Appropriate timing curve

[Rat Patrol]

SrtMAX cam into a carb inducted 6.1 using an MSD 6013 ECU.

What sort of total timing at WOT would be considered safe for pump gas premium?

What RPM should I target for the timing to be "all in " that will be safe from detonation.

Im assuming AF of 12.5 at WOT , 13-14 at part throttle and 15 at cruise will be acceptable?

Thx in advance

 

[lxmodguy]

Good luck with that. The srtmax is an annoying cam when you have the complete controls of EFI to tune it.

Total timing depends on a lot of things. Assuming you have good exhaust, good plug gap, decent pump gas, and consistent fuel delivery......25 should be a good all in number in your setup.

I would setup the timing something like this

1500 - 17
2000 - 19
2500 - 21
3000 - 22
2500 - 22
3000 - 23
3500 - 23
4000 - 21
4500 - 21
5000 - 23
5500 - 24
6000 - 25

 

[Rat Patrol]

Cheers for your reply...

Couple of questions-

Why is the SRTMAX "annoying" and will it be as difficult using the MSD 6013?

Why does your proposed curve "dip" around 4000 - 4500?

 

[lxmodguy]

There is a bit of resonance in the hemi valve train in that rpm range and if you ramp timing up through that area you will get knock.

Annoying because a stock srt cam is like a 117.5 lsa and 119 icl. That srtMax is most likely a 112 lsa and 108 icl. Its not a really big cam, but that kind of LSA/ICL change makes for a lot of other changes that need to happen to idle right. You are going to have stumples and stalls. Plus I really havent seen that cam make anywhere near the power they claim. Honestly, its a joke what they claim on their website. That cam makes 360-370 wheel horsepower on my dyno. We have a cam we sell for stock heads that idles like stock and picks up 50/50 everywhere with an underdrive pulley. Auto cars make 380-390 with stock exhaust and stock manifolds, manual cars make north of 400 with no other mods. Plus, it will idle and run on the stock tune with minor tweaks. You guys with carbs want something like that as opposed to the srtMax. Sure it will have a nice healthy sounding idle, but you aren't going to enjoy the car much with the driveability issues it will cause with a carb

 

[Rat Patrol]

There is a bit of resonance in the hemi valve train in that rpm range and if you ramp timing up through that area you will get knock.

Thats great info - thanks!

Annoying because a stock srt cam is like a 117.5 lsa and 119 icl. That srtMax is most likely a 112 lsa and 108 icl. Its not a really big cam, but that kind of LSA/ICL change makes for a lot of other changes that need to happen to idle right. You are going to have stumples and stalls.

Not being a smarta$$ - but I'm interested in how tuning a carbed Gen 3, with a SP intake, 3.9 gears and 800 AVS would be any different to tuning my old small block stroker with a 110LSA and 108 ICL with the same gears, SP intake and same carb?

I mean, we're still dealing with the same stall converter, same induction type, same gears , same ignition principles ...no AF sensors or computers to worry about.......

.....so why would a relatively mild cam cause "issues" when its effectively like any other carb inducted push rod engine? :-k

lus I really havent seen that cam make anywhere near the power they claim. Honestly, its a joke what they claim on their website. That cam makes 360-370 wheel horsepower on my dyno.

With all due respect I never compare rear wheel dyno results - Ive seen 10psi tyre pressure gain 30 RWHP...you never know what the environment is like so its impossible to compare.

We have a cam we sell for stock heads that idles like stock and picks up 50/50 everywhere with an underdrive pulley. Auto cars make 380-390 with stock exhaust and stock manifolds, manual cars make north of 400 with no other mods. Plus, it will idle and run on the stock tune with minor tweaks. You guys with carbs want something like that as opposed to the srtMax.

Can you provide the duration and lift figures of your cam profile?

Is it compatible with Factory springs and lifters?



Cheers for your input and appreciate your interest!

 

[lxmodguy]

Well compare this, the cars that make 450 on his dyno make 380 on mine. The cars that make 450 on his dyno run low 12's. Cars that make anything over 400 on my dyno typically run 11's. (4000+ pound new challengers and chargers)

There isn't a difference in tuning in your comparison. If you were happy with the way your old small block idled and its street manners you should be happy with this. Assuming they are the same amount of cubes it should behave the same.

As far as cam profile, it is a proprietary grind. I will tell you its a 21x/22x on a 115 LSA. .56x/.58x lift and needs an inexpensive aftermarket spring that does require and mods to the heads or to the valve seals. It runs with stock lifters. Its not going to be really lumpy, but on average it makes about 20 more hp/tq than that srtmax


when you say no sensor to worry about, that stuff is a saving grace. You would be amazed how smart the computer is we you know how to compensate for a lot of overlap

 

[Rat Patrol]

Well compare this, the cars that make 450 on his dyno make 380 on mine. The cars that make 450 on his dyno run low 12's. Cars that make anything over 400 on my dyno typically run 11's. (4000+ pound new challengers and chargers)

OK...the MPH /weight thing is the real test - and I've read enough to know low 12s in those "fatty" LX cars is the standard with the SRTMAX...so I don't doubt what you're saying.......assuming gearing is the same?

There isn't a difference in tuning in your comparison. If you were happy with the way your old small block idled and its street manners you should be happy with this. Assuming they are the same amount of cubes it should behave the same.[ /QUOTE]

The old small block was twenty more - but that was a solid flat tappet with more duration and it wasn't too crazy.

As far as cam profile, it is a proprietary grind. I will tell you its a 21x/22x on a 115 LSA. .56x/.58x lift and needs an inexpensive aftermarket spring that does require and mods to the heads or to the valve seals. It runs with stock lifters. Its not going to be really lumpy, but on average it makes about 20 more hp/tq than that srtmax

I'll give it some thought - although I didn't really want to get into swapping valve springs.....

Great to have a sensible discussion about this stuff though:thumrigh:

 

[Rat Patrol]

Well compare this, the cars that make 450 on his dyno make 380 on mine. The cars that make 450 on his dyno run low 12's. Cars that make anything over 400 on my dyno typically run 11's. (4000+ pound new challengers and chargers)

Just a question on your RW Dyno - what losses do you factor in for a factory diff and factory converter?

The "as factory" rear wheel figures I'm seeing show around 12-15% losses from quoted HP...depending on the air. .....

 

[lxmodguy]

We dont. I have two dyno's, one is a mustang dyno the other a dyno dynamics. We make sure the weather cell data is right and the gear ratios and weight are correct for the car and we roll.

We could correct them to read like a dyno jet, but why? Customers who want to have a huge number on a dyno sheet can go somewhere in town and get one that says they make 40 more. My customers for the most part go out and run the ET's. The dyno is a tool, if you are hung up on what the dyno spits out then you are really missing the point.

 

[Rat Patrol]

Sorry there's some onfusion going on....

What I'm asking is if an LX makes ..say 370 REAR Wheel on your dyno....what would you ESTIMATE its making at the crank?

I'm trying to work out what parasitic losses you recokn the factory converter, trans and diff is worth?

 

[lxmodguy]

On an LX that makes 425 at the crank with an auto trans they make 330-340 with a manual trans they make 350-360. That is a 6.1. Those numbers are through completely stock cars on my dyno. Thats 20-23% on the autos and 16-18% on a manual.

So if it is making 370 at the crank on my dyno its making 444-455

 

[Rat Patrol]

On an LX that makes 425 at the crank with an auto trans they make 330-340 with a manual trans they make 350-360. That is a 6.1. Those numbers are through completely stock cars on my dyno. Thats 20-23% on the autos and 16-18% on a manual.

So if it is making 370 at the crank on my dyno its making 444-455

Awesome ...thanks! Thats what i was after!

Those are some pretty serious losses for a factory converter and trans etc...I woulda guess around 18% for the auto with a tight converter.

I'm glad you run a company thats not "pimping" dyno figures for business......but if you don't mind me saying, I reckon yours may be a tiny bit conservative?

I base this on the estimated losses...they just seem a little high for the auto.

FWIW I know Ford Australia used to claim about 18% on their Boss quad cam 5.0 liter ....but that was running the German ZF 6 speed auto which is a pretty efficient trans....

 

[lxmodguy]

ours is a bit conservative.

You have to realize the LX's come with an AUTO, independent rear suspension, and 20 inch wheels that weigh 65# a piece with tires. It eats up a lot of power. Our converter builder does a great job, we really dont loose anything up top when we put anything under a 4000 stall into cars

 

[Rat Patrol]

Thanks for the explanation - wheels is somethig I hadn't taken into account.

If you're not losing anything after installing a 3500 converter - then your guy really IS doing a good job! LOL!