neat

Ok, I spoke with the engine builder today about a cam for my car. The engine is an LT1 based 383 with 11:1 compression, and forged guts. Everything was built with N20 in mind, so I plan to shoot it with a 100-150 shot once I have selected a cam. I had pretty much decided on this cam until today:

.536/.571
230-239
all on a 114 LS

That's the one competition motorsports in Las Vegas recommended, without knowing the head flow numbers. The engine builder uses a computer program to pick cams for him, this is what his computer program recommended:

.525/.535
232/232
on a 115 LS

I am kinda inclined to go with the engine builder's recommendations, because he had head flow numbers. Unfortunately the flow numbers have been lost, and only the cam profile remains.

The only reason I didn't go with that cam is because of the nitrous. I am under the impression that N20 really likes a split pattern cam, .010 isn't enough to make the engine happy on the bottle, IMO.

Another complication is the block has been decked, and the heads have been shaved a tad. Should I worry about valve/piston contact with a bigger cam? The psitons are 10:1 but the final compression is closer to 11:1 with the block decked, and heads milled.

What you guys think?

jburnett

I always want the flow numbers when selecting a camshaft...That's the PROPER way to do it. I would suspect he's using the same program I use which is Engine Analyzer Plus, a very expensive, very precise modeling program that I've found to be within 2% of the actual dyno numbers an engine produces... It has iterative functions that will suggest the best possible components for your specified application; cam specs, runner lengths, valve sizes, header primary diameter and length, collector diameter and length, etc... Now having said that and looking at the cam specs I have this to say:

Are you planning on running nitrous A LOT? Because in all honesty you'll be leaving a lot on the table naturally aspirated. If you're talking about only shooting 100-150 on this mill (assuming it's an all forged motor) you'd be better off camming it for N/A conditions. Yes, you'll gain quite a bit with these cam specs even on this very mild shot; but you'll give up even more when the little **** on the blue bottle is cranked clockwise! I would honest put a little more duration and lift in there and narrow the LSA to 114; that way you'll split the difference between N2O and N/A capability.
-Jeb

neat

The n20 use would prolly be about 20lb. worth a month. That's about what I went through on my TA, I figure it would be same with this.

So you would recommend something like a:

.555/.585
236/244
on a 114 ?

How would the driveability be on a cam that big? I have to have something my wife can drive around in the middle of summer with the AC on and not worry about it stalling at lights or anything. Thanks a TON!

:hurray:

jburnett

If you're talking about your wife driving it and seeking the utmost in "drivability" I would suggest something milder... The cam you listed first is very similar to one of my favorite "mild" N2O/blower/turbo grinds: mine is a custom ground piece from Crane that's 232/238 @ .050" with .575"/.595" lift with 1.6 rockers (.539"/.558" with 1.5) on a 114 lsa. This cam is very mild in a stroker with idle quality much like stock and will produce in excess of 525 hp on a well-built motor with good heads and 11.00:1 compression. On spray it generally picks up 10-20% over a more radical cam with narrower lsa.
-Jeb

lcvette

I have to agree with Jeb here,

unless your going for just nitrous numbers, use a N/A derived camshaft, one of my favorite grinds is 235/242 .567/.596 on a 112, but bump that LSA up to a 114. i have run this on 350 CI LT1's and the Idle at 950 was kind of lumpy, but still very streetable. just gave it a "HELLO" lope. power on the 350 of course was from about 2800-6800 on an M6 car with 4.10 gears so it was a pig out of the hole with the smaller cubes, but the extra 33 CI's should do two things here,

A- tone down the Idle lope some

B- bring the RPM power/torque range down the scale a little

we are now running a 242/248 .613/.619 112 solid roller in a 96 LT4 with hand ported AFR 195 heads that are now around 210 cc Intake runners and there is no P2V clearance issue with the heads milled about .008" and a stock deck height with a .039" compressed felpro head gasket P/N 1074. this motor is built strictly for having fun at the strip and makes power to around 7600 RPM on the little 350. Idle quality has left the building and is set at 1250 for any kind of steady rythm, but when the car hits 4500 RPM it begins to pull as if it were a boosted application.

Important, don't undercam your 383, you will regret it until you eventually decide to go back in and swap it which is about as fun as pulling nails. and adds additional costs with gaskets and time etc.. perhaps a comp cams CC306 or a GTP 6 cam for a shelf cam or something similar to the specs stated above would make for a fantastic combination. all this is of course relevent to the flow characteristic of the cylinder heads. no sense having a cam with more lift then the heads flow best at on the intake side, in that case a cam that ramped quickly and had longer dwell at the best peak lift flow point would be prudent. the split duration will help immensly with nitrous as the amount of nitrous added on the intake side will create exponentially more pressure in the chamber to be relieved on the exhaust side, so the larger exhaust duration and lift will help compensate and keep from robbing power from poor xhaust flow. the exhaust side cannot truly be analyzed with flow numbers at 28" H2O as the spent air fuel mixture exiting the chamber will be under a great pressure which would ultimately change the flow characteristics of the exhaust port. I am sure the software mentioned above takes this into consideration when modeling a camshaft selection for an engine package. hope this bit of insight helps, and keep us posted on the decision!

thanks,

Chris


[Modified by lcvette, 7:55 PM 8/20/2003]

JUAN J SANCHEZ

:iagree: with jeb unless your gonna spray all the time you should cam for NA and let the nitrous fall where it may. Good Luck! :thumbs:

neat

Ok, I'm ordering it this Friday.:

.560/.570
232/242
on a 114 (maybe a 115)

I dyno'd it about a week ago and it peaked at 5700, which is plenty high for my tastes. RPM breaks parts, I don't want to rev to 6500 to effectively use the power. Do you think I'll raise the power band beyond what it is now with the biiger exhaust duration?

I would go more lift, but my 383 has 6 inch rods and I've heard that you run into clearance problems with 6 inch rods and a lift above about .575, any comments?

:hurray:

SPD DMN

I am running a 230/238 with mid .5's lift on a 114 and I peak around 5900-6100 depending on air conditions. With better heads I would probably be peaking a little higher but I would expect with that cam on a 383 to peak around 6K +/- 200.

JUAN J SANCHEZ

Vette 92 , any idea how much power your making with that cam? What intake? heads? :confused:

SPD DMN

Juan,

Heads : Stock LT1 head castings that have been gone over a couple times and flow in the 260 range on the intake at .550 lift.
Intake : Stock LT1, ported by MTI.
Power: The last dyno was in about 100 degree heat and it came up right around 404rwhp/414rwtq [start excuses here] with an electrical problem up top and I made it about a mile from the Dyno before my Opti gave out completely [end excuses]. My MPH at the strip is generally between 118 and 122 with ET Streets at a 3600 lb race weight.

Overall it is a strong running car that is very streetable.

Chris

JUAN J SANCHEZ

Thanks! Vette92. I hope I run that good! Sounds like you got a stick? I'm hoping for 400RWHP give or take 20HP. I've got a old style SBC with 11.0:1, 280cfm heads @.500" and 383 cid. Should make 500HP or I'll take it back apart! Again, sounds like you got a good ride there! good luck! :thumbs:


[Modified by JUAN J SANCHEZ, 3:01 AM 9/3/2003]

neat

Thanks guys.

MasterDave

I gotta chime in here on this one. I've had 6 different cams in my engine over the last two years. My inclination is that for the street what you're choosing is a little large. Your split duration choice is right on though. The absolute best cam I've used to date in my 125 shot forged 355 (see sig for setup) is the Isky 270/280 megacam (hyd). This cam with 1.6 rr's for the 383 would keep your engine smokin' IMO. Great range of power. Isky part # is 201271/281-12. The engine has a definate idle but will clean out at the slightest blip of the throttle. My engine is power on at 2200 and over at about 6200, your 383 would come in lower and pull very hard in the mid range. This cam is very streetable and easy on the valvetrain. I'll use it in my next rebuild, maybe going to the solid version. :cheers:

neat

Well, its pretty much over. I ordered the cam tpday from combination motorsports. It's a bit on the big side, .565/.576 232/242 on a 114 LS, so we'll see how it does. Combination Motorsports didn't seem to think I would have to rev it much past about 6300 with the stock gear ratio's in the transmission to see the best power. Should peak right at 6k or so. I will dyno after install and post results.

FWIW I dyno'd 370 to the wheels last week. See the sheet here:
http://www.fearlessperformance.com

Handy7rick

I totally agree with this suggestion for an Isky cam, My experience is that Isky cams always make more power and turn more RPMs than any competitors of the same size( lift and duration) and they Last. When installed properly.I also, recommend using a cam such as this one with more exhaust duration if using nitrous although this cam will make quite a bite of horse power on its own.Using up to 10:5:1'maybe even 11:1 compression.Preferably 10:5:1 at most.

Handy7rick

That .465 lift will go easy on the valve springs as well as the rest of the valve train.

Handy7rick

Rpm power band on that Isky cam is 2200-6500, and my experience is they pull strong into Their power band Ratings.

ANTI VENOM

Good information, but that post was started 12 years ago.