Engine Backfire Diagnosis Led to Wiped cam Lobes

[rich weyand]

A word on cams for you.

12-230-2 will work fine. With dual-plane and long-tube headers, 290hp/420lbft. Lift is .432/.444. RPM range is 600-4600.

12-235-2 will wind a bit tighter. With dual-plane and long-tube headers, 290hp/415lbft. Lift is .421/.451. RPM range is 1000-5200.

12-300-4 is what I am running. With dual-plane and long-tube headers, 275hp/420lbft. Lift is .390/.390. RPM range is 600-4600.

So all of these are in the same ball park. 12-230-2 has the same hp and torque as the 12-235-2, but will run out of pull at 4600 rpm. 12-235-2 will match that, and pull to 5200, which is a better fit with stock shift points. 12-300-4 gives up some hp on top, matches the torque in the bottom, but keeps the stock .390/.390 lift, which is easier on the valve train (and cam lobes). That's why I picked the 12-300-4, for engine lifetime sake, since they are so similar in performance.

All three cams will work with stock lifters and springs. Note: NEW stock lifters and springs.

For the 12-230-2 and 12-300-4, you should replace one weight in the TH350 governor with the next bigger weight to bring the stock shift points down 500 RPM. If it's a stick (sorry, I don't remember and it's a lot of posts back!), then you will time the shifts yourself, so no worries.

The cam that's in there is an old cam design. In an ideal world, valves would be open or shut, with no in-between. That would maximize flow while giving you an earlier intake closing for more dynamic compression and a later exhaust opening for longer pressure on the exhaust stroke. Unfortunately, we can't do that -- cams are ramped. You can tell how long the ramps are by subtracting the .050 duration from the advertised duration.

The cam that's in there has ramps in the mid- 70-degree range. All three Comp Cams have modern computer-aided designs with ramps in the mid- 40-degree range. That's 30 degrees less dead space in both the intake and exhaust cycles. The difference that makes in the ability to tune the other cam parameters cannot be overstated.

I think you will be very happy with whichever of those three cams you pick. Not a bad choice among them, really.

 

[firebane]

^ Wise words.

 

[HotRodPC]

Did you get a cam yet? Take a look at something around these specs. This one might a have a little lope when it's cold and at lower idle, but it'll be a nice running cam for low end, yet still have some mid range and a bit of pull over 5000 rpm. Keep in mind, these guys going for a lopey cam are making an all show no go motor. Why? Because to have lope you need valve overlap. Valve overlap means loss of compression so you need to have higher compression pistons or small combustion chambers to compensate for the compression loss and most are using an 8.5:1 dish piston 76 CC headed motor that is just a gutless wonder that SOUNDS mean.

http://www.summitracing.com/parts/sum-1103/overview/

 

[HotRodPC]

Now I see Rich's post. Those are all good mpg bottom end cams that will work well with a low compression motor. That one I put up there is more of a higher rpm cam but should still work with low compression.

 

[Skweegle89]

Did you get a cam yet? Take a look at something around these specs. This one might a have a little lope when it's cold and at lower idle, but it'll be a nice running cam for low end, yet still have some mid range and a bit of pull over 5000 rpm. Keep in mind, these guys going for a lopey cam are making an all show no go motor. Why? Because to have lope you need valve overlap. Valve overlap means loss of compression so you need to have higher compression pistons or small combustion chambers to compensate for the compression loss and most are using an 8.5:1 dish piston 76 CC headed motor that is just a gutless wonder that SOUNDS mean.

http://www.summitracing.com/parts/sum-1103/overview/

I have not ordered anything yet. Just got my year-end from work yesterday so I'm trying to see how much I've got for a budget. The lope doesn't interest me anymore. The cam I just pulled out of it had all kinds of lope and it was pretty gutless. The truck will rarely see 65mph. Will mostly be driven around town and to the deer woods. Those summit cams do seem like the most cost effective option and appear to be pretty good cams. If my help shows up today the motor will be out and I can get the heads pulled off and figure out what to do about those and that will help determine how much I have left for a cam and lifters.

 

[rich weyand]

I have not ordered anything yet. Just got my year-end from work yesterday so I'm trying to see how much I've got for a budget. The lope doesn't interest me anymore. The cam I just pulled out of it had all kinds of lope and it was pretty gutless. The truck will rarely see 65mph. Will mostly be driven around town and to the deer woods. Those summit cams do seem like the most cost effective option and appear to be pretty good cams. If my help shows up today the motor will be out and I can get the heads pulled off and figure out what to do about those and that will help determine how much I have left for a cam and lifters.

Subtract the .050 duration from the advertised duration for that Summit cam. It has 74 degrees of ramps, so it's an old grind. Not necessarily a "bad" cam, but just much less capable than a modern design.

A note about lope. Everybody thinks they want it, but what it means is that the engine doesn't want to run at 700 rpm. So how much torque do you think you're going to get at 1000, or 1500? An engine that's going to generate torque at low rpm is going to LIKE running at low rpm, so it will idle really smooth.

The way they get launches at the drag strips out of engines with a lot of lope is to run high-rpm lockup torque converters so they can wind the engine up to where the hp is. High-rpm torque converters are great for the drags, but a PITA to drive around on the street, and they're hard on transmissions.

 

[Skweegle89]

I did learn some things today about summit products. Take it with a grain of salt because I didn't get this direct from summit, but:

Summit intakes are made by Weiand.

Summit turbo mufflers are Dynomax.

Summit headers are Dynomax

Summit cams are made by Crane

Summit SFI flex plates are made by Pioneer

Summit oil pans are Mildon.

I know there has been some debate on wether or not some of these things were China made crap, so there ya go.


Sent from my iPhone using Tapatalk

 

[350runner]

If you by a summit cam make sure you check to see if you have to use a degree wheel to degree the cam

Sent from the dust in front of you!

 

[DoubleDingo]

Crane cams are made in the USA and are of good quality. Unless someone can prove to me differently, I stand by that. I don't buy Summit brand stuff and only buy some stuff that is made in China if I absolutely without a doubt need it. If I don't need it, I take it back or simply won't buy it period. It's funny the look on the clerk's face when they ask why it is being returned, "It's made in China, I didn't check that before taking it home, as soon as I saw it was made in China I brought it right back to you".

 

[Skweegle89]

Crane cams are made in the USA and are of good quality. Unless someone can prove to me differently, I stand by that. I don't buy Summit brand stuff and only buy some stuff that is made in China if I absolutely without a doubt need it. If I don't need it, I take it back or simply won't buy it period. It's funny the look on the clerk's face when they ask why it is being returned, "It's made in China, I didn't check that before taking it home, as soon as I saw it was made in China I brought it right back to you".

I rarely hear anything bad about Summit products. I run that stage 3 intake and don't have any complaints about it. Its just a little more top end than I want. I know several people that run their mufflers without complaint. I have bought several smaller things such as throttle cables and things like that and they all seem to be of good quality. Their bigger ticket items like intakes and cams are made by American companies, and are just discounted due to small blemishes in the finish and things like that. I think they offer good products at better prices and stand behind their products. If anything you get from them doesn't work you can send it back. People talk crap on the skip white distributors that are made in China, but they have an unconditional lifetime warranty. who cares if it craps out in 2 years. I NEVER HAVE TO PAY FOR ANOTHER DISTRIBUTOR. Their fuel pumps are the same way.

 

[DoubleDingo]

 

[SkinnyG]

A note about lope. Everybody thinks they want it, but what it means is that the engine doesn't want to run at 700 rpm....

I really like a choppy idle. It is therapeutic for me. It's like magic.

But magic always comes with a price:

This is my cam: 231@050/.470/108LSA, which sounds like this.

Which required healthy compression (10.9:1).

Which required the Rochester to be modified.

Which required an HEI advance kit so I can run 20° base timing, without having detonation anywhere else.

Which required a 2500 stall converter.

Which required a big transmission cooler (I already had).

Which required 3.73 gears.

It idles fine (subjectively), currently 10inHg in gear at about 550rpm. It has enough vacuum to run the power brakes, but only just.

Even with the converter, it drives perfectly normal around town, almost stock-like, and does not feel like it's "slipping." When you put the hammer down, though, the engine flares right up to 2500rpm, which puts heat into the transmission (and heat kills).

I couldn't tell you if it has less torque than stock, since I did not drive the truck before I molested it. A friend's '76 LeMans with a SBC and a small Edelbrock cam is slower everywhere.

All of this isn't the best for fuel economy, towing, carrying loads, or any real sensibility. But I wouldn't change a thing. I knew the compromises, and made the choices. I'd foolishly do it again, too.

 

[rich weyand]

I really like a choppy idle. It is therapeutic for me. It's like magic.

But magic always comes with a price:

This is my cam: 231@050/.470/108LSA, which sounds like this.

Which required healthy compression (10.9:1).

Which required the Rochester to be modified.

Which required an HEI advance kit so I can run 20° base timing, without having detonation anywhere else.

Which required a 2500 stall converter.

Which required a big transmission cooler (I already had).

Which required 3.73 gears.

It idles fine (subjectively), currently 10inHg in gear at about 550rpm. It has enough vacuum to run the power brakes, but only just.

Even with the converter, it drives perfectly normal around town, almost stock-like, and does not feel like it's "slipping." When you put the hammer down, though, the engine flares right up to 2500rpm, which puts heat into the transmission (and heat kills).

I couldn't tell you if it has less torque than stock, since I did not drive the truck before I molested it. A friend's '76 LeMans with a SBC and a small Edelbrock cam is slower everywhere.

All of this isn't the best for fuel economy, towing, carrying loads, or any real sensibility. But I wouldn't change a thing. I knew the compromises, and made the choices. I'd foolishly do it again, too.

If you aren't already, you might want to run full-synthetic ATF in the transmission. Full-synth will result in lower transmission temperatures.