Gutless Wonder

[fallguy]

The truck's acting up. Acting like a 180hp truck. Pulled a pontoon and couldn't go over 55mph with any wind...then it'd have to shift to 4th gear to make any moderate incline causing it to almost over heat.
Not much for power, if I floor it from zero it tries to get up and go but not as quickly/smoothly as I think it should.

Originally the PO told me the carb had a horrible flat spot, he wasn't kidding. Moderate acceleration killed it every time. Edelbrock tech support suggested specific metering rods and helper springs which fixed the problem. I also added a phenolic spacer which eliminated my vapor lock issues.

I get about 8mpg highway. A full tank will not take me 120 miles.

We pulled plugs and they were wet...really dumping gas. So it's a bit rich id guess but then under load it's too lean....???

GM 350 Crate 290hp motor...2 years old
Edelbrock Performer carb
Edelbrock Performer Aluminum intake
Dana 44 front and Corp 14 rear with 4.10 ratio
Accel distributor

Noone seems to be able to set the timing. Everyone has to do it by ear as I am told there are two marks on the pulley and they can't figure which one to use.

This most recent guy pulled plug from cylinder one to find TDC and then time...still want to know why we can't use the factory marks?

I'm told that after finding TDC and proper timing, I need to add in a vacuum advance kit to the distributor to allow for more power. I understand the new set of weights, but there are 3 sets of springs...what should I use and why?

Could my timing chain or cam/crank gears be off from factory?

This truck is so caps able of more but no one not even 2 GM dealerships, can get it there!

 

[smurph20]

Could be the wrong balancer or the wrong timing tab on the cover.

 

[Green79Scottsdale]

Reminds me of the issue HR had with a spun balancer on his BBC. Do your homework and get the timing marks lined up and correct, then go about putting in the recommended settings for that engine. For what it's worth, I don't think the cam in that crate motor is the best choice for a heavy truck. I have been following a guy with that exact same motor, he put a different cam in it and really changed the attitude of it for the better for his '78. Good luck with this.

 

[77 K20]

My dad has that same motor and has been fighting with it now for a few years. Would not pull his 18' 5th wheel. Had it re-timed multiple times. That stock cam is more for mid to upper end power, and was used in the old high compression engines. It doesn't like the low compression of this engine. Some say the factory even had even degreed the cam back a few degrees to make it run (cam is mismatched for that engine).
The truck was taken to a dealership and 2 independent shops. All said it is running as good as it can.
My dad then had an edelbrock cam put in it. Helped out a bit- but not too much. His engine was advertised with 8.0:1 compression. By playing with a compression calculator I came up with 7.8:1 compression. Hot rod magazine I believe did an article on this same engine. They tore it apart, measured everything and also came up with 7.8:1 compression which is pretty pathetic.
Tomorrow my dad is awaiting a shipment of new rocker arms and then will be putting on a set of 64cc Edelbrock aluminum heads on it. This will bump the compression up to around 8.7:1. Not great, but should make a big difference. In about a week it is supposed to be done.

The engine is only rated at 326ft/lbs of torque- and that was at 3750 RPM.

 

[77 K20]

I can't find that original article but did find this:

http://www.chevyhiperformance.com/techfaq/0808chp_chevy_performance_tech_questions/viewall.html

Tooooo Much Cam
Q I have a GM crate engine, PN 12499529, with 290 hp and 326 lb-ft of torque. I have had two of these engines; both required approximately 30 degrees of initial advance to run properly. The first engine was replaced under warranty by a GM dealer, but nobody could explain why this engine needed so much advance. Any idea? Thanks.
Ike Byers
Butler, PA
A When GM combined a pile of off-the-shelf parts to create the 290hp crate engine, it picked the L46/L82 small-block hydraulic camshaft, developed back in '69. The L46 was released for Corvette use at 350 gross horsepower. This engine was equipped with very good (for the time) 186 casting heads and 11:1 compression. Then GM used the camshaft in the Corvette again in the L82 smog-era 350s. They also had decent cylinder heads and a true 9:1 compression. The L82 was rated at a whopping 250 net horses before the catalytic converter years. Now, let's talk about the 290hp crate engine on the market today.
The base long-block is derived from the solid foundation of the GM Goodwrench replacement 350 engine. In its stock form (with stock inlet and exhaust manifolds), the engine produces 230 hp and 330 lb-ft of torque. The engine is a replacement for the GM LM1 small-block and is rated at 8.5:1 compression; however, every one I've disassembled and cc'd came in around 8:1 compression. The 290hp GM Performance Parts crate engine starts with this base Goodwrench engine with the L46/L82 camshaft. As I said above, this camshaft was designed back in the '60s to run with much more compression. The camshaft specs out at 222/222 degrees duration at 0.050-inch tappet lift, 0.450-/0.460-inch max lift, ground on 114 centers. Why your engine likes so much timing is because it has very low cylinder pressure at low engine speeds. These engines are great for stick shift, lightweight vehicles and for light street rods that want a cool cruiser engine.
If you swapped in a Crane Powermax 260 or a Comp Cams Xtreme Energy EX256, you would have a much happier engine. This engine, with either of those camshafts, will still make 290 hp with a street-performance inlet manifold and a set of 15/8-inch headers. This is the gain of current technology in camshaft lobes. Is there something wrong with your engine to make GM warranty the engines? Absolutely not. It's just a case of misapplication. Good luck.
Sources: compcams.com. cranecams.com


Read more: http://www.chevyhiperformance.com/t...nce_tech_questions/viewall.html#ixzz2gRA5THhe

 

[HotRodPC]

Could be the wrong balancer or the wrong timing tab on the cover.

Reminds me of the issue HR had with a spun balancer on his BBC. Do your homework and get the timing marks lined up and correct, then go about putting in the recommended settings for that engine. For what it's worth, I don't think the cam in that crate motor is the best choice for a heavy truck. I have been following a guy with that exact same motor, he put a different cam in it and really changed the attitude of it for the better for his '78. Good luck with this.

Yep, Do the homework and MAKE SURE you have the correct or not spun balancer. I timed mine by ear best I could with a misadjusted carb due to the EGR Valve in the way since the mark never lined up right. Long story short, I ended up finding out my balancer was spun almost 1/3 of a full turn throwing timing lights wayyyyyyyyyyyyyyyy off. Also cured a vibration problem I always had that I assumed was the beat up torque converter I used. You're timing may be way off and you just don't realize it due to other factors. 8mpg flat SUCKS !!! Something is very wrong.

 

[HotRodPC]

I can't find that original article but did find this:

http://www.chevyhiperformance.com/techfaq/0808chp_chevy_performance_tech_questions/viewall.html

Tooooo Much Cam
Q I have a GM crate engine, PN 12499529, with 290 hp and 326 lb-ft of torque. I have had two of these engines; both required approximately 30 degrees of initial advance to run properly. The first engine was replaced under warranty by a GM dealer, but nobody could explain why this engine needed so much advance. Any idea? Thanks.
Ike Byers
Butler, PA
A When GM combined a pile of off-the-shelf parts to create the 290hp crate engine, it picked the L46/L82 small-block hydraulic camshaft, developed back in '69. The L46 was released for Corvette use at 350 gross horsepower. This engine was equipped with very good (for the time) 186 casting heads and 11:1 compression. Then GM used the camshaft in the Corvette again in the L82 smog-era 350s. They also had decent cylinder heads and a true 9:1 compression. The L82 was rated at a whopping 250 net horses before the catalytic converter years. Now, let's talk about the 290hp crate engine on the market today.
The base long-block is derived from the solid foundation of the GM Goodwrench replacement 350 engine. In its stock form (with stock inlet and exhaust manifolds), the engine produces 230 hp and 330 lb-ft of torque. The engine is a replacement for the GM LM1 small-block and is rated at 8.5:1 compression; however, every one I've disassembled and cc'd came in around 8:1 compression. The 290hp GM Performance Parts crate engine starts with this base Goodwrench engine with the L46/L82 camshaft. As I said above, this camshaft was designed back in the '60s to run with much more compression. The camshaft specs out at 222/222 degrees duration at 0.050-inch tappet lift, 0.450-/0.460-inch max lift, ground on 114 centers. Why your engine likes so much timing is because it has very low cylinder pressure at low engine speeds. These engines are great for stick shift, lightweight vehicles and for light street rods that want a cool cruiser engine.
If you swapped in a Crane Powermax 260 or a Comp Cams Xtreme Energy EX256, you would have a much happier engine. This engine, with either of those camshafts, will still make 290 hp with a street-performance inlet manifold and a set of 15/8-inch headers. This is the gain of current technology in camshaft lobes. Is there something wrong with your engine to make GM warranty the engines? Absolutely not. It's just a case of misapplication. Good luck.
Sources: compcams.com. cranecams.com


Read more: http://www.chevyhiperformance.com/t...nce_tech_questions/viewall.html#ixzz2gRA5THhe

I'll agree totally with this article. Makes perfect sense. I myself too always wondered how they come to 290 hp with that cam in an 8.5 comp motor that I never figured was really 8.5:1 since with dish pistons and 76cc heads, it doesn't take a mathematician to figure out it's not 8.5:1, although with the cam there is not overlap so the static and dynamic compression ratio would be about the same and I'm sure that's what keeps that motor running.

Someone else a couple weeks ago was complainging about this motor not having any torque. That XE256 makes a great RV cam spec. And don't mistake the HE (High Energy Cam) with sorta the same specs because they are very different when all things like lobe center angles are taken into consideration. Be sure to get the Xtreme Energy Series cam.

 

[MrMarty51]

 

[fallguy]

Here's what I've done/noticed.

On the vacuum advance canister I took an Allen wrench and backed the adjustment screw all the way out. Then I screwed it back in 4 turns which gives me about 12 degrees. I do now notice a more effective quicker advance under load.

Should I add in a vacuum advance kit into the distributor and use the lightest spring set, medium or heaviest?

My timing issue...my harmonic balancer has two timing groves on it...which confuses me to start with. When warmed up and running at idle, those marks are at 11 and 10 o'clock. The timing tab is at 2 o'clock. WTH!?! So basically we're timing from ear!

I went to parts store and ordered a new harmonic balancer for a 350...they gave me same balancer....so it must be right

Suggestions/explanations?

 

[fallguy]

My dad has that same motor and has been fighting with it now for a few years. Would not pull his 18' 5th wheel. Had it re-timed multiple times. That stock cam is more for mid to upper end power, and was used in the old high compression engines. It doesn't like the low compression of this engine. Some say the factory even had even degreed the cam back a few degrees to make it run (cam is mismatched for that engine).
The truck was taken to a dealership and 2 independent shops. All said it is running as good as it can.
My dad then had an edelbrock cam put in it. Helped out a bit- but not too much. His engine was advertised with 8.0:1 compression. By playing with a compression calculator I came up with 7.8:1 compression. Hot rod magazine I believe did an article on this same engine. They tore it apart, measured everything and also came up with 7.8:1 compression which is pretty pathetic.
Tomorrow my dad is awaiting a shipment of new rocker arms and then will be putting on a set of 64cc Edelbrock aluminum heads on it. This will bump the compression up to around 8.7:1. Not great, but should make a big difference. In about a week it is supposed to be done.

The engine is only rated at 326ft/lbs of torque- and that was at 3750 RPM.

Let me know what happens please!


JH

Sent from my iPad

 

[fallguy]

I'll agree totally with this article. Makes perfect sense. I myself too always wondered how they come to 290 hp with that cam in an 8.5 comp motor that I never figured was really 8.5:1 since with dish pistons and 76cc heads, it doesn't take a mathematician to figure out it's not 8.5:1, although with the cam there is not overlap so the static and dynamic compression ratio would be about the same and I'm sure that's what keeps that motor running.

Someone else a couple weeks ago was complainging about this motor not having any torque. That XE256 makes a great RV cam spec. And don't mistake the HE (High Energy Cam) with sorta the same specs because they are very different when all things like lobe center angles are taken into consideration. Be sure to get the Xtreme Energy Series cam.

Is this the right one?

http://www.summitracing.com/parts/cca-12-242-2/overview/make/chevrolet

 

[77 K20]

Is this the right one?

http://www.summitracing.com/parts/cca-12-242-2/overview/make/chevrolet

I don't think so. That one has the RPM range from 1600-5800 which is a bit high.

Did find a reference to comp cams and their grind # is XE256H-10, and the part number for it is then 12-234-2. It is for 1000-5200 RPM.

http://www.jegs.com/i/COMP-Cams/249/12-234-2/10002/-1?parentProductId=

 

[77 K20]

Comp has a dyno chart with this cam, but they are using DART heads instead of stock.

http://www.compcams.com/Technical/DynoSheets/XE256H-10_001.asp

 

[77 K20]

Found a dyno chart of the 290hp 350 that actually shows the lower part of the RPM scale. Back when my dad bought his the chart was only from 3000 RPM and up.

You can see that at the "normal" RPM the engine would see for cruising is all at below 300 ft/lbs.

You must be registered for see images attach

 

[HotRodPC]

Found a dyno chart of the 290hp 350 that actually shows the lower part of the RPM scale. Back when my dad bought his the chart was only from 3000 RPM and up.

You can see that at the "normal" RPM the engine would see for cruising is all at below 300 ft/lbs.

You must be registered for see images attach

Good Point 77 K20. So by the looks of the chart, (if accurate, and I have a feeling it is, since it makes sense with the comp ratio and cam spec) the advertised HP and Torque ratings are correct but at much higher rpms, which is fine if you want to be ricky racing and hot rodding around town. This also seem to match the performance of my CP Crate motor. Motor runs good and loves the higher rpm band. I've not towed a load with the truck or carries alot of weight, but I have a feeling it's going to fall flat on it's face when I do. Again, I think these motors need a cam swap to bring the HP/Torque curves down to a lower rpm for those who want to use them for towing.

I still can't hate the motors though. I know several people with them, seen other experiences on forums, and I've seen of noone having an catastrophic failures. There is 2 local guys here who have them in mud trucks and they love them. Again, not pulling any weight and just spinning up the rpms going thru the mud and slinging it everywhere. They're also only 31 and 33 in tires. I'd imagine with some wide 35's they might not like them so much.

I just wonder how putting an RV cam grind in one of these motors will affect the performace. If it will actually help the situation being that the compression ratio is low.