[4dblnkldude]

I am putting together a 400 for my 81 TA. This car will be street driven with maybe the occasional blast down the 1/4. I have a new 400 short block with what I think is a comp xe262 from my measurements. I have read much on here about similiar combos but nothing exactly like this. So the heads are 6x4 and milled down .020 with stock valves, 988 comp springs, and will be using comp roller tip rockers. Pretty sure my comp ratio is right around 9.4 to 1. The intake will be a stock 70 unit topped with a 7274 q jet that was rebuilt. The trans is a stock rebuild with a shift kit and 3.08 gears. Exhaust... well stock manifolds with 2.25 head pipes, flow masters, and 2.5 tails (head pipes were in good shape FM dont make 2.25 tails) I may change to RARE oversize manifolds later. Oh and piston is .010 in the hole. Stick with the cam I think is a xe262, move to a 60916, or move to something else? Thanks in advance.

[Half-Inch Stud]

Should run strong with a cam 10* less than shown in my 12.2 ET Signature

[b-man]

I doubt your compression ratio is anywhere near 9.4:1, it’s probably in the neighborhood of 8.5 to 8.75:1 at best.

I’d opt for the the Summit 2801 or equivalent.

[Cliff R]

The best cam I've found for "low" compression 400 builds with mostly stock drivetrain is the Crower 60240. 210/222/112 LSA. It makes around 12" vacuum at 700-750rpms. Strong power off idle and in the normal driving range. You don't need a stall converter or tall rear gearing.

The Crower 60916 is better suited for higher compression builds and at least 3.42 gears with a manual trans or 2400-3000rpm converter. It makes great power in a 400 build but too "soft" off idle and low RPM's for the kind of build you are doing......IMHO.....

[25stevem]

As posted your no where near 9.4 to one compression.

I come up with 8.57 to 1 by these numbers.
6X heads with valve job and milled .020"= 91.67 CCs.
Head gasket = 9.7CCs
Piston notch volume ( assuming 4 notches) =6.7 CCs
.010 deck clearance = .1352 CCs
Ring land volume= 1.5 CCs
Cylinder Bore @ .030" over=51.72 cid, converted to CCs=831.1 CCs
With this I assumed no Intake valve chamfers in the top of the Bore which at .030"would still be atleast 2 CCs.

You need to pick your Cam with this compression ratio in mind.

[Stan Weiss]

Originally Posted by 25stevem

As posted your no where near 9.4 to one compression.

I come up with 8.57 to 1 by these numbers.
6X heads with valve job and milled .020"= 91.67 CCs.
Head gasket = 9.7CCs
Piston notch volume ( assuming 4 notches) =6.7 CCs
.010 deck clearance = .1352 CCs <<<< 2.217 cc's
Ring land volume= 1.5 CCs
Cylinder Bore @ .030" over=51.72 cid, converted to CCs=831.1 CCs
With this I assumed no Intake valve chamfers in the top of the Bore which at .030"would still be atleast 2 CCs.

You need to pick your Cam with this compression ratio in mind.

Steve,
Using your numbers with correction shown above I get 8.436:1

Stan

[4dblnkldude]

Yes, you guys are correct on the compression, I made a mistake on that and realized about an hour after I posted. Perhaps I should cc the heads to be sure. So they all get me in the ballpark, thank you! It just sucks not knowing the cam, I should be able to use the comp lifters?... I don't think there's an issue there.

[78w72]

i have a very similar combo in a 78 400, 6x-4 heads but use the xe268 with comp lifters & roller tip rockers, speed pro forged pistons. its a manual with 3.42 but it runs very good on the street with no cooling or tuning issues. i know some on here dont like the xe cams but i installed it before reading all the negatives & after 10+ years i cant say i have experienced any of the claimed problems like detonation or hard to get running right. runs upper mid 13's at 103-104mph taking it pretty easy with lower rpm shifts & old hard BFG street tires.

the 6x-4 heads usually come in around 89-93cc, so if they were milled .020 they are probably less than the stated 91.6cc. best to have them cc'd to get an accurate number if thats a concern, but a couple cc's here or there wont change the final compression too much. 8.5-8.75 is a good estimate to pick a cam, 9.0-9.5 will obviously want a different/bigger cam. check for a part # on the cam too. the cam cliff suggested or the summit will be a good pick for lower compression.

on the intake, ive read that for mid 70s heads like these you need a 72 or later intake, cant recall the issue, maybe the exhaust crossover?

[b-man]

I had a set of ported 6X-4 heads done by SD Performance over 20 years ago. I asked Dave when he surfaced them to only remove the minimum amount required for surface cleanup.

The chambers ended up at 94ccs.

So another data point.

[25stevem]

Sorry gang!
I forgot to change cid ( 1352) to CCs.

[napster]

I know I will hear BOO HISS for what I'm about to post.

I have a 406 in a '78 TA. It makes 380HP & 420 TQ with Doug's Headers. Absolutely no issues with it at all with cooling etc... It is the 988 XX block with 6x4 heads milled and generate 9.45 to 1 compression. Here is where the BOO HISS starts. It has the XE274H-10 cam with 1.5 to 1 ratio roller tip rockers. It has a 700R4 behind it with 3.73 rear gear. Very satisfying ride.. I recently changed the X-pipe to an H-pipe. What a difference. I can hear the lope of the cam like never before. It has plenty of power for what I want from it. I'm not a racer, but I think it is low 14 to high 13 second car. It sounds like a bad a**, but has very good manners on the street.

In closing, even with the 110 LSA it has plenty of vacuum for power brakes.

[P@blo]

I run the summit 2801 in a 9.25:1 CR 400 with headers and second B-man's motion. Had a magnum 280H prior to that and was clearly not a good choice. Sounded cool at idle but that is about it.

The 2802 would work with more compression, gearing, and a manual transmission (or a good converter with an automatic). It was more sensible to size my cam for my set up not change my set-up so I could run a certain cam. Save a lot of work and money in the process and love to drive my car.

3.08 is a great gear.

[Stan Weiss]

Originally Posted by napster

I know I will hear BOO HISS for what I'm about to post.

I have a 406 in a '78 TA. It makes 380HP & 420 TQ with Doug's Headers. Absolutely no issues with it at all with cooling etc... It is the 988 XX block with 6x4 heads milled and generate 9.45 to 1 compression. Here is where the BOO HISS starts. It has the XE274H-10 cam with 1.5 to 1 ratio roller tip rockers. It has a 700R4 behind it with 3.73 rear gear. Very satisfying ride.. I recently changed the X-pipe to an H-pipe. What a difference. I can hear the lope of the cam like never before. It has plenty of power for what I want from it. I'm not a racer, but I think it is low 14 to high 13 second car. It sounds like a bad a**, but has very good manners on the street.

In closing, even with the 110 LSA it has plenty of vacuum for power brakes.

Just who would say that?

What is your ICL at?

Have you ever done a cranking compression test on the engine? If so what is it cranking?

Thanks,
Stan

[napster]

Originally Posted by Stan Weiss

Just who would say that?

What is your ICL at?

Have you ever done a cranking compression test on the engine? If so what is it cranking?

Thanks,
Stan

Stan,

I won't touch the first question with a ten foot pole.

Attached is the cam card and build sheet. Never checked the compression as this engine runs that good. Build took place in 2011. Engine held 380 HP from 4,700 to 5,200rrpm. Also, I hope I remember this correctly the cam was advanced 4 degrees.BTW, the intake manifold is an Edelbrock Performer.

[AG]

Originally Posted by napster

I know I will hear BOO HISS for what I'm about to post.

I have a 406 in a '78 TA. It makes 380HP & 420 TQ with Doug's Headers. Absolutely no issues with it at all with cooling etc... It is the 988 XX block with 6x4 heads milled and generate 9.45 to 1 compression. Here is where the BOO HISS starts. It has the XE274H-10 cam with 1.5 to 1 ratio roller tip rockers. It has a 700R4 behind it with 3.73 rear gear. Very satisfying ride.. I recently changed the X-pipe to an H-pipe. What a difference. I can hear the lope of the cam like never before. It has plenty of power for what I want from it. I'm not a racer, but I think it is low 14 to high 13 second car. It sounds like a bad a**, but has very good manners on the street.

In closing, even with the 110 LSA it has plenty of vacuum for power brakes.

I have a 400 with that cam, 9.6 CR at a 106 ICL and love the motor. In my '65 at 3890 lb it went 13.0 in the 1/4 with a 2200 rpm stall converter and 3.55 gears.

[4dblnkldude]

I am going to CC the heads tomorrow. The crower cams are not available for months. I was looking at the butler customs today. Any experience with those? I drove this car 90 miles tonight, the engine is tired, somehow it ran a 15.2.. LOL. I have a fast track window with my body guy, the car will be broken down saturday so I wanna get this engine done soon so I can have it back together by April. (Well see how that goes) I'll report back with the exact CC next day or so. Thank you for the discussion!! All thoughtful replies.

[SD455DJ]

Here is a comparison of the last 400's we built and dyno'd as they are about as different as you can get factory equipment-wise, but both relatively mild builds. They both had Icon forged pistons and Eagle forged H-beam rods, stock cranks, and Ferrea 1-piece SS valves. The W72 400 had only 8.75 compression and the Summit 2800 cam, but with factory RA exhaust manifolds. They both run their respective year cast iron intake manifolds and Q-jets, as well as factory stamped steel 1.5 rocker arms.

Dennis

[25stevem]

Nice info!
The old adage that goes "at some point you should not sacrifice breathing for compression " I think is showing up between these two motors .

The added 15 to 20 Intake cfm the 6X heads have over the small valve 16 castings, plus the better Exh Manifolds I think is key here.

The numbers are darn close even with the 1970 motor having more Cam !

[79firebird_99TA]

Originally Posted by b-man

I doubt your compression ratio is anywhere near 9.4:1, it’s probably in the neighborhood of 8.5 to 8.75:1 at best.

I’d opt for the the Summit 2801 or equivalent.

I agree. I'm right around 9.2:1 and that's a 400 with 6x-4s that were shaved .065"

[4dblnkldude]

Originally Posted by SD455DJ

Here is a comparison of the last 400's we built and dyno'd as they are about as different as you can get factory equipment-wise, but both relatively mild builds. They both had Icon forged pistons and Eagle forged H-beam rods, stock cranks, and Ferrea 1-piece SS valves. The W72 400 had only 8.75 compression and the Summit 2800 cam, but with factory RA exhaust manifolds. They both run their respective year cast iron intake manifolds and Q-jets, as well as factory stamped steel 1.5 rocker arms.

Dennis

Those are impressive numbers, if I could get close to that I'd be a happy camper. The heads are 91cc.