Hello everyone I really need some feedback from cam brainiacs because I can not seem to find the answer for specific Piston-to-Valve clearance issues.

Let me give you some background about my setup first:
*LS1 (stock bottom end)
*243 heads (stock valves)
*LS6 intake
*LS7 lifters
*1.85 SLP rockers
*Longtubes
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Now the cam I was looking at is the Texas Speed 233/239 (.595"/.603") with 112 LSA.
I'm doing PRC .650" Double springs
and 7.40" hardened push rods.

Now, since I have the 1.85 rockers it would increase the lift a little bit more.
I understand the equation for figuring out what the new lift would be with the 1.85 rockers... but I really need to know when PTV clearance becomes an issue. I do not want to flycut the pistons.

A simple yes you will have PTV clearance issues or no you wont have PTV issues would suffice as an answer. I just haven't read anything about a specific number for PTV issues especially with the 1.85 rockers.

 

First off I'd be willing to bet that Texas Speed does NOT suggest using a 1.85
rocker on that cam because of the agressiveness of the lobe profiles.
Second you did not specify what thickness of head gaskets you intend to use.
And lastly NO-ONE will be willing to tell you "you should be fine" unless they
just don't care if you ruin a perfectly good engine. EVERY single PTV thread
will get dozens of "you have to measure to be sure" responses; and for good
reason.

 

Thanks appreciate the input on the 1.85 rockers. Thats why I need to know if I should replace them or not.

As far as head gaskets go I was looking at the 0.40" cometic for a bump in compression, although if I shouldn't do that because of PTV issues then I can run different gaskets.

And I understand I have to measure... I am going to measure and make sure it would work... this doesn't help me when I don't have the cam yet. Thus, my reason for asking about PTV issues.

 

That cam has no advance ground in, so it should work with an otherwise stock engine with unmilled heads and stock valves. Even with the .040" gasket.

Of course, the valve events for that cam really call for more compression. A lot more. So what you have here is a less than optimal setup trying to avoid flycutting. I just flycut my pistons and it's not bad at all. The problem, as you're probably aware, is as you increase cam size, you decrease clearance and make it harder and harder to get the compression where you need it.

Luckily, you can probably mill those heads quite a bit to help since you have no advance in the cam. And advance ground in would decrease PTV, but also lower your IVC, which would help build more torque and require less compression. You should measure your PTV with the stock heads and .040" gaskets, see how much clearance you have and then decide on a mill. I'd also wait on ordering pushrods for that very reason.

Either way, I would definitely take a step back, ditch the 1.85 rockers, and think about your setup. A different cam would probably work far better for what you're trying to accomplish. Something like a 227/234 111+2 would work well with 64cc heads and .040" gasket and make more usable power throughout the powerband vs a 233/239 112+0. You could even mill the heads down as much with the 227 and really bump up torque and power under the curve, and have a stronger performing car that drives better.

 

Thanks JakeFusion that gives me a better idea of what to do. I realize why go with such a big cam when you can make similar power with a smaller cam. I am trying to make the most power from a broad power range like 2000-7000, but I also want a cam that nets me the most horsepower and torque overall.

 

To be honest, something like what I have probably gives the most usable power in the 2500-6700 range. Smaller cams might make more torque and power to 5500 and larger cams more power after 6200, but the avg power would be higher across the range with something like a 234/242 111+3... Of course, I had to flycut with my heads milled to just 62cc.

 

I will not be milling the heads so I would have more PTV clearance.

I guess let me ask a more direct question: is there a certain threshold or maximum value that can be applied to the piston-to-valve clearance? As in should I stay under a certain lift or duration.

 

If you don't mill you can run a T-Rex 242/248 110 in theory.

I would talk to Martin @ Tick or Geoff @ EPS about your setup and let them spec you out a custom cam. That's the best way to go.

 

I've seen really nice dyno numbers coming from the EPS cams. Thanks for the suggestion JakeFusion, I'll have to get ahold of someone at EPS.

 

I am in the same position right now first off as everyone has stated the rockers will not work I have them and am going back to a stocker second to be safe stay under .600 I bought a custom ground Ed Curtis cam .625/.624.235/.239 on 111 obviously won't work this is a quote from one of the guys on my other forum helping me with my build.." my cam was 230/230 .612/.598 but I had 243's milled down to 61cc's....Stock heads should be safer, I think they're 66cc'?" When they tore his heads off found every intake valve tagged the piston. I think we would be safe with a .600 .232/.234. I will be going with the torquer v2 I've heard lots of great thing and have seen awesome power gains on cam only cars. Hope that helps

 

I think that cam will clear fine with stock head gaskets. Mocking up with an old one will give you an idea. My clearances with a 228/232 cam were .100 and .120 with .010 cut 243s on a GM MLS gasket. I milled them an additional .030 for final PTV numbers of .070 and .090. This was my threshold for being comfortable, others run PTV even closer. I suspect yours will be similar. The joy of measuring is you know exactly what you're working with. Good luck.

 

Just as a rule of thumb you will want to be no less than .050 on intake and no less than .080 on exhaust

 

Ditch those rockers and get a custom cam the .040 head gaskets are good. You do not want to be winding that motor to 7000 rpms if you want it to live on stock rod bolts. Anyway your intake starts running out of breath around 6300-6400 rpms. A cam that makes more muscle with power under the curve is much better for a street car. How much time are going to spend at 7000 rpms. See what I mean. These LS series engine make a lot of HP/TQ with smaller cams than the one that you listed. A 224/228 or 228/232 duration cam is more along the lines of what you should be considering. I make 452/418 with a heads/cam and all the bolt ons engine in a DD. Makes plenty used able power under the curve. I could make another 10-15 HP with a larger cam but I don't care about peak numbers. Too many people get caught up in big dyno numbers and big cam numbers. Keep in mind that HP is for show and TORQUE is what hauls your azzzz. I'm much more proud of the 418 RWTQ that my cars makes than its HP.

 

Thanks for the info this helps me put things a little more into perspective. Do you happen to know your lift specs and lsa on that cam?

Lol I have a bone stock ls1 with just a tune and it goes to 7000 no problem on a six speed, but I hear what you are saying, basing it on how high of an rpm the cam makes power still is irrelevant since you don't need to make power at the rev limiter lol.

Those are nice numbers btw. Looks more like LS2 numbers. What cam are you running?

 

.612/.612 and 113+4

 

I'm not saying you can't rev to 7000 rpms but especially in a stock motor why would you want to. Your way past the peak power numbers for that motor. I used to run a considerably larger cam than I do now. I shifted at 7300 rpms and it was still pulling hard at that shift point. Which was way past what I was comfortable with using stock rod bolts. Its street manners were not what I wanted and had to run tall gears to make the motor happy. It was not what I was looking for. Went to a much smaller cam and shift it at 6500 rpms. Peak power is generated at 6200-6300 rpms. I do not go to the track so I don't care about peak power numbers. Usable power for the street was my goal. I make 375 RWTQ at 3200 rpms. Which is more than a stock LS1 makes at peak torque rpms. (4800 rpms) My combo is designed to make power where I can use it which is under the curve. My whole deal was to make good torque at a lower rpm which is much easier on the valve train and the rotating assembly. Which leads to a long engine life span. I change valve springs at 50,000 mile intervals and have never had a spring failure. I just changed short blocks. I had 261,000 miles on the original short block. (no oil consumption problems) It had a pecking noise in the valve train which turned out to be a badly worn lobe on the camshaft. (2nd time doing that no more Comp Cams) I run things for a long time. Car is a DD and I can't drive a dull car plus I hate new cars. I'll just rebuild the old short block and use it in my next project. (An El Camino with late model LS drive train) Most people have a goal in mind or at least they should have one when they start to do a hot rod project. Mine was well planned and I accomplished what I set out to do. I've been hot rodding for over 50 years so I'm starting to get the hang of how this **** works. But what works for me may not be what works for you. If we were all the same it would be a dull world. Cruise till it hurts!!...

224/228 .595/.595 110+0 LSA

 

Appreciate the info everyone. I actually came across a different thread talking about the Trex cam being a maximum for piston to valve clearance so this helps me get the idea.

And slt200mph... that is a pretty low LSA to run. That wasn't a daily driver was it? And the specs on the duration are pretty good looks to be perfect with the lift for no PTV issues.

From what I can see so far it would be wise to get a cam in the 220-230 range for duration and try to stay under a .600" lift max.

 

It has been a great daily driver for the last 180,000+ miles. A great street cam. The 110 LSA lowers the peak power to a rpm level (6200-6300)that I wanted for my engine. As I posted before I had a plan. Horse power is for show torque is what hauls your azzz.