Hey Guys, the engine is finally at the engine shop, and is time for a cam decision. I used to run solid flat tappet cams in my SBC race motor, but am curious what the Pontiac guys think about a solid cam in a street car? I will probably put less than 2K miles on per year, so is not like I will be adjusting lash more than once per year. Here are the specs so far…
--1971 455 Block w/.030 flat top cast pistons/zero deck (why the last guy put this much work in the block with cast pistons, I will never know)
--Stock rods & crank
--Qjet & cast manifold
--4spd & 3.36 gears
I noticed that almost all of the engine recipe’s in the Jim Hand Pontiac book use Hydraulic cams, but is that more of a convenience factor?
I am curious to hear from you guys that have run both in your Pontiacs.
I'm running a solid roller in my car and really like it. Traditionally, you run a solid cam to get more rpm out of it (no lifter puimp) and if there's one thing a 455 ain't, its not a high rpm engine. Neither is my 461, but I went with a solid roller for reasons other than RPM. I did it because a roller profile, having more aggressive opening and closing rates, permits you to run a cam with more duration without having to also run lots of overlap (overlap is what kills idle vacuum and idle quality), and also because hydraulic roller lifters are by comparison VERY heavy. If you're going to run a flat tappet cam, then I'd say there's no big reason to pick a solid over a hydraulic in a 455. Pick one that puts your torque peak where you want it, rpm wise, and go for it.
With a street engine, the main concerns are:
Transmission type (auto or manual, and if auto - stock or "loose" converter)
Rear gear ratio
Need for vacuum accessories (power brakes, factory a/c)
How the car is going to be used (street, highway, race... i.e. what rpm range is it going to "live" in most of the time?)
Also, to some degree --- compression ratio. (If you're pushing the limit on compression you're going to want a relatively late intake closing event to help control peak cylinder pressure - and thus tendency towards detonation - you can accomplish this with a "longer" duration cam, or by installing the cam a little retarded. Both of those however tend to shift the peak VE (maximum torque) to a higher rpm.)
All those things have a bearing on rpm range and driveability.
Cam selection is a big deal and it will pay you to spend lots of time thinking about all the things that go into it and deciding what's right for YOUR situation. This is definitely one area where it doesn't pay to just copy what someone else has done.
I just "ran" your numbers (455 +0.30, zero deck, flat-tops, 7k3 heads) and if those heads actually have the factory nominal chambers (96 cc's) that will put you at 9.45:1 compression. That's close to the limit with iron heads (in my opinion) so you're probably going to want "enough" intake duration to manage pressure. The zero-deck is going to help you there because it promotes cylinder turbulence and masks sharp edges at the top of the bore, both of which help to prevent detonation. You've also got a manual trans and 3.36 gears, so you don't have to worry about converter stall for launch (if you're going to race it any). That leaves the question of power accessories. Do you have power brakes and/or factory a/c? For brakes you'll want to keep idle vacuum above 15 inches or so.
I fired up Engine Analyzer and ran some simulations. CompCams XE 274 grind will make some good torque and power, but idle vacuum is low for brakes - around 13 inches. Also the HP peak occurs between 5000 and 5500 rpm which in my view is WAY too risky in a 455 with stock rods. Good forged steel, no problem - but not with stock. Dropping back to Comp's XE 262 looks a little more reasonable. Peak power happens around 4700 rpm and it makes around 16 inches of vacuum. Peak power and peak torque are less than with the XE 274 though. Lunati's 307A2 looks better. It makes about 10 more HP than the XE 262 and also has a wider/smoother torque curve - probably because it has a wider LSA (112) vs. the XE 262 (110). Vacuum is also passable at 16 inches. Peak power (439) with the Lunati happens at 4900 rpm, peak torque (495) at 3400. The Crower 60243 is borderline. Installed 4 degrees advanced the power peak (443) happens just above 5000, torque is gorgeous - peak (504) occurs at 3700 and is nice, wide, and flat. It only makes 14" of vacuum though. Advancing it a little more (6 degrees) pulls the power peak back to 4900 and costs you about 6 HP, but the torque is even better - 507 @ 3500 and it's still making 470 at 4900. Vacuum is still between 14 and 15 though. To my surprise, the Crower 60918 looks pretty good too. It makes 425 HP at 4800, 494 lb.ft. at 3400, with 17" of vacuum. The torque curve isn't as consistent and pretty as the 60243, having a dip between 3700 and 4400, but other than that it looks pretty nice - and shouldn't have any problems with brakes. That's with the cam installed "straight up". I played with retarding it a little and that shifted the peak power slightly higher, but didn't make much difference otherwise - in fact torque looked a little worse.
In your case, if you've got power brakes and this is going to be mostly a street car, I'd go with the Crower 60918 or the Lunati. If power brakes aren't a concern (or if you're willing to solve that problem "independently" like I did with something like a hydroboost system), then in a flat tappet cam I'd definitely go with the Crower 60243 and advance it about 4-5 degrees.
Just to make your mouth water a little bit, I ran one more simulation with "my" cam. Peak power was 465 at 5350 peak torque was 508 at 3700. Vacuum was only 13.5" though...
Thanks for the great info Bear. You will like this... Here is the cam card from the cam that was installed in this motor when I bought it. Keep in mind it also had 1.6 roller rockers: Cam Spec Card :: Lunati Power
I am surprised the rods were not sticking out the side of the block!
Speaking of the roller rockers, I would like to use the 1.6 rollers that came with it, so will need to adjust the cam accordingly. Worst case is a new set of rockers, but these have very few miles on them.
Very important if you're going to run 1.6's -- make sure the pushrod holes in the heads have been elongated top to bottom (mostly on the bottom) otherwise the pushrods are likely to rub on the heads - you don't want that.
245/245 @ .050, 108 degree LSA, .534/.534 lift with 1.5's --- and stock rods?
Oh my..... I ran that through the simulator and got 464 HP at 5400 rpm, peak torque was down compared to the other ones I ran but the curve was wider, higher into the rpm range which is why it makes more HP. EA predicts a whoppling 11" of vacuum though.
That's actually a decent cam *IF* you've got good rods and can tolerate the low vacuum. No way would I try it with stock rods though.
[QUOTE=BearGFR;319237]Very important if you're going to run 1.6's -- make sure the pushrod holes in the heads have been elongated top to bottom (mostly on the bottom) otherwise the pushrods are likely to rub on the heads - you don't want that.
Yeah, there was some rubbing on 8 of the pushrods because the holes were not reamed out. There were very few miles on the engine since the cam/heads/rockers were installed, so no damage.
I have been considering a set of forged rods, but may just keep this engine as an econo-runner since I will have less than $2k invested when all finished.
Well, consider this. Factory rods are the weak link in Pontiac engines, especially with longer strokes like the 455. Run stock rods and hold your breath and cross your fingers every time the tach kisses 5-grand, wondering if that's going to be the time the bottom end spreads itself on the pavement (along with your 2k), or spend a few hundred for some good forgings and breathe easy.
Hey Bear, I talked to "Steve" at Lunati today, and he spoke highly of the 307A2, saying it was a popular cam for the 455. He also suggested a custom grind they have in a solid flat tappet, which has 272/282 Duration, 238/248 @ .050, and would have a net valve lift of 500/530 with my 1.65 rockers and suggested lash setting. As with the 307A2, LSA is still 112. Sounds like my valve train should be fine as long as rpms are kept below 6k, which of course should not be a problem for a 455!
I picked up a set of KB pistons on ebay, and also going with a set of H-beam rods. Along with some pocket porting on the heads, should be able to handle a little more zip.
If you get a chance, let me know how this cam reacts on your software dyno!
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