[Steve C.]

Not uncommon to see Pontiac street/strip engine combos making peak power at 5500+ rpm using XE roller lobes with 125-135 lbs seat pressure (not a recommendation for this situation but for conversation). Keep in mind more often than not the engine will be rev'd higher than where it actually makes peak power at. If drag racing typicaly your going to shift at a higher rpm. And much involves the valvetrain mass involved with a lot of 'Pontiac' situations.

Always run enough seat pressure to control the valve action as it returns to the seat. Heavier valves require more seat pressure. Strong, lightweight valves require less seat pressure. When in doubt, run slightly more seat pressure . . . not less.

http://www.cranecams.com/faqview.php?s_id=33

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[paul s.]

Seat pressures are absolutely important, but something a lot of people don't talk about are open pressures (over the nose) and spring rate to control loft, a major player in lifter pump up. Gaining 1000 RPM just by a simple valve spring swap is extremely cheap horsepower.

[Steve C.]

Might relate to Paul's point.

With a solid roller if you lose enough spring pressure and the lifter loses contact on the lobe as the valve closes, and note this is important..... after time the springs will further deteriorate to the point it can cause issues other than nosing over at rpm. When people call it 'valve float', more often than not this is what happens.

Not sure about a hydraulic roller lifter. maybe Paul will comment.


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[tr709]

Just a clarification on my 'layover' comment. The car doesn't fall flat on it's face like it's running out of fuel (trust me I've chased that down once before and this is different) it's more like it keeps revving past 5000rpm but no more power, it's done!

[tr709]

On the cam timing it was done a few years back there's a whole thread back when this was first put together, I decided to try and get 5 years out of that cam and the 5yrs were up in may.

cam was degreed on the recommended 106 ICL. It has 4* adv ground into it, so the timing set is "straight up" or dot-dot but the cam is at the recommended ICL

old thread if anyone is interested - I'm re-reading it too

http://forums.maxperformanceinc.com/...d.php?t=614468

[paul s.]

Originally Posted by Steve C.

Might relate to Paul's point.

With a solid roller if you lose enough spring pressure and the lifter loses contact on the lobe as the valve closes, and note this is important..... after time the springs will further deteriorate to the point it can cause issues other than nosing over at rpm. When people call it 'valve float', more often than not this is what happens.

Not sure about a hydraulic roller lifter. maybe Paul will comment

The same thing would happen with a hydraulic roller lifter as well, only now, as rpm increase and the valve spring can no longer maintain control of the valvetrain, instead of the entire lifter body losing contact, it may be only the internal hydraulic mechanism gaining volume as the lobe tries to fling the lifter and pushrod over the nose. Oil pressure is still being applied to the internal cavity of the lifter in all directions. That pressure is now exerting force against the pushrod only, allowing the slack to be 'taken up' by the internal plunger mechanism, thereby changing our preload setting to one where the valve(s) will now be held open--- disrupting airflow in a positive direction.

Originally Posted by tr709

On the cam timing it was done a few years back there's a whole thread back when this was first put together, I decided to try and get 5 years out of that cam and the 5yrs were up in may.

cam was degreed on the recommended 106 ICL. It has 4* adv ground into it, so the timing set is "straight up" or dot-dot but the cam is at the recommended ICL

old thread if anyone is interested - I'm re-reading it too

http://forums.maxperformanceinc.com/...d.php?t=614468

Between your first post and these last two, you have given A LOT of information as to the condition of your COMBINATION.

To make sure we are on the same page, let's look at our terminology; The terms used can be somewhat deceiving from one person to the next. If I hear of an engine 'shutting down' or 'nosing over' then I look at fuel and spark if the person has never addressed those items. But if they have, such as in your case, I then look at valve springs, and the severity of the problem could be a severe 'nosing over' to a mild lack of rpm capability where the engine just doesn't want to pull--- it will depend on the lobe, the weight of the valvetrain components, spring load, rocker arm ratio--- it all matters. But the one simple place where we can do something about all of that is the valve spring.

That is where using a roller cam really benefits the end user; you can jack up the pressure without fear of flattening a cam lobe. Now, with the acceleration and lift of some of these lobes out there, as well as the mass of the roller lifters vs a flat lifter, there is no way I would use flat tappet seat and open pressures to control them.

ASS-UMING that valvetrain geometry is correct and such, I believe you would see another 200-400 rpm increase by increasing valve spring load. I know, not the increase you were looking for. But the information given in those posts, there are a couple of items that jump out at me. Some guys on this site won't want to hear it, but, it isn't the duration that is hurting you. You DEFINITELY have enough duration for your engine to pull to 6,000 rpm--- not just revving--- but making useful power! That's where Steve C's comment about simply changing duration really comes into play. It simply moves the rpm range up or down. When you increase LIFT, you MAKE POWER ACROSS THE ENTIRE RPM RANGE. Speaking only in terms of duration SEVERELY limits the potential of any engine! With a low numerical gear and low stall convertor, your combination screams low rpm torque. Generally speaking, that means keeping the duration in check, increasing lift, and tightening the LSA. Good valvetrain components and proper assembly will assure good USEABLE rpm potential.

Sometimes it is the fundamental assembly and how it relates to the combination as a whole... in MY opinion, there is no reason to advance a short cam in a big displacement engine with adequate static compression ratio... you can build TOO much cylinder pressure.

If you would like to discuss this in more detail, feel free to PM me or call using the info on my site... what I would suggest to you will only cost you a weekend and I would not make a dime off of it.

Good luck on your project.

[Formulajones]

It sure does sound like it's running out of valve spring. If you're running a 1.65 rocker it will compound the issue as well if the springs were already boarder line. Springs are an easy swap and cheap to buy.

A nice little tool I like to use here...

It's great if you suspect a spring pressure issue. Quick and easy. Not exactly accurate or precise, but if you have seat pressures that are off 10-15 lbs. or more, you can find it with this tool. Take a valve cover over and check them over in about 5 minutes. Great for an engine that's hard on valve springs to do periodic checks from time to time.



Edit: I agree with Paul who posted while I was typing, looking at your spring specs (the 995's) they appear to have flat tappet seat pressures and not much more over the nose. With a hydraulic roller cam, even a mild one such as yours, with all that added weight of the lifter, I'd personally like to see more spring pressure.

[tr709]

ok, I'm learning, so if it is valve springs, that would be impacting power in the upper rpm's correct? This might be a good short term fix

What if my goals were to move the power down in the RPM range and I was willing to do a cam change? I'm no cam expert, but I thought that was less duration and more LSA? Not sure if I was clear on my goals, this car will never see a drag strip, it's a cruiser. I would just like it to make more power, say 425ish at the crank? I'm guessing I'm at about 350 now

[paul s.]

Originally Posted by tr709

ok, I'm learning, so if it is valve springs, that would be impacting power in the upper rpm's correct? This might be a good short term fix

What if my goals were to move the power down in the RPM range and I was willing to do a cam change? I'm no cam expert, but I thought that was less duration and more LSA? Not sure if I was clear on my goals, this car will never see a drag strip, it's a cruiser. I would just like it to make more power, say 425ish at the crank? I'm guessing I'm at about 350 now

Everything is a compromise; one cannot just say that a wide lobe separation angle will give you low end or A tight lobe separation angle will narrow your Power curve too much. It all depends on the rest of the camshaft parameters such as lift and duration. More lift equals more power everywhere! More duration focuses the power curve higher up in the RPM range. More duration and a tight lobe separation angle will narrow the RPM range but it will be higher up the RPM scale, that's why a lot of people advocate the use of wide lobe separation with longer duration camshafts because it makes it more drivable by widening the power curve. On the contrary, A Small flat tappet extreme energy camshaft like the 274 on a 110 LSA will make power @ 6000 RPM undoubtedly. It won't peak there but it will carry the power to 6000 RPM. A wide lobe separation angle extends the RPM range by closing the intake valve later and opening the exhaust valve sooner allowing it to blow down and evacuate the cylinder more effectively at a higher rpm. Unfortunately, that keeps the intake and exhaust tracts from tuning, lowering peak torque. At that point you can raise the compression ratio to make up for the lack of torque and cylinder pressure.

A 75 hp increase would entail additional RPM capability. The use of lightweight retainers and enough valve spring pressure will help that out immensely. I would like to see more lift from the camshaft with the use of 1.65 rocker arms. I've seen a 50 hp increase through the installation of stiffer valve springs allowing more RPM. Would it be the same for you? I can't say but, I know a hydraulic roller camshaft with your duration but with higher lift on 110 or 108 LSA will work very well for you and make the power you want.

[tr709]

Interesting update

Since the car was in the shop to have the steering box replaced, I had them do a leak-down and compression test to get an idea on the health of the internals. Results of the leak-down, cylinder 2 is not that bad, less than 10% getting past the rings and it held for a long time. All the other cylinders were really good. Compression on all cylinders was 175-180. Now here's where it gets good and head scratching at the same time. Turns out there was an issue with the carb linkage so the carb wasn't opening all the way when you floored it. Went for a test drive and I'm happy, car pulls harder than ever, good burnout on take off, barks when you hit 2nd (has NEVER done that), tires are on the edge of breaking loose all the way through first gear. It was a short test drive, but I'm pretty sure this is the best the car has run. I think no other changes for now, going to enjoy it for a while.

Thanks for all the replies!

[69 Limelight]

Have followed your posts from start to finish including those from 5 years ago. Have similar setup and same detonation problem. Was detonation problem better, worse or same after the shop retimed camshaft from 4 degrees retarded to 106 intake centerline 5 years ago?
Glad to see you got power issue resolved. Too bad it took 5 years to find carbureator was't fully opening. How's the full throttle detonation now?

[tr709]

It was a quick test drive, but no detonation and I'm running 36 degrees total timing. Cam degreeing did seem to help 5 years ago.

Yea the carb thing is crazy, hard to say if it was always that way or someone messed it up sometime in the last 5 years when the q-jet was first put on

I know I'm probably leaving some HP on table that different valve springs and going to 1.65 rockers would address, but then I bet I would have serious traction issues, especially winding out 1st gear. Plus I'm thinking of going to stock chrome valve covers and putting the ram air pans on, I think the higher rockers would make that a bit of a PIA. I'll probably drive myself crazy thinking this stuff over and over.

[Ed Fitzgerald]

Am I missing something here or didn't Cliff identify the carb as a problem---due to the secondary plates. That was early on in the other thread. Ed

[Ed Fitzgerald]

Post 78 seems to me to be where Cliff diagnosed the problem. FWIW . Ed

[tr709]

Ed,
You are 100% correct, I was told at the time that this was checked. Am I happy about it? F**K No. But I'm not going to have a stroke over it either. Thanks