496 falling flat

1bad69 · Nov 8, 2018

Not sure what is going on. This motor has never run right. i have had it since 2012, with multiple issues, but thought I had all my issues fixed.

It is a 496 with Straub Cam, oval port Alum heads, (Pro Comp, I know... i know...) Victor JR with Fitech Meanstreet Injection, 700r4, 3200 stall, and 3.42 posi.

It runs pretty good from a dead stop holeshot. But when i am driving, i will drop it into low gear and stomp it, and it will barely turn the tires if it does at all. I know this thing should obliterate the tires, even when it is a roll and go. It did this when it was carbed also. and believe it or not. It runs MUCH better with the Fitech than the 850 Holley i had on it. Plus it gets great gas mileage now compared to what it was.

I had 781 heads on it with bigger valves and had the Victor JR gasket matched. I thought the guides were weak in the heads as it kept oil fouling plugs. But my intake was soaked with oil in 2 ports and found out it was an intake gasket leak. I sold the guy those heads, and old cam setup and he took them apart and said all the guides were great... SO he got a deal. LOL

Could it be in the timing? I have a MSD 6ALN and a Pro Billet distributor. It is timed at 38 degrees total. With good 91 or 93 gas, it doesn't spark knock.

This engine never did RPM well, and it's all in at about 5800. I never see 6000 rpm as it never goes there. It gives up before it gets there. Maybe i should change the intake on it? Maybe I have had problems with it the whole time? It's the only thing I haven't changed. It worked great on my solid roller 468, but that was before i had it gasket matched at a performance shop. Maybe a weak valve spring?

anyone have any suggestions? I am at my wits end and just about to scrap the whole big block setup to an LS3!

MikeN · Nov 8, 2018

My similar 496 went a best of 7.19 in the 1/8 mile and 11.37 in the 1/4 mile, with 3.42 gears, just like you, and 2800 stall. It would obliterate street tires, even from a 35mph roll. What are the specs on your cam?

When I first put my 496 together, I was using 781 heads, untouched but for 2.19/1.88 valves, and an Isky HR cam that was 228/238 @ .050. After about 6 years of racing and street duty, we freshened the engine and swapped to Brodix RR aluminum heads, and a slightly larger Lunati cam. I didn't really run noticeable better or faster with those changes.

1bad69 · Nov 8, 2018

Georgia69 said:
My similar 496 went a best of 7.19 in the 1/8 mile and 11.37 in the 1/4 mile, with 3.42 gears, just like you, and 2800 stall. It would obliterate street tires, even from a 35mph roll. What are the specs on your cam?

When I first put my 496 together, I was using 781 heads, untouched but for 2.19/1.88 valves, and an Isky HR cam that was 228/238 @ .050. After about 6 years of racing and street duty, we freshened the engine and swapped to Brodix RR aluminum heads, and a slightly larger Lunati cam. I didn't really run noticeable better or faster with those changes.

The cam is actually around that... found the figures.

280/294 adv duration
221/235 @ .050
.578/.578 lift
109 lobe sep

Jsavdog · Nov 8, 2018

What kind of exhaust do you have on it? Just wondered if it's possibly restrictive. Are the valve springs matched to the cam? Also you might want to verify your timing pointer is accurate with a position stop. Also you might want to check with Straub about the rpm range for your cam. Can't imagine it wants to be revved much past 6k

1bad69 · Nov 8, 2018

Jsavdog said:
What kind of exhaust do you have on it? Just wondered if it's possibly restrictive. Are the valve springs matched to the cam? Also you might want to verify your timing pointer is accurate with a position stop. Also you might want to check with Straub about the rpm range for your cam. Can't imagine it wants to be revved much past 6k

It's 3 inch exhaust iwith Flowmaster Super 40's dumped at the rear end. Same exhaust I always have had except for I used to have pipes until my driveway tore one of them down. Then I cut both of them off.

Could be the valve springs... They are the ones that came with the heads. But they measured fine for pressures for the cam. I don't remember what they were, but they matched really close to the springs spring rating wise that I had on my old heads from Straub, so I did not change them.

Jebchevelle · Nov 8, 2018

1bad69 said:
It's 3 inch exhaust iwith Flowmaster Super 40's dumped at the rear end. Same exhaust I always have had except for I used to have pipes until my driveway tore one of them down. Then I cut both of them off.

Could be the valve springs... They are the ones that came with the heads. But they measured fine for pressures for the cam. I don't remember what they were, but they matched really close to the springs spring rating wise that I had on my old heads from Straub, so I did not change them.

who measured the springs? and how close is close? meaning how many lbs lighter.

cstraub · Nov 8, 2018

1bad69 said:
Not sure what is going on. This motor has never run right. i have had it since 2012, with multiple issues, but thought I had all my issues fixed.

It is a 496 with Straub Cam, oval port Alum heads, (Pro Comp, I know... i know...) Victor JR with Fitech Meanstreet Injection, 700r4, 3200 stall, and 3.42 posi.

It runs pretty good from a dead stop holeshot. But when i am driving, i will drop it into low gear and stomp it, and it will barely turn the tires if it does at all. I know this thing should obliterate the tires, even when it is a roll and go. It did this when it was carbed also. and believe it or not. It runs MUCH better with the Fitech than the 850 Holley i had on it. Plus it gets great gas mileage now compared to what it was.

I had 781 heads on it with bigger valves and had the Victor JR gasket matched. I thought the guides were weak in the heads as it kept oil fouling plugs. But my intake was soaked with oil in 2 ports and found out it was an intake gasket leak. I sold the guy those heads, and old cam setup and he took them apart and said all the guides were great... SO he got a deal. LOL

Could it be in the timing? I have a MSD 6ALN and a Pro Billet distributor. It is timed at 38 degrees total. With good 91 or 93 gas, it doesn't spark knock.

This engine never did RPM well, and it's all in at about 5800. I never see 6000 rpm as it never goes there. It gives up before it gets there. Maybe i should change the intake on it? Maybe I have had problems with it the whole time? It's the only thing I haven't changed. It worked great on my solid roller 468, but that was before i had it gasket matched at a performance shop. Maybe a weak valve spring?

anyone have any suggestions? I am at my wits end and just about to scrap the whole big block setup to an LS3!

That cam in a 496 is going to peak around 5700-5800 rpm. From idle to that point is should fry the tires. MSD is not the company it use to be. I don't trust any of it. ProComp heads, did I send you the springs or did they come on the heads? I would check spring rate.

Jsavdog · Nov 8, 2018

Jsavdog said:
What kind of exhaust do you have on it? Just wondered if it's possibly restrictive. Are the valve springs matched to the cam? Also you might want to verify your timing pointer is accurate with a position stop. Also you might want to check with Straub about the rpm range for your cam. Can't imagine it wants to be revved much past 6k

I meant a piston stop, not position stop. Site would not let me edit my reply.

BillK · Nov 8, 2018

1bad69 said:
Could it be in the timing? I have a MSD 6ALN and a Pro Billet distributor. It is timed at 38 degrees total. With good 91 or 93 gas, it doesn't spark knock.

I was thinking along those lines too. Are you sure your TDC mark on the damper is correct ?

What kind of timing light are you using. I know of two instances I witnessed personally where a dial back type light was waaaay off on a MSD system. Both times the timing was almost 10 degrees retarded compared to a non dial back light. That is why MSD tells you to use a non dial back light.

1bad69 · Nov 8, 2018

BillK said:
I was thinking along those lines too. Are you sure your TDC mark on the damper is correct ?

What kind of timing light are you using. I know of two instances I witnessed personally where a dial back type light was waaaay off on a MSD system. Both times the timing was almost 10 degrees retarded compared to a non dial back light. That is why MSD tells you to use a non dial back light.

It's a Matco digital light. has the rpms and the advance all on one screen. Pretty handy. I bought it new 2 years ago. I can see if i can find someone with a manual dial back light. Don't know if I know anyone. LOL

1bad69 · Nov 8, 2018

cstraub said:
That cam in a 496 is going to peak around 5700-5800 rpm. From idle to that point is should fry the tires. MSD is not the company it use to be. I don't trust any of it. ProComp heads, did I send you the springs or did they come on the heads? I would check spring rate.

Hi Chris. Thanks for responding. They are the ones that came on the heads. That is why i am kind of skeptical of the springs. They were very close in dimensions as far as specs, and pressure to the Lunati ones you sold me. I don't have the specs anymore. I might just have to buy a set from you again and see if that works. This thing should be a rocket!

The MSD stuff i run is at least 10-15 yrs old.

BillK · Nov 8, 2018

1bad69 said:
It's a Matco digital light. has the rpms and the advance all on one screen. Pretty handy. I bought it new 2 years ago. I can see if i can find someone with a manual dial back light. Don't know if I know anyone. LOL

You need a light with no dial back whatsoever. The one that I had showing ten degrees off was the best Snap On digital you could buy a few years back. I brought my ancient Sun light over to his place and woke the engine up a bunch.

https://www.ebay.com/p/Old-School-Sun-Timing-Light-Model-7501-Inductive-Pickup/1723132350

BillK · Nov 8, 2018

Jeremy,
Just for a quick check bump the timing up 5 or 6 degrees with what you have and take it for a spin. See what it does. Just dont stay in it if it starts to ping.

That will at least tell you if timing might be the issue.

dirtlips408 · Nov 9, 2018

Have you taken it to the track to see how it does to try and get some performance numbers???

1bad69 · Nov 9, 2018

no. not yet. I know I'm not getting all of the performance i can get out of it, so i want to get it running correctly before I do that, or do an LS swap. But I would like to get the potential out of it if i could before I do a swap. I get 14-16 mpg on the highway now. I am liking that!

1bad69 · Nov 9, 2018

BillK said:
Jeremy,
Just for a quick check bump the timing up 5 or 6 degrees with what you have and take it for a spin. See what it does. Just dont stay in it if it starts to ping.

That will at least tell you if timing might be the issue.

i have done that and it does ping alot. and doesn't like to start easy.

dirtlips408 · Nov 9, 2018

1bad69 said:
no. not yet. I know I'm not getting all of the performance i can get out of it, so i want to get it running correctly before I do that, or do an LS swap. But I would like to get the potential out of it if i could before I do a swap. I get 14-16 mpg on the highway now. I am liking that!

You have been wanting to do the LS swap for along time if I remember correctly.

1bad69 · Nov 9, 2018

dirtlips408 said:
You have been wanting to do the LS swap for along time if I remember correctly.

Yeah.. but if i could get this one to run right... it already gets decent mileage now.. so if i could get it to fry the tires when i stab it i'd be good i think... I like the looks of my motor so much better than an LS... i know there are tricks you can do to make them look better, but you still have the ugly accessory drive on the frt.

gnicholson · Nov 9, 2018

that thing should absolutely annihilate the tires. i have an 8 to one hyd flat tappet 454 with 331s that will fry the tires at will and you should have a bunch more torque than i do so something is amiss. sounds like ign timing is close based on what youve said. did you degree the camshaft? definitely check the valve springs.are you getting full throttle? a restrictive or clogged exhaust will cause your symptoms.

dirtlips408 · Nov 9, 2018

1bad69 said:
Yeah.. but if i could get this one to run right... it already gets decent mileage now.. so if i could get it to fry the tires when i stab it i'd be good i think... I like the looks of my motor so much better than an LS... i know there are tricks you can do to make them look better, but you still have the ugly accessory drive on the frt.

Take the car to a good tuner and see what he comes up with on any issues.

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