Is there any way to determine the compression ratio of an engine without knowing details on the pistons? I have a 79 F-150 with a supposed 9.5-1 compression 400 in it. Its got all the extra goodies like ignition, carb, intake, headers etc. The bottom end is the only thing I don't know details on. Its a 400 bored 4 over. I don't know what the cam is and it "supposedly" has badger flat top pistons to put it at around 9.5-1 compression. I did compression tests on every cylinder and didn't get over about 145 for a high... This engine seems as gutless as stock so I am wondering if it has stock cam and pistons. Any help is appreciated, thanks.

 

No way to accurately figure it without pulling the heads. A cam change would likely fix it, try a Summit Racing P/N 5200 cam. This is around a .484/.510 lift, 204/214 duration cam, works great with the stock compression 400. Really wakes one up.

 

Could having a stock cam in a higher compression engine with all the extra goodies still make it gutless? Does the cam play that much of a part?

 

The cam is EVERYTHING, it's basically the brain of the engine. At the same time,(generally speaking) a stock cam grind in a high compression engine would cause problems with detonation as the dynamic compression would be higher (in most instances), it would basically limit the rpm range as opposed to a performance cam grind. Installing a performance cam and timing the cam the wrong way can also inhibit performance. Be that as it may, it's unlikely your 400 is what you could call a high compression engine, unless the person who built it, really knew what he was doing. But that's doubtful if you think it's got a stock cam in it. I'd work with the ignition timing first before tearing into the engine. Not enough timing (retarded initial) can cause one to be lazy. A non functioning advance (both mechanical and vacuum) can do it as well. The vacuum advance would be the most likely of the two to do it.

 

The compression is supposed to be around 9.5 to 1... I have set the number one piston to TDC with a compression gauge and by a wire to be sure. This is where my harmonic balancer is at 0 so it has not slipped. I can advance my timing until the distributor (a brand new MSD unit with vac advance) hits the thermostat housing which is almost 40 degrees advanced. My engine still does not ping... I am plugging the vacuum hose and everything just like you are supposed to. Anyone have any idea how this is possible?

 

You shouldn't plug the vacuum hose if you've got it plugged to the ported vacuum source on the carb. This port only sees vacuum when the throttle is opened, so at idle, it should see no vacuum. Set the initial timing to about 12* BTC (with the hose connected to ported vacuum) and see how it runs. I'm not familiar with MSD's stuff, so I'm not sure what type of advance mechanism they use. Seems to me I've heard that the curve is adjustable though. As far as the comp ratio, just because someone said it's 9.5 to 1 doesn't mean that it is. There are too many variables in chamber volume, piston top, compression heights, etc. to make a guess like this. It's been my experience with 400's that they're highly susceptable to pinging due to the open chambered heads and the pistons falling well short of the deck, even if you build one that's got a 9.5 to 1 comp ratio. I built one using 351C flat tops that had an actual 9.7 to 1 ratio and it would ping on everything except 93 octane premium.

 

I was meaning I plug the vacuum hose when timing it. How can I advance the timing to 40 degrees and still not get it to ping!? Something doesn't add up...

 

Why do you feel you need to time it to 40* ? Set the initial to 12* and then drive it and see how it runs. I've never set mine for the max total advance, only initial, then test drove em to see what worked. I'd also check to see that the vacuum advance is even working. Unplug the hose from the carb, remove the distributor cap and rotor, and while sucking on the hose, watch for movement inside the distributor of the breaker plate. The vacuum diaphram on the distributor will sometimes develop a leak, I've had one go bad, all the sudden and for no apparent reason.

 

Would I need new springs if I went with this cam? What about the comp 255 or 265?

 

I think up to and close to .500 is the limit on the old springs, but the retainers start being an issue as well after that.

 

I used it with the stock springs and retainers. No problems. It would be best to change to new springs if the old ones have 100K miles or more on em though. The motor I put that cam into was of unknown mileage, it came with the truck when I bought it. But as I said, I had zero problems with the cam and old springs. Really woke it up. Ran it with a Holley 500 2 bbl and Hedman long tube headers.

 

The motor is only about 3 years old and has about 15,000 on the rebuild. I think I will try putting in a more aggressive cam and hope my springs are okay as I do not want to take my heads off.

 

You should be fine with those springs and the Summit 5200. The stock Ford 351/428CJ springs are fine with cams up to about .525 lift. The std springs that were on that 400 were fine with the .510 lift. I used a Crane 272* Energizer with stock 68 390 springs and it had something like a .516 lift. Both engine familes used the same springs.

 

So what camshaft would be the best for my situation. My pickup is mostly just a toy that does some mild offroading and hot-rodding around. The engine is bored 30 over and has edelbrock intake and 600 cfm carb. Straight up double roller timing chain. Machine shop said it has somewhere around 9.5:1 compression. It has a full MSD ignition system (coil, wires, box, and dizzy). It also has a set of hooker 1.75" headers with 3" collectors dumping into true 2.5" duals. Running a 3.50 rear end with 33" tires. Are the Summit brand cams as good as comp, crane, lunati, etc? I am open to all suggestions but want something this is good quality and will last. Thanks for all of the help.

 

Summit dosn't grind their own cams, they're likely made by one of the other major cam grinders. That same grind I listed is offerer by several companies. I find it strange that the machine shop gave you all that info, but failed to tell you what cam they put in it ?