[AJ-]

Thank-you to all the pros and fellow gearheads who frequently go out of their way to lend a hand on here. This will be a bit of a lengthy post, but more info is (almost) always better. I picked up a 400 this spring that sat in a guy’s garage for about 15 years. He had built it for his car, then sold the car but kept the motor. The motor was said to have very low miles on the rebuild. I believe it after looking inside, it is very fresh-looking. It had good compression and oil pressure when I gave it a short run on the stand before installing it. However, when I put it in the car and tried to tune it it quickly became evident that something was wrong. Turns out the cam was toast! 3-4 lobes half gone and a few more noticeably ground down. Metal in the oil filter and the one rod bearing I checked is down to copper. I paid about core value for it so not too upset about the purchase--it was more the broken dream of being excited about it and then let down by the failure after installing it.

I do want to try to resurrect this thing if I can do it reasonably. I’m not at a point in my life (young kids, mortgage, single income family, etc) where I can just drop it off at a machine shop and let them have at it carte blanche. I also get that most of you will say replace the rods and pistons with forged but I’m not there budget-wise. One day I’ll get there, but I am hoping in the meantime I can just get the block tanked, crank turned, new bearings all around, and then do all the re-assembly myself. The part I don’t know about and I worry about is whether or not the cam failure was a result of improper break-in or a mismatch of parts. I don’t want to set myself up for failure again.
If anyone can help tell me what’s okay in this combo and and/or what needs change or at least be looked into it would be appreciated. I’ve tried to do a lot of research but it’s one of those things where the more you know, the more you realize you don’t know!

Combo as acquired:

Bottom End: Stock rods +0.030 KB Silvo-lite’s 10cc of relief. Lame parts, I know, but it’s what I’ve got.

Heads: 6x-8 – look to be pretty seriously ported and milled to around 88-89cc based on my little diy cc setup. Positive valve seals. Bronze valve guides, aftermarket valves, pushrod holes enlarged.

Single valve springs (Crane?). Stock retainers with shields removed. Have read these are not a good choice?

Crane 1.65 roller rockers, 7/16 studs / polyloks

MPR-317 pushrods (shorter than stock to match milling?)

Crane 068 copy cam (now scrap metal). Was thinking to replace with Summit 2801.

[JLMounce]

The 2801 I think would be a good choice. I would be doing valve springs as well regardless of what cam you choose. Make sure they are adequate for the total valve lift you'll be running with the 1.65 rockers.

Since this engine is probably somewhere in the 8.2-8.6:1 compression range with it's piston and head choice, you could possibly think about doing something like a Lunati VooDoo in there. Something that will help build a little more cylinder pressure. I kind of like the VooDoo 701 for a strictly cruiser, or the 702 if you want something with a little more umph.

[steve25]

Most Cams that fail do so during break in when the motor gets cranked and cranked and cranked without firing, or shortly there after from the non start issue.

6X-8 heads that have had a valve job would have had to have been milled .072" to get to 89 CCs.

Note that the Intake Manifold flange of the head Intake flange would need to get milled atleast about .040" to get things to bolt back up, and also the valley pan lip may need to get trimmed back to get the Intake to seat up right or you might get away with using on gasket on just forma gasket.

[AJ-]

Thanks for the responses. I do think the heads have been milled quite a bit but that seems like a lot... I think both sides have been milled, but I did notice the intake alignment wasn't perfect...but I did get a good seal on it.

Will something like comp cams 988-16 or crower 68404 springs just drop in?

I started taking apart the short block and looks like the bearing spun on on journal. It's got some good scoring on it. Hopefully the crank is salvageable.

I also happen to have some #62 heads. They wouldn't take much work to be useable and already have 995-16 springs on them. I just hesitate about the high compression and the lack of alt bolt hole.

[Frank T]

AJ
I have a similar 400 block on my stand now (+40 and ported 7K3 heads, same pistons, Eddy dual plane intake) and have been reading a lot on PY and other sites about different combos from Street-wild to mild so given your existing parts here is what Id do…

I think you are on the right track with cooking the block, getting the crank checked (and cut if necessary or buy a used stock 400 crank from a local Pontiac guy for cheap). Also have the bores and mains checked along with the rods. Then new chain, bearings (cam brgs too), freeze plugs, rings, gaskets etc. Save money and Replace anything questionable, Have patience and don’t pay twice.

Cam: probably wiped at start up so just get a new one along with lifters and matching springs. If you are sure the rockers are 1.65 Id look at the Summit 2800 or Crane 968781 (Crane’s 068 blueprint). Both those cams have lower lift points that will keep you under the 450 with 1.65 rockers and make more static compression for low end torque/HP. If you buy 1.5 rockers definitely step up to the 2801 or Crane 283941.

Cam Reasoning: The cam choice may seem lame but here is what I believe…. The heads you have likely don’t flow much past 500 lift. Even some of the more desirable stock heads like your 6X-8 Ive seen ported on this site by pros, have minimal gains past 450 lift on the exhaust side (maybe someone can post better numbers?). So if you open the valve past the 500 lift point you are wasting engine Power trying to open a valve that cant move anymore air thru the port. Valve springs eat HP. We all experienced turning a motor over by hand with the valvetrain set up is exponentially more difficult than with just crank and pistons. So your engine has to work hard to overcome that additional spring pressure (cam lift) with no extra power (air flow to the cylinder) being added to turn the crank. That’s a net loss in HP.

Heads: The heads and pushrod issue would worry me a little. If the heads were cut down and needed special pushrods, the geometry of the heads and intake could possibly be misaligned so the flow between them would likely be impeded (less flow than 450!). Also double check the geometry of the lifter, pushrods, rockers and guide plates. Confirm the rocker pattern crosses the top of the valve in the middle while turning the motor by hand and making sure the pushrod is free to move.

Budget tip: Color the top of the valve with a sharpie, & buy a light valve checking spring to make this easier. If something is wrong, buy an adjustable push rod and find the correct length! Ive had a few issues with the blue plastic valve spring checker lots of folks use, so I cant recommend it.

Don’t forget piston/head Quench: Check if the block was decked. Measure how far the piston is down the cylinder at TDC. Its likely .005-.025. Get a head gasket thickness (torqued thickness) that when added to that number is in the .035-.055 range. Eg. .025 down + .015 head gasket = .040.

Your combo will have 8.8 SCR & 6.87 Dynamic CR with the 2800 cam, which should net around 330hp and lots of torque.

Hope this helps
Frank T

[Frank T]

AJ
Id go with the #62 heads and confirm the springs you have are equal in spring pressure to the recommended specs for the 2800 cam.
The #62 heads (75cc chamber) take you SCR to 9.8, but the DCR is 7.7 with the 2800 cam (better than the 6.87 with the 6X heads). A good DCR range for best power on 92 octane pump gas is 7.5-8.5.
Likely a 30hp bump up with the 62s
Frank T

[Bruce Meyer]

If you go with the 62 heads I would look at the Summit 2802 or at a minimum 2801. IMHO the 2800 is way too small for a 400 with 62 heads. You could run into pinging problems.

[AJ-]

Thank-you, Frank for your info and good explanations and Bruce for pointing out the difference it would make for cam selection. So would the higher compression of the 62's trump the higher flow of the ported 6x heads? 30hp is a big difference! If i did the 62 heads I'd probably stick with 1.5 stock rockers.

For additional info the car is a '73 Ventura. 3.42 gears, th350. Have both a stock stall or 2500 stall converter depending on what would work better for the combo.

[AG]

Originally Posted by Bruce Meyer

If you go with the 62 heads I would look at the Summit 2802 or at a minimum 2801. IMHO the 2800 is way too small for a 400 with 62 heads. You could run into pinging problems.

I agree with this. Just for a comparison, I have a 400 0.060" with stock rods, TRW forged pistons, CC 274XE cam (230/236 degrees at 0.050" duration) and stock 670 heads rebuilt, stock intake and 750 cfm 3310 holley. In my '65 with a TH400 trans and 3.55 rear, 2500 rpm stall converter, the car went 13.0 in the quarter. Pretty basic combo runs pretty good and is a great street combo. I'm not advocating that cam, but with 72 cc big valve heads and a similar sized cam the combo will work well. The 6X heads will have such low compression it will need something like the 2801 or 2802 cam from Summit. Just offering an example of what you can do on the cheap, the car used the cheap 3 tube headers also.

[Frank T]

AJ
In your case I’d opt for the 62s because: of the unknown geometry of the 6x heads being cut, big chamber and their unknown flow rate. If you can figure out the geometry and get both heads flowed ($?) then we can look at the flow numbers and possibly get a bigger cam that matches the increased head flow of the 6x. But on a budget the 62s would be an easy choice for me. Like AG said above, that 6x chamber has low compression (AKA a big chamber) so a lot of air has to get into the cyl to make power. IMHO that 6x head will work best on a longer stroke motor (455,461…) that spends more time (Piston travel down) pulling air into the cyl.

As for flow vs compression. My Flow goal is based on KNOWN max head Flow at a given lift, then find a cam that does not exceed that given lift (Again not to waste valve spring compression making little to no power). When the flow starts to diminish excessively, spring pressure will be eating HP.

For a pump gas motor, my compression goal is the highest DCR within 7.5-8.5 (8.25 max is my actual target). The DCR uses compression ratio (head chamber, stroke, bore, quench, piston reliefs) as its related to opening and closing (cam duration, ILC, LSA, overlap) of the valves on the intake and compression stroke. Because how much actual air that gets pulled in (stroke), trapped (both valves closed) and compressed (chamber volume) is what really matters when the plug fires.

I think the 62 heads, 1.5 rockers and the 2801 cam is going to be a great set up and a safe DCR of 7.38 to run pump gas with minimal tuning required.

BTW.. AG's set up above comes out to be ...
SCR - 10.48
DCR - 8.43
That 8.43 DCR is right on the edge of being out of the pump gas territory for me. Great cooling. efficient carb set up/fuel injection, timing and a dyno tune would be a must. If I built that engine I likely would have went with a bit larger cam or degree'd that cam to 110 ICL to get the DCR to 8.17… that’s a number I could feel good about.

Frank T

[AG]

I doubt the CR is that high it's probably more like 9.8. I had another 0.060" 400 with 68 cc heads and the CR was only 10.3 and I measured everything. Ran fine on 92 pump.

[Frank T]

AG- thanks for the update. I dont want to hijack AJs thread so Ill PM you later on my calculations. Id appreciate if you could confirm the values I used for your motor so I can correct the higher compression ratio Im seeing.
Thanks
Frank T