Camshaft selection

[delcowizzid]

i only buy quality unless there is none suitiable for the vehicle im working with. i use pacemaker headers where i can. pipe over cone high build quality quarenteed fit and lots of r&d and also they are just accross the pond from NZ in australia.we did just use some hedman headers on an elcamino as they were cheap and all we could get here and they were known to fit LHD but they were awefully short looking and a couple of bends were questionable but all in all ok

[EagleMark]

Headmen also makes cheap headers...

[mecanicman]

I tend to agree with everything that has been said. IF you do decide to go the 700r4(not saying do it, just IF) put it in first before you do the cam swap as it may not be as big of a deal afterwards. A th400 has a 2.48:1 first gear where a 700r4 has a 3.06:1 first gear. The extra gearing with your 3.73 rear end may give you the off the line you are looking for and get you into the cam sooner. Just food for thought......

[EagleMark]

I tend to agree with everything that has been said. IF you do decide to go the 700r4(not saying do it, just IF) put it in first before you do the cam swap as it may not be as big of a deal afterwards. A th400 has a 2.48:1 first gear where a 700r4 has a 3.06:1 first gear. The extra gearing with your 3.73 rear end may give you the off the line you are looking for and get you into the cam sooner. Just food for thought......

Never thought of that?

I think the only point talked about was strength of 700R4, which could be built up at $$, but then why not just 4l80E...

[Fast355]

I tend to agree with everything that has been said. IF you do decide to go the 700r4(not saying do it, just IF) put it in first before you do the cam swap as it may not be as big of a deal afterwards. A th400 has a 2.48:1 first gear where a 700r4 has a 3.06:1 first gear. The extra gearing with your 3.73 rear end may give you the off the line you are looking for and get you into the cam sooner. Just food for thought......

Food for thought too is building the TH400 as a switch pitch model. Its not overly complicated to do and they work very well. 3,000+ stall at WOT and falls back to a tight 1,800 rpm once moving. The GMC Motorhome guys build their TH400 based TH425s to switch pitch capability all the time with great results.

[1project2many]

I've got a switch pitch 400 in my Monte. I was excited to find it in '89 when I built the car but these days I wouldn't work too hard to find one. They were only made for a couple of years and AFAIK they're a bit hard to find. Getting the wide stall range means sending a stock converter out for rework which adds to cost or getting exactly the right converter which is even harder to do. The stator splines are smaller which is OK for low torque apps but it needs to be considered when you climb over 400 ft/lbs. And the change in stall takes a little time which makes it feel a tad sluggish. I suppose a SP might be neat if I ever rebuild my Quadratrac equipped 78 CJ. There aren't many ways to replace the 400 + AMC bolt pattern with an OD trans. But for a heavy rig with computerized engine the 4L80E is still my first choice. You can buy lower 1st and 2nd gearsets to get into the cam faster and if you're on a tight budget get a stock converter to fit a 4L80E on a one ton van with 4.3 for higher stall.

BTW, the big block suggestions earlier came from seeing the 406 engine size and thinking you'd found an old truck engine. I'm not sure why the SBC TBI intake looks good with the Comp Cams software but it is optimistic for sure. If TBI is your game you're better off putting TBI on top of a tall carby intake with larger ports and a larger plenum. The downside is tuning requires more work/time since the intake won't have coolant flowing through it all the time.

[andyk1500]

Just curious if you've ever done a compression test? Cranking compression can be a great indicator on what an engine wants for a cam. Idle vacuum reading would be interesting too...
If it truly has 8.5:1, it probably needs less cam.
Big cam+low compression=dog! I know cause I've done it!

[Xenon]

Never done a compression test... Idle vacuum is pretty low though, about 12-14 in/hg

[EagleMark]

In the data it looked like 15 for vacuum converted from MAP.

Your Idle spark looks good for this kind of cam and idle quality. For the off idle blah, you could add a little more spark and also look at TPS AE and MAP AE and increase by 25% increments if you see improvment. There's only so much you can do to improve what is not there because of the way the cam develops power.

[Xenon]

Ok, thanks

[delcowizzid]

thats good idle vacuam cam cant be too over the top.i run a lot of cams round 225@0.050 duration on long runner inlet manifolds and small cubes 304cu in and idle around 11" 60-70kpa.to much throttle movement = blase the tyres down the road from a standstill.they like to be richer in lower map regions than most stock tunes are tuned for i generally richen the command fuel ratio tables 1 or 2 kpa colomns to the left when running map tunes.if running maf hitting PE at lower tps or hz helps with throttle torque

[405cubes]

Assuming you have a dual plane intake, and heads aren't humongous, 268 ends up off-idle to 5500 ish on the 400.

In the 400 the rv cams will actually get you making enough torque you're going to see mpg numbers go up.
You can cam a 400 a little larger than the stated rpm power curves stated by cam makers.
If you have stock 400 heads a dual pattern is really needed.

Low rpm power is what the 400 is good at. 262-268 gets you strong upper mid and good low torque.
The comp 264/268 works good on stock-ish heads like 882's etc.
The weak link is in the factory 400 heads, If I had to use them, I would go bigger like a 264/268 extreme energy comp.That would band-aid the factory 400 heads and do good on low end.

[andyk1500]

Never done a compression test... Idle vacuum is pretty low though, about 12-14 in/hg

Would it be possible to do a compression test? If you're reading are below 160 psi, you are definitely over cammed.
Bigger cams bleed off cylinder pressure and will make your low end torque suffer, a lot!
I stole this off another forum but it explains the relationship of cam and compression. If you see low cranking compression, I would highly recommend swapping to a milder cam in such a heavy truck like you 'burban.

An engine’s compression ratio is actually a theoretical number. This ratio compares the cylinder volume of the piston at bottom dead center (BDC) versus top dead center (TDC). So if we have a volume of 45 ci at BDC and 4.5 ci at TDC, then the compression ratio is 10:1 since the volume at BDC is 10 times the volume at TDC. While this is a useful number, it ignores one crucial variable. The amount of actual cylinder pressure at low >> engine speeds is determined by the intake closing (IC) point.

All performance camshafts close the intake valve 50 to 60 degrees or more after bottom dead center (ABDC). The longer the duration of the camshaft, the later the intake valve closes. It should also be obvious that the engine cannot begin making cylinder pressure until the intake valve closes. Therefore, the distance that the piston travels up the cylinder at 60 degrees ABDC versus 52 degrees ABDC reduces the volume of the cylinder, reducing the cranking pressure.

Keep in mind that we are talking about a street engine here. Early closing intake valves (short-duration cams) tend to maximize cylinder filling at lower engine speeds, while late-closing intake valves (long duration cams) tend to move the peak power point higher in the rpm range. With a given compression ratio, adding a longer-duration camshaft will decrease the cranking compression and therefore low-speed throttle response and power.

This is where the compression gauge comes into play. By checking cranking cylinder pressure, you can use this as a tuning aid. We checked the cranking cylinder pressure on several modified small-blocks >> and discovered an interesting correlation between soggy low-speed performance and low-cranking cylinder pressure. This comes back to long-duration camshafts with late-closing intake valves combined with a relatively low static compression ratio.

It appears that building a performance street engine that combines a decent-duration camshaft with enough static compression ratio to create 175 to 190 psi, will reward you with a very snappy engine that is not only responsive and fun to drive, but makes decent power as well. For example, you can run 11:1 compression on pump gas if you use a long-duration cam with a late-closing intake to bleed off some of that low-speed cylinder pressure. This is the main reason why camshaft companies recommend higher static compression ratios with longer-duration camshafts. This is an attempt to improve power at low and midrange engine speeds by making up for the late-closing intake valve with more static compression.

[streetperf]

I'm going to jump in and give my $.02. Having built quite a few TBI engines in trucks and researching camshafts I have come to the following conclusions:
computer controlled engines like min 112 lobe center camshafts. this gives the map a better signal, higher vacuum
400 SB like 106 intake lobe center line.
with a vehicle this heavy, and with a flat tappet camshaft(not roller) my recommendation would be a 209/216 @.050 lift. this cam is available through Elgin Industries. I have personally used this cam in a 4 wd drive truck application towing a boat through the mountains of AZ. This engine was a 383.
As for intake manifold's the edelbrock 3705 is eddy's version of a tbi manifold, it only has a 11% drop in flow from an open head on a flow bench. I tested this, the stock manifold as someone said is junk, it has a 20% drop in flow on the same head.
As for your going to a 700R4, Don't do it with that heavy of vehicle unless you like R-R ing transmissions and buying parts. The tranny wasn't made to do that much weight. Stick with your 400. 3.5 tons is a lot of weight to get moving.
When you get this all done, don't forget to change the injectors to the police car style injector, the stock 350's just can't supply the fuel with the modifications you made.
You didn't say what size tire you have on this vehicle. This will affect the final drive ratio.
I hope this gives you some direction on your project. Yes Isky makes great camshafts, and a comp 268 works well up to about 4800 rpm, however it is short on power, depending on what cyl head you have on the engine.

Good luck

[Xenon]

Thanks for the input everyone.

Im running 3.73 gears with 285/70/17 tires. I'm running the 350
throttle body with 454 injectors in it, so fueling isn't a problem.

What at is the story with all these 700r4s advertised to handle 400+hp? Still not stout enough for a 6500lb truck? I would go 4l80e but I like the idea of the lower 1st gear and higher overdrive in the 700r4...

all I'm looking for is some more low end torque and the best economy I can get. Which I know may not be much. I had a '74 F250 with a 390... Had a rv cam in it and I was happy with it... Good torque, good economy. Not the fastest, kinda died out by 4000rpm, but that doesn't bother me.

Thats why I was thinking maybe an "rv cam" for this truck. What do the specs look like for a cam like that? I don't even know.

is the edelbrock manifold for tbi heads or the old style heads?