I actually posted this earlier today and it never came onto the board. Weird. I hope it doesn't duplicate now.

Firstly, I checked and got ok'd by Chris to post this on the advanced tech. I had a thread going on LT1 and have gotten very limited help.

I seriously need cam and computer advice. My problem is I think, twofold. The car has been out of commission for a long time. Here are the cam details on the one that I just removed:

224 intake/236 exhaust @ .050
.570 / .590 Lift with 1.7 rockers (I actually have 1.6)

The above dyno'd at about 340rwhp and just fell down after 5000rpm. Weird since even a stock cam peaks at 5400. I also know of other 396 guys running this exact cam making 400+rwhp.

The current PCM is OBD I with Ed Wright tuning - just a preliminary tune to get things going. Obviously a dyno tune will have to follow to maximize performance, but could it be costing me 60 or 80 HP??? Do I need to use LT1 edit or some other alternative before proceeding any further? I thought that this set up would obtain around 420rwhp, but it is obviously well short of that goal. Am I just being unrealistic?

All pertinent car details and my preferences are show below. I have no intention of running this car at the strip. It is full weight with a suspension and brake setup better suited for autocross. Someone once described it as a 'drag strip engine in an autocross chassis'. A good analogy I think of a fast street car.

I would like 'some' lope in the cam, but not much... I can't have any vacuum or idle issues. I want to run the A/C in Houston Summers and be able to drive this in traffic without any lurching or bucking or any of that– i.e. my girlfriend has to be able to drive this car. I think a hydraulic roller and not a solid roller is the best
choice for me.

I would prefer a broad, flat torque curve (wouldn't we all). Though this engine should be of revving over 7000, I won’t be doing any 150mph Silver State cruises, so a long/flat torque line is much more attractive than high / peak HP numbers-I want a pounder and think a power band in the 3000-6500 range should be doable?

I would like to be able to use nitrous on this motor – but only very occasionally. If there is any power loss in the day to day driving to accommodate for a ‘nitrous cam’ I would rather lose power in the nitrous and keep it day to day. I have a wet kit for a dual 75HP shot that is not even installed yet.

What would a cam with 244/250 and .577/.600 lift act like? I hope I have included enough information and clarity on performance preferences. I know this is a long thread and that all of this information is probably too much, but I’d rather give too much than not enough. I simply do not know enough about cams to be able to make an educated decision on my own. I would really appreciate any advice you guys can give me on specific cam and computer recommendations.

Thanks in advance!
Mark Potter
Houston, Texas
__________________
1996 T/A. 396 LT1 stroker with M6 & Street twin clutch

Motor:
Patterson Motorsports built 396 corvette block (4 bolt mains) stroker motor with:
OBD I w/ Fastchips tuning (just an initial OBD 1 tune – a dyno tune will have to be done after cam installation) on all forged drivetrain- Callies crank, Eagle rods, Clevite bearings & JE Pistons
Note: compression ratio with these pistons and heads calculated out to 10.8:1
GTP stage II heads & lightly ported intake
Comp cams stud girdle kit & AFR hydra rev kit (high revving possible, but not necessarily wanted-more for ‘insurance’ than anything else)
Bullet proof Comp cams valve train (all came from GTP with the heads-magnum roller rockers, dual springs, etc, etc)
SVO 30# injectors
Extreme duty timing chain
Hooker ceramic coated long tube headers with Mufflex off road Y pipe & SLP dual/dual catback
58mm AS&M TB
160 deg Thermostat
WS6 factory hood w/ SLP airbox kit & K&N Filter
MSD 6AL & Timing retard
Taylor 10mm wires.
NGK's

Suspension & Drivetrain:
Moser 12 bolt with 3.73 gears
Hotchkiss STB
BMR LCA's & adjustable panhard bar
Custom SFC’s
Spohn track version torque arm
ZR1 wheels with Yokohamas- 275/40ZR17 and 315/35x17's
Baer Track front Brakes
ACPT carbon fiber drive shaft
1LE sway bars front & rear
ES poly bushings throughout (except tranny and motor mounts)
HAL shocks front and rear (lowered 1 1/2'' in front only)


One other thing has come to mind. The street twin clutch seems to be very much an off/on unit with little or no slippage. While probably fine for launches, it makes it tougher to drive in town – particularly since the disengagement point is way high in the throw… is there any way to adjust this or anything I can add or change to alter this characteristic?

again, many many thanks
Mark Potter
Houston, TX

 

Hey Mark just a side request mind editing your sig down a smidge to around 5 lines?

Thanks a bunch.

 

First off it's probably not the cam, even though that's a small cam for a 396 it's not that.

How about a few more specs......... if that page of sig isin't enough

Fuel pump setup?

Valve springs? What part number?

Maybe a ignition problem? But you have a 6AL????

The 340rwhp I think has more to do with a lack of fuel or a bad valvetrain problem. Those are the first things I can think of.

Anyone else have an idea? Something isin't right here and the problem is going to be obvious, when we find it cause that's big problem. Might be some simple mechanical thing, we would never know unless we saw it in person.

Bret

 

I'm going to throw my support behind Mark posting this here... hoping someone can help him out. We needed that "signature" to know whats in the car, and even more info.

I know he has been royally hosed by two of Houston's big name shops. The whole story would rival some of the Hennessy crap - it's truely gruesome. Just don't blame anything on the T56 or the Street Twin... he got those from me

I would check the fuel pressure. Those 30# SVO's should be fine at stock fuel pressures, but they are going to be weak if the fuel pressure is falling off.

Although it probably isn't the cam... are you sure about those lift #'s.... with 1.7's? That would leave you at .536/.558 with 1.6's (are you sure they are 1.6's?). Sort of low.

Did they put a wide-band on it for the dyno pulls?

 

Bret said it well.

Things id like to see-
Part # for valve springs.
Make/Model of fuel pump.
Log of a run via datamaster or some software.

 

Guys, thanks so much. Kmook, like Fred said I never actually make my sig that long... I just wanted to include every detail I could think of so you guys would have all the information possible.

I do not have a log of the dyno run. Let me check on that, as well as the springs & secondary (in line) fuel pump part numbers.

And thanks Fred - I appreciate the clarification. I didn't want to bore anyone with all that sad story (there is more that you haven't even heard). I am pretty confident on those numbers.

But whatever else we find (and I really, really hope you can help) I am still going to need cam advice. The motor is out of the car and so is the cam, so I am not going to put that same one back in.

I'll get back with those details as quickly as I can.

Many, many thanks!
Mark

 

No problem, nothing like getting hosed and then sticking with the hobby.

Bret

 

Thanks Brett,

One other thing has come to mind. I am having the heads flowed today, but presuming they flow as advertised, (we measured them at 68cc chambers) with 280/210 flow numbers sufficient for a 396? Could that be the restriction?

I know the flow numbers on the LS1 are quite a bit higher than that stock, but of course they are a different chamber design. Could that be the next place to look after the cam?

I am getting the info together on the valve train as well, but have confirmed magnum rockers, 1.7rr, twin springs, Series R lifters, so I am thinking the valve train is rock solid. Nonetheless, per your collective request, I will confirm all details I can.

Mark

 

Sry to burst your bubble but I have never seen any GTP heads flow over 255cfm..Mine were advertised at 286/209 but I got them flowed at 2 places and they were 255/180.

Maybe Craigs flowbench is off or maybe he is pulling numbers out of his hat
If that is where you are getting them flowed plz get a second shop to flow them..

If the graph is flatlining it could be a few things..
-Valve springs could be floating at 5krpms
-Your heads could be getting very turbulant around 5k
-Running out of fuel

Just a few thoughts..

G'Luck getting her figured out..

Cody

 

FWIW, I picked up some used GTP heads a while back, along with a GTP cam. The springs that were on the heads were the incorrect springs for the cam - installed by GTP.

340 is low, even for GTP heads - I would go through and thoroughly check everything. Good luck Mark

Ryan

 

Just to update you guys, I am still waiting on the information you asked for. I will get back to you as quick as I can.

 

OK. I finally got some news. The GTP heads were advertised to flow 280/210. Flow test found 260/212. Not too far off, but obviously not optimum. Also got these numbers:
Intake cc - 183
Ehaust cc - 73
Chamber cc - 55

I am still waiting on confirmation on the spring rates. Could this alone account for such low HP numbers with that old cam?

 

Man, it's like getting someone to pay a bill to get information out of these shops!

I finally got some information on the spring rates. 120# seat, 300# open. Looks like pacalloy.

With the head flow numbers, what do you gurus think the problem is? By the way, I have contacted GTP and they have agreed to 'make it right' on the heads, i.e. get the flow up in the 280/215 range. Will this be sufficient or am I still looking at trying to match a cam with some other heads anyway?

I hope this is enough information for you guys to find something. I am at my wits end!

Many, many thanks
Mark

 

Mark

I’m very sorry to hear you’re having problems. All I’ll say is don’t feel like you’re the lone ranger as I’ve bent over and touched my toes a few times myself with this hot rodding stuff.

I would whole hardily recommend to anyone whom buys ported heads to get a second set of flow sheets regardless. I had a set of GTP Stage II lt4 heads that Craig said flowed 283 intake and 208 exhaust. When independently tested, they were only 1 cfm off. Guess I was one of the lucky ones from what I keep hearing on this list.

However, I bought another set of AFR 227 heads from another vendor and they were not even close to what they said they were. The supplied flow sheets said 317/218…… when tested by B&B they flowed 285/190. Hummmm..

Anyway….. 260/210 isn’t bad for 183cc intakes if the low lift numbers are decent. Not something you would hang on the wall as a trophy set of heads, but about average. Your problem is not in the heads….. it’s somewhere else.

A dyno sheet may be helpful as you can tell a lot from the curve.

 

Doesn't sound like a high enough spring rate, though it's alittle hard to tell from the info you have. If they are 120# on the seat, and 300# at ~.55" the rate is ~325lb/in, which is low assuming those are steep lobes (CC XE?). Still 5,000 is low for valve float under these circumstances. Still, I would check the springs, see what the rate really is. Maybe some are bad? Or else just chuck them and don't bother checking and get something with a rate of 400lb/in or maybe a bit more.

Obviously, fuel and spark are the other biggies. An extreme exhaust restriction could be another. Though what would cause it since you don't have cats makes that a pretty far out possibility.

Rich Krause