As some of you are aware, I'm slowly but surely selecting and buying parts for a new 383 that is going in my Grand Sport.

Although the car is primarily used for track days (road course), it also sees time on the street as well. As a result, my goals are not all-out power but rather a nice balance of power and street manners. This means that a cam that has tremendous hp and rpm potential but horrible idle and low rpm cruise qualities is a non-starter.

Today I finally had time to sit down and run some simulations of various cam profiles in my engine. Of particular importance was using the correct specs for my AFR cylinder heads, including valve sizes, port size, and flow from .200 to .600 lift in .100 increments.

I spent time pulling various lobe profiles out of the Comp and Crane catalogs, as well as the GM HOT Cam, 846 Cam (both of which I used in my stock engine at various times), the GM 847 cam, and several cams from friends and forum members.

My going in position was that I wanted a cam that was ~230/236 (I/E) from a duration perspective and .590 / .610 lift on a 112* LSA.

I ran the sim from 2000 to 6500rpm. All results are at the flywheel (brake hp).

Generic cam specs:
Intake
Opening: 34*
Closing: 73*
Exhaust
Opening: 82*
Closing: 32*
Lobe Centerline, deg
Intake: 110
Exhaust: 114
Lift
Intake: .590
Exhaust: .610

Results: peak tq 487, peak hp 537 / Avg tq 413, avg hp 347. DCR is 8.14. Idle vacuum is 15.2"Hg which suggests a slight chop at idle.

The GM 847 Cam resulted in the following:
peak tq 437, peak hp 503 / Avg tq 389, avg hp 323. DCR is 7.71 and the idle vacuum is 13.7"Hg which says the idle will be noticeable. This suggests the 847 is showing it's age as has often been claimed.

I ran several more profiles, focusing on the 230/236 duration numbers but varying the lift, lobe centerlines, etc. There was not a lot of change in the results I saw versus my "generic 230/236 cam". Basically I was moving the curves around a bit. As a reminder, street manners are a must. Therefore a bunch more duration or adding a bunch of overlap isn't acceptable.

For my last run of the afternoon, I ran a profile a friend of mine has in his stock bottom 350 (he's making 374 to the wheels with CNC ported stock castings and what turned out to be a broken a valve spring). Here are the cam specs....

Intake
Opening: 29*
Closing: 70*
Exhaust
Opening: 77*
Closing: 29*
Lobe Centerline, deg
Intake: 110
Exhaust: 115
Lift
Intake: .605
Exhaust: .622
LSA is 112+2

Results: Peak tq 491, peak hp 538 / Avg tq 419, avg hp 349. The DCR is 8.38 and the idle vacuum is 16.6"Hg which suggests it'll have minimal chop at idle, and frankly if I tune it to idle at 875 it's probably darn near chop free.


Would like to hear opinions, particularly on the last cam

 

Get a custom cam:
http://www.jonescams.com/2006catalog_003.htm

 

WOW!! I'm surprised my camshaft did so well. Jim, you've driven my car and the camshaft works really well in a 350ci. You can lug it around at 1000 rpms without a sign of cam surge. There use to be a forum member running this camshaft in a 396ci LTx, just can't remember his forum name. Having said all of that, I would probably try to find a larger camshaft if I was building a stroker LTx.

 

Careful w/ your cam choice.

People always talk about cam lope, or idle. They never seem to discuss exhaust smell at idle w/ a higher duration cam.

I have a 93 LT1 6spd w/ the hotcam. I have LT headers w/heated O2 sensors. I do not run cats on my setup. I have had a custom tune by both Ed Wright and Alv!n. The smell at idle is absolutely terrible. It 'smokes' you out of the car and makes you not want to drive it. The smell sticks on your clothes and lets people know you've been driving the corvette.

I am also not a very smell sensitive person. Its just that bad.

Maybe its bc I have speed density based system, and the MAF systems better tolerate mods.

Ive been round and round on here trying to figure out why my car stinks so bad. Nothing.

So theres more to consider then lope or smooth idle in a cam choice.

 

I ran the LT4 HOT Cam and then the larger GM 846 cam for years. Always with cats. Smell was not an issue.

The cam of interest has duration figures of 224/230 @ .050, which I recall to be less than the 846 cam I ran in my 350 (vs the new 383). My hypothesis is that the power is being made via the AFR heads and the .600+ lift of the camshaft. Peak hp is around 6100rpm and it's all done by 64/6500 which is fine for me.

I appreciate the feedback. Smell is certainly a concern. I suspect it's the lack of cats that drives what you're experiencing.

 

I have a 95 with headers, stright pipes, no cats, and PCMFORLESS tune. There is zero smell inside the car even with the top down. You have to literally sit down behind the car to smell the exhaust fumes. I'd also like to know if it's the cam addition or the speed density causing the smell issues. I'm about to swap out the stock came on mine for a more radical one. Something around 22x/23x .56x/.56x 109 LSA maybe.

 

A friend of mine pulled the cats on his stock 94 and it smelled like that. He was even embarrased to drive it on a date. Get some cats and maybe a little better tune and the smell won't be an issue. It amazes me why so many want to run without cats.

 

originally, i thought itd be great to ditch the cats. For peak power and weight reasons. Man, I sure wish I didnt do that!!!

Hey see if your sim software can predict how crappy the exhaust will smell with a more radical cam as it pukes out unburned HC's at idle.

As for a better tune? I had it tuned in person by the best person here.

 

Look for a cam without split durations. It will slightly reduce choppiness and have a better overall low-end. 232-236 looks like it would be acceptable for street, with .62x lift should net you 20ft-lbs more torque over the generic and a possible 5-10 increase of average HP.

 

I ran the sim, provided it's predictions, and asked for comments. You mentioned smell. Good input as I stated.

For the sake of clarity I also stated I have been running a more radical cam in my 350 with no smell issues. Mike is running the 224/230 cam in his stock bottom '94 with no smell issues (we used to live near each other when I lived in St. Louis. I've been in, around, and have driven his car). Both of us have cited a key difference between your experience and ours being the use of cats. Mike uses bullet cats with his LTs. I had factory cats. The 383 will have RT bullet cats aft of the EM LTs.

Not sure why the dig at running the sim. If someone wants to pay for it, I'm more than willing to swap multiple cams into my 383 build versus simulating the results and using the data to make a decision.

 

Jim,

Man that 847 is a stone!

I didn't see your posted Sim CR...assume less than 11 to 1...might be a bit low for the big cam to run. Nonetheless as you said, technology must have come along way from that cam (unsure how old that grind is!)

I just did a back to back test of no cats and cats on my newly installed EM headers...lots of smell/loud before...with cats almost no smell and actually civilized music out the tail pipe. They make a significant difference!

Which software are you using?

 

I run no cat on my 383 with a large 230/245 cam on a 109 lsa and have no real smell of exhaust. Not sure why the hotcam on a 350 will have that bad of a smell, its not a big cam at all.
its in the tune, run it lean and it will work just fine at idle but you may have abit hotter exhaust temps. not a big deal tho.



Whats the specs on that last cam at .050? I'm getting 279/286 advertised... i do like what i see with that. I love the higher lift too. 112 lsa is ok, gives nice idle and smooth torque curve but i wouldnt be afraid to try a 110. 58 degrees of overlap on a 383 isnt that bad at all, infact thats very mild. I run 78 degrees and i think my car is very well mannered, but its very choppy and loud. It drives extremely well tho for how it sounds and the power it makes. Can putz around 1100 rpms with converter locked at very low speeds no problem. Tuned out 97% of any cam surge so the car was very nice around traffic even tho it idled 950-975 rpm. It was almost two-faced, it sounded wicked and was a powerfull motor, but drove no worse than stock L98, just louder. In fact i wanted to try a 240/243 cam on a 108 lsa since my car is more street strip oriented

My suggestion for a LT4 383 with any great flowing head would be something in the 233/236 range on a 110 lsa with near .600 lift with w/e rocker you run. That should be pretty darn streetable and make killer power and give abit of idle chop that we all love, but it wont kill off your streetability. Should peak near 6000-6200 rpm.

 

MTI installed the XE COMP Cams 230/236 cam in my 396 when they built my motor eight years ago. Been real happy with this choice. Primarily bracket race in the Texas Muscle Car Challenge series pro class. Dyno'd at 415RWHP/420RWTQE. Fairly mild on the street.

Gross valve lift is 510 Intake 520 Exhaust
LSA 112 0
Lobe Lift 3400Intake 3470 Exhaust at 108 intake Center line
Duration at .050 230/236

Have interchangeable high flow cats and off road pipes. Pick up 10-15 LBS of torque with the off road pipes on. No smell problem.

 

Played around a little more tonight and can tweak another 5hp and 8tq messing with the duration...little more on both intake & exhaust and less split as Master_Shake suggested. Need to mess with the lift just a little bit next.

Orr89rocz...the duration on the last cam I listed is 224 In / 230 Ex @ .050

Tim, my CR is 10.9:1, so yes just a tick under 11

Red Rocket...I'm surprised at the lift numbers, but nice power

 

Hey STL94LT1 what cam are you using ?
Is it A out of the box cam ?

 

No, it's a Comp Cams custom grind.

 

A buddy of mine on another forum has a motor similar to my 383. His has 10.5 to 1 or so compression and holley stealth ram. AFR 195 heads as well. His custom grind was a 226/232 cam with mid 500's lift on a 112 or 113 i think it was. Very nice cam for that setup. Extremely streetable and makes darn near 390whp or so judging by his track times and its not 100% dyno tuned. His car traps about 2 mph less than mine did and i made 400whp. His car may be heavier than mine too tho

 

Hi Jim

Kevin here, before I got the GS I raced my 68 with a 377 with ported bowties and an 850 Holley and had a Sim on Perf Trends EA3.0 for it.

Had a Crane Solid cam and made so much torque it couldnt hook up on 285-40x15 Yokos. From memory 234/248@050 and 512 lift but will need to check. It was streetable just until I put a button flywheel a 3-plate then it wasnt!

Contact me through the register and ill give you the specs as I dont logon here that often.(But I should have because I missed out on those heads!!!!!)

Cheers
Kevin

 

97GS, could you do all who plan on a build similar to yours and sometime down the road make a complete parts list with part numbers for all of the parts you had to buy for your motor. Thanks a lot.

 

Jim, run your sim using a 224/236 on a 112 or even a 113. I recently used that cam with high lift lobes in a 350 LT1. The combo was AFR 195 LT4 Comp Ported Eliminator heads, Crane Gold race 1.6 rocker arms, Edelbrock LT4 intake ported to match, Long tube headers by Hooker/Jet Hot and a CAT LESS exhaust. I was amazed that the combo yielded 400+ on my dyno, in a 1995 F body with a M6 transmission. Drivability was excellent, it had a lopey idle at 800, no noticable cam surge anywhere.