[Carmine]

Hi everyone. I'm starting to think of what I might like to do with the original 400 motor in my '71 GTO. I'm looking for a little more performance from it. It just seems sluggish to me. I may very well take out the unknown performance camshaft which I think is a liability and robs my engine of vacuum that I need for the power brakes. What would you replace that with?? I have #96 factory heads and know nothing more about them. I don't know if they have been reworked or not. I would prefer to leave them as is, but would take them off if it was to my benefit and would really matter on performance. The stock intake I would want to keep, but the Q-jet I would consider replacing, although I really wouldn't want to. I paid a lot of money to purchase and have it rebuilt. I have factor headers which would be staying. The car has a TH400 with 3.55 gears. I'm not looking for a screamer. Just something that can get out of its own way. I just feel that there is something holding it back and it has more potential. I know I'm going to be limited as to what I can do, but I really think my problem is the camshaft. I have a suspicion someone put this cam in without considering all the working parts, because it sounded good. Maybe one of those thumper cams. I wouldn't doubt if the engine still has stock compression which I believe is 8.2:1. Anyway, I'm open to opinions/advice/suggestions. I don't discount what anyone says. I appreciate the effort. Thank you, Carmine.

[ponyakr]

Voodoo 262 cam.

http://www.lunatipower.com/Product.aspx?id=1775

https://www.summitracing.com/parts/c...BoCReIQAvD_BwE

Or:

http://www.ebay.com/itm/New-Hydrauli...xZODlz&vxp=mtr

Establish a good ignition advance curve, with total mechanical advance all in by no later than 3000 rpm.

Go with an adjustable vac advance can, so you can limit total advance at cruise rpm. Crane sells a kit, for both HEI & points type dist, which includes the can & 3 sets of mechanical advance springs.

https://www.summitracing.com/parts/c...01-1/overview/

https://www.summitracing.com/parts/c...xoCxtEQAvD_BwE

Some of the experts here can help you correctly dial in your ignition curve. At WOT, most Pontiac engines seem to run best at somewhere between 34-36° of mechanical advance. At cruise rpm, some say total should be less than 50°. Obviously, too much advance can encourage detonation. And too little advance will decrease power & can increase coolant temp. Will also decrease gas mileage.

Then, obviously, your Q-jet needs to work correctly, with a strong, full pump shot, and with the rear air flap opening at the correct rate for your set-up. And, make sure the butterflies open FULLY, when the pedal is to the floor. Lots of guys, including me, have discovered that sometimes the pedal does not have enuff travel to fully open the butterflies. Could be carpet or insulation under the pedal, or something bent, in the pedal/linkage. Bent linkage rods and/or other linkage problems, on the carb, can also prevent correct operation.

[Carmine]

Originally Posted by ponyakr

Voodoo 262 cam.

http://www.lunatipower.com/Product.aspx?id=1775

https://www.summitracing.com/parts/c...BoCReIQAvD_BwE

Or:

http://www.ebay.com/itm/New-Hydrauli...xZODlz&vxp=mtr

Establish a good ignition advance curve, with total mechanical advance all in by no later than 3000 rpm.

Go with an adjustable vac advance can, so you can limit total advance at cruise rpm. Crane sells a kit, for both HEI & points type dist, which includes the can & 3 sets of mechanical advance springs.

https://www.summitracing.com/parts/c...01-1/overview/

https://www.summitracing.com/parts/c...xoCxtEQAvD_BwE

Some of the experts here can help you correctly dial in your ignition curve. At WOT, most Pontiac engines seem to run best at somewhere between 34-36° of mechanical advance. At cruise rpm, some say total should be less than 50°. Obviously, too much advance can encourage detonation. And too little advance will decrease power & can increase coolant temp. Will also decrease gas mileage.

Then, obviously, your Q-jet needs to work correctly, with a strong, full pump shot, and with the rear air flap opening at the correct rate for your set-up. And, make sure the butterflies open FULLY, when the pedal is to the floor. Lots of guys, including me, have discovered that sometimes the pedal does not have enuff travel to fully open the butterflies. Could be carpet or insulation under the pedal, or something bent, in the pedal/linkage. Bent linkage rods and/or other linkage problems, on the carb, can also prevent correct operation.

OK. Thank you. Let me ask this follow up question. I've looked for the answer myself but can't seem to find it. Stock cast iron intake vs. Edelbrock aluminum Performer. My car came with the Edelbrock manifold and a 800 cfm flow Holley. I replaced them both with factory stuff. How does the factory cast compare to the Edelbrock for performance. Same question in regards to the stock Q-jet vs. an Edelbrock. Lets says a 750 CFM although that might be too much?? Would those changes be a moot point because the stock #96 heads are capable of just so much?? Thank you, Carmine.

[455GRIN]

Either increase the compression of the 400 but cutting heads (not my choice) or stroke the 400 to a 462, the #96 heads work perfect on a street 455. Put in a new cam, keep the intake and Q-Jet.

[Carmine]

Originally Posted by 455GRIN

Either increase the compression of the 400 but cutting heads (not my choice) or stroke the 400 to a 462, the #96 heads work perfect on a street 455. Put in a new cam, keep the intake and Q-Jet.

OK. Thank you. So I would like to ask, why you wouldn't cut the heads to increase the CR?? If I understand it correctly, to stroke my 400, I would have to have it bored and buy a new crank. Maybe some other parts and machine work. Wouldn't all that be much more expensive then cutting the heads?? Many thanks, Carmine.

[carbking]

Just as a suggestion, before determining what modifications to make, why not try to determine WHY your current engine is not performing to your satisfaction?

(1) Compression test - all the bolt-on aftermarket parts in the world will not fix bad valves
(2) Vacuum leak - you are having issues with the power brakes. Disconnect ALL vacuum lines from the engine (except vacuum advance) and check the engine vacuum. A vacuum leak can really mess things up.
(3) Defective vacuum advance unit - will mess things up royally

If no vacuum leak, and good compression - degree the camshaft. Find out what you have before deciding to change.

You replaced the Holley with a Q-jet, which Q-Jet??? A Pontiac Q-Jet from a similar engine, a non-Pontiac Q-Jet recalibrated by Cliff (or others), or just a Q-Jet?

Knowing what you have will make going forward (or just fixing a problem) much easier.

Jon

[ponyakr]

"...I would like to ask, why you wouldn't cut the heads to increase the CR??..."


I'd say that the reason most guys wouldn't recommend cutting the heads to increase CR, is because they don't think any engine with less than 9.5 CR is worth having, therefore if cutting the heads a reasonable amount won't get you up to at least 9.5 CR, it's not worth doing.

I choose to disagree. If all you want is just a spunky street cruiser engine, a properly built low CR engine can be just what you need. And you won't have to worry as much about detonation, as with 9.5 & higher CR.

Some don't wanna leave any power "on the table". This has probably been responsible for lots of guys spending more money than they needed to and/or ending up with much more power than they needed, and/or having a cam that's not right for the kind of driving they'll be doing.

Some guys have a street/strip mentality, when it comes to engine builds. But, most Pontiac street guys will never make a drag strip pass. And most of their driving is done at under 4000 rpm. Therefore having a cam that makes less low end torque, but more hp over 5000rpm will likely be exactly the opposite of what they need.

IMO, most street only guys would be much happier with a good idle, lots of low end torque & vac, and good mid-range hp, even if it meant having 30-50hp less, above 5000 rpm. The extra power, above 5000 rpm, would be absolutely useless, to many street only guys.

This seems to be hard for many forum users to understand. So, when you consider the many differing opinions, you need to keep in mind that some are offering opinions based on what they'd build, rather than what you actually need, in order to accomplish what you desire. Many consider anything under 400hp & 500ft lbs of torque, not worth building.

There are experts on this forum. I'm not one of 'em. This is just my observation, from several years of reading engine build opinions.

[ponyakr]

"...How does the factory cast compare to the Edelbrock for performance..."

Assuming you are referring to an Edelbrock Performer Pontiac, and not a Performer RPM or Torker, it has been proven in street, strip, end dyno testing, that the Performer Pontiac will produce very similar power levels, to a stouock iron intake, in a mild 400 street engine, below 5000rpm.

In larger cube engines, and at rpm levels above 5000rpm, the iron intakes seem to show an advantage. So, if you'll be operating a mild street 400, at mostly below 5000rpm, a Performer will be OK. Some prefer the lighter weight, and the look of the alum intake.


"...Same question in regards to the stock Q-jet vs. an Edelbrock..."

There are a few guys who like Edelbrock carbs. But, most here, including me, prefer the Q-jet.

If I had to use an Edelbrock brand carb, it would be a Q-jet. From sometime in the mid '90's thru early 2000's, Edelbrock sold Q-jets, which were made for them by Weber. Cliff has said that most of these E-Q-jets are OK if properly rebuilt & set up. They are much newer than any GM Q-jet. Only negative I can think of is the Chevy style, side fuel inlet, and throttle linkage which may require mods, in order hook up a Pontiac throttle cable.

http://www.carburetion.com/Rochester.asp

http://www.mre-books.com/quadrajet/edelbrock.html

[ponchjoe]

Carmine, how far do you want to go? The first step is to determine what you want from your street only car. Do you want to rebuild or just make it run better? What do you know about the motor today, rebuilt with receipts, unknown? If the compression is good then why not a good valve job, cam, carb and distributor tune? I believe stock compression on the 71 400 is 8.2 which with the right cam can be a decent street performer (068?) The 3.55s definelty help.
I have always read that the only real bene for using the standard performer is weight savings.

[poncho-mike]

A 1971 GTO with a 400 with 96 heads, TH400, and 3.55 rear end should offer reasonable performance.

I would start by investigating the low vacuum readings. The main things that could cause low mainfold vacuum readings are: 1) A radical cam with a lot of overlap. 2) A big vacuum leak somewhere. 3) Incorrect valve timing, and maybe ignition timing.

Do you have any specs on the cam in the engine? In general, I like to look at the duration @ .050" lift. For an engine with a CR of 8 - 8.5:1, I wouldn't run much over 215 degrees @ .050 on intake. If you go up to the low 9's on compression, you can get by with 220 @ .050" lift on intake. Historically, most Pontiacs like the exhaust duration to be 6- 10 degrees more than the comparable intake duration @ .050. I allso like to run total lift in the .460 - .480" range. If the duration of your cam is greater than this, you really need to select a different cam.

Next I would start looking for vacuum leaks. It is very easy to check a vacuum advance. Remove the distributor cap and rotor, disconnect the vacuum advance hose from the engine, and suck on it. If you suck air, you have a bad vacuum advance unit. If you can pull a vacuumby sucking on the hose, check to see that the point plate on the distributor moves. You should be able to see the plate move. If the plate moves, the vacuum advance unit is good. Next, I would baseline the vacuum readings with the engine as is. Then cap off all potential sources of vauum leaks (especially he power brake booster), then take more readings. If the readings are significantly different, you need to identify what the source of the leak is.

Next I would start looking at spark timing. Do you know if the engine builder verified TDC on the harmonic balancer mark actually coincides with the piston reaching TDC? On a Pontiac harmonic balancer, you have an inner and outer hub with rubber bonding the two hubs together. The inner hub is keyed to the crank, but the outer hub with the TDC mark is used to set spark timing. I have seen several engines where the outer hub slipped, causing spark timing to be way off. You might also want to consider changing to an HEI or improving your ignition. That points distributor leaves a lot to be desired.

In addition to spark timing, you have valve timing. Degreeing a camshaft insures the valves open and close when they should. If the timing chain was not properly installed or the keyway on the cam is not properly cut, your valve timing can be off. I bought a new cam, and found it to be about ten degrees retarded when I degreed it on the engine.

For performance, I like a 455 with #96 heads. This engine has low 9's CR and lots of torque. One of my favorite cams for this combo was the Wolverine Blue Racer WG-1096, which is pretty close to the specs of the Lunati Voodoo 262 cam. Summit sells the Blue Racer WG-1096 equivalent as Summit SUM-2802.

In my 74 Trans Am 455 D-port with stock 8:1 CR, I run the SUM-2801. It has a nice lope, strong torque curve, and good manifold vacuum.

There are several things to be aware of should you decide to replace heads or intake on your engine. If the previous owner put a big cam in the engine, he probably also milled the heads. When you mill the heads, you alter the valve train geomety by moving the valves and rockers closer to the pistons. As long as the milling isn't excessive, it won't be a problem but you will need to adjust your valves using zero lash plus 1/2 turn. You don't want to just run the rocker nut down until it bottoms. In addition, shaving the heads alters the intake runner to head port alignment. The machine shop will compensate for this mis-alignment by shaving the mating surface of the head or intake. If you change heads or intakes, you need to check this alignment.

Good luck.

[ponyakr]

"...I like a 455 with #96 heads. This engine has low 9's CR and lots of torque. One of my favorite cams for this combo was the Wolverine Blue Racer WG-1096, which is pretty close to the specs of the Lunati Voodoo 262 cam. Summit sells the Blue Racer WG-1096 equivalent as Summit SUM-2802..."

I wasn't familiar with that 1096 cam, at all. So I just looked it up. And if the specs shown for it, on the Wallace site, are correct, it's specs are not even close to the same as a Voodoo 262.

WG1096 ------ adv dur 290/300 -- 224/234 @ .050

Voodoo 262 - adv dur 262/268 --- 219/227 @ .050

http://www.wallaceracing.com/cam-specs.htm

http://www.wallaceracing.com/cam-specs.htm

That's nearly a 30° difference in adv duration, and 5° @ .050 lift. The Voodoo has a much steeper ramp. The only similarities appear to be the total lift.


"...In my 74 Trans Am 455 D-port with stock 8:1 CR, I run the SUM-2801. It has a nice lope..."

Just curious: You say the 2801 has a "nice lope" in a 455. Most info I've seen indicates that cam should have an almost dead smooth idle, in a 455. Not saying your wrong, since I haven't heard your engine run. Just saying that what your saying doesn't jive with the other info I've read.

I'd think that a Voodoo would be a better cam, for a low compression engine. For a 455, some would go with a 268 Voodoo. But, as everybody knows, I'm not an expert on cams, or anything else. Just going by what I've read.

Haven't used any of the 4 cams mentioned. But, I can say that an 041 clone/Rhoads lifters, produced what I called a smooth idle, in a high comp 455. But, that is, as they say, " comparing apples to oranges ". Maybe the lower compression results in a rougher idle, than the same cam would produce, in a higher comp engine, with the same stroke & cubes. Or, to say it another way, maybe compression affects idle quality in a similar way to how stroke/cubic inches affects idle quality, if using the same cam.

[Carmine]

Some great suggestions and experiences here. Many thanks to all who responded. I don't discount anything that was said. I take everything under advisement and I'll read these threads many, many times trying to absorb everything, then make a decision. I know that I contribute to the problem, because of my expectations of the car. I forget at times, that this 400 engine is low compression and only capable of so much. It's rated at factory 300 HP, but just doesn't feel like it. I've owned and driven Chevys with a 327/300 and they moved along quite well. Might not be a fair comparison, but there is just something lacking here. I really feel it should perform better as is. I've run this motor up to darn close to 5000 rpm's, a few times, manually shifting the transmission, and it scooted along nicely. No missing. Steady power. But that is at WOT which I don't necessarily need. I normally don't drive the car like that. Normal driving and rpm's, it's just sluggish. Seems like it needs a lot of throttle to get it up to cruising speed. Maybe has a lot to do with the cam in it which I don't have a clue as to what it is. Might be designed for top end speed and rpm. I need low/mid range torque and power. So, that's pretty much where I'm at. Not going to do anything before the snow comes. Going to drive and enjoy this car until then. I just thought of a few additional questions re. shaving the heads. I'm assuming that the head surface gets shaved, so how does this increase the CR?? How much increased CR can you hope to gain?? Does shaving the heads also create an alignment issue with bolting the intake onto it?? Many thanks, Carmine.

[carbking]

Carmine - shaving the heads will increase the compression ratio because it lowers the volume of the compression chamber in the head, thus the total volume. The mixture is now compressed into a smaller volume, thus the compression is raised.

Shaving the heads MAY ALSO upset the valve/pushrod/lifter geometry to where one MUST install an adjustable valve train.

Excessive shaving of the heads MAY ALSO change the relationship of the intake manifold and cylinder head passages to where port matching is required.

There are certainly enough different Pontiac heads with different chamber volumes (read Pete McCarthy's book) to increase the compression simply by changing heads WITHOUT adjustable valve train and port matching. For a street engine, (opinion) the head change is far superior to the other.

Still believe that before you decide to change engine accessories, you should find out why you aren't happy with the performance. Could be nothing more than a vacuum leak, or the need of an electrical tune-up.

Jon.

[ponyakr]

"...Does shaving the heads also create an alignment issue with bolting the intake onto it?? "


The correct procedure is to shave the same amount off the intake port surface of the head as is shaved off the combustion chamber surface. This is said to maintain intake bolt hole alignment.

[poncho-mike]

ponyakr,

On the WG-1096, the lift is about the same as the VooDoo 262 cam, but the duration @ .050" is only 5 degrees more. As you point out, the overall duration of the WG-1096 is much greater than the VooDoo cam. In my opinion, the short opening and closing ramps is not an advantage for a street driven engine. From what I've read, you're not getting much air flow at low valve lifts. However, the time spent lifting the valve off of its seat and setting it back down is a tremendous concern for reliability. About 25 or so years ago, I bought into the Comp Cams logic that advances in cam technology allowed cams to be ground with much more aggressive opening and closing ramps. I installed a Comp Cams 280 (230 duration @ .050" lift, .480" lift I think) in a 72 455HO 4-spd with mildly ported heads. I used HO-Specialties valve springs good for .500" lift and had seat forces at open and closed lifts measured and documented on the build sheet. The engine was run in with no glitches, but it ate the cam very quickly. When I tore down the engine, I also found severe valve recession on all of the exhaust seats. I rebuilt the engine again, this time adding hardened exhaust valve seats and using the WG-1096 cam. The engine lived a fairly long life, and it had great performance.

In my opinion, the risks of running a cam with fast opening and closing ramps in a cruiser isn't worth it. That cam is more suitable for someone who is building a street/strip car.

I mentioned I was running a WG-2081 in a 1974 455. This cam has about 2 degrees more duration @ .050" than the 455HO cam (212 @ .050" on intake), but with more lift. This cam will give you a similar lope to what a stock 455HO cam would have in a 455.

I guess there is no clear definition of a "nice lope". To me, the stock 455HO (I think it's called the S cam) has a nice lope. The 71-72 455HOs were offered with a/c, so this cam had to be mild enough to provide good performance without affecting drivability. The lope in my 74 T/A is probably mild by most people's standards, but the idle speed is set at the standard. I would consider a Ram III cam to have a lot of lope, and would be suitable for a manual tranny car.
"

[ponyakr]

Paul Carter and many others think the Voodoo cams are very streetable. And, to me, an 068 cam has no lope at all, in a 455 engine. If the Voodoo cams were as bad as you say, they would have been deleted by now. Instead, they are quite popular.

It just once again proves that different guys have different opinions and have had different experiences.

[poncho-mike]

I'm curious how many miles the engines running the VooDoo cams have on them. I'm going from memory, but I think I wiped out the Comp Cams 280 in 5 - 8K miles. The WG-2082 ran for about five years with me driving it around 60K miles. I sold the car to a friend who drove it less miles. As far as I know, the engine was running fine the last time I saw it about five years later. I was using these cars as daily drivers in the 80s and 90s, so reliability was important.

[ponyakr]

" I'm curious how many miles the engines running the VooDoo cams have on them..."

Don't know. But you can ask Paul Carter. He has probably built more Pontiac engines with those cams than anybody else. He goes by something like GTOfreek. Also has his own FB page, & works @ Koerner Racing Engines.

https://www.facebook.com/groups/365435830492976/

https://www.facebook.com/pages/Koern...58663244168447

http://forums.maxperformanceinc.com/...d.php?t=809111

[poncho-mike]

I have also seen machine shops shave intake surfaces to achieve proper alignment. I don't know why, since I always thought you should shave both surfaces of the head. It may have been because the machine shop doing the original head work only shaved the surface that mates with the block, so machining the intake was an afterthought.

Originally Posted by ponyakr

"...Does shaving the heads also create an alignment issue with bolting the intake onto it?? "


The correct procedure is to shave the same amount off the intake port surface of the head as is shaved off the combustion chamber surface. This is said to maintain intake bolt hole alignment.

[Carmine]

Lets just say I was going to replace my #96 heads with another higher compression head. Which one's should I be looking at?? Assuming I would go with that Voodoo cam also. Thanks, Carmine.