[kookykrispy]

68 GTO

TH400, stock convertor

highway gears. Not sure of exact ratio but feels like probably standard 3.23. 275/60r15 tires

The 400 has been rebuilt at a production shop. bored .040 over, nothing special

Most likely has stock rods and cast replacement pistons. I will post 'in-the-hole' measurements and valve reliefs later when I remove the current 4x heads.

I am planning on using a set of 6x-4's that have been milled down to 81cc to yield approximately 9.6:1 compression (figured on the wallace racing site)
Heads have extensive professional porting done on both intake and exhaust, and some minor bowl and chamber work too. I don't have any flow numbers, but the work was done by a specialist and they look beautiful. The pushrod slots are enlarged to work with my Harland Sharp 1.65 roller rockers

no-name 4 tube headers, 2.5" exhaust, flowmaster mufflers

Mallory Comp SS 42 series distributor, promaster coil

First of all, I want a cam that will absolutely work well with today's crummy pump gas without any harmful detonation. I don't mind buying super unleaded, but often I am forced to fuel at military posts, where the gasoline is often of questionable quality. Here in Western WA, and on the west coast in general, we also have 10% ethanol in the gas and often you have to settle for 91 octane. Sucks, but its a fact of life.

This car is a street machine/cruiser that will see regular friendly stoplight action and daily freeway commute operation. Actual dragstrip competition use will be extremely limited, or not at all. Since its a heavy, mild geared, automatic trans car, I'd like it to hit hard right off idle with lots of low and mid range torque. I want a big, fat torque curve but while also taking advantage of the increased flow characteristics of the ported 6x heads. Some higher rpm performance would be nice, but is not the primary goal. Redline should probably remain near 5500 since heavy stock type rotating parts are still in use.

I want good street manners, with a strong idle and lots of vacuum... but it would be fun to have a nice rump to the idle, just because I love the sound.

Due to budget constraints, I'd prefer to use an off the shelf cam with a flat tappet hydraulic grind... I'm trying very hard to resist the urge to overcam this engine, because I want lots of low end torque, but I also want to take advantage of the sweet porting job on the heads.

I'm considering the summit 2801 cam... but wonder if its actually a bit too big for my intended goals and maybe the 2800 would be a better choice? I like the summit cams because they're cheap and I've run them before. I would consider other cams, however...

like possibly the 068? I am not sure about the big 116 LSA on that cam though.

Roller cams are probably out of the question, since this is a budget project.

I figured it made sense to pair my ported heads with the 1.65:1 rockers for additional valve lift to try take advantage of the sweet port job. Will this help at lower engine speeds, or only affect higher-rpm operation? Should I use a performer or RPM intake for this application? What size carb?

[b-man]

I would run the Summit 2802, plenty of low-end torque and a nice little rumpy idle that's not out of hand in any way. The 2800 and 2801 are both too wimpy for your combo.

Just a couple of weeks ago I had the pleasure of riding in a '69 Chevy C10 long-bed pickup powered by a 400 engine very similar to yours that belongs to PY member SergeF.

Home ported 6X-4 heads (Serge does very nice work, no flow numbers), stock iron intake with an 800 Q-jet built to one of Cliff's recipes and running 3-tube headers with a 2-1/2" exhaust. This truck has a TH400 trans and a 4.10 rear but has 28" tall 235/75-15 tires.

That heavy truck (4500# ?) flat out moves with a 400 engine, running the 1/8 mile in 8.6 seconds with slicks (equivalent to 13.5s in the 1/4 mile). The fact the Serge can tune an engine quite well does factor in of course. Under the hood it's all Pontiac blue metallic, no aftermarket pieces to be seen and nothing fancy.

I'm sold on that 2802 cam for street 400s.

[kookykrispy]

B-Man,

Serge's truck sounds badass. I actually have a 2802 and lifters in my parts stash and I also am a big fan of that cam! I was considering throwing it in my '68 just to try it in this combo. I've run the 2802 cam before in a 400 in my old 4 speed Tempest ... I loved it, but only after I swapped in 4.10's. I'm a bit worried it would be overcammed not provide enough low-end grunt for a highway geared automatic car?

I guess I could simply put it together with the 2802 first since I have the cam already, and then replace it with something smaller if I felt the low-end was not enough?

Do you, or anyone have experience using the 2802 in a 400 in an auto car with highway gears?

[b-man]

I really wouldn't call 3.23s a highway gear, just a good all-around combination street and highway performance gear.

In a car roughly 1000# lighter than Serge's truck I think the 2802 cam would be a slam-dunk with 3.23s. A decent performance torque converter is a key element here, the right one (Continental) will make all the difference.

[kookykrispy]

Originally Posted by b-man

I really wouldn't call 3.23s a highway gear, just a good all-around combination street and highway performance gear.

In a car roughly 1000# lighter than Serge's truck I think the 2802 cam would be a slam-dunk with 3.23s. A decent performance torque converter is a key element here, the right one (Continental) will make all the difference.

I really need to pull the cover on the rear diff and see exactly gears what this car has in it. Its a GM 12 bolt, which is not stock 1968 pontiac equipment... right?

What's a continental convertor like that cost these days? I can't seem to find a price online. If I run the 2802, then I could use my cam/lifters money for a convertor instead.

[b-man]

Only 455 cars had 12-bolt rears, no 1968 Pontiac had a 12-bolt. Definitely check your ratio ASAP.

Here's a nice Conti converter being sold by one of my good friends for a very good price, fresh and ready to go: http://forums.performanceyears.com/forum/showthread.php?t=675600

[kookykrispy]

OK, I'll pull the cover and check the actual gear ratio after work tomorrow (army reserve drill weekend). I haven't sauced myself in gear oil in awhile so its about time.

Woah, those conti convertors ain't cheap I guess?... That convertor for sale seems like kind of a mystery... how would I know what it would stall at behind an engine combo like mine? I'm a little afraid of buying a 10" 'race' convertor to go in my street car. I sent Harry a PM for more info.

[b-man]

The Conti 10" converters are nice street converters, they couple up well and don't slip a lot at the track or on the street. They're not cheap, but worth every penny and then some.

No need to pull the cover to check your ratio: http://forums.maxperformanceinc.com/...iveshaft+count

[steve25]

Your statement that your 6x heads are extensively ported with minor bowl work done is a large contradiction, what are the air flow numbers at 28" if a flow test was done to them?

[kookykrispy]

OK,

I know its been awhile, but I finally got around to messing with my gto again. Jacked up the rear axle and counted about 2&3/4 revolutions of the driveshaft for one tire rotation... so I'm going to figure it has 2.73 rear gears. No wonder it is so comfortable on the freeway! Its turning about 2100-2200 rpm at 65mph. 3rd gear feels like an overdrive. I really love the freeway manners of this car, but the stoplight performance needs improving.

Is there a good low end torque cam that would help this combo out with the th400 and 2.73 gears? or is it a lost cause without a gear swap?

Steve25, I do not have flow numbers for these heads.

[Tim Corcoran]

Mr KooyKrispy

So you have 2.73 gears, a nice gear for a street car that will be driven a lot. You will enjoy driving the car with those gears. In your post you mentioned "extensive professional porting", so if this is true then you are already out of ballance with a car with 2.73 gear. Everything is a compomise and your heads are on one extreme and your gear is on the other. So if you cam for the heads then you need gears and converter to make it work. If you cam for your gear and driveability then you won't be using the power potential of your heads. If the heads are extensively ported then your runners will be large and velocity will be down from a stock head, this works against your goal of low end torque especially with a 400. If you decide to run the hwy gears and those heads you will not be satisfied with your results regardless of cam choice. If you cam for your heads then you will need some higher stall to make the cam work and with a tall gear your loosing your street manners. Your best choice at this point would be a hydraulic roller cam. If that is not in your budget I would get a set of unported 6X heads, have some minor bowl work done leave the runners alone, put in a small flat tappet hyd cam, stock intake, nicely tuned Q-jet and you will have a great running street car with good street manners. Another option but still not ideal would be to run the larger cam with Rhodes lifters and maybe a 2800 stall converter. IMHO.

[Half-Inch Stud]

Iron D-Port heads "Extensively Ported", without welding/epoxy, that flow well, will have excellent Street manners. Virtually impossible to blame such heads for poor idle/MPG/Vacuum.

Such Street-manner concern/blame is solely the Cam & Exhaust leaks. Then maybe the carb.

MY opinion; The Factory 068 Cam ought to do well with the 2.73 rear gear. Since the heads are ported, then the 1.65:1 on the Intakes will actually help performance. I trust the Pushrod buldges have been knocked-back.

Other folks here know how to "cam a 400" better than I.