Not thrilled with power from new 350

[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!

[Fitz]

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!

Before doing anything with add ons or replacing parts it is best to work on the basics. Set initial timing at 12-14 degrees and check the max. It should be near at 36. Once that is done is the carb jetted correctly? Fuel/air ratio needs to be about 14.7:1. You can measure that indirectly and not very accurately by 'reading' the plugs. Black and sooty, too rich light tan just about right. Remember that for the plugs to read anything but idle mixture the vehicle needs to be driven and keep rpm above 2500. If these things are spot on then begin chasing gremlins elsewhere.

[AirSpeed]

Originally Posted by Fitz

Before doing anything with add ons or replacing parts it is best to work on the basics. Set initial timing at 12-14 degrees and check the max. It should be near at 36. Once that is done is the carb jetted correctly? Fuel/air ratio needs to be about 14.7:1. You can measure that indirectly and not very accurately by 'reading' the plugs. Black and sooty, too rich light tan just about right. Remember that for the plugs to read anything but idle mixture the vehicle needs to be driven and keep rpm above 2500. If these things are spot on then begin chasing gremlins elsewhere.

Thanks, I now things like this are suggestive but to me I don't think this sucker could even spin a tire, not that I go around doing burn outs (with my tires costing me $1300 I can't afford to!) but my old tired engine would spin them pretty good! I'll check out the timing tomorrow. I have noticed I don't have a lot of vacuum, At least to my brake booster. looked up vacuum issues with this engine and saw a few complaints. So far most the people I've seen comment on this engine seem content with the power. As far as power at higher rpms I'm so far very happy but the low end seems weak! I'll play around with the timing some more and see what happens. The paperwork says to run without vac advance which I've been doing so I may try hooking it up and see if that makes a difference..thanks again!

[Coach]

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!

Hey Airspeed, as the engine starts to break in, you will notice the low end power increase, which is what I noticed with my 290hp/350. I ordered mine with the Chevy performance aluminum intake, HEI Distributor & Holley 670 Street Avenger carb. I pulled off an Edelbrock intake and carb off the old 350 that crapped out on me. They are in great shape - if you are interested, let me know and we can work something out. I was also thinking about increasing the timing, but didn't want to mess with the warranty, so I left it at the specs recommended by Chevy.

[mechanicalman]

Originally Posted by AirSpeed

Thanks, I now things like this are suggestive but to me I don't think this sucker could even spin a tire, not that I go around doing burn outs (with my tires costing me $1300 I can't afford to!) but my old tired engine would spin them pretty good! I'll check out the timing tomorrow. I have noticed I don't have a lot of vacuum, At least to my brake booster. looked up vacuum issues with this engine and saw a few complaints. So far most the people I've seen comment on this engine seem content with the power. As far as power at higher rpms I'm so far very happy but the low end seems weak! I'll play around with the timing some more and see what happens. The paperwork says to run without vac advance which I've been doing so I may try hooking it up and see if that makes a difference..thanks again!

I doubt hooking up vacuum advance will help, that's mainly for cruise but maybe help a tiny bit on tip-in and light load before it drops out on heavier load. I'd advise you to tune it the best you can without it, then hook it up later.

That particular engine has too much cam for too little compression, and it needs a faster advance than a normal engine.

Put total advance at 36 like Fitz said, and see if you can live with what you get for base (cranks good, no ping). If still sluggish, you might try weaker springs on the mechanical advance. ALSO check the advance shaft and make sure it's not hanging up (very common problem on HEI). If you have problems with a sticky advance shaft, or base timing being to much for it, send me a PM I know a couple tricks.

When you are done playing with the advance, and if you still want more bottom end, try a cross-over pipe if you have duals.

[mechanicalman]

Originally Posted by AirSpeed

Thanks, I now things like this are suggestive but to me I don't think this sucker could even spin a tire, not that I go around doing burn outs (with my tires costing me $1300 I can't afford to!) but my old tired engine would spin them pretty good! I'll check out the timing tomorrow. I have noticed I don't have a lot of vacuum, At least to my brake booster. looked up vacuum issues with this engine and saw a few complaints. So far most the people I've seen comment on this engine seem content with the power. As far as power at higher rpms I'm so far very happy but the low end seems weak! I'll play around with the timing some more and see what happens. The paperwork says to run without vac advance which I've been doing so I may try hooking it up and see if that makes a difference..thanks again!

Trust me, you need more timing. Don't worry about the warranty, who will know and if they sent someone to check you could just dial it back.

If you are running HEI, you need this kit. Not so much because it's an adjustable pod, but because this particular pod will give you more timing range if you need it after setting total timing to 36-38'. You will get the springs you need as well.
http://www.summitracing.com/parts/crn-99600-1

[1972BlueC20]

I'm not happy to hear this as I just ordered the same engine but in this configuration :

http://www.summitracing.com/parts/nal-19244450

I spent about $3,400 in parts with the engine. I'm also replacing every component that attaches to the engine....starter, fuel pump, radiator, waterpump, HEI, plugs, wires, flywheel, harmonic balancer ect with all brand new parts. My transmission was recently rebuilt with a shift kit and TH400 torque converter.

I'm having it installed professionally by a classic car restoration / auto mechanic shop.

I will report back on my impressions when I get behind the wheel. I should have my truck back on the road sometime next week if all goes as planned.

The guy that's doing the work on my truck has been working on classic cars since 1966 and if he can't get my truck running good with a brand new engine and all new high quality parts then I will be blaming the engine!

I too heard that the 290 hp version is over cammed, but from what I understood it wasn't really a big issue as for affecting the performance. This belief led me to choose the 290 over the 260 version. I hope I didn't incorrectly understand peoples comments regarding this engine. I also wanted the most HP that I could afford for my budget for this particular truck.

Please let me know if you figure it all out and start getting better performance!

[turp mcspray]

The cam in the 290hp engine was designed for a 10.0 compression engine. GM used it in the goodwrench engine, because they wanted a crate engine that was a step up from their base 350, and this cam was already in the parts bin. The big drop in compression takes its toll on cylinder pressure, which = low end torque. As already stated, cranking in a bunch of initial timing as a crutch, is about all you can do, to try to make up for some of the lost cylinder pressure.

[Churchill]

I have a 1st gen 350 in mine as well as a TH350. Looked up the details on my engine (suffix TAX) and it was supposed to give 255hp stock. I have added an aluminum edelbrock intake manifold, edelbrock 1406 600cfm carb, headers, HEI distributor, new plugs gapped at .045 inches, and MSD superconductor wires. I would imagine my HP is somewhere pretty close to 290 now but I have no confirmation of that. All this said, I think my powerplant is similar to yours and so the following information may help you out.

I did use that Crane Cams HEI recurve kit as mentioned above, in conjuction with the information in this thread: http://www.73-87.com/7387garage/drivetrain/hei.htm

I am very pleased with the results of this kit and information, I feel it gets into the power range much sooner now than it did before I recurved the distributor. I have absolutely no problem burning rubber, that said the rear end has 4.10 gears.

Happy tinkering!

[MAC71]

I just looked at the specs. Wow 8:1 compression with a cam that has 222 duration at .050. Is this the same engine? It will have no off idle torque and would really perform well in a light vehicle with deep gears. You don't want a bigger intake or carb because that will make it worse on the low end. You need more compression and less cam. What gears and tire size do you have?

[jeffahart]

I thought the low compression is intentional to control detonation. Is he going to start pinging with the extra advance?

[AirSpeed]

Originally Posted by MAC71

I just looked at the specs. Wow 8:1 compression with a cam that has 222 duration at .050. Is this the same engine? It will have no off idle torque and would really perform well in a light vehicle with deep gears. You don't want a bigger intake or carb because that will make it worse on the low end. You need more compression and less cam. What gears and tire size do you have?

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.

[no1udknow]

So I am reading a few things in here that sound good, and a few things that don't sound accurate. First, checking your plugs is a fantastic idea. Color of plugs is one of the best indicators of how your truck is running. The idea that your mixture will be 14.71 (stochiometric mixture) is only true at cruising speed. Under low end acceleration you should be a little closer to 9 parts air to 1 part fuel. So you may be lean on the low end. The vacuum advance may also be a factor. Hook it up and find out. It is not for cruising, it is actually for acceleration. Which is why it gets hooked up above the vacuum plate. Fuel only burns at a specific rate determined by its octane rating. Higher octane, slower more controlled burn, so under acceleration the speed of the piston increases but the speed of the flame does not, therefore you need to ignite it sooner to compensate for the combustion lag. I am surprised that they suggest not using the vac add as it would seem that that would cause pinging and damage the piston surface????.

Lastly, how long has the truck been down? Possible transmission slippage? Well. Good luck, I would think a new motor has plenty of power to get a little scratch,... but that's just my $.02

[AirSpeed]

Originally Posted by no1udknow

So I am reading a few things in here that sound good, and a few things that don't sound accurate. First, checking your plugs is a fantastic idea. Color of plugs is one of the best indicators of how your truck is running. The idea that your mixture will be 14.71 (stochiometric mixture) is only true at cruising speed. Under low end acceleration you should be a little closer to 9 parts air to 1 part fuel. So you may be lean on the low end. The vacuum advance may also be a factor. Hook it up and find out. It is not for cruising, it is actually for acceleration. Which is why it gets hooked up above the vacuum plate. Fuel only burns at a specific rate determined by its octane rating. Higher octane, slower more controlled burn, so under acceleration the speed of the piston increases but the speed of the flame does not, therefore you need to ignite it sooner to compensate for the combustion lag. I am surprised that they suggest not using the vac add as it would seem that that would cause pinging and damage the piston surface????.

Lastly, how long has the truck been down? Possible transmission slippage? Well. Good luck, I would think a new motor has plenty of power to get a little scratch,... but that's just my $.02

The truck was parked for three weeks, the trans doesn't seem to be slipping, actually seems to hook up faster than with my old engine.

[steves1967]

put a slightly higher stall torque converter in it, it'll get into the engines powerband sooner.

[mechanicalman]

Originally Posted by turp mcspray

The cam in the 290hp engine was designed for a 10.0 compression engine. GM used it in the goodwrench engine, because they wanted a crate engine that was a step up from their base 350, and this cam was already in the parts bin. The big drop in compression takes its toll on cylinder pressure, which = low end torque. As already stated, cranking in a bunch of initial timing as a crutch, is about all you can do, to try to make up for some of the lost cylinder pressure.

THANK YOU I thought I was all alone on that. LOL

They should have kept making the old 186, 041 and 492 heads and put them on there. Shoot you could put a set of 305 heads on that engine even with the smaller intake valves and make more power.

IMAGINE how that engine would run with a set of aftermarket aluminum 64cc chamber 190cc intake runner heads on it? Like lighting a fire?

Or even iron vortec heads would be an instant HP.

[MAC71]

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.

The tall tire makes it worse. That engine will run well when it gets into its power band but will be sluggish off idle. Does the transmission shift "better" or later and firmer? I would expect later and firmer because of the lack of vacuum to the modulator over a engine with a smaller cam.
As suggested you could use a converter with a higher stall speed but it's going to use more fuel and reduce the life of the transmission.
Your best bet is to go with a smaller cam. With out knowing the gear I can not really suggest a cam but you don't want to be over 214 at .050 with you set up. Also it depends on what you want the truck to do. Call comp cams or summit and talk to them about a cam size that would work but figure out what gear you have first or your just wasting time. If you just want to live with it keep a small carb and intake and small exhaust system and give it lots of timing, both initial and mechanical.

My 71 c10 has a 9.5:1 350 with a cam that is 212 at .050 a 700r4 3.73 gear with posi and only stops smoking the tires only when I let of the gas and gets 17 mpg at 75 mph and I run regular fuel.

[Hugh Mongus]

I bought that same engine a few months ago. I used a performer RPM intake with an Eddy 1405 carb. I was not impressed by the performance; however, the reliability was great.

After about 1000 miles, I ended up installing vortec heads, changing the cam to the Lunati 60102, and installed the Eddy Performer EPS vortec intake with a Holley Street Avenger. It's a totally different engine. Then I had it professionally tuned. I am happy with it now. My timing is at 19 degrees. That's where the guy that tuned it set it.

In my opinion, those crate engines are great for someone who just wants to putt around town. If you are looking for any kind of performance, I would not recommend that engine.

[Fitz]

Originally Posted by no1udknow

So I am reading a few things in here that sound good, and a few things that don't sound accurate. First, checking your plugs is a fantastic idea. Color of plugs is one of the best indicators of how your truck is running. The idea that your mixture will be 14.71 (stochiometric mixture) is only true at cruising speed.

Absolutely true! Reading the plugs after a short cruise is the easiest way to determine if the carb is jetted correctly because at cruise the accelerator pump is not adding more gas to the mixture. get it correctly jetted then the accelerator pump is the only other (and somewhat unlikely) contributor by that carburetor to poor acceleration and poor low end torque.

I went through this process with my ZZ572 when I was breaking it in. The engine pulled like a dog fresh out of the box, timing was intermittent and the fumes from the back would kill your neighbors cat from a block away. A new chip for the HEI dizzy cured the intermittent timing and dropping THREE jet sizes on the Holley 850 got it close enough to that mythical 14.7:1 fuel air ratio. That truck woke up! From lazy 13's to low 11's in just one day of test and tune. I don't know a better way to pick up 2 seconds on a quarter mile pass.

If the compression on that engine really is only 8.0:1 there will be other things that might be needed to get it to perform. Look on the bright side, 8.0:1 is just PERFECT for an abnormally aspirated engine! Supercharger anyone?

[1972BlueC20]

Damn now I'm really bummed about ordering this engine, it's already shipped....it will be here on Friday!

I'm not looking for performance, it's a C20....but I was just hoping for more power than my stock 175Hp 350.

Will it be stronger than my stock engine??

I have a 4.10 gear in the rear end.

[Lattimer]

That engine should be fine if you get it tuned right. Getting the timing set up and the fuel set up right will make a night and day difference.

I had a worn out 220 HP (rated) 327 in my truck. Replaced it with a 355 crate. Crate came with a dyno sheet showing 381 HP. First got it broken in and running and it sucked. No power off idle, seemed to rev slow, and drank gas like crazy. The 327 felt better!

New springs in the dizzy, switched to manifold vacuum on the advance, and went up 2 sizes on the accelerator pump nozzle, and now its very fun to drive. I get about 12 mpg in mixed driving, combo of 75mph highway and driving like I stole it between lights. Kind of hard getting going from a light with the open diff sometimes though......

[mechanicalman]

Originally Posted by Hugh Mongus

I bought that same engine a few months ago. I used a performer RPM intake with an Eddy 1405 carb. I was not impressed by the performance; however, the reliability was great.

After about 1000 miles, I ended up installing vortec heads, changing the cam to the Lunati 60102, and installed the Eddy Performer EPS vortec intake with a Holley Street Avenger. It's a totally different engine. Then I had it professionally tuned. I am happy with it now. My timing is at 19 degrees. That's where the guy that tuned it set it.

In my opinion, those crate engines are great for someone who just wants to putt around town. If you are looking for any kind of performance, I would not recommend that engine.

I was thinking that Vortec heads would be the answer for this engine, with the cam you chose I'll bet you are getting around 375HP.

Curious, did you change the cam with the heads or did the cam change come after the heads? I expect you wanted the split duration nd thae 112 lobe seps.

I'd be tempted to leave that cam if upping the compression with the Vortec heads being 12cc smaller than the factory "76cc" heads. I'd be curious to try 1.6 exhaust valves and mild ex porting to off-set the 290HP cam's straight up duration.

[mechanicalman]

Originally Posted by Hugh Mongus

I bought that same engine a few months ago. I used a performer RPM intake with an Eddy 1405 carb. I was not impressed by the performance; however, the reliability was great.

After about 1000 miles, I ended up installing vortec heads, changing the cam to the Lunati 60102, and installed the Eddy Performer EPS vortec intake with a Holley Street Avenger. It's a totally different engine. Then I had it professionally tuned. I am happy with it now. My timing is at 19 degrees. That's where the guy that tuned it set it.

In my opinion, those crate engines are great for someone who just wants to putt around town. If you are looking for any kind of performance, I would not recommend that engine.

I was curious about the 19' timing, assuming it's base with vacuum pod dis-connected. That is a lot of cam so I guess that kills excessive pressure at cranking speed. Are you running manifold vacuum or ported? Do you run vacuum assisted power brakes?

[Hugh Mongus]

I changed the heads and the cam at the same time. The guy I bought the refurb heads from installed the springs from my cam kit for me when I picked them up. He also made sure they had enough lift for that cam.

The 19 degrees of timing is initial with the vacuum unhooked. It gets 38 degrees all in ( I cant remember where in the RPM range, thinking 2700). I had it set at 14 degrees prior to his tune.

I use ported vacuum and I have vacuum assisted brakes and they work fine. The engine has around 15 inches of vacuum at idle.

I have zero complaints about the performance of the engine now.

[Hugh Mongus]

Originally Posted by mechanicalman

I was thinking that Vortec heads would be the answer for this engine, with the cam you chose I'll bet you are getting around 375HP.

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.