L31 towing cam upgrade

[kylenautique]

I actually broke out some engine modeling software a few minutes ago. I modeled a stock L31 then added the 08-500-8, the 08-409-8 cam as well as the Summit 8800. The Summit 8800 also carries nearly identical specs. The power curves of all 3 you could lay over the top of each other with the only difference being under 2,000 rpm and above 5,000 rpm. At 1,500 rpm the 08-409-8 cam is about 5 ft/lbs stronger than the 08-500-8. At 5,500 rpm the 08-500-8 makes about 5 more hp than the 08-409-8. Then comes along the 8800. When I plugged in the specs off the Summit cam card, the 8800 was down about 10 ft/lbs at 1,500 rpm but up 10 hp at 5,500. I then noticed that the 8800 shows to drop in on a 111 ICL with a 112 LSA. The Comp cams both have 4* advance. Like any engine builder in the same situation, I modeled the effect of using the inexpensive Cloyes single roller 3-way adjustable timing set advancing the cam 4*. The 8800 fell right between the 08-409-8 and the 08-500-8. It splits the difference down low as well as up top and fell right in the middle of the two Comp Cams on the extreme ends. From 2,000-5,000 rpm the computer model does not show more than 1-2 tq or hp difference anywhere between the 3 cams. Given the cost difference and Comp Cams lack of availability, I would go with the Summit 8800 and Cloyes 9-1157.

Wow great info! I might give summit a call too. I emailed Comp Cams last light and asked them about the 08-500-8 and the 08-049-8, and this was their response.

Go with our Xtreme Energy camshaft part# 08-500-8

Since you are replacing your valve springs as well, take advantage of the additional lift of that camshaft. You will get a better bump in power from the additional lift.

Also, use drop in valve spring kit part# 26918VCS-KIT

It is a drop in spring kit for the vortec heads that is good to .540” lift

 

[SNCTMPL]

I actually broke out some engine modeling software a few minutes ago. I modeled a stock L31 then added the 08-500-8, the 08-409-8 cam as well as the Summit 8800. The Summit 8800 also carries nearly identical specs. The power curves of all 3 you could lay over the top of each other with the only difference being under 2,000 rpm and above 5,000 rpm. At 1,500 rpm the 08-409-8 cam is about 5 ft/lbs stronger than the 08-500-8. At 5,500 rpm the 08-500-8 makes about 5 more hp than the 08-409-8. Then comes along the 8800. When I plugged in the specs off the Summit cam card, the 8800 was down about 10 ft/lbs at 1,500 rpm but up 10 hp at 5,500. I then noticed that the 8800 shows to drop in on a 111 ICL with a 112 LSA. The Comp cams both have 4* advance. Like any engine builder in the same situation, I modeled the effect of using the inexpensive Cloyes single roller 3-way adjustable timing set advancing the cam 4*. The 8800 fell right between the 08-409-8 and the 08-500-8. It splits the difference down low as well as up top and fell right in the middle of the two Comp Cams on the extreme ends. From 2,000-5,000 rpm the computer model does not show more than 1-2 tq or hp difference anywhere between the 3 cams. Given the cost difference and Comp Cams lack of availability, I would go with the Summit 8800 and Cloyes 9-1157.

I like the Summit cams, they are a great value and made in America. As we have discussed before, I have a Summit store about a mile from work, and I have grown to trust the quality and value of Summit branded parts.
I just purchased the 8801 for a mild 383 build for my son’s truck and I think the 8800 would be a great choice for a Vortec headed 350. Summit probably has some valve springs for vortecs, cheaper than comp, and probably made by comp.

 

[L31MaxExpress]

Wow great info! I might give summit a call too. I emailed Comp Cams last light and asked them about the 08-500-8 and the 08-049-8, and this was their response.

Go with our Xtreme Energy camshaft part# 08-500-8

Since you are replacing your valve springs as well, take advantage of the additional lift of that camshaft. You will get a better bump in power from the additional lift.

Also, use drop in valve spring kit part# 26918VCS-KIT

It is a drop in spring kit for the vortec heads that is good to .540” lift

Some vortecs quit flowing at 0.450 and actually fall off at 0.500 so more is not always better with them. The Mexican 062 heads are the bad ones. There is more to the cam specs than lift alone. The 08-409 has a tighter LSA and more advanced intake close, later exhaust valve opening all of which make a bigger difference than a small increase in lift. The 08-409 will make power sooner and have more off-idle throttle response and torque than the 08-500 will which is important towing.

Furthermore I compared the GM 6395 to the other cams and it does fall off above 5,000 rpm compared to the other offerings but betters the other offerings by as much as 30 ft/lbs at 1,500 rpm. The 6395 carries better torque to 3,000 rpm than even the stock cam. From 3,500 to 5,000 the 6395 matches the other cams. The 6395 works with the stock cylinder heads including stock spring package.

I guess I should also state when I went from the Comp 4x4 to the 6395, I had a factory B82 high stall in the 4L85E, it stalled ~2,500 rpm behind the cammed 350. I probably would have noticed some low-speed power gains with the 6395 had it not been for the looser converter (compared to a stock 4L60E 1,397 rpm stall speed).

 

[L31MaxExpress]

Here is a build using a 6395 cam with power numbers. When I had the 6395 in the van I shifted it at 5,200 and the Comp 4x4 at 5,500. When you change cams you will need to change the timing map in the PCM. The 6395 needs a little timing pulled at lower rpm and heavy loads because of the added cylinder pressure where the Comp 4x4 wanted additional advance.

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[L31MaxExpress]

While not my personal favorite the 6395 is also hard to ignore for a towing application in a stock engine. Especially given the power improvement it gives and cost point for a steel billet roller cam as well as the fact it works with the 100% stock heads and valvetrain including the stamped steel rocker arms and pushrods. Yes it barked the tires in an over 6,000 lbs van with a 4L85E and 3.73 geared G80 14-bolt.

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The 6395 cammed 350 broke the tires loose here just hammering down on the go pedal too. I had P255/70R15s on it here.

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[Road Trip]

That's impressive acceleration, especially factoring in the weight involved!

After watching those videos, I have a question concerning the oil pressure
readings? Specifically, in the 2nd video the oil pressure starts out at 60psi,
and then drops down to 40psi as the speed climbs, and then finally right
at the very end (when you let off) it pops back up to full pressure? (The
general trend is decreasing oil pressure w/increasing rpm?)

Q: Are you partially uncovering the oil pump pickup due to the oil
stacking up on the back of the pan during acceleration? Stock oil pan?
Windage tray? Not to be overly nosy -- I only ask because I've been
sensitized to loss of oil pressure during hard acceleration
and fast sweeping turns on my own stuff. (At least Chevy puts
fairly responsive gauges in their trucks & vans!)

 

[L31MaxExpress]

That's impressive acceleration, especially factoring in the weight involved!

After watching those videos, I have a question concerning the oil pressure
readings? Specifically, in the 2nd video the oil pressure starts out at 60psi,
and then drops down to 40psi as the speed climbs, and then finally right
at the very end (when you let off) it pops back up to full pressure? (The
general trend is decreasing oil pressure w/increasing rpm?)

Q: Are you partially uncovering the oil pump pickup due to the oil
stacking up on the back of the pan during acceleration? Stock oil pan?
Windage tray? Not to be overly nosy -- I only ask because I've been
sensitized to loss of oil pressure during hard acceleration
and fast sweeping turns on my own stuff. (At least Chevy puts
fairly responsive gauges in their trucks & vans!)

It was an internal engine problem I found later. The pickup tube had fallen off the pump. Came close to spinning a rod bearing because of it. Which is why the 383 went in. At first I thought the issue was instrumentation, but it was a real issue.

 

[Road Trip]

It all adds up - makes perfect sense. Thanks for the insight!

 

[L31MaxExpress]

This is what the #1 lower half bearing looked like. Rest of the bearings looked perfect like new. The shiny spot is almost 1/2 melted away. I rebuilt that short block and have it sitting on a stand in the shop waiting to go into a future project. No damage to the crank or rods. Very little metal anywhere. I had to polish that rod journal because it had some aluminum melted to it.

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[kylenautique]

It was an internal engine problem I found later. The pickup tube had fallen off the pump. Came close to spinning a rod bearing because of it. Which is why the 383 went in. At first I thought the issue was instrumentation, but it was a real issue.

Yikes! When I worked at a boat shop, we always tack welded the pickup tubes for this very reason.