Not thrilled with power from new 350

[AirSpeed]

Thanks everyone! I'll take into account all the suggestions! Going to play with the timing now. If I could just get a little more out of it i would be content. Living in the moundains it's nice having more power (than I used to) at higher rpms, I'm constantly slowed behind cars and trucks not familiar with curvy and steep hiways, it's nice to be able to pass them! Now if I could just get a little more on the bottom. Thanks again!

[Lattimer]

Originally Posted by Hugh Mongus

Since installing the heads and cam, the engine revs much faster. Before it seemed like it took forever to get it going under WOT. The mechanic that installed this stuff for me told me I should be between 375-400hp. I have not had it dyno'd to see. It's currently getting painted.

All I can say is that it's a completely different engine with those two changes.

My crate has vortec heads and the cam is:

.480 Intake .486 Exhaust
224 Intake / 230 Exhaust duration
@ .050 - 112 degree lobe separation

supposedly 9.5:1 compression

Engine dyno showed 381 with a 600 holley and long tubes. I run a street demon 625 and long tubes.

I'd like to chassis dyno it but don't want to spend the money.

[mechanicalman]

Originally Posted by AirSpeed

Recently installed a crate 290 hp 350 in my 72 GMC 4X4 with th350, after a fiasco with broken valves in the first one delivered I got the second in and running. Broke in the cam, have been driving as GM suggest so I haven't really had the nerve to floor it yet but what I'm feeling now is a little disappointing. I have decent power after about 2000 rpm, my trans seems to shift better than ever but low speed power is not there. As I said I haven't really got on it at all but it feels like a dog.
I'm running the stock intake and quadrajet and an HEI out of an 80's truck. After I ordered the engine I was told by a few people here that I would have been better off buying the 250 hp version but of course it was to late.
I am curious if I'm going to be happy with the power after I have it broke in enough to drive it harder, anyone here have this engine in a similar configuration? Are you happy with it? Whst can I do to this engine to squeeze more power out of it? I really don't want to pull the heads or change the cam. Will an aftermarket intake help? New carb? What else can I do to it?
I don't have a lot of money to spend on my truck after just buying new tires then having my engine take a dump so I'm looking for cheap upgrades! Any suggestions on cheap and fairly easy power upgrades would be appreciated! I'm also interested if others with this engine have had similar issues? Thanks!

This whole time I assumed it was the red SWB pulling the AirSpeed. Low as it is, looked like 2WD 1/2 ton.

I'll bet on that old of an HEI the mech adv probably isn't even working. You gotta check that out, just pop the cap and see if the rotor turns against the weights/springs and if it snaps back all the way. Let me know if it's sticking, I can tell you how to fix it if it's salvageable (the pins that hold the weights are probably acutely worn or worn clear through) or save yourself some work and just get a new one (if it's sticking). On top of that, other components that are old are ticking time bombs, like the module and the pick-up coil. EVERY time the vacuum pod moves the pick-up coil wires flex and are that much closer to breaking.

This is the distributor I recommend:
http://www.summitracing.com/parts/pro-141-682/overview/ This distributor, IMO, will be closest suited for your engine out of the box, but you still may need weaker advance springs. It has a steel gear, I would not put that on your cast iron flat tappet cam. You need a cast iron gear.

Or get a cheap one like this: It also has a hardened gear so needs cast iron.
http://www.ebay.com/itm/SBC-Bbc-Smal...605848&vxp=mtr

Put the GEAR off your OLD distributor on either one as it's already been on the new cam so putting on a new one now would put more strain on it. If for some reason you want a new one, measure your shaft if it's .500" use this one.
http://www.summitracing.com/parts/pro-141-682/overview/

BTW, line up the dot on the dist gear with the rotor electrode.

[davepl]

290hp with low compression that doesn't match the cam design will never be fast. But to be honest, a small block in these trucks with that much weight and a 4x4 to boot, plus tall tires, guarantee it will never be fast.

That's not a bad thing. It's just the way they are. If it makes you feel any better, the factory big blocks were only 310hp so you're only 20 short of that anyway, and FAR ahead of the small blocks of the day.

There's no way you're going to get 375-400 out of a 350. Sure, with monster heads and an unusable cam and a single plane intake you can, but not for a street motor.

Keep in mind the 1970s LT1 was (arguably) the most powerful small block made and it came nowhere near that in SAE net power. Gross was 370, but by the time they knocked some compression out of it and switched to net, it was more like 260hp. Yes there was a 327/375 but I'm not buying that number.

If any questions remain, I'd get a dyno tune by someone who knows what they're doing. And don't be sad when you see 215hp on the rollers, that's to be expected. If you can unlock the front hubs (never had one of these in a 4x4 so I don't know) it'll be easier otherwise you'll need a four-wheel dyno, which is usually a Mustang dyno.

Also 38 degrees is way too much total timing, IMHO. You cylinder pressure might be low enough that it doesn't detonate, but the piston is still likely working against a lot of initial pressure before TDC.

Seems like you're happy now, but if it were me that's the route I'd go, and I'd get the vacuum advance put back together properly and the total timing set accordingly. You will need to run more initial than the sticker says, as you've found out. But that additional needs to be backed out of the total.

At the end of the day, there's no replacement for proper basic tuning. Then you can go from there.

[AirSpeed]

Just got back after six runs, seemed to get the best out of it at 12* with the vac advance connected. It idles very smooth and starts with just a tap of the starter which is nice. Still not what I was hoping for but it is a little better. I'm not after a hot rod, just want to be able to keep up with traffic! I live in the mountains so there's lots of long steep hills, it does great up the hills at hiway speeds, plenty of power, if I can squeeze a little more out of the low end I'll be content. I'm going to drive it awhile like this and see how it goes. Will probably get a new distributor anyway, no clue how many miles are on my 80s era HEI. The truck it came out of was in an old junkyard, who knows what it's been through. I replaced all the other accessories because I want dependable, I drive this every day. Thanks again for all the advice, I've learned s few things here today.

[So.Cal.Super]

I agree with Fitz on Tuning the Carb also. I think your biggest benifit would be a cam swap. I think Gm should have rethought that Cam when trying to build a low compression Run on 87 octane motor.

just my .02

Best of luck, keep us informed.

[mechanicalman]

Originally Posted by AirSpeed

Just got back after six runs, seemed to get the best out of it at 12* with the vac advance connected. It idles very smooth and starts with just a tap of the starter which is nice. Still not what I was hoping for but it is a little better. I'm not after a hot rod, just want to be able to keep up with traffic! I live in the mountains so there's lots of long steep hills, it does great up the hills at hiway speeds, plenty of power, if I can squeeze a little more out of the low end I'll be content. I'm going to drive it awhile like this and see how it goes. Will probably get a new distributor anyway, no clue how many miles are on my 80s era HEI. The truck it came out of was in an old junkyard, who knows what it's been through. I replaced all the other accessories because I want dependable, I drive this every day. Thanks again for all the advice, I've learned s few things here today.

Hey AirSpeed-would you clear out some old messages so I can PM you?

mechanicalman

[WhiteWhale]

Originally Posted by Lattimer

switched to manifold vacuum on the advance.....

I was wondering about this as my old 66 Buick wildcat had the advance hooked up to manifold vacuum where as all the later trucks Ive had always used ported vacuum (for smog Im sure).

What is your idle timing with no vacuum attached, idle timing with vac attached and total advance with vac?

[AirSpeed]

Originally Posted by mechanicalman

Hey AirSpeed-would you clear out some old messages so I can PM you?

mechanicalman

Just did! Thanks

[Lattimer]

Originally Posted by WhiteWhale

I was wondering about this as my old 66 Buick wildcat had the advance hooked up to manifold vacuum where as all the later trucks Ive had always used ported vacuum (for smog Im sure).

What is your idle timing with no vacuum attached, idle timing with vac attached and total advance with vac?

Vac plugged I'm at 14. At 750 idle vac hooked up I get about 22. 15" of vac at idle.

All in at 2900 I get 34.

I have the Jegs generic HEI with the lightest springs.

I originally had the vac advance hooked to the timed port, and no matter what I did it bogged really bad at tip in. Had to pump the pedal to keep it going. Swapping to the manifold vac fixed most of that, the rest was getting more squirt from the accelerator pump.


From everything I have read, the timed vacuum advance was strictly an emissions thing.

[AirSpeed]

Originally Posted by Lattimer

Vac plugged I'm at 14. At 750 idle vac hooked up I get about 22. 15" of vac at idle.

All in at 2900 I get 34.

I have the Jegs generic HEI with the lightest springs.

I originally had the vac advance hooked to the timed port, and no matter what I did it bogged really bad at tip in. Had to pump the pedal to keep it going. Swapping to the manifold vac fixed most of that, the rest was getting more squirt from the accelerator pump.


From everything I have read, the timed vacuum advance was strictly an emissions thing.

How much vacuum is required to run a vac booster? I just replaced mine after my engine swap, my old one had an obvious vacuum leak, my new one seems no better than the leaky one. I'm going to put my vac gage I the engine tomorrow to see what I have. My brakes work just okay when I press them once, if I use them again I get no boost or very little.

[Lattimer]

Originally Posted by AirSpeed

How much vacuum is required to run a vac booster? I just replaced mine after my engine swap, my old one had an obvious vacuum leak, my new one seems no better than the leaky one. I'm going to put my vac gage I the engine tomorrow to see what I have. My brakes work just okay when I press them once, if I use them again I get no boost or very little.

I think 17 minimum is recommended. Mine work just ok with the stock booster, I'm going to upgrade it with one from a 90's pickup when I do the front disc swap over Thanksgiving.

I had the same booster with the other engine, and that made 21" at idle, and I still had "just ok" boost.

[AirSpeed]

Originally Posted by Lattimer

I think 17 minimum is recommended. Mine work just ok with the stock booster, I'm going to upgrade it with one from a 90's pickup when I do the front disc swap over Thanksgiving.

I had the same booster with the other engine, and that made 21" at idle, and I still had "just ok" boost.

I hope I'm not going to have problems with enough vacuum to run my brakes on top of everything else! Now I'm going to have to find an auxiliary vacuum pump!

[Lattimer]

Originally Posted by AirSpeed

I hope I'm not going to have problems with enough vacuum to run my brakes on top of everything else! Now I'm going to have to find an auxiliary vacuum pump!

Measure it first and see what you have. That engine should make ok vacuum if the carb and timing are set right.

[mechanicalman]

Originally Posted by AirSpeed

Recently installed a crate 290 hp 350 in my 72 GMC 4X4 with th350.

OK here is a trick. Put the balancer mark on the 16 "before" and make a mark on the 8 "after". So, that mark is actually 24'. Then take the 24' mark and turn it counter-clockwise to the 4 "before" and make another mark at the 8 "after". Now the last mark is 36' BTDC.

For accuracy use a lead pencil and make a "carpenter's vee". Then on the 36 mark use something on top of it to make it easy to see like "whiteout" or something.

The following link shows how a timing tape is installed and should give you some perspective.
http://www.jegs.com/InstallationInst...1/121-8985.pdf

[MAC71]

Originally Posted by AirSpeed

I hope I'm not going to have problems with enough vacuum to run my brakes on top of everything else! Now I'm going to have to find an auxiliary vacuum pump!

Use a vacuum canister and your brakes will be fine. I have a corvette that has 9-10 in of vacuum at idle. With out the vacuum canister there is no power assist but with it the brakes work well, even at a road track or auto x.
In the past I had a large cam in my truck wilt little vacuum and the vacuum canister worked well. Plus you still have power assist after the engine is shut down for one or to stops.

[MAC71]

After following and reading everything on this post I have to add a few things. Some of the info given is really good and some is just wrong. Not here to point out who is wrong or right, just want to make a statement and hope help. I feel for you on your disappointment on your engines performance and hope you get it to where you like it.
Here’s the thing, the truck is a system and every part has to match, a good build can be a screamer or a dog by having one part that does not match the system. Your engine, for the price is a good solid driver and in the correct application will perform well. Problem here is its not in the correct application. You have not given adequate information such as gearing to say what would work well for you. I can tell you this, too much cam for the weight, transmission and tire size. I know the cam you have has similar specs, and may be the same one as the 70’s corvette l82 that had a lot more compression and ran really well in a 3500 lbs car with a 4 speed manual, 3.55 gears and a 27 in tall tire. In a c10 that is a little over 4000 lbs with 10:1 compression maybe a 700r 4 transmission and a 3.73 gear and 28 in tires that engine would run really well. It would be a system thats matched(but still needs more compression).
You stated your in the mountains, but at what elevation are you at? That is needed to know when tuning. You really drop a lot in performance at elevation. You need more timing and smaller jets at elevation.
Lets say you have a 3.55 gear, you would want a cam around 204-210 degrees at .050 max if your looking for good off idle torque.
Can you check the compression? That will tell you a lot about how the cam and compression ratio are working together by knowing what your cylinder pressure is.

[Coley]

Originally Posted by MAC71

After following and reading everything on this post I have to add a few things. Some of the info given is really good and some is just wrong. Not here to point out who is wrong or right, just want to make a statement and hope help. I feel for you on your disappointment on your engines performance and hope you get it to where you like it.
Here’s the thing, the truck is a system and every part has to match, a good build can be a screamer or a dog by having one part that does not match the system. Your engine, for the price is a good solid driver and in the correct application will perform well. Problem here is its not in the correct application. You have not given adequate information such as gearing to say what would work well for you. I can tell you this, too much cam for the weight, transmission and tire size. I know the cam you have has similar specs, and may be the same one as the 70’s corvette l82 that had a lot more compression and ran really well in a 3500 lbs car with a 4 speed manual, 3.55 gears and a 27 in tall tire. In a c10 that is a little over 4000 lbs with 10:1 compression maybe a 700r 4 transmission and a 3.73 gear and 28 in tires that engine would run really well. It would be a system thats matched(but still needs more compression).
You stated your in the mountains, but at what elevation are you at? That is needed to know when tuning. You really drop a lot in performance at elevation. You need more timing and smaller jets at elevation.
Lets say you have a 3.55 gear, you would want a cam around 204-210 degrees at .050 max if your looking for good off idle torque.
Can you check the compression? That will tell you a lot about how the cam and compression ratio are working together by knowing what your cylinder pressure is.

Very good points and well worth considering.
I think a lot of guys get caught up in the 'horsepower number' game....never a good thing, but it happens all the time....pretty much every week here in one thread or another.
I think better results would come much from what MAC71 has stated here and to look at the application from a standpoint of Torque rather than horsepower.
(ie: oversize tires (33"+), 4wd. 4000+ lbs, and a standard 3:07 rear diff.....very difficult to move quickly off the line with a small block unless very well thought out and specified)
Torque in a heavier vehicle generally rules the day in most situations....yet its the hp number that people often chase.
My two bits.
Coley

[Turbo1dr]

I would not buy a engine based off of HP. I'd be asking for the torque figures. I'd rather have a 280HP/400 ft-lb engine over a 325HP/340ft-lb engine.

[AirSpeed]

Thanks guys! I have to admit I fell for the hp rating! I'm really not kicking myself for buying this engine, it really does run nice, smooth, sounds good and I am getting more power after playing with the timing. I am going to invest in a new distributor for reliability of nothing else and hopefully a bit more power. I've had to call a tow truck twice this year, in my 51 years I've never had to be towed and being towed sucks! I think once I get the timing and carb dialed in I will be perfectly content, I'm not looking for a hot rod by any means, thats what my future Chevelle will be for! I will try as you suggest mechanicalman, I'll let you know what I come up with! Thanks again everyone! Appreciate the help!

[AirSpeed]

Originally Posted by MAC71

Use a vacuum canister and your brakes will be fine. I have a corvette that has 9-10 in of vacuum at idle. With out the vacuum canister there is no power assist but with it the brakes work well, even at a road track or auto x.
In the past I had a large cam in my truck wilt little vacuum and the vacuum canister worked well. Plus you still have power assist after the engine is shut down for one or to stops.

Does a vacuum canister require a check valve? How big does the can need to be? Thanks for the suggestion!

[MAC71]

Originally Posted by AirSpeed

Does a vacuum canister require a check valve? How big does the can need to be? Thanks for the suggestion!

Yes you need a check valve. Look on summit and they have a few

[leddzepp]

Have you done a compression check to confirm the rings have seated?

[mrein3]

Originally Posted by AirSpeed

This is the engine I bought
http://m.summitracing.com/parts/nal-12499529

It's in my 72 GMC 4X4, TH350 33" tires. Not sure of the gears but it's stock. I just had the trans rebuilt a couple years ago and had them install a shift kit. One thing I did notice is my trans shifts a lot better now. With my old engine it wouldn't downshift to pass unless I was going 50 mph or under, now it will shift at 60. My old engine was much stronger on the low end but was weak at higher rpms.

Originally Posted by davepl

290hp with low compression that doesn't match the cam design will never be fast. But to be honest, a small block in these trucks with that much weight and a 4x4 to boot, plus tall tires, guarantee it will never be fast.

snip

Originally Posted by Coley

snip

(ie: oversize tires (33"+), 4wd. 4000+ lbs, and a standard 3:07 rear diff.....very difficult to move quickly off the line with a small block unless very well thought out and specified)

snip

As I was scanning through this long post it took a while but I think I know what is wrong with that engine. Nothing. Tall tires, ESPECIALLY if you have 3.08 gears, will never get off the line that well.

All stock diffs are 10% different from the next one. So if you have a 3.08, the next gear would be a 3.4something (GM skipped this one in our trucks). 10% more is 3.73. Then 4.11. There even was a 4.56. My buddy had them in a '66 or so 4x4. That thing was a beast off the line but literally was done at 50 mph.
The reason I bring this up is those 33" tires. Stock tires are approximately 28".
Add 10% (2.8") to that (28") you get 30.8". 10% more of that is close to 33 inches. See where I'm going? If you have stock 3.08 gears and 33" tires, you effectively have a 2.5 or so final gear ratio. If you have stock 3.73s, you made them 3.08s. You would need GOBS of power to spin those tires with 2.5 or 3.08 gears.

Long story short, I think you engine is fine. Get it all dialed in tune-up wise and drive it. You ain't ever spinning those tires on dry pavement.

[AirSpeed]

Originally Posted by mrein3

As I was scanning through this long post it took a while but I think I know what is wrong with that engine. Nothing. Tall tires, ESPECIALLY if you have 3.08 gears, will never get off the line that well.

All stock diffs are 10% different from the next one. So if you have a 3.08, the next gear would be a 3.4something (GM skipped this one in our trucks). 10% more is 3.73. Then 4.11. There even was a 4.56. My buddy had them in a '66 or so 4x4. That thing was a beast off the line but literally was done at 50 mph.
The reason I bring this up is those 33" tires. Stock tires are approximately 28".
Add 10% (2.8") to that (28") you get 30.8". 10% more of that is close to 33 inches. See where I'm going? If you have stock 3.08 gears and 33" tires, you effectively have a 2.5 or so final gear ratio. If you have stock 3.73s, you made them 3.08s. You would need GOBS of power to spin those tires with 2.5 or 3.08 gears.

Long story short, I think you engine is fine. Get it all dialed in tune-up wise and drive it. You ain't ever spinning those tires on dry pavement.

Thanks! My old engine would fry the same tires, I was hoping this one would be as strong if not stronger, it is at higher rpms. I'm not actually looking to spin the tires, just want decent power. I'll live with it, it's running better now, going to play around with it more when I get my new distributor.