[GTOKIDRH]

Originally Posted by Sirrotica

Basically what I said earlier, but was met with, "I have 670 heads already". 670 heads aren't going to be the answer to the question, IMO.

Throughout the years the 670 head has been given a lot of ink, but there are better choices for the car in question. This is a cruiser, not a racecar. They surely wouldn't be my choice if I were going to try to wring power from a street car. They likely won't run on pump fuel, even premium fuel. I had a 67 engine for my 67 GTO racecar that I took off the 670 heads in favor of 62 heads before installing in my car, because I always felt the open chamber was superior to the closed chamber bathtub.

The regular fuel 400 basically used the 66 389 heads, hence the reason for one year only pistons with the older holdover valve inclination angle. In 68 the regular fuel engine became the same valve inclination angle as the premium fuel engines. I believe they gave up the bathtub combustion chamber also in all 1968 engines. When I worked at a Pontiac dealer in 1970 I remember a running change during the 1967 model year for broken valve springs, so depending on where in the model year the heads fell, they may have the old springs that were recalled.

If the car runs as poorly as the OP says, there has to be something fundamentally wrong with the engine, but I already have mentioned this in my previous posts. Putting hi compression heads on an engine that runs poorly is just a waste of time. Finding out why this engine runs so poorly would be my first priority, before pouring a bunch of money into a unknown quantity.

If the engine is worn out, or has low compression due to a mechanical defect, the OP might be ahead to find a 428/455 in running condition, and come out with more engine, for less money. Win, win

This is exactly why I made this post. I appreciate all of the comments and information. I see now why I cant nor shouldnt use the 670s. My plan now is to do the 2.42 to 3.23 gear swap first. The car runs well. It's just a heavy slug. As far as I know the timing gears are original so a new set is in order at 108K. Obviously I will do a compression check prior to doing anything with the engine. If the compression is good than I will pick out a new cam because I'm there. Replace the timing gear set and install the 4BBL setup. As far as a choice of cam I'm thinking about one that makes power down low. Like you said it's a cruiser not a racer. Any suggestions? TIA



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[b-man]

Factory 066 cam used in many medium performance 4-barrel applications. No changes to the valvetrain are necessary, this is the go to cam for all the rebuilders.

By now the cam most assuredly has a couple badly worn lobes as well as a stretched timing chain, usually the timing set is worn out by 50 to 70k miles and yours may have already been replaced.

[GTOKIDRH]

The 066 looks like a decent cam for me. Im also looking at the Summit 2800. I know that i will have to replace the valve springs if I go this route.

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[25stevem]

Even if you do not go for a bigger cam you should change the springs out.

Many many times even with a factory cam I have seen a difference all across the power band, and yes even down low!

If you do pull the springs be sure to be ready with new valve stem O-ring seals.

[mrmark1957]

I've replaced the 066 cam with a Summit 2800 cam in half a dozen low compression 400's for myself and customers cars. The 2800 has the same low speed driveability as the 066,feels like stocker
but it pulls about 500 rpm higher before it flattens out.

[GTOKIDRH]

So i did a compression test today. Seems to be healthy for 8.6 c.r. and almost 110K on the clock. Plugs looked good. All were tan in color with absolutely no sign of oil.115 to 130 psi. Most were 120. Preparing for the gear swap.

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[25stevem]

Thanks for the check out results !

[Skip Fix]

A summit 2801 is pretty mild in a low compression 400 also -one in my 81. degreed right on the button also dot to dot.

[GTOKIDRH]

Originally Posted by Skip Fix

A summit 2801 is pretty mild in a low compression 400 also -one in my 81. degreed right on the button also dot to dot.

I've actually already started seriously considering the 2801 over the 2800. Thanks for the info! Can you offer a y more feedback on it as well as the specifics on your ride it's in?

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[amcmike]

Drive with the new gears first. Once you get a feel, I think you'll want to keep the bottom end torque that the U cam is giving you hauling 4500lbs. In which case, the 2800 would probably be a better choice' since it'll lose very little low end, and still give much more mid-range and top end together with the 4bbl setup.

Not that the 2801 is radical, but especially in a heavier vehicle, it's a combination that would like a little more gear, a little more compression, and a little more stall. If you did decide to go with the 2801, probably want to consider Rhoads lifters if you don't mind the sound.

[mrmark1957]

The Summit 2801 cam doesn't do much in a low compression 400 until about 3000 rpm. A buddy tried it in a 72 Lemans with 2.78 open rear and a stock THM 350 converter and it was soft on the low end.He spun a rod bearing holding the trans in gear to get the cam to work in its powerband. We swapped in a stock 455 short block with everything else the same. With the extra cubes and point of compression the car was very strong. I wouldn't use more than the 2800 in your wagon

[Formulas]

ive ran a 2800 2801 068 cams pretty much back to back as far as power band they start to make power in the order i have them
the 067 and 2800 are close RPM wise but 2800 has a bit more torque in my experience

i wouldnt even consider the 066 cam in any 400 build i would go 2800

[Skip Fix]

0.030 400 block 6X-4 heads cleaned up in pockets and port matched. Camber ridge smoothed milled 0.050 but still 93cc. TRW 2262 pistons , cast rods. 28ormer intake 73 Qjet. RA manifolds. A/C 4WD PS 3.08 rear gears. Planty of bottom end even with 3.08s.

[25stevem]

With any car that's over 3400 lbs and with less the a 3.42 rear gear it's better to have a tad too small of a Cam in the motor then a tad too large.
Any Cam company on the face of the planet will tell you besides folks own looking back in hind site experiences.

[PunchT37]

Originally Posted by 25stevem

it's better to have a tad too small of a Cam in the motor then a tad too large.

Yep. Always.

[mrmark1957]

I have heard the expression " When picking a camshaft it's better to guess on the small side and be disappointed rather than choose too large and be miserable "

[Formulas]

yeah you should probably get the smallest cam know to man and put in it it will be great ..

[SD455DJ]

Originally Posted by GTOKIDRH

I've actually already started seriously considering the 2801 over the 2800. Thanks for the info! Can you offer a y more feedback on it as well as the specifics on your ride it's in?

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GTOKIDRH - Here are actual dyno results of a '78 W72 400 with 8.75 to 1 static compression ratio. It was a fresh rebuild and used the Summit 2800 cam like you may be considering:

"Dan had a good dyno session today with the W72 400. This is the original numbers matching engine that was removed way back in the late 1980's to make way for an SD455 build with a Doug Nash 4+1 5-speed trans. The original owner of the car rebuilt the W72 engine in 1980 with an H-O Racing TurboForce system and went to .030" over TRW's on SD455 forged rods. When the Mike bought the car in the mid 1980's he immediately went to work pulling the turbo'd 400 and building the SD455 engine.

Long story short, Dan rebuilt the original numbers matching engine with .040" over Icon forged pistons w/4.5 cc valve reliefs that are .006" out of the hole and with .045" x 4.328" Felpro head gaskets to provide .040" quench depth. The 6X-4 heads were minimally cut for trueness and measured 92.45 cc's average for a final static compression ratio of 8.75 to 1. Dan replaced the cast rods with forged Eagle H-beam rods. New 1-pc valves (2.11/1.66) with CC dual springs were installed. A Summit 2800 cam (204/214/114 @ .422”/.444”) with new 'old' Crane hydraulic lifters along with a new Melling 60 psi oil pump. The one modification was the use of old factory D-port ram air exhaust manifolds with the 2.1" outlets with Pypes 2.5" mandrel headpipes. The original 17058263 Q-jet on the factory cast iron intake with the EGR system and plumbing were reinstalled.

The base runs were made with 42 degrees total timing in by 3000 rpm, 45 primary rods/74 jets/CH secondary rods on an I hanger. The 3rd (and best) base pull made a corrected 360.3 hp @ 5000 rpm/456.1 lbft torque @ 3600 rpm (351.2 hp/444.5 lbft uncorrected). The correction factor was a low 1.026 as the weather conditions were very good...low humidity, high barometer, and very cool temperatures (65 in dyno cell). After rejetting the carb to 40 primary metering rods/72 jets/DA secondary rods on an 'I' hanger (same total timing at 42 degrees), employing the 'big' dyno room dumps for the headpipes, and installing the air cleaner base, the max hp jumped to 371.4 hp @ 5000 rpm/459.2 lbft @ 3600 rpm (362.0 hp/447.6 lbft uncorrected) on the final pull (#14). The highest torque reading was on pull #13 at 460.3 lbft.

This engine surprised us by exceeding our first 350 hp/450 lbft prediction. It should move that heavy '78 TA with some authority."

It's installed back in the 3800 lb. Trans Am and it flat out hauls with 3.42 gears.

Dennis

[PunchT37]

Originally Posted by Formulas

yeah you should probably get the smallest cam know to man and put in it it will be great ..

It`s all in the combo, man.

[Formulas]

you know what they say theres no replacement for displacement so why even fool with a 400 anyways