Looking a a budget friendly cam swap. Needs to be a hydraulic flat tappet. Here's what I have:
'84 Monte SS, 700R-4, 3.42 gears, stock stall (swapping to 2400 or so)
2 bolt 400 .040 (decked), hyper pistons 6cc dish, stock rods/crank
AFR195s w/1.6 RRs, Voodoo Cam 262/268 (219/227@.050)
HSR w/730 ECM

The cam I have now is fairly mild and I was afraid too pick something too big
when having the engine built. I know because of the short rod I should stick
to shift points under 6000 (5500 is fine with me). This cam sounds stock and
idles easy. But the power dies off when the heads and intake have more to go. Plus I think the extra exhaust duration is not needed with the heads, 1 5/8 headers and dual 2-1/2 exhaust. I'd prefer a cam swap that did not involve needing new valve springs (2K miles on heads) or anything else. Can someone recommend a cam that would have more power over the current
cam but yet would keep the idle decent (800 rpm or under)? I've got this cam tuned now but I have to keep the timing conservative because I think my DCR is on the high side. I've been looking at the magnum 280 (230/230@.050) but I am not sure how docile that would be. Anyone else have a cam around there that can share idle characteristics and maybe a dyno or timeslip?

 

Ok, I read an excellent article on the Popular Hot Rodding site by David Vizard. Based on his article I first need to decide on an overlap range for my performance goals. That would be the 50-75 range, then I need to decide on an LSA. This is where the problem starts. Mr. Vizard has a nice sheet that is a guideline for choosing LSA based on CI. This is for max performance so in my case I would choose to go a few degrees wider for idle quality. In his article he says that companies usually spread the LSA wider on long duration cams to make it street friendlier and what ends up happening is the valve events are delayed and this causes a soggy bottom. If you play with dynamic comp. ratio calculators you can see the intake valve delayed in closing. So his article would have me looking at cams that are around 108-110 LSA while companies like Comp with their XFI cams spread the LSA out to 113. Questions is does it all come down to overlap for a cams performance? Meaning I can choose a cam that is 108 LSA with an overlap of 58 and it will idle just as well as a cam ground on 114 with an overlap of 58? I am leaning towards the 280/280 (230/230@.050) cam or something around there. It just seems like that puts my DCR@8.2:1 vs. the 8.65:1 I have now (41 degrees overlap). The only thing I don't like about the 280 cam is the lift is a little low. Lunati suggested the Voodoo 60104 cam (233/241@.050) cam but I am afraid that it might be a little too much. I definetly like the lift on that Voodoo. The one step smaller voodoo keeps my DCR still a bit high.

 

What is the shift point for the cam you have now? The reason I ask is I ran a similar grind with a pair of old TFS heads on a 11:1 406 with a Victor Jr and 850dp and I was shifting around 5600 or 5700 rpm. I would think that with the AFR heads that are better than what I was running, you would be shifting at least that high. That same head and cam combination in a 355 with a HSR and 52mm T/B was shifting at 6400rpm,, which should equate somewhere between 5600 and 5800rpm in a 406.

What I’m getting at is there may be some other reason for the engine to lay down up top other than the cam. Have you pulled the plugs or seen a wide band dyno reading to make sure you’re not running lean up top? How much timing are you running? Too much will cause the engine to lay down up top. Lean and high timing will really make one drop like a rock in the upper RPM range. I had to run a good bit of initial timing (or heavy on the programming) for the lower rpms but kept total around 34-degrees with the 11:1 406 and 38-degrees on the 10:1 355.

I’ve seen the rubber ducting to the T/B collapse when you rev the engine and choke off airflow,,, might want to check that if you’re using any. What filter or filters are you using? Maybe it’s an airflow restriction somewhere if it is not timing or fuel related.

How much pre-load do you have on the lifters? If you have more than a quarter turn, back off the adjustment to a quarter turn and see what happens? Did you run the recommended springs with the Voo-Doo cam? Could be valve bounce causing the car to fall off up top. If that’s the case going with a larger cam will only make things worse.

 

Me personally, I don't like the single pattern of the 280 cam. I would look into one of Comps XFI grinds, they work extremely well. A good friend of mine just switched from a voodoo cam to an XFI. Both cams were on the small side for his DD 350, but he reports that it is a night and day difference even with his mild combo.

Just my humble opinion... I like cams with about 8* of split, and 113-114 LSA for EFI.

 

I've been out of town a few days. Thanks for replying. The shift point I am not sure. My trans was recently rebuilt and I need to adjust the governor. But holding the gears and manually shifting the car feels not quite were it should be. Granted I am running a DIY tune and running no more then 28* timing in WOT. Most likely I am running a richer then 12.8:1@WOT. I am using a heated NB O2 so I can only guess. I haven't read the plugs yet.

As for the pre-load I am running more then 1/4 turn so that can be changed easy enough. On the intake ducting I am using a 4" DIY tube but my air filter might be a restriction. Key off shows the map around 95.5 kpa and my WOT kpa is hitting about 91. So there is a restriction somewhere. The filter is one of those filters that fit on the stock TB only it is now mounted on the end of a 4" tube in an enclosure behind the headlights. The enclosure is nothing more then a wall of a plastic container that blocks the underhood temps. I probably need a larger air filter because this one did not mount easily on the 4" tube.

The valvesprings I am using are the stock ones that the AFR heads came with. So if the cam requires something stronger then that's an issue. I don't want to install another XE/Voodoo/XFI. I know the XFI require beehives so that rules them out. I see through summit you can order a custom cam from a few manufacturers. I might check into that. I have been using a program called engine analyzer to simulate different cams. I need a cam that can bleed off a little cylinder pressure but yet not loose a bunch of low end and still have a good bit of top end. I plugged in the 280 cam and it is clear there are better grinds out there that give better average power instead of more peak power. It is interesting what some of the LSX cams do when you adjust the valve lift to what a typical flat tappet can handle. They all are ground on a 112-114 LSA with typical duration @.050 about 220-228. Low end falls off but the top ends really comes on. And they idle with 16-20" of vac. Even more interesting is some of the cams are like 228/224@.050. Which seems to really spread the torque across the higher RPMS at the cost of a few peak HP vs. a 224/228 you typically see for GEN I SBC.

 

Instead of upgrading your cam, why don't you spend the $200 for a Wideband O2 and really dial-in what you have? Sounds like you have a fair amount of money into this project, why skimp here?

-Dave

 

Wideband 02 could be helpful if he doesn't have any exhaust leaks and he wants to know what AFR his motor makes the most power at. Personally I don't care what AFR mine makes the most power at, I keep tuning until it doesn't go any faster.

His cam is a little on the small side I'd think, but we don't know his compression ratio.

-- Joe

 

A wideband isn't out of the question. If you had read earlier I did say that I have tuned the combo pretty well at this point. The NB reads the commanded AFR starts at about 12.5:1 at low rpm and rises to 11.8:1 up top. The problem is I am getting some knock counts with a really conservative timing curve at WOT. It's not a mechanical issue and isn't another noise like the exhaust rattling or something like that. In fact my spark table in the 50+ kpa is really conservative otherwise I get more knock counts. I've tried adding more fuel adding a little timing and taking fuel out and the only thing that got rid of the knock was to drop some timing. My water temp is normally about 180+/- while cruising despite having a 195 thermo. My MAT temps are about 80-90 with outside temps in the 50s. I need to get the V6 IAT as the brass in the stock MAT heats up from underhood temps. The compression ratio is estimated to be about 10.3:1. The figures used to arrive at that are as follows:
400 .040 (4.165 bore), decked (pistons .005 in the hole)
Heads have 74cc chamber, gasket is .039 thick with 4.166 bore size
Stock 3.75 stroke, and 5.565 rod length

A Dynamic compression ratio calculator says the DCR is 8.76:1 using those specs. While the static compression is 10.32:1. The Voodoo cams intake centerline is 106 and changing that to be straight up at 112 brings the DCR to 8.4:1.

I've added my current spark table including PE spark. Also I've hit some pretty high kpa numbers for a performance build. The engine idles at about 32kpa, cruise at 25 kpa under 60 mph, about 32-35 kpa 60-75 mph. I'll easily hit sub 20 kpa when decelerating from a high load (I've seen as low as 7 after a WOT romp). I don't know how the 730 ecm handles sub 20 kpa fueling but it has never leaned out too bad.

 

Where do you have your base timing set? You have 27 built into the chip with PE adv at 4800. Are you sure that the timing pointer is correct - meaning when the engine was built was the engine set to TDC and the timing mark on the balancer and timing tab set to zero? If so,, do you get any spark knock at WOT with the base timing set at 3-degrees (for a total of 30 degrees)? You shouldn't for sure with the base at 0. Which would give you a total of 27 with 22-degrees at 2800,,, which these 400 are very timing sensitive in the midrange,, 22 might be all it could take on premium gas around that rpm with your combo,, depending on the piston and chamber prep.

 

Base timing is 8* btdc which is what I have set in the prom. So the timing in the txt file is wsywyg. The balancer was/is correct when the engine was built. It was a new balancer also. Not sure what the you mean by piston prep. If you mean the gaps I am not sure as that was done by the machine shop. I would assume they use specs suggested by speed pro for hypers. As for the combustion chamber the heads are new and left untouched except for drilling steam holes. So the consensus here is that the dynamic compression ratio being around 8.7:1 is not an issue?

http://www.empirenet.com/pkelley2/DynamicCR.html

I do sometimes get a little knock around 2800 with this timing setup. That's why I started this thread. I've ruled out a lot of things before coming to this conclusion but buying a cam and changing it out is an expensive guess. A WB and a cam swap are not in the budget. The plugs look good though and the engine runs great just doesn't have as much power as I thought it should. Of course it could be the valvesprings as someone suggested.

 

Your issues sound similar to what I am experiencing with my setup. The top end just "should" have more oomph to it but it just doesn't seem to be there.
sounds good, tune, WB and plugs look good.
The one thing that could be contributing is your converter. I run a crappy 2200-2400 stall and there may be slippage at high RPM that makes it seem like the motor is not performing. I've suspected this for a while now because once the RPM comes up, The response from the drivetrain does not "match" the revs from the motor. You could have the torque up high but its just not making it to the wheels.
Just thought about that after reading your post and figured I'd throw it out there for ya to ponder.
Jp