoretically passes 506 cfm @5000 rpm's. 400 cubic inches theoretically passes 509 cfm @4400 rpm's. So, you might make the argument that the L31 heads on a 400 are theoretically done at 4400 and could stall at rpm's over that.

I'm aware that other members of this board will suggest that L31 heads will make power to XXXX rpm's and that's fine. I'm just trying to make some sense to the OP.
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  #35 (permalink)  
Old 12-20-2012, 06:51 PM
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Quote:
Originally Posted by vinniekq2 View Post
OMG! I feel sorry for the poor car hop girl at the drive in that gets the combo wrong! wrong tomato:cheese ratio with the wrong amount of onion rings.Wont get enough quench with a small rootbeer.Have to watch the compression in order to get the bun at the correct installed height. The roller skate wheels are the wrong diameter causing poorly matched RPM for the distance to the kitchen.
Thanks Vinnie, LMAO.
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Old 12-20-2012, 06:55 PM
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Originally Posted by cadillacdave1 View Post
350 vs 400. With the 400, you are looking at an extra 40lb. ft of torque and an extra 40 horsepower, with the same cam as the 350, all of which will occur lower in the RPM range. You can also cam up a step or 2 with the 400 which will handle a larger cam. Peak Hp will be 400-500 rpm lower in the 400.
even if there was zero HP gain, and I gained 40 lbsft at launch rpms... thats worthwhile IMO..
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  #37 (permalink)  
Old 12-20-2012, 07:03 PM
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Originally Posted by techinspector1 View Post
OK, this is just my opinion.
L31 heads, as good as they are, are still heads that were designed by engineers to feed a 350 cubic inch engine up to about 5000 rpm's. 350 cubic inches theoretically passes 506 cfm @5000 rpm's. 400 cubic inches theoretically passes 509 cfm @4400 rpm's. So, you might make the argument that the L31 heads on a 400 are theoretically done at 4400 and could stall at rpm's over that.

even with a tiny 216 duration cam all my vortec 350's pulled well past 5000. the 230 duration combo would pull my lifted fullsize 4x4 truck to 5900rpms in fourth gear.. In my expereince they easily support 6500rpm shift points on a well cammed 355. So if a 400 would peak 5500 and hang on til 6000 thats plenty for me if it charges out of the hole harder..
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  #38 (permalink)  
Old 12-20-2012, 07:13 PM
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Quote:
Originally Posted by cr480r View Post
even with a tiny 216 duration cam all my vortec 350's pulled well past 5000. the 230 duration combo would pull my lifted fullsize 4x4 truck to 5900rpms in fourth gear.. In my expereince they easily support 6500rpm shift points on a well cammed 355. So if a 400 would peak 5500 and hang on til 6000 thats plenty for me if it charges out of the hole harder..
Just because it revs to an RPM does NOT mean it makes power there. A lot of people think that just because they can "feel it pull" at a certain RPM then it must be making big power. That's part of the reason everyone that owns a sbc with an aftermarket muffler is making 500+hp, they just hope and wish and think about the power until it's magically there.
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  #39 (permalink)  
Old 12-20-2012, 08:10 PM
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The thing about how new cars w/o a lumpy cam can run higher CR than we can w/sbc carbed engines is mainly because we don't have electronic feed back from sensors to a computer that can retard timing when knock occurs, trim the fuel/air ratio, and change the cam timing just to name a few.

Now that's not to say we cannot use higher than 'normal' compression on a finely tuned engine. But w/only about a 4% (according to prevailing opinion) gain- all else being equal- to be had for each point of CR, I see no reason to run at the ragged edge of detonation. And I don't believe that's what TI is saying to do, either, but I do not presume to speak for him- he can do that just fine w/o my help.

Too much of ANYTHING is not good. Like the medical profession says, "The only difference between a poison and a cure is the dosage." I keep the CR for pump gas engine w/iron heads in the 9.5:1 range and aluminum a point higher, max. BUT- the Vortec (and other) modern fast burn chambers allows more CR w/o detonation than what could be safely used in the older heads. Obviously cam timing matters, as does ignition timing, air/fuel ratio, plug heat range, air inlet temps, engine coolant temps, etc. So there is no ONE right way. ALL the parameters have to be considered.


DCR vs. the real world:

The thing about DCR is (IMO) it DOES try to account for what an engine "sees" in in a running condition. That's the whole reason in calculating DCR in the first place. Now, if DCR used cranking pressure as a datum point, I could see how an argument could be made that it doesn't reflect what a running engine sees, but it doesn't.

DCR is not the end all, do all of engine parameters. But it IS a 'tool in the chest', so to speak. I think the more info the better, at least if that info is able to tell something useful. And DCR has- in the right hands- been shown to do just that.


Vortec heads vs. cam timing:

The following are my opinions.

The L31 Vortec head is probably the most over-cammed head GM has ever produced!

Guys think that because it's said to flow better than the old Bow Tie heads, they can run 240 degrees @ 0.050" duration, no problem. If it were only that easy...

The facts are the heads do not continue to flow well cammed much more than about 0.500" lift and 224 degrees on the intake side. And even there the exhaust is lagging well behind the intake, ratio-wise, and needs help. A split pattern cam will help but the exhaust port actually should be ported to gain the intake to exhaust ratio that's needed. And to use more cam effectively, the head needs help on both sides.

I say to use the Vortec head as-is (with the usual clean-up, valve job/guides, etc, as needed). If more head flow is needed, go to the aftermarket.

Last edited by cobalt327; 12-20-2012 at 08:25 PM.
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  #40 (permalink)  
Old 12-20-2012, 08:19 PM
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Just because it revs to an RPM does NOT mean it makes power there. A lot of people think that just because they can "feel it pull" at a certain RPM then it must be making big power. That's part of the reason everyone that owns a sbc with an aftermarket muffler is making 500+hp, they just hope and wish and think about the power until it's magically there.

well obviously i shift past peak. But who doesnt to some extent? In some applications a lil over rev is very helpful.. like in mud.. or climbing up a sand dune for example.. I believe people sell these heads short. most cookie cutter street builds have low compression ratios and streetable torque converters, so of course they work best with the smaller cams... small cams dont pull as far as larger ones...true story. If a statement was made like "vortec heads are done at 5500 on street engines" i would agree with that, but circle track guys have proven over and over there is more hp potential to be found with these.. it comes at the expense of streetability... and i have already stated that is no concern of mine. its purely a toy.
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  #41 (permalink)  
Old 12-21-2012, 08:32 AM
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Quote:
Originally Posted by cr480r View Post
well obviously i shift past peak. But who doesnt to some extent? In some applications a lil over rev is very helpful.. like in mud.. or climbing up a sand dune for example.. I believe people sell these heads short. most cookie cutter street builds have low compression ratios and streetable torque converters, so of course they work best with the smaller cams... small cams dont pull as far as larger ones...true story. If a statement was made like "vortec heads are done at 5500 on street engines" i would agree with that, but circle track guys have proven over and over there is more hp potential to be found with these.. it comes at the expense of streetability... and i have already stated that is no concern of mine. its purely a toy.
almost everyone revs past peak power when racing, that has nothing to do with the point. Your cam is too big for your rpm range, by a very good margin, you can think and wish and argue about it all you want but it is what it is. It will run, but you're giving up a LOT by not using a smaller cam. Power, torque, fuel, durability, etc.
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  #42 (permalink)  
Old 12-21-2012, 08:47 AM
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you new hydraulic cam is not all that big really. What are the rest of the specs on the cam?lobe separation
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  #43 (permalink)  
Old 12-21-2012, 09:20 AM
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Originally Posted by ap72 View Post
almost everyone revs past peak power when racing, that has nothing to do with the point. Your cam is too big for your rpm range, by a very good margin, you can think and wish and argue about it all you want but it is what it is. It will run, but you're giving up a LOT by not using a smaller cam. Power, torque, fuel, durability, etc.
Check out the 280xfi cam from Comp, but have it ground on a 108-110 for your combo instead of the 113 they usually offer.

It's a good match for ported vortec heads.
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Old 12-22-2012, 01:06 AM
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Originally Posted by vinniekq2 View Post
you new hydraulic cam is not all that big really. What are the rest of the specs on the cam?lobe separation
240/244. 108 sep. .335 lobe lift.. will give .536 with my rockers
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