[doubleClutch]

I am switching from 6x heads to #16 heads to up the compression ratio. The Magnum 280H cam wants more compression on the 77 400. How much will I gain on this switch, with a stockish bottom end. I am switching out the headers, and I am told the Edlebrock RPM intake will bolt up. Is there any other parts that need to be changed with this swap?

[70KGOLD]

your pistons, cooling system, and I would consider updating your stockish bottom end.

[66bonne]

The RPM will fit, nice intake.
I have a friend with 16s on his 400. Took a little bit of doing to get the timing dialed in so that it wouldn't ping under full throttle. I'll see if I can get his timing specs for you, it would at least give you a good starting point.
I'm in the middle of a head swap myself [to KREs], lot of work but you should find it worthwhile.
Also, you'll have to run premium gas with the 16s.
Good luck, Jim

[doubleClutch]

70KGOLD are you sure I have to change the pistons. I am only going to run around 350hp on this block. I can have the timing done by my mechanic, but he will charge big time labor for bottom end work. The seller of the heads is telling me all factory stock Pontiacs are flat top pistons w/valve reliefs you can put any pontiac head on with no problems?

[bobzdar]

I just made the same swap on my car. Have yet to fire it up but I wouldn't pay anyone to set the timing on my car. Get a timing light and set it conservatively at 28-30 deg total timing and then play with it from there. You may have to play with vacuum advance or disable it to run with no part throttle ping on pump gas, but other than that it should be fine. If your stock bottom end is in good shape, it should be fine with the new heads, it's no different than the bottom end of the engine the 16's originally came on. Valve reliefs shouldn't be an issue.

[70KGOLD]

doubleClutch, 9 times out of 10 the 20 yr old stock cast pistons wont hold up. You will get detonation with todays -water-pump gas and overheating problems. Yes you can retard the timing to the point no audible pinging is noticeable but it will still be there hammering away at the top of your pistons. and if you retard the timing to 28 deg. you have killed the performance so whats the point right? If you want a nice street mannered car grab a set of cheap 6x 8 heads, and bolt them on. or cc you heads and see what you have then pick a cam. If you like to drive you car more than work on it take my advice. what ever you decide good luck. I wish someone would have told me this 20 yrs ago.

[67 Lamnas]

Originally Posted by doubleClutch

.....all factory stock Pontiacs are flat top pistons w/valve reliefs.........

Not true....stock '75 and later factory 400 pistons have a chamfer around the outside of the piston that lowered the CR farther than the 74-earlier pistons. You might be just fine with the static CR with the #16 heads due to the added "dead volume" of the factory pistons.

Your factory bottom end might hold up just fine, and it may not......bolt 'em on and have fun.

BTW, the early heads won't have all the bolt holes that the later heads have.....you'll have to improvise a bit to use your factory accessory brackets for the power steering and alternator.

You might need longer pushrods, also......check for sure

[rtanner]

ditto on the pistons. if your cranking compression is within 10pounds per cyl. and oil consuption is light do it you will really like the power improvement.

[doubleClutch]

So what is the more cost effective option? Port the heads I have now, or replace them with the older heads. The engine has been rebuilt, but most likely with similar to factory type pistons. I need to go from a CR of 8 to 10.

[67 Lamnas]

Originally Posted by doubleClutch

but most likely with similar to factory type pistons. I need to go from a CR of 8 to 10.

Doesn't sound like you know what you have......get the facts before you make any decisions about how to proceed....

You need to find out FOR SURE what you have for pistons and deck height so you can ACCURATELY calculate CR and make an informed decision.

That way you'll have no regrets later......

[Dragncar]

428s had dished pistons from the factory.
10-1 is too much,9.5 is where you want to be with iron heads and a 400.A set of 13s or 62s would do it.

[70KGOLD]

67 Lamnas, you are quick to say NOT TRUE to the advice I give, but you use phrases like “You might be just fine” “might hold up just fine” and “you might need”.
Well if he takes your advice he MIGHT just destroy his engine. Give your advice but don’t direct any comments toward me or my post.

[doubleClutch]

I finally got ahold of the guy who sold me the car. Unfourtanetly he does not know about the bottom end, and the person he bought it from doesn't either. All I got was a shop name called Thunderbolt Racing. I think I will take 70k's advice and replace the pistons. What type of pistons do I need with this setup to get to 9.5 CR? I am guessing I need to replace rods as well? Also, I am guessing its pointless to replace the pistons, and rods if the block isn't up to par. Is a Compression check is the best way to test the blocks integrity?

[Bumper]

Would there be that big of a difference going from a 221/229 cam to the 230/230 on a tighter lsa? Once the intake requirements are met, say at 220 degrees, how much of an impact do you think the 10 degrees extra intake duration would have?

I wouldn't expect to have a total different animal but assume a little low speed performance will be gained with changing to the 60242. Obviously the smaller cam would have been a better choice in the beginning, but not having that luxury I don't think the two cams are worlds apart.

Some stall and gear along with the increase in compression you plan would really wake up the 280H. So change the heads and see how the old cam acts with the new compression before you swap out. If you end up staying with the stock compression/gear/stall, I would look at the Summit 2800 or the Crower equivalent.

[67 Lamnas]

Originally Posted by 70KGOLD

67 Lamnas, you are quick to say NOT TRUE to the advice I give, but you use phrases like “You might be just fine” “might hold up just fine” and “you might need”.
Well if he takes your advice he MIGHT just destroy his engine. Give your advice but don’t direct any comments toward me or my post.

You stated a fact.........."all factory stock Pontiacs are flat top pistons w/valve reliefs".........

Your fact is simply not true, and I pointed out why.......

I stated my opinion.......

Lighten up.....it's the internet....

[doubleClutch]

Sorry if any of these questions seem too simple. This is my first Pontiac build, and I have built forced induction cars my whole life. A lot easier to make power when the only thing that matters is an A/F. Building power of a cam is new, I'm used to factory cams holding 450hp+
Anyways, I had a summit 2800 in there before. I was told its the closet to stock you can get. It wasn't making the power I was looking for, and I tried building up the car around the smaller cam (3.42 gears, rhoades lifters, timing chain, Proform Distributor+MSD wires, RPM intake, 1.5 roller rockers, new push rods, headers, exhaust cutout, professional timing adjustment+carb tune). That gave the car a little boost, but still not near 300hp. I am also aware of the stall converter. I have a 2000 stall converter, and I will upgrade to a 2600-2800 as soon as the engine is running better.

Also after putting the magnum 280H the car had more power, but started having major problems after about 500 miles. I had the timing set a 30 degrees advance like suggested above, and by the shop I took it to. It still wouldn't pull much after 3600RPM. The car also starting leaking oil where it never leaked oil before, and overheated for the first time since I bought it.

Anyways, I will take the car in for CR check because I am starting to doubt the bottom end's integrity since I have fixed everything else on the car. Also I decided to buy #16 heads because the machine shops charge insane amounts of money around here.