97 5.7 vortec

[L31MaxExpress]

The Lunati Bare Bones 218/228 made 290 whp and 330 wtq in my L31 with a marine manifold, through a 4L85E in 2nd gear and GM 9.5 14-bolt. I suggested the XM270HR because I like specs a little better than the XR270HR or the Lunati Bare Bones.

 

[BeXtreme]

There is documented data of a 330 HP 350 HO engine upgraded to a GM Hotcam and 1.6 rockers making 401 hp and 428 tq with the crappy flowing Mexican 062 heads that came on that engine. The comp cam I mentioned is slightly more aggressive for the same 0.050" duration as the hotcam.

Back in the day when the L31 head swaps were just getting popular Hotrod Magazine took a mid 70s 350, put a Comp XE268 cam and vortecs on it. They managed 394 hp out of that. Vortecs do not need huge cams to make 380-400 hp.

Vortec Blazer put a marine intake and XR270HR in his L31 swapped ~1987 S10 Blazer and went from 210 whp to 311 whp. He gained 100 hp at the wheels and from what I have learned swapping a ported stock manifold to a ported Marine manifold, I gained nearly nothing with the Marine manifold on my 383 making ~500 hp. There was another guy that went by VortecStroker or something like that back in the day. When his truck had the stock L31 bottom end and heads he put a GM LT4 Hotcam in the truck. It made 305 RWHP with the stock heads, intake manifold and injection. That was around 380 hp at the crank on his truck and possibly a touch more.

The EFI connection owner, Mike Noonan put together a L31 with a Hotcam and a Ramjet intake in his S10. It made 311 whp.

Edit- Mike Noonans S10 was 311 whp. I was remembering his torque number when I said 330. What Mike Noonan got from Hecho en Mexico 062s and a LT4 Hotcam. So 218/228 @ 0.050 will make over 300 whp in a L31.

I had a stock long runner TPI setup on a 10:1 355 I setup in a 1987 Firebird that made 290 whp through a TH400 with a 2,800 rpm converter. It had the older design Dart Iron Eagle 180 heads which are arguably worse flowing than Vortecs and a LT4 Hotcam. for reference a stock 113 aluminum head L98 makes about 240 whp through a 700r4 with free flowing exhaust. Flow numbers show the 113s are about the same flow as the 180 iron eagles used on that engine. So a little compression, shorty headers and a LT4 hotcam added 50whp through a slippy, loose converter and TH400.

This was Mike's result with his S10.

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I guess we can argue numbers all day long. We all know how "dyno numbers" can get sketchy depending on how people chose to do the correction on their machines. You can find just as many "documented" dyno runs that make nowhere near that power on stock vortec heads.

Either way, it doesn't really matter. We are both saying the same thing for what he should do, just arguing over what the "theoretical" number is going to be.

He can make great power with the stock vortec heads and a mild cam. It will be great street drivable power and will be cheap. The stock L31 is only putting like 225hp to the ground. I've seen before and after numbers from an LT1 cam swap that showed it only pick up 10hp, That LT4 hot cam is even bigger than the 274HR, so I'm not sure its a very good comparison. Just the cam is going to get you 20-100hp depending on what cam you choose. I would expect the LT4 cam needs a much looser converter though, so you would need to look at that too. Total cost maybe $800 for the cam and valvetrain upgrades. Another $300-600 to get the stock vortecs redone depending on if they need new guides and a valvejob or not.

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Here's a video of the LT4 cam in a stock L31 engine where they give the part numbers and cam specs. I think the LT4 cam can be had from chevrolet performance for significantly less than a Comp cam would cost.

If he wants more power than that, $1000 more gets him an extra 50hp and a few points of compression bump. The AFR heads with the LT4 cam would probably be in that 450hp at the crank range. Maybe even more with the better flow the AFR heads will have at those high lift numbers.

 

[best97obs]

Is there a way to get an upgraded manifold without changing the spider injection? If not what's a good efi kit that isn't 2,000 dollars like the pro flo.

 

[L31MaxExpress]

I guess we can argue numbers all day long. We all know how "dyno numbers" can get sketchy depending on how people chose to do the correction on their machines. You can find just as many "documented" dyno runs that make nowhere near that power on stock vortec heads.

Either way, it doesn't really matter. We are both saying the same thing for what he should do, just arguing over what the "theoretical" number is going to be.

He can make great power with the stock vortec heads and a mild cam. It will be great street drivable power and will be cheap. The stock L31 is only putting like 225hp to the ground. I've seen before and after numbers from an LT1 cam swap that showed it only pick up 10hp, That LT4 hot cam is even bigger than the 274HR, so I'm not sure its a very good comparison. Just the cam is going to get you 20-100hp depending on what cam you choose. I would expect the LT4 cam needs a much looser converter though, so you would need to look at that too. Total cost maybe $800 for the cam and valvetrain upgrades. Another $300-600 to get the stock vortecs redone depending on if they need new guides and a valvejob or not.

xc_hide_links_from_guests_guests_error_hide_media

Here's a video of the LT4 cam in a stock L31 engine where they give the part numbers and cam specs. I think the LT4 cam can be had from chevrolet performance for significantly less than a Comp cam would cost.

If he wants more power than that, $1000 more gets him an extra 50hp and a few points of compression bump. The AFR heads with the LT4 cam would probably be in that 450hp at the crank range. Maybe even more with the better flow the AFR heads will have at those high lift numbers.

The LT4 Hotcam is the same 0.050 duration as the XM270HR and less lift. The GM cam was ~$550 last I checked.

EDIT-Actually just looked up the GM LT4 Hotcam, it is $564.11.

LT4 Hotcam and similar work very well with the 4.3 W S10 converter.

 

[best97obs]

I'm gonna get the same valve springs and retainers no matter what cam I get I just need to know if I should get the lt4 hot cam or the XM270HR.

 

[L31MaxExpress]

I'm gonna get the same valve springs and retainers no matter what cam I get I just need to know if I should get the lt4 hot cam or the XM270HR.

You will need springs and retainers as well as rock arms with nearly any cam change.

Most cams would be better suited with a torque converter upgrade as well.

 

[best97obs]

not a millionaire lol.

 

[FourEightZero]

400 HP is going to cost you some money unless you really know what you're doing (including hunting down deals) and can work some mechanical alchemy.

Not to mention.. $1000 really isn't that much money in 2023. Hooray for fake, fiat currency!

Knowing what I learned from my first build.. I would have made some different decisions going all the way back to the purchase of the used truck. I don't regret it though.. I like my ride and the experience was more than worth it.

 

[L31MaxExpress]

400 HP is going to cost you some money unless you really know what you're doing (including hunting down deals) and can work some mechanical alchemy.

Not to mention.. $1000 really isn't that much money in 2023. Hooray for fake, fiat currency!

Knowing what I learned from my first build.. I would have made some different decisions going all the way back to the purchase of the used truck. I don't regret it though.. I like my ride and the experience was more than worth it.

400 hp at the crank is not overly hard starting with a Vortec 350. It is the supporting modifications that will kill you. The engine modifications to get 400 hp are about 1/3 of what you need. It is a snowball effect from there. The 4L60E will not like it long. You will realize the brakes and front end need attention. Your tires and open differential will become inadequate, etc.

 

[best97obs]

I've already installed a limited slip diff in my 2wd. Also just replaced almost everything on the front end after I did my drop no to long ago. Just replaced tires after drop too.