greddy91

iTrader: (2)

I wholeheartedly regret not going with 3.55s. I went 3.90 instead and first and second gear are a joke on daily compound tires.

barrok69

There is no way I would go bigger than the 3.73's that I currently have. I'm sure 3.55's would be fine, but i'd estimate that it would be more useful if I were in the high 600whp range which I don't have a desire to hit.

With the current power and rear end I have I don't even have to shift out of 6th to make a clean pass at 70mph and bumping up another 50whp or so shouldn't change much from a drivability factor. I really don't need to be driving around at lower RPM in the city.

TorchRedRob

iTrader: (1)

Thanks for these informative posts, Martin. I'm working on a setup very similar to barrok69's. What is the life expectancy of the springs with the cam in the kit you spec'd? I love the idea of a cam, but since I drive the car about 15k miles a year, I can't stand the idea of checking and/or replacing valve springs all the time. If it was once every 40-50k or something, I'd probably be okay with it. Thanks in advance!

rand49er

Even with the 3.73 OEM rear the static frictional coefficient of street tires is greatly exceeded in 1st gear and even in 2nd gear. With the 3.90 (or 3.91), it's even greater. It is, however, one way to get more power to the rear tires (as in "whp") which is the OP's originally stated goal. How he gets it to the road is another matter.

(I know it's a picky point, and you're correct to point out why a, say, 3.55 rear might be a better choice.)

barrok69

Randy,
I'm not trying to come off as rude, but please drop the Diff gearing discussion. It is not in the scope of what I am looking for and doesn't increase the output of the engine. On a dyno the torque output will increase with the Larger numerical gear and the RPM value will change as well, but the horsepower will remain the same. It's simple math. HP = Torque x RPM ÷ 5252

88BlackZ-51

I wish the V came with a 3.55 instead of a 3.73 gear. I find 1st gear useless and even more so with the TQ of the Maggie. I certainly think a 3.91 would make the car even worse to drive from a start. Randy is a good guy but I agree with the above. Back on regular schedule program. Some good info in this thread!

barrok69

I dunno. My traction issues only occur when I'm being a derp. Get some good tires wider than 245 section width, they make all the difference

88BlackZ-51

I was referring to starting off in 2nd gear. My Michelin Super Sports do very well in fact considering. I have owned a few vettes prior to the V and they had 3.42's and 3.07's. I get why the V got the gear to compensate on the chunk but I'd rather rev lower on the highway then higher.

So are you going to buy that cam mentioned??

barrok69

I tried calling Martin to talk about some different options but haven't been able to get a hold of him, and his voicemail is full. So no. I'm in a holding pattern right now.

Here is what has been recommended to me from BTR and Martin Smallwood

BTR:
225/235 116+5 .605/.595
BTR Trunion+bolts
5/16" 7.400" pushrods
.660 Dual Platinum springs + Ti retainers
C5.R Timing chain

Martin Smallwood:
222/234 117+4 .612/.603
Straub tech Trunion + ARP bolts
Chromoly 5/16" pushrods
.660 Dual Platinum springs + Ti retainers
IWIS single roller timing chain
Gasket kit

I think my only concern is the higher lift suggested by Martin. It's not crazy high by any means, but in terms of valvetrain durability and reliability I'm wondering if I should be sticking closer to the BTR spec'd cam for longer life and worry free operation.

I'm also curious as to why they are advancing the timing so much on these particular cams instead of spec'ing the cam differently outright. I've read that anything beyond +4ish is not exactly ideal. I'm no cam expert so I'm looking forward to learning why this is the suggested route to go.

serik21

I think he mentioned early to help scavange exhaust gases

88BlackZ-51

The higher lift suggested by Martin is really peanuts compared to the other cam. My concern is more the duration in a small 346. My last engine that I had built was a 421 with 236/242 and the idle was perfect for my liking.

DMM

The two are essentially similar. Get a feeler gauge and see how much 0.010" really is. You'll never feel or see any difference I 0.010", 1* of LSA, or 1* in duration.

And you're not advancing timing, you're advancing valve events. By doing so you bring the power band of the cam down in the RPM range, which works to the advantage of a PD blower.

I believe both Brian and Martin utilize a similar lobe profile as well, which will be very easy on the valve train. It also looks like Martin may have suggested Brian's valve springs, not sure. There was a guy with an aggressive cam that tested the BTR springs after about a year or two and found them almost at the original specs.

It's an apples/apples comparison between the two grinds from what I can tell. Congrats, you've just confirmed this is the best grind for your application from two of the best in the business.

barrok69

Agreed, I was happy to see that both were very similar. I was just wondering if there was really anything that stood out between the two, but I see your point on how close they are.

Interesting information about the BTR springs although these cam choices are pretty tame I'm guessing compared to the guy that tested the springs. Both shops recommended them. What would you recommend for valve springs that have better proven results?

Martin Smallwood

iTrader: (2)

The cam has -6 degrees of overlap @.050 and 48@.006 which is seat to seat overlap. It will have a slight chop to it at idle, and sound very similar to this:


A set of BTR Platinum .660" springs will last roughly 30-35k miles with this camshaft, possibly even longer if you take the time to pressure test the springs at that mileage. If the springs show within 5psi of what they were they could easily go another 10k miles and could also be shimmed .015-.030" for peace of mind which would increase spring pressure.

Spring life isn't just determined by the cam lobe being used which is a popular notion especially online. Spring life is also determined by the amount of spring pressure used and the OD diameter of the spring itself. Lobe intensity and engine cycles do play a part in spring fatigue, but they are not the only variables that need to be accounted for.

When you compress a spring it creates heat due to friction. This heat dissipates at a given rate based on how much surface area the spring has (OD diameter). If you have a given amount of spring pressure for two different valve springs. We will use 150 seated and 400 open as an example. One spring is 1.30" in OD diameter and the other spring is 1.40" in OD diameter. The spring with the smaller OD diameter will wear at a quicker rate than the spring with the larger OD diameter. This is because the larger OD diameter dissipates heat quicker due to surface area and doesn't heat up as fast as the smaller OD diameter spring. This is similar as to why it takes a larger body of water longer to heat up than a smaller body of water.

Since the larger OD diameter spring dissipates heat quicker, heat created due to friction from compression of the valve spring doesn't fatigue the spring wire as quickly as it does the smaller OD diameter spring.

We can also achieve the same end result of using a larger OD diameter spring by using less spring pressure with a smaller OD diameter spring. A stock LS cylinder casting and the majority of aftermarket castings can only use up to a 1.32" OD diameter spring. Using a beehive spring will also slow the fatigue rate of the spring wire since a beehive spring uses less spring pressure which creates less heat.

I could take the lift on the cam down to .595 intake lift and .587" exhaust lift which would then enable a customer to use a PAC 1218 beehive spring that will easily last 50k-60k miles. I've had customers get up to 75k miles out of a quality bee hive valve spring. These springs were pressure tested until it was determined that they had fatigued past an acceptable limit.

Valve lift is not the end all be all in determining how aggressive a cam lobe is. If you look at the 3 examples I gave in one of my last posts. Lobe #1 has the same valve lift as the other 2 lobes, but it is the most aggressive by far. It has a much faster opening ramp and a faster seating ramp due to decreased duration @.006 and the amount of duration between .006 lobe lift and .050 lobe lift. Lobe #1 also has the most .200 duration which makes it have more negative acceleration over the nose of the camshaft at max lift.

To determine lobe intensity you have to look at the entire picture and not just one part of the photograph. The lobes that I use are very smooth and stable at high engine speeds due to their slower opening ramps and gentle closing ramps. They're also quiet at idle and will keep wear at a minimum. Not only that, but my lobes are proprietary meaning that no one else can grind my lobes as they're mine and mine only. I only use Cam Motion to grind my camshafts and I highly recommend the 8620 core as well. Cam Motion polishes their camshafts with a very expensive machine they just received not too long ago (they used to do it by hand) and they also cam doctor all of the cams before they go out the door, that way you know what you purchased was ground correctly.

When it comes to advance in the camshaft, you can't just say, "It has to have this much advance or the cam is ground wrong." Or say that, "They should just grind the cam differently instead of using advance."

It's all about valve events. Whenever you change duration, LSA or ICL and power changes, RPM changes, idle quality changes or drivability changes it's not the change in duration, LSA or ICL that allowed this to occur. It's the change in valve events that allows this to occur. Brian and I both do not specify camshafts based on duration, LSA or ICL. Brian and I do not care what the duration, LSA or ICL is until we have chosen our valve events that we feel are correct. Once we have those events picked out, we compute those events into duration, LSA and ICL. Then and only then does Brian or I care about duration, LSA or ICL. The amount of advance in the cam is it what is, a culmination of proper valve events needed to achieve the customers wants and needs.

barrok69

Great information Martin. Thank you for the clarifications!

That cam idle video sounds nasty, I love it haha

I think my biggest concern is durability right now. Like you said 30-35k miles on the springs then having to swap... That sucks. Where is the 100k mile solution! Clearly I can't have my pie and eat it too so I'll need to make some decisions and compromises somewhere on how to go about this dilemma while still trying to achieve the power goals I initially set forth. It may not be possible. hmm.

Martin Smallwood

iTrader: (2)

No problem on the help.

The 100k mile solution is to take the lift down even further to .560/.545 and use LS6 springs. This would allow you to take the spring change interval out to 75k miles at least.

Naf

iTrader: (1)

Why not use compcams .660 beehive springs? Or even psi valve springs?

They are easier on the valves in regards to pressures which should give you more durability

Martin Smallwood

iTrader: (2)

The PAC 1218 has worked well for my customers in the past. There are also other PAC beehive springs that could be used such as the 1211X ("drop in" style spring such as the 1218 beehive), 1219X (non "drop in" style spring), and other PSI beehive springs that could be utilized.

I mainly mention the 1218 spring as it is very affordable and drops right in so that it can work with the factory locators, retainers and locks. The only thing needed is a new set of "hat" style locators/seals and voila, you have your ready to go spring kit.

serik21

Martin I sent you pm about some cam info

Martin Smallwood

iTrader: (2)

I'll take a look at it right now.