GDaina

Yes Mr. Chuckles, so true, so true....by freeing the exhaust....like getting shot out the cannon...difference between night and day.

:skep: That Mr Spiral Jim, last time I'm lettin' 'im sit in my cah.... :D

427Hotrod

Isn't it fun to help folks spend $$$???

First off, go with forged anything on pistons. I wouldn't use hypereutectics in anything except maybe a pickup I was trying to improve on. They are much better than normal cast, but no where as good as forged. The only reason OEM's use them is for that reason...they're cheaper than forged and better than normal cast. It allows them to get the added strength they need for little $$, still run tight clearances for noise and oil control etc. Ford used real forging in the 5.0 Mustangs up 'till '94 and they were fantastic. You could spray 'em, add blowers etc. Oil control was fine (mine has over 200K on it and still doesn't use a drop). Hypereutectics are still a casting and are not worth the trouble for a an engine you are going to invest serious money in.

That being said, the lower cost TRW's will be fine. They are much heavier than the SRP's etc, but you aren't running a huge dome piston, so it won't be too bad. You won't be revving past 8000 rpm so no big deal. My 427 still has the GM/TRW OEM 11.0 forgings in it. It has survived 20+ years of 7500+ rpm, loads of nitrous and 9 sec ET's as well as a gazzilion street miles.

The 288 AR will be much more street friendly than either of the flat tappets listed as well as make more power. I just can't imagine anyone not liking it. Those other two are good cams for sure, but a .660 lift flat tappet is getting into the area where wear will become an issue

The 288AR is far from aggressive as roller cams go. That's why it can be so forgiving and last a long time. It doesn't require much spring pressure at all. I ran a little extra (190 psi seat) and it was fine. I just think that overall, it's a great piece in a 427-454 size motor...and still pretty decent in a 496.

Compression ratio.....you REALLY need to know what your heads actually CC to. I've seen lots of heads CC much larger than what the specs say. I had a set of early closed chamber "bathtub" heads that should have been in the 95-100cc range. They actually checked out at 115 cc since apparently they had a few valvejobs in their life. It took serious angle milling, flat milling and new valves to get them back to 95cc. PITA!!

Your average stock head will end up with a real 9.8-10.0 compression with those 10.25 pistons IF you use thin metal head gaskets. It gets worse with .040 Fel Pros. I would definitely use basic .020-.022 steel shim gaskets to keep Quench decent (.035-.040 range) with a block that has not been decked and pistons are likely .017-.020 down in the hole. This is CRITICAL stuff for getting high compression to like pump gas.

You might consider the .300 dome 11.0 closed chamber pistons. They allow you to open chambers some for better flow and still maintain compression ratio. Easy to get too low with the 10.25's without paying real close attention. It's easy to lower compression...hard to add it back!

I had 195 psi cranking compression with the 288AR using 11.2 static compression. But I spent time tuning it real tight and it ran on 93 octane at WOT fine. I did use 87 for long highway cruises and it actually did fine there too under WOT. Lots of "11.0" engines are more like 10.2-10.5. For a nice bulletproof no hassle setup, I'd shoot for an honest calculated 10.5 with the iron heads. You'll be fine. If you're feeling adventurous you could push it some more, but the power gain isn't much really.

It doesn't take huge work to improve heads for a deal like this, but you will need to do some basic bowl porting at least. You can easily pick up 30-40 hp for next to nothing in $$...just time.

You're on the way to well over 400 RWHP and the potential to run 11's@120+ mph here! That's a FUN ride!


JIM


[Modified by 427Hotrod, 11:26 AM 3/14/2004]

GDaina

I'm glad to read your numbers on cranking compression...mine read 205-210 and I thought something was out of line. I'm using the SRP's 10.5's though I think my CR ration may be closer to 10.25. Did some crude calculations, even measured the combustion CC's and came up with 10.25-10.40 on various cylinders.

Mr D.

427, so if I'm reading this right your saying go with the larger 11.0:1 pistons, have some work done on the head bowls, and end up with 10.5:1? I have been living by the rule anything over 10.5:1 and pump gas becomes a problem. However, I have has several people say they run stock 435hp cars on pump gas with no problems. Hmmmmmm :confused:

Ironcross

However, I have has several people say they run stock 435hp cars on pump gas with no problems. Hmmmmmm
Premium pump gas works just fine. I have no problems at 11-1. :thumbs:

427Hotrod

What you're shooting for is REAL compression ratio. Most "11.0" compression 427's and 454's are in reality around 10.2-10.4 when actually measured. "IF" they were built to the correct minimum tolerances, they would be 11.0. The crate LS-6's were at best a little over 10.0. They used open chamber heads with closed chamber 11.0 compression pistons. The LS-7's were a little better, but more like 11.5 or so instead of the 12.5 they advertised.

The advantage of the 11.0 piston is you have more room to play with. It's theoretically not as good as a flat or dished piston with a super small chamber head, but we don't have anything like that to work with. We have stock closed chamber LS-6 type heads.

If you were running aluminum heads we could sneak up nearer to 11.0 with confidence, but I'd rather see it end up with a real 10.5 or so and then crank in as much timing as it likes. Much better than high compression and retarded timing.

There is much talk about Dynamic Compression ratio. There are lots of calculators on the net to play with it. It's a very real thing and is actually what you are working towards here. The factory upped compression on the bad boy motors because the cams used had much later intake valve closing. This allows piston to be much higher in cylinder on the compression stroke before valve closes. This reduces the amount of trapped mixture. So they used a higher compression ratio to squeze the "smaller" remaining charge better to get power. That's why "big" cams can be doggy at low speeds. Nothing is trapped in cylinders. But let RPM climb and the time to push mixture back out is reduced and you get much better cylinder filling and power.

Don't be mislead by some of the DCR calculators. While they are good to study with, they can be a little whacked out. For example, they will tell you that I should be able to run pump gas with my current cam and use a 12.2 compression ratio! Sure it will work for cruising, but when I get my foot in it and it starts filling cylinders, it would self destruct in no time. I've been doing this long enough to have an idea what I can get away with.

Your best bet is to stay with proven combos. The cam you are contemplating will run fine at 10.5 static compression with iron heads. However you have to juggle things to get it!


JIM