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Viban 12-01-2012 12:45 AM

Expectable horsepower?
I recently got my hands on a '98 chevy silverado with a 5.7 vortec in it. I got it for a steal because it didn't work, turns out that it spun a bearing and tore up the crank something fierce, new one was required. While I was busy rebuilding it I decided to go ahead and rebuild the entire thing, and maybe drop in some new parts for a little added "get up and go". I got a new(bigger) cam with the following specs
ADV DUR:262/264
D @.050: 206/210
valve lift:.450/.480
What kind of horse power could I expect from this engine with the new cam?
Further down the line I also plan on adding a cold air intake and headers. What could I expect from that?

Thanks in advance

vinniekq2 12-01-2012 01:30 AM

should be 330 ish

vinniekq2 12-01-2012 01:35 AM

you will need good exhaust though,if its still stock?

454C10 12-01-2012 05:05 AM

stock hp is 275 with the tiny stock cam.
should make maybe 300 with the bigger cam.
330 with headers and exhaust

Are you going to put on a intake and carb or use the stock efi?
That engine has a factory roller cam so I hope your cam is also a roller cam.
You also need to modify your vortec heads to handle more lift.
I would also recommend doing a little DIY bowl smoothing on those vortec heads, especially around the exhaust ports.

cdminter59 12-01-2012 09:24 AM

Expectable horsepower?
The headers are a good idea but don't waste your money on the cold air intake. It does nothing to add power just a sales gimmick. Like was said save the money for your retune of the computer. Ask for recommendations on who to get to retune the computer here on this site.

Viban 12-01-2012 10:03 AM

The replacement cam is indeed a roller cam.

As for the exhaust, it is stock for now, however I do plan on getting a decent set of headers in the near future. I will likely end up using the stock intake as I'm only 15, and it was enough trouble talking my dad into the upsized cam (BTW I read somewhere that this cam should give me an enhanced midrange, and that it'll give me a slight lope?).
The guy at the performance shop I got it from said that this was actually the biggest I could go without the necessity of modifying anything.

I also already have the crank, rods, and pistons in already, we'll probably end up re-using the lifters as they have minimal wear.

I'll probably end up taking some of that valve grinding compound I have and the suction cup thing I bought and giving the contact surface for the valves a slight cleaning.

Thats all I can think of for now.

I would also like to add that the stock cam was indeed rather tiny, there was quite a visible difference between the new one and the old one.

Viban 12-04-2012 09:46 PM

I actually did it with the valves facing me and just reached my hand around back to spin them, it went rather easily. They are now completely assembled and ready to roll. Got the timing chain on and ready to go. Pretty much all that needs to happen now is the flywheel needs to go on, the heads need to go on, the oil pump go in, and then the goodies on the front, and the transmission before it goes in, because they decided to hide on of the transmission bolts right above the starter, so its impossible to get to from underneath. Then comes the adventure of finding where all of the dozens of wires. I'll make sure to keep ya'll updated, and drop you a video of original startup if possible.

Speaking of original startup, any advice? Things I should do fresh after a rebuild like gas in the intake? That kind of stuff?

454C10 12-05-2012 05:21 AM

did you get the heads modified to handle more lift?

Viban 12-05-2012 06:18 PM

The guy at my shop said that this was the biggest I could go without that being necessary.

75gmck25 12-06-2012 03:40 AM

It sounds like you made some good choices for a moderate horsepower increase. You will still have an engine that still gets decent gas mileage and has good low end torque - nice if you plan to use this pickup as a real truck.

Now take a look at the other items you can upgrade to get a little more power.
Good headers with full duals, an H pipe and high flow mufflers (I like Dynomax turbo mufflers) will help power, and you should be able to keep the sound at a level acceptable to your Dad. Tuning the computer is the next step I would take, but watch out for tunes that require premium fuel. They will work fine, but take more out of your pocket each time you fill up.


Silver Surfer 12-06-2012 10:20 AM


Originally Posted by Viban (Post 1619563)
The guy at my shop said that this was the biggest I could go without that being necessary.

The .480" lift on exhaust is cutting it pretty close. There are a lot of variables in the production of cast heads and some have more or less clearance than others. You should have at least .060" between the valve retainer and valve seal at full lift. After reading your post, you never even verified clearance.

Also it doesn't appear that you replaced the stock springs with the proper springs for the cam. Stock L31 springs will go into coil bind around .420" lift. Furthemore, the stock springs lack the seat pressure to keep the roller tappets on the face of the cam lobes which means:
-.060" clearance between the retainer and seal may not be enough
-if a lifter jumps off the nose of the cam you have instant engine destruction

I suggest getting the correct springs and retainers and verifying clearances before you attempt to start the engine.

More info can be found here:

Silver Surfer 12-06-2012 10:25 AM

I would also add that you ought to replace the distributor gear as well anytime you get a new cam. Using an old one will accelerate wear and will also cause your ignition timing to faulter.

454C10 12-07-2012 04:23 AM

I only have measured one set of vortec heads and the retainers hit the seals at 0.430" lift.

Get your heads done at another machine shop and yes, use the recommended valve springs.

Viban 12-07-2012 02:02 PM

I'll upgrade the valve springs and work on the rest, this is why I cam here, cuz I knew ya'll would know things that I'd overlook

Viban 12-19-2012 08:03 PM

This is a bit of a bump, but everything is all together now, made suggested upgrades where needed and things. My question is now, will I need a bigger distributer or will an OEM one be fine?

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