Camshaft selection

[Xenon]

There are many people that claim to be experts on camshafts, some are and some are not.

you guys all seem to be very knowledgable so I thought I'd ask you.

My 406, I've been told by mark has a somewhat aggressive cam. I'm starting to think I may have been built to be a circle track engine or something, as it lacks power until higher rpms.

Wanting to change cams, but I don't know much about them honestly. I'm thinking maybe an RV type cam? It's in a 6500lb suburban, 3.73 gears and a th400, soon to be th700r4. So looking for really good low end torque, not worried about much over 3600.

What would your suggestions be? Thanks.

[EagleMark]

What would your suggestions be? Thanks.

Keep the Turbo 400?

Most stock cams can be considered an RV cam. Power from idle up. So don't get stock on a name, RV cams are sometimes so close to stock it does not matter. That said I'm not the cam guy, I can tune any cam you put in! But I can't change... much... the cam if it starts to work at 1500 RPM. If it starts at 1500 RPM and you have an auto trans? Well you should also have a higher stall converter! Which would also solve your issue right now. But this ends up running higher RPM always and does nothing but hurt fuel milage. Works great for going fast!

One of the cam guys/engine builders will jump in. My quick recommendation is cam recommendations that state idle to ? RPM! Not 1000 or 1500 RPM up to ? RPM. What does the cam you have say?

[Xenon]

Well I don't exactly know. I bought the engine with 0 miles on the rebuild but it had changed hands a few times since it had been rebuilt. But in tuning you said that if everything was in good condition, which it is, the low vacuum would indicate a more aggressive cam. Which makes sense.

I just want good low end torque, good drivability, and good fuel economy.

Id keep he th400 if it had overdrive, that's the only reason im leaning towards a 700r4 swap.

[EagleMark]

Id keep he th400 if it had overdrive, that's the only reason im leaning towards a 700r4 swap.

Better build it to handle the BB or it will be short lived.

Well I don't exactly know. I bought the engine with 0 miles on the rebuild but it had changed hands a few times since it had been rebuilt. But in tuning you said that if everything was in good condition, which it is, the low vacuum would indicate a more aggressive cam. Which makes sense.

I just want good low end torque, good drivability, and good fuel economy.

You can have all that in a BB Suburban except the fuel economy...

So I take it your burb is kind of blah/dead until you rev it to higher RPM then it has loads of power?

[Xenon]

Pretty much. After 2500 it just flys, but its mediocre off the line. It's not a really built engine or anything, just 8.6:1 cr but it should do better than this I think.

[EagleMark]

It sounds like a poor choice of camshaft selection for the vehicle and driving needs...

[delcowizzid]

i leave the cam selection to the pros ive used my guy since i was 12 and started camming 4 stroke dirtbikes for some extra punch and then nearly every car ive built since.arm your cam guy with all the info you possibly can from compression ratio to diff ratio and they will punch you out a nice cam to suit your application.off the shelf cams generally leave a lot on the table

[1project2many]

A good cam guy is really invaluable.

The BBC pfi setup from the 97+ engines is great for torque to about 3500 rpm. Match that with a cam for low end and you'll have a really strong puller on the bottom. Most people can do a fair job of picking cams for mild street use with just a little practice and understanding how the vehicle has to be built to work as a whole package. Look around for Comp Cams dyno software. It's free and after you enter some fairly simple data about your engine you can look at what they offer and the power it will create. That will give an idea about what the cam numbers have to be for lift, duration, centerline, overlap, etcetera. Then you can look at similar cams in other brands and maybe ask someone with dyno software to run a few profiles.

If you have roller tappets I know this cam will feel strong and the cruise range is probably right for a non-OD trans: http://www.cranecams.com/product/car...detail&p=24280

If going OD please skip the 700R4. Save pennies and get a 4L80E. There's more to a transmission than just the clutches inside. The 400 / 4L80E is just a better design all around.

[delcowizzid]

off the shelf isky cams are allways worth a look ive never seen a bad isky cam nor one with wiped lobes 256/262 Best overall cam for towing, trucks, vans R.V., etc. Broad torque band. Good vacuum. 3.55-4.10 axle ratio. 9.5:1 compr. Computer compatible. Smooth idle. RPM-Range (1800-5000) Valve Lift (.490 .488) Valve Lash hot (.000 .000) ADV Duration (256 262) .050 Duration (202 208) LC 110

[Fast355]

If going OD please skip the 700R4. Save pennies and get a 4L80E. There's more to a transmission than just the clutches inside. The 400 / 4L80E is just a better design all around.

I agree you can buy hundreds of gallons of gas for the agony and pain a 700r4 will cause. The are TRASH along with the 4L60E. At 6,500 lbs there is not a prayer of keeping it togather long enough to pay for itself. I LOVE my 4L80e though.

[Xenon]

So I was looking at comp cams cam selector thing... leaning towards the Comp 252BH-11... Fairly stock grind, works well with computer, which in my mind means good drivability and economy.

The thing that jumped out at me was the performance gain the Factory TBI manifold gives you over a dual plane 4bbl manifold... My only problem is I have the old style heads on my rig, and the TBI manifold wont bolt up. What would be a good choice of manifold to use with the tbi? the Holley tbi manifold maybe? or???

The other thing that made big gains was exhaust... It raised the tq numbers by up to 60 lb/ft and lowered the peak by 500-1000 rpm... is there a good set of headers & etc that work well with the tbi?

thanks guys


As an aside, I updated my avatar too. Truck has come a loooong way since the old pic. This one was taken just a week ago.

[Fast355]

So I was looking at comp cams cam selector thing... leaning towards the Comp 252BH-11... Fairly stock grind, works well with computer, which in my mind means good drivability and economy.

The thing that jumped out at me was the performance gain the Factory TBI manifold gives you over a dual plane 4bbl manifold... My only problem is I have the old style heads on my rig, and the TBI manifold wont bolt up. What would be a good choice of manifold to use with the tbi? the Holley tbi manifold maybe? or???

The other thing that made big gains was exhaust... It raised the tq numbers by up to 60 lb/ft and lowered the peak by 500-1000 rpm... is there a good set of headers & etc that work well with the tbi?

thanks guys


As an aside, I updated my avatar too. Truck has come a loooong way since the old pic. This one was taken just a week ago.

The factory TBI manifold is JUNK. I ran a Performer RPM with a marine adapter and a 2" bore 350 marine TBI and saw torque gains from off-idle through redline. I was running TBI heads and the stock cam even.

[Xenon]

Ok, thanks.

[EagleMark]

The other thing that made big gains was exhaust... It raised the tq numbers by up to 60 lb/ft and lowered the peak by 500-1000 rpm... is there a good set of headers & etc that work well with the tbi?

Pretty much all headers will help. But do not cheap out here! Good headers are expensive and worth every penny.

Ceramic coating keeps the heat in exhaust instead of it leaking out more under hood because of more tubes. Also keeps heat on O2 sensor. Besides they don't rust and rot! They will also look great years later! Good headers will not have exhaust gaskets blowing out at head constantly. Spark plugs will fit and not burn the wires.

I installed a set of Headmen Elite Ceramic coated headers on a 1990 Blazer I had a few years ago. Perfect fit! No spark plug or gasket issues in the year that I had the truck. Also kept enough heat in it was very noticeable when opening hood with a hot engine in summer and the single wire O2 sensor never got cool and went OL. Well it did but it was closer to 5f and low RPM highway drive...

[Fast355]

Pretty much all headers will help. But do not cheap out here! Good headers are expensive and worth every penny.

Ceramic coating keeps the heat in exhaust instead of it leaking out more under hood because of more tubes. Also keeps heat on O2 sensor. Besides they don't rust and rot! They will also look great years later! Good headers will not have exhaust gaskets blowing out at head constantly. Spark plugs will fit and not burn the wires.

I installed a set of Headmen Elite Ceramic coated headers on a 1990 Blazer I had a few years ago. Perfect fit! No spark plug or gasket issues in the year that I had the truck. Also kept enough heat in it was very noticeable when opening hood with a hot engine in summer and the single wire O2 sensor never got cool and went OL. Well it did but it was closer to 5f and low RPM highway drive...

I just picked up a set of coated thorley headers for my Express and they are a work of art. Definately do not skimp and buy cheap headers. Definately not worth it when you have to replace them a short time down the road.