350 Vortec tune is close, but not perfect.

I have a 350 Vortec in my 00 Blazer. The tune is just about right. I took it to a dyno tuner and he said he didn't really have to change anything, but I still think I should be getting more hp and better mpg. A guy that did almost the same exact swap is getting 25mpg while I get 16-17mpg. The only real difference is that he is running true duals and a stock cam whereas I'm running a single muffler and LT4 Hot Cam. I've noticed my exhaust has a slight gas smell, nothing real strong, but I think it's running slightly rich. Anyone know what I can do?

Your cam is pretty big for stockish motor, not going to improve your mpg. Your exhaust will always have a slight fuel smell with no cats, especially with a cam that has more overlap than stock. What did dyno results show?

Dyno showed 229rwhp.

Not much looks different then when I saw it last other than your timing table. Your timing has been increased through your torque peak and decreased at higher rpm? As I recall you dont like to rev this thing because of your trans, but a lot of timing pulled that you butt dyno said was improving. Your hi/lo timing tables are the same also which is normally bad but as I recall you dont have working knock sensor so probably does not matter.

Yes you're correct. I found a guy that has almost the identical setup only with a near stock exhaust and stock manifolds, I think his dyno sheet showed him making about 50hp more than me. I figured the knock sensor out a while back, it's working but I can't remember what the problem was.

I would suggest your camshaft is your problem. Was it degreed when it was installed? Whats the cranking compression of your motor vs his? Your cam is not going to start really performing until 5000 rpm plus, as I recall you didnt like to rev past 5500. What did it rev to on the dyno? Also, not all dynos are equal. Was his run on the same one? If you were on a mustang and he was on a nonloaded dyno jet that can be the differance right there. Have to compare apples to apples.

Your current timing table does not make a lot of sense for your motor. If your knock sensor is working you do not want to leave your low octane timing table the way it is.

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Was it degreed when it was installed?

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Yes.

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Whats the cranking compression of your motor vs his?

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I don't know on that one.

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Your cam is not going to start really performing until 5000 rpm plus, as I recall you didnt like to rev past 5500.

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Correct. It's that I've been told by a bunch of people that the NV3500's aren't a trans that you want to be too hard on. If it was a auto or a t56 then I wouldn't mind going over 5500.

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What did it rev to on the dyno?

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5500, but I told him to rev it at whatever he thought would be best.

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Was his run on the same one?

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Nope.

I would be interested to see the dyno sheet, if it only revved to 5500 thats where your leaving your power at. I would suggest pulling all your plugs and doing a compression test. Then doing it again on a stock vortec or asking your comparison vehicle to do the same. Your likely to find yours is lower, probably by a fair bit(due to cam events not engine condition). If sticking with the nv3500 is the plan, your cam is for sure the wrong choice.

I think there is some more power in your timing table, your current one does not make a lot of sense for a 350 vortec. Not sure your going to catch your comparison vehicle though.

His:
http://i243.photobucket.com/albums/f...ps536258b3.jpg

Mine:
http://i.imgur.com/tVJoOTj.jpg?1

Yours is the bottom, with peak power showing at 4500? Explains what he did with your timing table but does not make sense.

Correct. Why does it not make sense?

You have a larger cam than stock. Your power peak should be at a higher rpm, your currect power peak is less than the stock cam.

So what do you suggest I do?

Still have my email? I cant find yours. Ill pm you mine, be easier to discuss off here.

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Originally Posted by mecanicman

Yours is the bottom, with peak power showing at 4500? Explains what he did with your timing table but does not make sense.

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The top dyno chart is my 97 Express. GM crate 8,800+ GVW L31, production LT4 camshaft 203/210 @ .050, .476/.479" lift, 115* LSA, 116* ICL, running a ported stock intake manifold, 70mm throttle body, LT1 B-car exhaust manifolds into the factor dual 2.75" factory cats and piping and a magnaflow dual in/single out muffler with a 3.5" tailpipe. 0411 swapped, had E-fans and an underdrive pulley in that dyno. 4L60E with a locked converter and 8.5" 10-bolt.