JL66REDCPE

I am posting this for a freind of mine. The car just doesnt seem to feel as strong as it should be. Torque seems to be poor across all ranges. The car should light the tires up all through first gear and it does not -- nor does it seem to pull very well. It just doesnt seem to be producing power. We think it may be due to a bad combination of components cretaing an incompatability. Your comment son this are appreciated.

The engine is a 454 bored 30 over. TRW 2399F forged aluminum pistons with a 15 cc dome. The heads are 1974 passenger 049 casting with a 110 cc comb chamber. They are open chamber oval port heads. He calculates comp ratio to be 9.5:1. The valves are 2.19 Int and 1.88 Exh and they are pocket ported and the gaskets matched. It has a comp cam 288AR roller with .623 lift on the int and exh. it has an Edelbrock Performer manifold - Dual Plane. It has a Holley 850 CFM Vacuum Secondary with staggereed Jets. It has 1 7/8 headers with 2 1/2 exhaust with flowmasters. It has a Turbo 400 trans with a 2800 stall speed converter. The rear is a 3:73 with 27" tall tires. It also has an MSD 6al ignition, matching distributor and coil. The timing is set to 10 deg initial and 34 deg total with full advance achieved at 2000 RPM. It has a stock crank, stock fuel pump and gas lines. He is using pump gas.


thanks

john lolli

TheOman

I guess my first comment would be that "Power is in the seat of the pants of the beholder"! Without some kind of yardstick measure of performance this is gonna be tough to comment on. Anyway you are on the right track with oval port heads for the street if that is where this car is driven. The Rectangles are ok but "nobody is home" in the engine room toill the RPM's build way up with the Rectangles relative to the Ovals. I have an LS-6 with the same pistons, same valve sizes and rectangle port heads. The big difference I see between your friends engine and mine (aside from the intake ports) is the cam.

623 is a fair amount of lift but you don't say if the engine is built for the street or for racing and if for racing for what kind of racing. It has headers and the converter which would indicate a drag car but I have seen crazier combos that people try to drive on the street. Anyway what is the duration and overlap of that cam? Those numbers are at least as important as the lift and possibly more important depending on what you want to do with the engine in terms of how you drive it and where you drive it.

Perhaps ( and I stress PERHAPS) that cam is overpowering the heads. Again depends on how you want to drive the car. If the duration and overlap are way out there in conjunction with the lift being 623 perhaps the ovals cant handle it. By the time the RPM gets up where the cam can work the Ovals are outta gas in terms of their ability to support the amount of mixture the cam can deliver.. Down in the lower range of RPM, where the Ovals are superior, the cam has not gotten into a range where it "works". In effect the heads are killed by the cam at lower RPM and the Cam is killed by the heads at higher RPM. Don't know just a theory. With the Turbo and the 3:70 gears you should have enough multiplication in the drive line so again I suspect that the gears and the trans get the engne up into higher RPM ranges quickly but perhaps the heads go out to lunch once the engine gets up in that range.

. More I think about this this might be a case of "Too much cam". But like I said you don't give us all the specs. Also at 9.5 Cr in a 454 you may or may not have enough compression. That depends on the overlap and duration not just the lift

By the end of the weekend there will be so many people jumping in with the oval / Rectangle debate that likely your head will spin. In my experience a milder cam, like the factory LS-6 cam and the Ovals is a nice powerful street combo. If I was flush with cash I would gen up a set of Ovals for my motor.

Vetterodder

Unless it's in a really heavy car, I'd expect that combination to make some really good power once on the cam. That cam is 246º/246º @ .050", 110º separation. Hardly a mild cam but with his cubes, gears, and converter, it shouldn't be that over cammed. The intake manifold may be less than optimum for the engine but it's shortcomings probably wouldn't be felt below about 5,000 rpm. I don't have any good guesses as to what the problem might be but I suspect that the problem may be a tuning issue.

tapio

Check the easy ones first. Is the carb linkage operating properly? That means when the gas pedal is floored, the carb should be wide open. I have seen cases where the carb linkage was worn and didn´t open the carb fully. If the linkage is faulty, you should find really cheap horses there.

How about the timing? Is the total advance verified? How about the mixture?

Hope these will help.

Corvette Cowboy

I'll add my two cents on this subject. I'd start with a check of the timing. It's obvious, you can't use the stock settings. Experiment a little bit and see if that helps.

oger

If he is running the std Performer intake the runners are too small to support a 454 at 4500rpm. Put an RPM or another brand on it.

JL66REDCPE

First of all - as always thanks for all the help

The cam is a 246/246 duration at .050" and 110 deg of separation. The cars is drivien on the street and the engine was built to run on pump gas for street purposes. If we assume the modified oval port heads are ok, then what do you think about replacing the Edelbrock Performer dual plane manifold with a single plane manifold keeping the 850 CFM carb..

396 RAT

Torque seems to be poor across all ranges

Is this a new problem? New engine? Was anything changed recently?
Is it an oval port intake?
Sounds like it might be over carburated.
I would not toss the dual plane for a single plane if its street driven automatic.
It looks like the heads might be the wild card here.
I would try a smaller carb and see what happens.
:D

Kid_Again

...john, i'm not an expert but i would stay with the dual plane for the street - single plane optimizes for high end....i dunno...sounds like a tuning issue to me...what do the plugs look like?

joe

JL66REDCPE

396rat - this is a new motor 600 miles. The manifold is an oval port. Yes the 855 holley could be considered fat however they put them on the L-88's and they ran ok. We have tried a 780 cfm holley and it is a little better however this engine is built for well over 500 hp and it just doesnt seem like it is coming close to making it. The cam is somewhat radical but comp cams says it is fine for the way the motor is built. Yeah -- it could be the heads.

Kid -- the single plane does make more sense for the street -- I agree with you. I am leaning towards the manifold runners just being too darn small.


[Modified by JL66REDCPE, 9:36 PM 5/5/2002]

kahuner

Morning John;

Your friend is in a tough situation. It's not easy finding the answer by continuously swapping parts, lotta work and frustration.

His engine isn't too far away from mine when you compare heads, valve size, both dual plane intakes (mines an Edelbrock Air Gap) I'm running a 750 Demon, MSD 6AL ignition, ignition curve, 3.55 gears, 049 heads oval port heads, my comp ratio is 10:1, pump gas, and roller lifters.

About the only differences are: I have a 509 CI, I'm using stock manifolds with 3" side exhaust from Stainless Works, and the cam.

Everything I've read says a dual plane is better for the street. A single plane will kill your low end!

Regarding the cam; mine is 236/244 duration @ .050" with a .544" lift. A 246 duration, like your friend has, is ok after 4000 RPM but it won't do much before then. My guess would be the cam is too radical. But before I did anything, I'd find a chassis dyno and see what I have as starting point.

I thought I'd reply to your thread, not because I'm an expert, but because the 2 engines aren't really that different and thought that the info may help.
Good luck John. I'm pullin' for ya!

Hasbeen

sence you mention that the carb is a vacume secondary, I`d play with the vacume springs in the secondary, with this cam you`re not getting much vacume and the secondaries may be coming in too soon!! Also you might take a look at the power valve, it too might be opening up too soon and causing a too rich condition before the RPM`s get up!!!

Just thinking!

HASBEEN :smash:

JL66REDCPE

First of all thanks to all who replied. The feedback was very helpful and not only led to the problem -- it also pointed to other fixes. My friend is embarassed. It turned out to be the throttle linkage. The carb was opening up less than 3/4. The accelerator was pushing the linkage to the external stop however the butterflies were not opening up all the way !! The manifold will also be swapped out as a further enhancement. It is ok for the 750 cfm Holley, however he wants to put the 850 Holley with the staggered jets back on. That manifold is only good up to 5500 rpm and the runners will only support a 750 cfm -- so that is next on the agenda to be changed. It seems we all agree he has the correct heads for a street application and a single plane manifold is not the way to go.

thanks again

john lolli


[Modified by JL66REDCPE, 7:04 AM 5/9/2002]

Kid_Again

...hey john......sounds like he has my luck :lol:

....ain't it amazin' what a "back to basics" approach and a little common sense will do..... :yesnod:

kahuner

I feel as embrassed as your friend.

How many times have we all told ourselves: "don't :smash: overlook the basics." If this would've been a contest.........

On the other hand, it probably came as a relief! :yesnod:

tapio

Been there, done that... I found at least 100 horses from my 63 convertible, when I realised that the throttle linkage was worn. It´s easy to overlook the most obvious.


[Modified by tapio, 8:03 PM 5/9/2002]

396 RAT

Glad it was an easy fix. :cheers: