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... :laugh:

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/cart.php?m=product_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.

[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
http://www.pacemaker.com.au/images/stories/virtuemart/product/ph5300la.jpg

[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? :thumbsup:

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 performancehttp://images.intellitxt.com/ast/adTypes/lb_icon1.png (http://www.gearhead-efi.com/Fuel-Injection/#) 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 powerhttp://images.intellitxt.com/ast/adTypes/lb_icon1.png (http://www.gearhead-efi.com/Fuel-Injection/#) 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 (http://stat.dealtime.com/DealFrame/DealFrame.cmp?bm=519&BEFID=96478&acode=531&code=531&aon=&crawler_id=1912695&dealId=TVLWTssM4VLD9QNUy-v5qg%3D%3D&searchID=&url=http%3A%2F%2Frover.ebay.com%2Frover%2F1%2F711-57618-1854-0%2F2%3Fipn%3Dpsmain%26icep_item_id%3D400585543678 %26icep_vectorid%3D240251%26kwid%3D1%26mtid%3D570% 26crlp%3D1_240251%26kw%3D%7Bquery%7D%26query%3D%7B query%7D%26linkin_id%3D%7Blinkin_id%7D%26sortbid%3 D%7Bbidamount%7D%26fitem%3D400585543678%26mt_id%3D 570%26icep_meta_categ_id%3D6000%26mid%3D446528&DealName=Atv%2Cdirt%20Bike%2C%20Motorcycle%2C%20Ca r%20Compression%20Gauge%2Ctester&MerchantID=446528&HasLink=yes&category=0&AR=-1&NG=1&GR=1&ND=1&PN=1&RR=-1&ST=&MN=msnFeed&FPT=SDCF&NDS=1&NMS=1&NDP=1&MRS=&PD=0&brnId=2455&lnkId=8070676&Issdt=131023051359&IsFtr=0&IsSmart=0&dlprc=51.95&SKU=400585543678) 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?

[Fast355]

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?

700r4 and 4L60E are both too weak for a 5,500 lbs vehicle, much less one weighing in at 6,500. Just asking and begging for problems. 80E is a much stronger transmission even stock than the best 700r4 or 4L60E.

[Xenon]

Wrote to comp cams for a recommendation and this was their reply:

A cam that best fit your mods is our xtreme energy cam (12-262-4)specs are below. The cam will have to be on a small base circle to clear the stroked out engine.


The cam will help increase power and torque, excellent throttle response, also will have a nice lumpy idle
The cam will be 218/224 @ .050 and the lift is .464/.470 on a 110 LSA


If not done so I always do recommend in upgrading valve-train to protect your investment. The upgrade helps in getting the most power from the engine/cam and keeps its safe. We do offer a cam kit which includes(cam,lifters,springs,retainers,locks,seals ,timing set)



What do you guys think of that?

[Fast355]

Wrote to comp cams for a recommendation and this was their reply:

A cam that best fit your mods is our xtreme energy cam (12-262-4)specs are below. The cam will have to be on a small base circle to clear the stroked out engine.


The cam will help increase power and torque, excellent throttle response, also will have a nice lumpy idle
The cam will be 218/224 @ .050 and the lift is .464/.470 on a 110 LSA


If not done so I always do recommend in upgrading valve-train to protect your investment. The upgrade helps in getting the most power from the engine/cam and keeps its safe. We do offer a cam kit which includes(cam,lifters,springs,retainers,locks,seals ,timing set)



What do you guys think of that?

Too much cam for a vehicle as heavy as yours with a stock converter and only 3.73s. I would look into something more like this. It may have to be ground on a small base circle depending on connecting rod clearance.

http://www.summitracing.com/parts/cca-cl12-235-2/overview/make/chevrolet

For mileage and throttle response this would likely be even better but would run out of breath by 4,500.
http://www.summitracing.com/parts/cca-cl12-231-2/overview/make/chevrolet

[streetperf]

Xenon,
If you do the math on your tire size you will find that you are not truly running a 3.73 gear ratio, If you go to a tire/gear calculator program on the net, you will find your final drive ratio. If you add a overdrive trans, which reduces the final drive approx 30% your driving rpm is actually lugging the engine. That is why you do not have throttle response, acceleration, and the result fuel economy.
The 3705 Edelbrock manifold is for TBI heads. It will not fit your 454 throttle body. The throttle plate size is for the 1 11/16" throttle blades. The manifold will have to me machined, to accept the 454 w/o an adapter, the machine of this is fairly expensive, because beside machining, tig welding is also involved for the water ports in the plenum area. This mod is not for the faint at heart or wallet. If you have the standard bolt pattern heads/non tbi heads, you can modify the center bolt holes to accept the older bolt pattern. If you are using a non high velocity head on a TBI (the old carb heads) you will not be able to get the throttle response needed to move 6500# efficiently. I have used a 170cc twisted wedge on a tbi and worked very well. I have also ported 093 tbi heads and worked very well also. Dart 180 cc iron eagles work well.
The 700R4 wasn't designed to haul 6500# from a dead start. GM thought the same as you are in the 80's in their 4wd's. The tranny just would not hold up. Too much heat, even with auxiliary coolers. 2nd gear usually goes out first, and with that OD.
I don't know what heads you have, however if you are using 454 injectors you are correct fuel isn't a troubled area, in fact it has too much fuel. Have you watched the map sensor on a scanner, and the O2 readings. How many crosscounts do you have?

Hope I have given you info to investigate

Street Perf

[Xenon]

Really appreciate all the information... I do have it tuned for the 454 injectors... Eagle Mark and others here helped me out with that. Runs as well as it can given the current setup.

If you were building a 400 small block for a suburban what would you do? I'm not opposed to changing heads, intake, cam, whatever.

[Fast355]

Really appreciate all the information... I do have it tuned for the 454 injectors... Eagle Mark and others here helped me out with that. Runs as well as it can given the current setup.

If you were building a 400 small block for a suburban what would you do? I'm not opposed to changing heads, intake, cam, whatever.

Depending on the pistons in the engine, I would use one of the two cams I linked, swap over to some vortec heads, run a water heated performer rpm dual plane intake with a TBI to carb adapter. Concentrate on low-midrange torque as that is what will propel that 3 ton monster.

[Xenon]

Not sure on the pistons, but it measures to 8.6:1 compression with 76cc heads, so they're not too special.

Don't remember what the heads are exactly, but I remember looking up the casting number and being rather disappointed. They were just some heads off a 350... And there was some failure they were prone to... Cracking or something.

it has a Holley spreadbore intake, but not really a performance one... It was an older one that was designed to be basically a stock replacement but in aluminum.

[Xenon]

For mileage and throttle response this would likely be even better but would run out of breath by 4,500.
http://www.summitracing.com/parts/cca-cl12-231-2/overview/make/chevrolet

well I've been looking around more and I really like this one you suggested.

How do I know if I need to have it ground on a small circle? And do I need different springs, pushrods or anything? Or will stock be ok?

thanks.

[streetperf]

Xenon,
With all the info you have received on your 400 TBI engine, You should be able to make an somewhat decision. I don't know how many dollars you have to spend on this project but to get gas mileage out of a 6500# vehicle that has the areo package of a brick, is going to be very difficult. Being a 400 is a good start in that vehicle, most chev camshafts are ground for a 350 application in the catalogs, unless otherwise stated, so in a 400 the cam will seem to be smaller due to the larger displacement of the engine and torque output. Therefore you can use a Slightly larger cam duration to achieve the desired results. For instance, a 204 duration camshaft works very well in a 350 application, in a 400 you can use a 209-212 and get better results and approx same power band increased toque, hence the increase in CID, and Stroke of the engine.
You have stated what heads you have, example- casting number. If you want to change them or not, again goes back to dollars. Newer heads work better than 80's open chamber emission heads by far. As was stated earlier install a set of vortecs and go. However that will involve a new intake manifold. Again dollars.

If I were you, and I'm shooting in the dark here. If you don't have allot of money to spend and you don't know how the expected results will turn out for you, I would be conservative on my changes. A camshaft that has been previously recommended be purchased with lifters, installed, tuned and test driven for results over a period of time.

[1project2many]

I have posted some links to a DIY type modification for the stock TBI intake that will help improve airflow. It will still fall short of what a 400 wants but it can help. The same would apply if using the TBI Vortec intake. Along with opening up the bores, this will help improve flow as engine rpm increases.
http://home.metrocast.net/~shannen/efistuff/L03_Intake_changes/L03_Intake_1.JPG
http://home.metrocast.net/~shannen/efistuff/L03_Intake_changes/L03_Intake_2.JPG
http://home.metrocast.net/~shannen/efistuff/L03_Intake_changes/L03_Intake_3.JPG
http://home.metrocast.net/~shannen/efistuff/L03_Intake_changes/L03_Ported_plenum_1.JPG

Ultimately, the rear gear and trans ratios should be in line with the cam's powerband. Trying to change intake, exhaust, etc when the cam is not appropriate is just an attempt to bandaid the problem.

[loadedi812]

Stage 8 locking header bolts help keep gaskets in good shape, just make sure to get six point heads instead of 12 point heads. That way you can get a wrench on them to tighten em up if tubing clearance becomes an issue. That is if you decide to run headers.

[lionelhutz]

Being a 400 it will require a bit more cam then you'd use in an equivalent 350. I'd think it would do well with around 215* @ 0.050" on the duration and as much lift as you can get in that duration, which will likely end up in the 0.425" to 0.450" range for a flat tappet hydraulic.

As for the cam size -check the existing push rods. You might find longer push rods that would indicate a smaller base circle cam. You could look at the lifters too to make sure there aren't longer lifters in it. Otherwise, you may need to pull the cam and see if it has a part number on it.

As for springs - You could keep the same springs if you know the old cam was more aggressive. Since it seems you don't know what the old cam was it would be a good idea to just use the recommended matching springs.

[Xenon]

As for the cam size -check the existing push rods. You might find longer push rods that would indicate a smaller base circle cam. You could look at the lifters too to make sure there aren't longer lifters in it. Otherwise, you may need to pull the cam and see if it has a part number on it.

As for springs - You could keep the same springs if you know the old cam was more aggressive. Since it seems you don't know what the old cam was it would be a good idea to just use the recommended matching springs.


thanks. That's what I needed to know