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Old 08-02-2005, 06:24 AM   #1 (permalink)
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Red face Motor Experts, I need your help!!

I need vacuum the easiest way possible. I have a chevy 383 and its only pulling 13 inches at 1000rpm. Here are a few details you might want to know.

The cam I have - 112 center line 498 - 510 lift corrected 1.6 ratio = 530/542 lift. 228/230 dur @ 050

The intake I have - Edlebrock RPM

The carb - 770 Holley truck avenger

The heads - Dart severe duty 2.02/1.60 valves ... 1.25 springs 7 degree super locks comp cam parts.3/8studs guide plates.gasket match p.c seals.chrome moly retainers


Keith black hyperutectic.S.I. pistons 9.8 to 1 piston set




I need 15 inches of vacuum at 1000rpm, what is going to be my easiest way to get it? Ive played with timing and gotten nowhere so far. Any ideas????
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Old 08-02-2005, 06:30 AM   #2 (permalink)
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Change the cam, you've got to much overlap.
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Old 08-02-2005, 06:34 AM   #3 (permalink)
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Quote:
Originally Posted by MrWillys
Change the cam, you've got to much overlap.

What do you mean by overlap? Duration? Would you suggest a roller replacement?
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Old 08-02-2005, 06:44 AM   #4 (permalink)
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Quote:
Originally Posted by Leslie
What do you mean by overlap? Duration? Would you suggest a roller replacement?
It's just a little more complicated than that. let's just say you had the very same cam your running, but ground on a 116 LSA. This would give you less overlap. Overlap is when the intake and exhuast valves are open together. It allows higher RPMs, but at the sacrifice of idle quality and vacuum.
Roller cam: With the motor you've explained. Why not run a roller valve train. Drop down to a Comp Cams extreme 4x4 with 218 degrees of intake duration at .050. This will give you the streetability your looking for, but allow you to still have some upper rpms. Keep the 1.6:1 rockers as these only make a slight difference.
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Old 08-02-2005, 06:54 AM   #5 (permalink)
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Quote:
Originally Posted by MrWillys
It's just a little more complicated than that. let's just say you had the very same cam your running, but ground on a 116 LSA. This would give you less overlap. Overlap is when the intake and exhuast valves are open together. It allows higher RPMs, but at the sacrifice of idle quality and vacuum.
Roller cam: With the motor you've explained. Why not run a roller valve train. Drop down to a Comp Cams extreme 4x4 with 218 degrees of intake duration at .050. This will give you the streetability your looking for, but allow you to still have some upper rpms. Keep the 1.6:1 rockers as these only make a slight difference.

My goal is not really to make it streetworthy at all, I want it as hot as possible, I am being disqualified from mud drag racing for not pulling enough vacuum. As far as power building, Ive got pleanty as it is and dont really want to lose any trying to get my vacuum back up to meet regulations. I do already have roller rockers if thats what you mean, I thought a roller cam might be the next step in the equation.
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Old 08-02-2005, 07:16 AM   #6 (permalink)
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Quote:
Originally Posted by Leslie
My goal is not really to make it streetworthy at all, I want it as hot as possible, I am being disqualified from mud drag racing for not pulling enough vacuum. As far as power building, Ive got pleanty as it is and dont really want to lose any trying to get my vacuum back up to meet regulations. I do already have roller rockers if thats what you mean, I thought a roller cam might be the next step in the equation.
Different animal here. Call 1-800-999-0853 and speak to them and explain what you trying to do. This is the Comp cams help line. Your right about a roller pulling a wider range with less duration. i wouldn't want to do this to many times though.
Just remember the closer the LSA the more power you'll get, but with a shorter powerband. I guess I'm wondering if you shouldn't be down towards a 110, or even 108 LSA. Does your sport use tight LSA's with less duration, or is 112 ok with more.
I run 113 LSA with 210 @ .050 with .317 lobe lift for .507 total, but I had them grind it at 112 intake centerline to keep my upper RPM's. call comp in any event, it can't hurt.
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Old 08-02-2005, 09:57 AM   #7 (permalink)
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Quote:
Originally Posted by MrWillys
call comp in any event, it can't hurt.
Remember that green CJ6 that spanked you? That's what they did, called 'em & got a grind specifically for that application.

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Old 08-02-2005, 10:33 AM   #8 (permalink)
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Quote:
Originally Posted by MrWillys
Different animal here. Call 1-800-999-0853 and speak to them and explain what you trying to do. This is the Comp cams help line. Your right about a roller pulling a wider range with less duration. i wouldn't want to do this to many times though.
Just remember the closer the LSA the more power you'll get, but with a shorter powerband. I guess I'm wondering if you shouldn't be down towards a 110, or even 108 LSA. Does your sport use tight LSA's with less duration, or is 112 ok with more.
I run 113 LSA with 210 @ .050 with .317 lobe lift for .507 total, but I had them grind it at 112 intake centerline to keep my upper RPM's. call comp in any event, it can't hurt.


I talked to them and they said that the cam I have SHOULD be able to pull 15 inches at 1000rpms and that I likely have a vacuum leak elsewhere. My problem is I have no idea where? I took either and propane and went around the carb and everywhere on the intake I could think of to try and find a leak and came up with nothing. Not sure what to do now.
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Old 08-02-2005, 10:54 AM   #9 (permalink)
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Quote:
Originally Posted by TEX
Remember that green CJ6 that spanked you? That's what they did, called 'em & got a grind specifically for that application.

TEX


I talked to them, they told me it should be fine. I do not understand, I thought they would at least try to sell me something.
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Old 08-02-2005, 11:03 AM   #10 (permalink)
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15 in lbs of vacuum with 228 degrees of duration @.050 with 112 LSA. I don't think so. Call Crane and see what they think.
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Old 08-02-2005, 12:48 PM   #11 (permalink)
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Originally Posted by trkklr77
hey leslie, you should not be in the stock class. stock is the only class that does a vacume test.
Thing is a lot of guys WAY hotter than him are already in Stock class.

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you should be in at least ssv8 or unlimited. even then that setup is pushing it in ssv8.
He's nowhere near fast enough for Super Stock. Those guys are all running full-roller big-blocks up to 632".

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you can try a vacume pump or a vacume canister.
Not a legal mod.

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Old 08-02-2005, 12:52 PM   #12 (permalink)
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BTW, one could certainly argue that Leslie & those quicker trucks don't belong in the lowest class. Most of the Illinois events run a class even lower than that with even stricter engine swap & vacuum rules. But, I've found the better rigs in that class to be very competitive in Street Stock anyway. So, I just went with the one class.

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Old 08-02-2005, 01:08 PM   #13 (permalink)
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I do not want to jump up a class, heck I only got 3rd in the stock class. But the guys that beat me probably shouldnt have been in stock class either


I called crane, they didnt help much. I will call them or summit racing again and hopefully get a different technician this time. Im pretty sure I need a new cam, if a roller makes the difference, I will definately take that route.
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Old 08-03-2005, 12:32 AM   #14 (permalink)
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How about setting your idle mixture correctly?
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Old 08-03-2005, 12:50 AM   #15 (permalink)
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Get a set of quick bleed lifters like Rhodes. They will bleed off some of the duration at lower RPM and might give you that extra vacuum you need. They would also be the quickest solution.
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Old 08-03-2005, 06:10 AM   #16 (permalink)
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Get a set of quick bleed lifters like Rhodes. They will bleed off some of the duration at lower RPM and might give you that extra vacuum you need. They would also be the quickest solution.


Ive heard this mentioned and it does sound like a decent solution to try.
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Old 08-03-2005, 08:50 AM   #17 (permalink)
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Quote:
Originally Posted by Triaged
Get a set of quick bleed lifters like Rhodes. They will bleed off some of the duration at lower RPM and might give you that extra vacuum you need. They would also be the quickest solution.

I agree. I ran them on my last 350 with about the same cam you have. It idled real nice. I used Crane fast bleed lifter, I had read somewhere they didn't bleed off as much as Rhodes. Hot rod magasine just did a piece on Rhodes roller lifters you should read, same pricipal.

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Old 08-03-2005, 09:56 AM   #18 (permalink)
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Originally Posted by trkklr77
i got put in the ssv8 class and tagged third place and i am no where near this setup. i think one of 2 things happend, no one hot showed up except one, he won it, or the classes were way off from what you guys call ssv8.
My guess is different classes. Paul Karch (who ram-rodded the race Leslie attended) runs with the national circuit as well as numerous other "name" events in the Midwest. So, I would imagine he uses pretty "standard" rules. Also, remember that Leslie went to a drag rather than a bog & the rules will naturally be different at both.


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Old 08-03-2005, 10:34 AM   #19 (permalink)
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Originally Posted by TEX
My guess is different classes. Paul Karch (who ram-rodded the race Leslie attended) runs with the national circuit as well as numerous other "name" events in the Midwest. So, I would imagine he uses pretty "standard" rules. Also, remember that Leslie went to a drag rather than a bog & the rules will naturally be different at both.


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Bogs are scary! I am going to one on saturday. Which tires would you suggest? The 34x9.50 TSL's I just bought or keeping the 33x15.50 SX's on?
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Old 08-03-2005, 10:36 AM   #20 (permalink)
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I agree. I ran them on my last 350 with about the same cam you have. It idled real nice. I used Crane fast bleed lifter, I had read somewhere they didn't bleed off as much as Rhodes. Hot rod magasine just did a piece on Rhodes roller lifters you should read, same pricipal.

Blake


It sounds plausable, but if there is a problem with cam lobe timing to where both valves are open together for a period of time like Mr Willy's suggests, I do not see how bleeding off the lifters will make any difference. But I may not be thinking clearly yet.
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Old 08-03-2005, 10:43 AM   #21 (permalink)
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Bogs are scary! I am going to one on saturday. Which tires would you suggest? The 34x9.50 TSL's I just bought or keeping the 33x15.50 SX's on?
The 34's are infinitely better in the deep stuff as well, however there might be a 33" class - that's pretty common. So, be careful. If it were me, I'd put the 33's on the rig & bring the 34's & a jack along to see what class they put you in. The 34's though will absolutely be the better performing tire.

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