MrVette83

A friend has built a 383 in a 98 Corvette. The tuner has told him the car feels sluggish and he thinks the cam is too big for the intake and is keeping the car from reaching it's full potential. He's now wanting to get some input on specing a new cam for his setup that will give him the most potential. So for you cam gurus out there, give me/him some input. The engine specs are below. If you have any other questions ask away and I will answer.

383cu in
12:1 Compression
215cc Trick Flow heads
Fast 92 Intake
Ported LS2 Throttle Body
Cam Motion Solid Roller Cam, 256/264 .680/.680 110+4
Comp solid lifters
T&D shaft mount rockers

Daniel

David Q

If the intake is the problem, why not just replace the intake. It is a giant cam, maybe could use some thing in the .615-.620 lift with a 240's duration if he really wants to do another cam swap. Fast 102 and some head work would be my route.

MrVette83

Thanks for your input. The heads have already been worked over and have a really good flow rate. I don't have the CFM for you but I remember the figures were good. I'm trying to reach my friend now to find out about the 102 swap. That seems to be a fairly obvious transition without having to pull the front of the engine apart. I would think there has to be a reason he hasn't already thought of this.

h0t

That is a pretty huge cam for that motor.

Agreed with post above on cam specs.

Or you could fully cnc/port/polish the heads and get a NW 102/LSXR 102 and fully port and polish those too...

From your post it sounds like the driver wants a little bit more of a street car whereas the motor specs lean more towards a track car.

MrVette83

Yes, it is a street car. I tried to talk him out of building an engine with compression that high and a solid cam that big. He wouldn't listen, now he has to redo some things. Thanks.

A.R. Shale Targa

iTrader: (2)

In order for an engine with that much compression to run on anything other
than race fuel probably mandates a cam with that much duration to bleed
off some cylinder pressure. Definitely the FAST102 upgrade(Mamofied)
Maybe heads with a 225-240 cc runner volume because he has the inches to
pull on a larger port, and like the one post said "a 240ish @ .050 cam" which will also be easier on springs and not need periodic valve-lashing like most
solid rollers need.

jimbob

iTrader: (4)

1. Not going to touch the 12 to 1, I use it all the time. Just watch heat or road racing (you can add a splash of 100/105 octane if needed).

2. A solid roller knocks about 6-12* duration from the actual (this depends on lash and cams ramp rates). So, really 248 duration with .660- lift with .020 lash.

3. Problem is with the manifold and cam combo.

A FAST LXR 102 would peak @6600ish or so with 383. His peak would be lower with that 90 version. With a cam that wants to rev to 8k and peak at 7500rpm, he is really off with that intake.

Another problem which does affect the ability of the combo to rev regardless of intake is DCR. DCR is much harder to calculate correctly with a mechanical roller than with a hyd roller (due to lash variations on the base duration numbers). And the Intake ABDC@.05 with this cam, "I bet" is not 46-48 degrees for this manifold to work correctly.

Basically, you have a cam that wants to peak at 7500 rpm, a manifold combo that wants to peak at 6600 or so, and no real idea of DCR (only SCR) and an ABDC of unknown number which could really affect your torque with this combo and its ability to rev.

Fixes...ported SP. or cam with 10* less duration (if mechanical). Custom Hyd roller in the 240's range that can be calculated to get the proper ABDC and DCR. Just because he has 12 to 1 doesn't also mean his actual DCR is anywhere useable....

While you can't go small on a cam with 12 to 1 SCR you can go small enough and get the correct abdc (playing with the ICL) and get the DCR below 8.8 It could be in the 7's for all that we know..And that will make a nice doggie rev with a big cam.

180ls1

iTrader: (4)

well its a good thing its on 110+4 and that it is at 12 to 1 compression. Even with that, the car will be pretty dogish down low because of the duration of the cam.

What does the car weigh and what gear is in it? Transmission?

180ls1

iTrader: (4)

is he looking for more power down low when he is driving or racing?

jimbob

iTrader: (4)

If I was setting it up, I would try a good single plane and see what happens (besides put those rockers to good use). I would also set lash as tight as possible (lowest lash cam manufacture recommends)...It might surprise him...And have a monster that revs to 8K rpm that pulls real hard. It's only money right..

180ls1 makes a great point. What are his goals..... Has he dynoed or are you just going off tuners BUTT. That manifold combo with cam still needs to be fixed if not going smaller cam. How about dynoing, and we could maybe see the double torque spike of a to late ABDC (although this doesn't always show up on a dyno, it sometimes just comes out as low/odd shape tq in the midrange). He may be surprised at what it does up past 6k rpm.....

Jim

MrVette83

Thanks for the info Jim. I'm forwarding it on to him. The car is a street car that sees the strip on occasion. He's had C4s and Gen 1 Camaros his whole life and all have been fast. The first car he built was a 68 with a 377 that put 502 to the wheels with a 100 shot. He knows way more than me about SBCs but I feel in this build he simply tried to build an engine around a big cam and now he's netting the results. I'm not sure of his goals and I've emailed him your two posts.

180LS1, the car has 3.90 gears and the mn6 transmission. The car weighs in the same ballpark of a standard 98 C5 as it has a full interior and glass roof. He did build a roll cage for it so it will have a little extra weight. And the valve lash is set a .010.

SOMbitch

iTrader: (8)

IMO that is not a good setup period. Nothing but mismatched parts.... With the right intake and gear it might be a decent track car but that cam will never make a good torquey streetcar regardless. The "right" intake will only move the power higher and be more of a street dog.

I don't know enough to spec cams but the best 383ci STREETCARS I see with those heads are HR cammed high 230/low240's intake duration with a 4*-6* split on a 113/114...

I would love to see a graph where that combo starts making power, where it peaks and how it carries power just for insight....

jimbob

iTrader: (4)

Aaaaaaa...............If this is a street car, I would sell that mechanical cam and go hyd roller. You could turn on the knock sensors, and get a proper specked cam for that combo... On a streetcar (some strip) 383, I like 235ish to low 240 intake for a duration (just like SOMbitch mentioned) but you can't go to small of cam with out really retarding your ICL, so 240ish looks to be closer to your needs. Set the DCR at 8.5-8.7 and abdc 46-48 (maybe 49-50 if you have to). That thing with those smaller intake ports he has and correct cam would feel like a rocket. As an example I used a 236/242 cam specked for a basic 402 with 2.5 Texas ported heads (these were left over from his 346). By just making sure his abdc was correct and that he had decent DCR 8.3, SCR was only 11.0. The car (3600 race weight) with CAT converters, full corked exhaust, and a heavy 9 inch, ran 10's first time out in the summer, and against 15mph head wind. I'm a fan of a small enough cam to get the job done.

Or, you could just go big SP manifold and hope he has enough head...Actually, we're building a 383 now (old school) with 18* heads, 14.4 to 1 comp, ethanol mixed with race fuel, Sheet metal intake and 260/272 @ .712 lift mechanical cam. The wide exhaust for our combo is for 400 N2O shot. Your basic low 8's car. But I would have no doubt that off juice low in the rpm this will be a little soft (even with that compression).

I don't do cams on this site, but "PAT G" does..have your friend give him all the info + "REAL WORLD," what he really wants out of it......ect, ect, and he'll spect a proper cam for him.

Jim

180ls1

iTrader: (4)

Agreed, even though that is one of the better off the shelf intakes out there it is not well suited for this setup. Have him Email PatG with specific goals in mind about what he wants and what the exact setup is and let him spec the cam. That would be your best bet, if it were me i would knock at least about 20 degrees off the intake and exhaust duration.

That fast 92 just isnt going to do the job with that cam, a ported fast 102 would hold up better imo if he kept the cam but thats even pushing it and then you run into issues with how much air the heads will push.

MrVette83

Thanks guys, I will let Lewis know. Sorry for the delay in getting back here, tax time sucks.

MrVette83

Just an update to those who responded about this problem. It appears the problem was not actually in the cam itself. The reluctor wheel was 3deg off and was causing the engine power issues. Doing a few different things to the car at the moment. I'll post dyno figures once we get them. It may be near the end of the month though. Have a great weekend.

MrVette83

Update with results. The car is back together and he took it to LSFest this past weekend. He wound up entering the Dyno Challenge and took the first place trophy in the NA competition with 502hp and 454 tq. Dyno sheet, pics and one short vid of the car upon initial start up below. Thanks for all those who helped by giving input earlier this year. The engine still has all the above components on it although he is now looking at larger intakes.







http://youtu.be/qyiMJBkrkjs

Thanks again for all the help.

Daniel

gt35built

iTrader: (1)

That cam is excessively big. Why bother with intakes when a much smaller cam could make the same 500hp at ~6300 rpm with the fast 92. Not to mention it would improve drivability.

That cam is huge! Have someone like patG or EPS spec a cam for the setup and see how it compares to the current one.