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Discussion Starter · #1 · (Edited)
Here's my combo:
383 stroker
vortec heads, 9.4:1 compression
performer RPM and edelbrock 600 carb
headers and 2.5" exhaust
3.55 or 3.73 gears, possibly 3.23 (don't have this yet, depends what deals come along)
3000 pound car, th350, stock converter

I'm thinking of getting a lunati voodoo cam (similar to comp XE), here are the specs:

duration at .050": 213/219
lift: .454"/.468"
112 LSA

Is this cam too small? This is a street car / daily driver, I want a cam that has a good idle and fuel economy, but I don't want to cut it too short and miss out on good power.

The next step up in the voodoo series of cams is this:
219/227 duration, .468/.489 lift, 112LSA
I'm casually thinking of this also but I figure it would want a bigger than stock converter and wouldn't be very good on gas

Any thoughts?

Russel
 

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I'd go for 1.6 rocker arms to get all the lift I can. But you must check to be sure if your valve seals to keepers clearance can stand more than .475. Some heads will, some won't. Rumor on this site has it that springs/keepers can be had that will allow up to .550 without head modifications.

Also spring pressures more than 300# over the nose with agressive cams are pulling the rocker studs out of the heads. 300# is max for a flat tappet cam anyway. Beehive springs would be a good idea, since they supposedly cure the clearance problem and the high poundage problem. If it were me I would always pin the studs to prevent pulling out.

The best thing you could do for your "street" driver power is tighten the lobe separation. Ideal is 108*, but might add some lope to the idle while it increases mid range torque significantly. Talk to your cam company.
 

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I had a vortec headed 355 with the xe268h (224 230 @.050 .477 .480 lift 110 lsa) that I used as a daily driver. I was really happy with it. In a 383, it will act a little more mild than in my 355 as far as the streetability goes. I had a 1900 stall 700R4 tranny (overdrive), and a 3.90 rear gear. That was in a 3400 lb car and it got ~17 mpg on the interstate.

Adam
 

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The Vortec ehads dont really flow much more at lifts over .500".

I like a cam with around more exhaust duration at 0.050" than the intake.

the HT383 that GM sells uses a 196°/206° duration at .0.50" with lift of .431"/.451" on a 109° LSA. It is rated at 340 hp @ 4500 rpm and 435 lb/ft @ 400 rpm. This is the same cam that is used on the Ramjet 350 crate but in that setup its used with the 1.6:1 roller rockers for .461/.481".

for the ZZ383 which uses the same shortblock as the HT383, but uses the 210cc intake port Fastburn Vortec style heads and their 12370846 roller cam with 222°/230° duration at 0.050" with lift of .509"/.528" on a 112°LSA. The ZZ383 is rated at 425 hp @ 5400 rpm and 460 lb/ft of torque at 4500 rpm. The ZZ383 uses 1.5:1 versions of teh same 1.6:1 roller rockers the Ramjet 350 uses.

I know a guy who is running a Vortec headed 383 with the stock 1996-99 GM truck CSFI 19 pph poppet injection intake manifold and is dynoing at 330 rwhp and 380 rwtq and runs a 13.7 in his 2wd reg cab shortbox fullsize truck.
He is running the GM LT4 Hotcam with 218°/228° with .525"/.525" lift with 1.6:1` rockers or .495"/.495" lift with 1.5:1 rockers on a 112° LSA.

I do like that cam you were talking about, this 1: duration at .050": 213/219
lift: .454"/.468"
112 LSA
The lift will work and the duration is fine. It will work well with your intake and light vehicle weight.

peace
Hog
 

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fiscus said:
One other this I'm wondering about is if my compression ratio will be too high at ~9.4:1 to run cheap gas with the small cam (213/[email protected]", 454"/.468"
112 LSA)

Should I try to lower my compression ratio or will the pressure be good?
the HT383 runs the same heads as you and teh same comp. ratio as you and runs a much smaller cam that you wnat to run. The HT383 runs just fine on 87 octane. You'll be fine.

peace
Hog
 

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Hogg said:
The Vortec ehads dont really flow much more at lifts over .500".

I like a cam with around more exhaust duration at 0.050" than the intake.


peace
Hog
Curious.

Why not lift a cam .550 when the heads max out at .500 ?
Why do you prefer an exhaust biased duration?
 

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fiscus said:
One other this I'm wondering about is if my compression ratio will be too high at ~9.4:1 to run cheap gas with the small cam (213/[email protected]", 454"/.468"
112 LSA)

Should I try to lower my compression ratio or will the pressure be good?

If you run an ideal tighter LSA, the dynamic compression will be lowered while increasing torque 20-30 lb/ft..
 

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xntrik said:
Curious.

Why not lift a cam .550 when the heads max out at .500 ?
Why do you prefer an exhaust biased duration?

Agreed, if your heads max out at .500 you can hit the max point twice and stay in the range longer with a bit more lift.

I've seen some data that vortecs are somewhat weak out of the box on exhaust ports. Many people run a split duration with them to compensate.

K
 

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killerformula said:
Agreed, if your heads max out at .500 you can hit the max point twice and stay in the range longer with a bit more lift.

I've seen some data that vortecs are somewhat weak out of the box on exhaust ports. Many people run a split duration with them to compensate.

K

But is that the correct thing to do? Or just popular?

I am trying to make you think, ok.

Opening the exhaust sooner and closing it later..... That adds exhaust flow at high rpms... at low rpms you don't need more flow...... but reduces the length of the power stroke because the exhaust valve opens sooner, thus reducing torque. PLUS those cams are ground with a wider than ideal LSA to preserve idle, reducing torque further so a little more can be gained at the higher rpms. They give up 20 lbft across the board for 20 hp gain above 5500 rpm. Good trade?
 

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Discussion Starter · #12 · (Edited)
I called comp and they reccomended the XE-262 for me, its a 218/224 at 110LSA. Would this be a better choice?

Also, I already have a comp cam thats meant for circle track racing, its new in the box (came with my engine parts)

280 advertised duration
232/237 duration @ .050"
.483"/.483" lift
108 LSA

I wasn't going to use it because I figured it would be a gas guzzler, what do you guys think about this cam?
 

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Posted by xntrik:
"The best thing you could do for your "street" driver power is tighten the lobe separation. Ideal is 108*"

I've been doing some reading and happened on the article in which David Vizard did testing on a 350. He made best power with a 108* LSA. The same article (Popular Hot Rodding) shows a graph that substantiates Vizard's findings and uses cylinder displacement divided by intake valve diameter to find the best LSA for a particular motor. Using that chart with a 383 and 1.94" valve, the best LSA for the motor would be 104*.

xntrik, I'd like to have your input on this please.
 

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Tech, I'm sure Xntrik will have better feedback than this, but one good reason to run a wider LSA, in the 112-114 range, is that these kind of grinds are often recommended for supercharged motors. Perhaps that's what Fiscus is considering for the future, or then again, perhaps not. I don't understand why wider LSAs are recommended for supercharged motors. Maybe Xntrik will chime in on that as well.

Regarding favoring the exhaust with a longer duration, that is done because through years of experimentation, the cam companys have found that it works. Perhaps the gauge of what works is the dragstrip, or a dyno horsepower result, I don't know. Perhaps it's torque area under the curve (that'd be my hope). In recent years, using EA 3.0+, I have run literally hundereds of combinations of cams, and I found that using AFR 190s (with actual airflow as measured in the CHP tests setting their parameters) an equal duration cam (actually, sometimes a longer duration on the intake, 'cause the exhaust is so strong) seems to produce the best overall torque curve. I'm sure that the weaker flowing heads (particularly with weaker exhaust ports) would favor the longer duration on the exhaust lobe. I know that software dynos have their limitations, but for "A" to "B" comparisons, in otherwise similar configurations, I think they offer some good input.

I do think that for a stock converter, Fiscus might wnat to look at the XE262. Just a shade more tolerant than the XE268.

Pat
 

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techinspector1 said:
Posted by xntrik:
"The best thing you could do for your "street" driver power is tighten the lobe separation. Ideal is 108*"

I've been doing some reading and happened on the article in which David Vizard did testing on a 350. He made best power with a 108* LSA. The same article (Popular Hot Rodding) shows a graph that substantiates Vizard's findings and uses cylinder displacement divided by intake valve diameter to find the best LSA for a particular motor. Using that chart with a 383 and 1.94" valve, the best LSA for the motor would be 104*.

xntrik, I'd like to have your input on this please.
Sure, :welcome:

I follow Viz. Viz is correct.... he invented the graph. So I don't assume to know more than the teacher.

First that CC circle track cam fiscus has is not cataloged... but it looks like close to 100* overlap on 104-5? LSA. :rolleyes: Big valve, 406.

Note that when you browse a CC catalog using the 383 cube, when you see the specs, read the cam characteristics for the next smaller cam..... remember you have another 30 cubes over the 350, so the cam seems 6* tamer in a 383, like firestone said. (their commentary is for 305-400 engines :mwink: )

Viz says 1) LSA, 2)overlap which determines 3) duration, 4) always all the lift you can get.

104.5* ideal on Viz's chart, .8* wider for 2.02 valves. (fiscus never said)

Remember Using higher lift 1.6 rockers for more lift, you can add 1*, so I did 105.3 + 1 = 106.3. A 107 ? If you use small 1.94 valves knock off 1* of LSA. (longer rockers open valves .005 farther at .050 tappet lift, IS a bigger overlap triangle)

My incorrect 108 would be much better than the 112 he was looking at. 8* more overlap, but more torque too.

Viz says about 55-60* overlap for regular street use 383.

Comp is recommending the XE262H split duration 110 LSA (462 lift 1.5, 493 lift 1.6) to smooth the idle that gives tame 0 overlap at .050, 46* overlap at advertised. If we use 1.6 rockers this makes it seem 1* shorter.

XE262H spreads the longer exhaust lobe, opening the ex valve 8* sooner and closing it at the same point as a single pattern 262/106 cam.
This shortens the power stroke 8*, lessening torque slightly, but allows a better blow out at higher rpms. That might answer PatM's question

Trade off is less torque, but better hp above 5200, and a straighter torque curve, though less peak.

If we look at firestone's split pattern XE268 on 110* (477 lift 1.5, 509 lift 1.6) it has a 54 overlap, and 7* overlap at .050 (right in Viz's range, but on a wider than ideal LSA).

A single pattern 218/218 (262 adv) special on 106* (454 lift 1.5, 484 lift 1.6) we would have 50* overlap/ 6* overlap at .050,

Will our young man be able to live with that overlap with his stock stall converter, even though it will make more torque from 1800 on up? I think he needs an actual 1800-2000 converter with a tighter cam. Remember too, he has a dual plane intake :thumbup:

Since fiscus's 383 is underheaded and undervalved.... it should make gut busting torque (probably 380 from 2400-4500, 440 peak) and pull well giving up some at 5400 or so, being great with 3.08-3.23 gears, and getting decent mileage at fiscus's 3200 running weight, I personally would go to true 2000 stall.

Now throw a wrench in this... :rolleyes: ....

The dynamic compression might stand a single pattern 224*/106*(270 adv) cam 477 lift w/1.5, 509 w/1.6, 12* overlap .050, 56 overlap

Since CC would be custom grinding the cam anyway, a different flat tappet lobe from the catalog could be used, and the lift could be increased slightly to about 530 w/1.6 .....

And you thought this would be simple. :mwink:

Added= Since CC cannot assume nor control the variables of exhaust systems, etc..... they made a good recommendation in the XE262H cam.

Me. I think either firestone's XE268H or my 224/106 single pattern with a 2000 stall would be :thumbup:
 
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