[Jay S]

I remember reading from someone’s IT manual Pontiac ran 130 lbs seat pressure on RA 3 engines. But they ran a lesser springs rate. 30* seat change the vector force angle and require more pressure than a 45*. That is why often catelog cams recommend to little spring pressure at the seat, usually 115-120 lbs is listed, that is for 45* valves.

Adjusting to higher seat pressure sometimes makes the over the nose pressure high. Springs like the 995 comp can get pretty high pressures over the nose when limits as pushed on them. IRC the spring rates for the 68404 are 336 lbs/inch, lunati 73949 are 363 lbs/in, Crower 68405 are 380 something and the Compcams 995s run 402. I sometimes pick a lesser spring rate on heads that run a lot of spring pressure on the seat to adjust the over the nose pressure.

The Lunati springs 125 lbs with just over 300 over the nose sounds ok. But I would have kept the Crower 68404 and aimed for 120 lbs on a 389 head just because have less surface on the valve seating face, little lighter valves, and the projected power band. The pressure over the nose with the 68404s would have been 280s versus 300s for the Lunati springs. Not a huge different, if a cam lobe is lost it would have likely happened with either of those spring pressures.

We have ran big springs on a couple small valve boosted engines, I never had a issue with them. It did have hardened seats though, the exh seat will get beat in quickly if the seats are not hardened. I had one engine turn 8000 rpm once for 30 or so seconds. Another spun 6700 for 4 minutes. Never noticed a negative impact from the extra spring pressure on those engines.

[Formulajones]

Originally Posted by phil400

Not to hijack but what's the longevity of a flat cam with springs at 130 lbs on the seat? For guys who like the use their cars alot, I mean wouldn't that incresase the rate the lobes wear down? Or atleast increase the chance of something go awry at break in?

I daily drive mine with that seat pressure. First engine I put together went about 20 years before a tear down, cam/lifters were fine.

About 3 or maybe 4 years ago now, I put the recent engine back together and shot for 130 lbs. seat pressure with the 68404's. Give or take a couple lbs. I broke the cam in with that, and have daily driven it and race it quite a bit since. Perfectly fine. Like mentioned they do tend to lose a bit of pressure over time. I wouldn't be surprised if they are hovering around 120 now, maybe less. I haven't had a reason to pull a valve cover off and check.

It's a large valve Pontiac head. You might be able to get away with less and be fine like Jay mentioned with smaller valve heads. The valve seat angle is a big player.

[Cliff R]

The factory was able to get away with considerably less spring pressure than we see used these days because they used low lift cams with very gentle opening/closing specs. This was necessary because of the long warranty periods provided to the consumer.

These days very few if any of these engines are daily driven and will see tens of thousands of miles put on them each year. Modern cam profiles also shove the valves around with great authority and require stronger springs to keep things happy, especially at high RPM's. So for the most part pretty heavy spring loads are used with these engines and for good reason.

In any case stronger springs drag the timing set a little harder, and put more stress on all the parts involved, cam, lifters, pushrods, rocker arms and valve tips. Considering all things involved here including much quicker camshaft lobe profiles and stronger springs typically used with them, it may be part of the reason we see more cam lobe and lifter wear issues. Doesn't help either that some of the parts involved are outsourced and often not of the best quality......Cliff

[Formulajones]

Originally Posted by Cliff R

In any case stronger springs drag the timing set a little harder, and put more stress on all the parts involved, cam, lifters, pushrods, rocker arms and valve tips.

That reminded me of something I forgot when you mentioned this. Paul mentioned to me that he likes to use a specific cam bearing as well with roller setups because of the spring pressures used. Which is typically about 150 lbs. on the seat and about 400-420 open for the custom hydraulic rollers he's done for me.

I forget the part number now but I've used them in the last couple of builds, and even put them in my own hydraulic flat tappet Pontiac engine I mentioned above just for piece of mind.

[Steve C.]

Obvious to most here I'm passing on much of this information that Paul Carter has already posted. I don't think there is anyone here that posts on any regular basis that has anymore hands on experience with Voodoo cams than Paul, and that includes actual dyno testing.

Do a advanced search under his user name gtofreek and type in voodoo... then read most of it. Or give him a call, I suspect he wouldn't mind passing on specifics, not a bunch of information out of a catalog ! I should also mention he was friends with Harold Brookshire and has learned quite a bit from him regarding some specifics, far more than salesman in cubicule number 82 at Lunati.

Note the spring pressures he uses. And note as Jay brings up how the difference in a 30 degree seat vs a 45 degree seat plays in. And note he has suggested keeping the distance from coil bind at 0.100" or less on some applications..... take notice regarding that scenario when trying to use the popular Crower valve springs often touted ! Also personally I wouldn't pay much attention to Lunati sales regarding their suggestions involving a Pontiac valvetrain mass in use. Last trying to compare a modern Voodoo lobe to a antiquated Crower lobe is meaningless unless all the pertinent information is provided. Example, anyone here try calling Crower and ask for the duration at 0.200" valve lift on one of there cams !!

Onward.


.

[Burningbird]

Originally Posted by Jay S

I remember reading from someone’s IT manual Pontiac ran 130 lbs seat pressure on RA 3 engines. But they ran a lesser springs rate. 30* seat change the vector force angle and require more pressure than a 45*. That is why often catelog cams recommend to little spring pressure at the seat, usually 115-120 lbs is listed, that is for 45* valves.

Adjusting to higher seat pressure sometimes makes the over the nose pressure high. Springs like the 995 comp can get pretty high pressures over the nose when limits as pushed on them. IRC the spring rates for the 68404 are 336 lbs/inch, lunati 73949 are 363 lbs/in, Crower 68405 are 380 something and the Compcams 995s run 402. I sometimes pick a lesser spring rate on heads that run a lot of spring pressure on the seat to adjust the over the nose pressure.

The Lunati springs 125 lbs with just over 300 over the nose sounds ok. But I would have kept the Crower 68404 and aimed for 120 lbs on a 389 head just because have less surface on the valve seating face, little lighter valves, and the projected power band. The pressure over the nose with the 68404s would have been 280s versus 300s for the Lunati springs. Not a huge different, if a cam lobe is lost it would have likely happened with either of those spring pressures.

We have ran big springs on a couple small valve boosted engines, I never had a issue with them. It did have hardened seats though, the exh seat will get beat in quickly if the seats are not hardened. I had one engine turn 8000 rpm once for 30 or so seconds. Another spun 6700 for 4 minutes. Never noticed a negative impact from the extra spring pressure on those engines.

Thank you for all the good information Jay. The heads have hardened exh. seats installed. I weighed the valves and the exh. valve is quite a bit lighter, 234grams vs 289grams for the intake valve. I also checked another of the Lunati springs in the set and got 120lbs@1.633", 125lbs@1.618", 129lbs@1.603", 134lbs@1.588". Maybe I should install the intake at 1.588" and the exhaust at 1.603" because of the lighter exh valve and 45° seat?

[Cliff R]

I like those "antiquated" Crower lobes Steve. Longer seat timing, gentle opening/closing specs, easy on parts and don't need a butt-ton of spring pressure. The "little" 60243 cam in a 400 build with iron heads on it put a street driven Firebird well into the 11's with nothing more than one of our TH350's, custom torque converter, 3.73 gears and a little traction.

He used one of those POS iron intakes I recommend too and factory Q-jet. I've seen folks put together 455 builds on here with aluminum heads and bigger cams that didn't run that quick........FWIW......

"Which is typically about 150 lbs. on the seat and about 400-420 open"

Think about that for a second. That much open pressure is like having 16 fat guys standing on your pushrods! Makes it difficult to comprehend how a tiny little film of oil on 5 skinny babbit faced cam bearings can take that much load and last any longer than it took me to type this!.....

[pastry_chef]

If you think the static pressures are high then you would be in shock about the dynamic pressures on the pushrod when the engine is running.

[Formulajones]

Originally Posted by Cliff R

"Which is typically about 150 lbs. on the seat and about 400-420 open"

Think about that for a second. That much open pressure is like having 16 fat guys standing on your pushrods! Makes it difficult to comprehend how a tiny little film of oil on 5 skinny babbit faced cam bearings can take that much load and last any longer than it took me to type this!.....

LOL That's a funny way of looking at it

[77 TRASHCAN]

Originally Posted by Formulajones

That reminded me of something I forgot when you mentioned this. Paul mentioned to me that he likes to use a specific cam bearing as well with roller setups because of the spring pressures used. Which is typically about 150 lbs. on the seat and about 400-420 open for the custom hydraulic rollers he's done for me.

I forget the part number now but I've used them in the last couple of builds, and even put them in my own hydraulic flat tappet Pontiac engine I mentioned above just for piece of mind.

Durabond?

[moontower69]

Bottom line is that with 3.08 rear and 389/400 in a heavy car, it's not gonna as fun to drive with the larger cam and will feel soggy below 2500 rpm (yes lots "experts" here will disagree and they always say a bigger cam with be fine).

Save the 703 for a 428 or 455. But make up your own mind and go with your gut. Almost everytime, ask anyone, as between 2 cams that are close, the smaller one is usually the better choice unless you're trying to wring out that last tenth of a second in the quarter mile.

[Burningbird]

Originally Posted by moontower69

Bottom line is that with 3.08 rear and 389/400 in a heavy car, it's not gonna as fun to drive with the larger cam and will feel soggy below 2500 rpm (yes lots "experts" here will disagree and they always say a bigger cam with be fine).

Save the 703 for a 428 or 455. But make up your own mind and go with your gut. Almost everytime, ask anyone, as between 2 cams that are close, the smaller one is usually the better choice unless you're trying to wring out that last tenth of a second in the quarter mile.

The engine is already in the car. Maybe the cam is too big, time will tell. What helps is the Hydramatic transmission with really low gears. With 3.08 in the back and the first 3-gears in the Hydramatic it equals using a TH350 with a 4.50 rear gear.

[Jay S]

I have mentioned it before. But I have a 389 from a 60 Bonneville daily driver that was running that 4 speed hydro Matic with an Isky Roller cam, 3x2s, 12s scr, home made fender well headers. Airplane tires on the back. Not totally sure what it had for gearing, IRC it was a 3.23. Same guy had a couple 427 vette’s and a 63 327 injected vette, and a 283 2x4s 55 Chevy with a solid front axle and the engine move back 2 feet that would do wheel stands. He always called the Bonneville the Strong Runner. Lol, those other cars should have given him some perspective. The Bonneville was rear ended while parked back in 1967 and totaled. It is great to see another 60 survived, I don’t know when the last time I saw one in person!

You can shim the springs on the exhaust so the seat pressure is 10 lbs less than the intakes if you want. It makes the split cams like the voodoo that have more exh lift have the similar pressure over the nose of the cam.

Cams and drivability is always subject to personal opinions and tastes. I enjoy bigger cams on my own engines.

If the cam ends up being a little big for your driving tastes install a V series Rhoads lifter and loosen or tighten the lash until you get the driving characteristics that you prefer.

Hopefully the 8VR pistons serve you ok. I think it is a good idea to polish or grind down the center vr’s to get rid of that ridge. But I know it is all together though. You have done nice work on your project.

[Speargun]

I have the 703 in a 9.75:1 scr (8.27 dcr) 400 +.030 with 16 heads, standard hyd lifters, and the idle is fairly tame. My GF says it's not "thumpy" enough. LOL
Good vacuum, pulls good, and no noticeable ping with 18* initial & 36* total timing. (Stock curve in a Summit RTR dizzy)

The car currently has a Continental "Jim Hand Special" 3600 converter, but I'm going to try a TCI 2400 next week.

'67 Firebird near factory weight.
TH-400
3.54 gear
Nitto 275/60R15

[moontower69]

Originally Posted by Speargun

I have the 703 in a 9.75:1 scr (8.27 dcr) 400 +.030 with 16 heads and the idle is fairly tame. My GF says it's not "thumpy" enough. LOL
Good vacuum, pulls good, and no noticeable ping with 18* initial & 36* total timing. (Stock curve in a Summit RTR dizzy)

The car currently has a Continental "Jim Hand Special" 3600 converter, but I'm going to try a TCI 2400 next week.

'67 Firebird near factory weight.
TH-400
3.54 gear
Nitto 275/60R15

That's my only point. With the 702 cam in a 400 you wont need such a big converter and have to worry about cooling issues in traffic and burning up tranny with the heat from a high stall. I'm sure 703 is super fun for weekend car but not for a daily driver. Just my opinion.

[Speargun]

Originally Posted by moontower69

That's my only point. With the 702 cam in a 400 you wont need such a big converter and have to worry about cooling issues in traffic and burning up tranny with the heat from a high stall. I'm sure 703 is super fun for weekend car but not for a daily driver. Just my opinion.

I only have about 150 miles on the new engine, but tranny, water, & oil temps where all good.

I was going to run a smaller cam, but I wanted to keep the DCR at, or below, 8.3:1 to avoid detonation issues and the IVC on the 703 put me where I wanted to be. If the OP's engine is going to be 10:1+, I would think that the 702 would push the DCR to a level that "I" wouldn't be comfortable with.

Disclaimer: I am far from a cam expert and am just stating what has worked for me so far. YMMV

[65sport]

I hope the engagement to D and R is not too harsh with that cam but I have no knowledge of the 4 speed hydromatic. Are these the pistons you have IC9946-STD ? If so, or if you have another version of the "8 eyebrow" piston, you have the option of going with later model larger chamber heads if the SCR proves to be too high and you get pinging that I would expect that to happen at highway speed. I really like the gear ratios on the 4 speed hydramatic. I hope this works out well for you.

[Burningbird]

Thanks Jay! I remember you wrote about that souped up Bonneville before, really cool car! Good point on those V-max Rhoads lifters if the cam is too big for the heavy car. I will update as soon as it's fired up!

Great to hear about your build Speargun. I was a little worried about the vacuum at idle but it sounds like that's no problem. I have lowered the SCR to 9.65:1. I chose this cam for the same reason as you did, to lower the DCR some. In a couple of weeks we will know if that was the right choice, lol!

Thanks 65sport. I rebuilt the transmission 2years ago and haven't had any harsh engagement when going to drive or reverse after that with the stock 472-cam. If I keep the idle below 750 rpm I think it will work. The pistons is Icon IC9946 STD. I opted for those pistons so I can switch to aluminum heads or big valve D-ports later if I want to.

[Formulajones]

Originally Posted by Burningbird

I plan to drive this car at least 3000 miles a year so I don't wan't a cam that wears out in a couple of years. I won't rev it past 5500rpm so maybe I should lower the spring pressure to 120lbs on the seat?

I've run mine for going on 3 years and over 20k miles with 130 lbs. on the seat.

Still runs the same consistent times at the track that it did when it was fresh, I drive it quite a bit, it's my transportation when I need to go somewhere.

[many birds]

Originally Posted by Burningbird

Thanks for the info, it's good to hear how the cam acts on the street in a similar engine! With a .030 over 400 and 74cc heads wouldn't your engine be closer to 10:1 or do it have dished pistons? I prefer a choppy idle as long as there is enough vacuum for the power brakes, so that's no problem. Do you remember were the intake centerline was installed at? I have read that the Voodoo cam runs a little better with the intake advanced 6° or with the 703 cam at 104°. Do you have stock converter or a higher stall converter?

Sorry for the late response. My engine has the crappy cast Pistons that are nearly 0.030 in the hole. Hence the lower SCR. In retrospect, I should probably have advanced cam the 6 degrees and changed out the Pistons, however I did not know that at the time. My converter is near stock, ~2000 stall according to PO. I'm using crower 68324 springs. My carb is setup per Cliffs recommended recipe 2 and his supplied parts. With the timing set to 10 degrees initial, I get about 12 mpg around town. I'm running a stock radiator and water pump with a fan shroud and clutched fan. No cooling issues at all, even in the Alabama summer heat.