Piston choices...

[Rickster]

I'm looking for a set of pistons for my 289 block. My research looks as though there is little to no diffrence between 302 and 289 pistons, it was the rod length and stroke that differed. I am initially going to be naturaly aspirated, but am thinking about "playing" with some low level boost at a later date, 8lbs. max. After searching the web today I found that opinion seems to be split as to wether I need to go forged for this little boost.

What are your opinions? Static compression would be around 9:1 and premium fuel is assumed.

[Bob Cowan]

I think it depends on what you're going to do. If it's a street car with some occasional drag strip use, cast or Hypereutectic will be fine. If you plan on some road track days (HPDE's) then I would use forged.

[G4AV8R]

Rickster, IMHO, go for forged pistons. It will give you a lot more options in the future.
Good luck, Randy Richards

[MJN]

Go forged and forget about it. You'll kick your self later if you go hyper.

[Rickster]

Thanks for the advise so far guys, another question though. Were the 5.0HO rods forged too? I've never heard of anyone having problems with them (within reason).

[narve00]

289 and 302 pistons should be the same. There are variations based on dished/domed and valve reliefs.

Lots of votes for forged. If for some reason you went hyper, avoid the KBs. I've seen more than a few complaints about the eyebrow on the valve relief cracking off due to detonation. Blowers and detonation don't mix, but you don't want pistons that add flying pieces to the mix. You would rather just burn them up.

5.0 rods are forged. If you want to go crazy you can have 3/8" bolts installed, but make sure it is done right. The rod can be weakened doing so.

[canuck1]

Rickster,

Although I've got hypereutectics in my naturally aspirated motor, I think anyone considering boost or juice should go forged. It is considerably more money (in relative terms) but a sound investment I think.

Sean

[Mac1]

Would really need more info, but my .02.
1. Forged pistons are set up with a lot more clearence, and ring selection will be more critical. Also, because of the looser clearence, you won't be getting 200K out of the motor...not that this should be a concern in a week-end toy.
2. Heads..Lot to consider. You mentioned 9:1, but if you are considering aluminim, this is about equivalant to 8:1 for iron. Can/will you upgrade quality and size of headbolts. Boost No2 issues show up here first.
3. Pre-ignition - forged will take a lot more punishment, but deal with the assumption it is going to exist with boost/No2 and you will be miles ahead. An ignition that will automatically retard, lower base timing for the street.
4. Turbo vs. supercharger vs. carb. vs. injection. Come up with a game plan before you start your basic engine rebuild, and remember:
1. It will cost twice as much as you think;
2. It will take you twice as long as you think;
3. You will eventially try to get twice the horsepower out of it then origionally planned.
...Afterall...it is going back in a Cobra.
Mac

[Rickster]

The heads are iron ported GT40P's with a spring upgrade. The timming module is a crank trigger driven, and computer programable based on RPM/TPS, and has a built in rev limiter that pulls timming based on RPM. I've read elsewhere that Hypers are OK only if you tune on the safe side (talking boosted here)...I was thinking that since (I think) I have the ability to do that with the prgramable controller, and if I tuned a touch on the rich side, I would be OK with 6-8#'s boost.

I've heard the same bad stories about the KB's. The speedPro's seem to get the nod though, any opinions on them, or a prefered hyper brand if I decide to go that route?

Thanks for all the input guys.

[Mac1]

I definately think you're on the right track, and my choice would be the quality Hyper.'s you're talking about as long as you stay to your game plan. Just the fact you can close up the piston clearance is reason enough for me...No thought of piston slap, tighter "V"/piston always pushing against cylinder on this motor, less blow-by, more oil choices all work. The only concern that I have, which sounds like you have already addressed is that there are cheapo Hyper's out there from China that are really crappy.

"Quality...pay for it the first time; and weep only Once."
Mac

[Rickster]

Well, I just got a PM on another local Mustang site, sounds like I might have a line on some used forged pistons...let me run this by the experts before I jump:

SpeedPro Power Forged Pistons #TRW-L2488F30 with a 1.619 compression height

The 289 block (65 6 bolt) has a deck height of 8.206, lets figure 8.2 to give some room for a deck job if needed. The rods are stock 5.0HO at 5.090 length, and the crank is a stock 5.0HO as well with a 3.000" stroke. that should put the pison top .009" over the deck, .003" if I dont need to deck the block. The head gasket should be at least .030" thick compressed if not more, so I should be OK right?

Thanks!

[MJN]

You'll find the factory 8.206 dimension can vary a lot. One of my decks was 8.221 before it was machined, the other was right at 8.206. Most head gaskets will be closer to 0.040", the Fel Pros are quoted at 0.038". I wouldn't run the pistons any more than zero deck just to be safe. There will be plenty of room to machine 0.010" from the top of those pistons if you wanted.

[Mac1]

SEEE...Sounds like you are already starting to deviate... [img]smile.gif[/img]

For the "killer deal" on the forged piston, I'm sure you could buy the best Hypers out there. I don't consider the forged "better" just different.
Now that you're looking at piston/Va. clearance issues on a motor with potential power adders, figure on going all the way.
1. Forged quality crank
2. Upgrade rods
3. Balance everything to a nats a$$
4. Definately use shimmed head gaskets
5. Pay the high $$$'s for the best machine work
6. Cam choice 1st thing on the list
a. check actual va. clearence Clay on the piston/assembled motor - minimum
7. With monies spent on above items, time to scrap/sell GT40's and go Trick Flows

Really, I'm not trying to talk you out of it. There's a lot of fun building a "killer" engine. Sounds like this will RPM like a banshee.
Mac

[Rickster]

Heh, I had everything planned and parts were in hand before I got ahold of this 289 block.... It's nuts how much things change, and how quickly you trash your previous plans when you change one little detail.... [img]smile.gif[/img]

Any prefrences on the small base circle retrofit cams that are availiable? I'm looking at CompCams 31-442-8 and 31-452-8...

Wow, this forum is great...just got another offer while typing this...wooHoo! I'll be recovering from this deviation in no time!

[ February 21, 2006, 12:37 PM: Message edited by: Rickster ]

[narve00]

302 with P heads and E-cam is good for 250 HP at the tires. Put 6 lbs on it and your close to 350 HP. There isn't a lot of extra flow on the P heads on the intake side lifting the valves high, saves money and wear keeping lift down.

I wouldn't go crazy on the bottom end. Many guys run a lot of boost on them. The block is the weak spot (around 500 HP). Pre 93's ran factory forged pistons and people get ridiculous mileage out of them.

The real issue here is that you claim you will stop at 8 lbs of boost, not a chance.

[Mac1]

Have had good luck with the Comp Cams tech support and would go with their recommendation.

Factory "forged" pistons (lead weights) set up @ .003-.004 clearance don't have much in common with a true "racing" forged piston.

At least you have 17 head bolts...oh, wait...thats a Chebbie.

Well...at least Ford saw fit to install larger head bolts on...oh, wait...this is a 289.

Physics doesn't have a favorite engine manufacturer and recipricating mass breaks things.

As the commercial sez..."pay me now, or pay me latter" 'cause as easy as it is to up the boost, you won't stop at 8.

[Rickster]

I'll be looking for a 12 step program once I hit 6#'s....

Thanks for the support guys!

[Porxter]

Rickster,

Your previous post:

The 289 block (65 6 bolt) has a deck height of 8.206, lets figure 8.2 to give some room for a deck job if needed. The rods are stock 5.0HO at 5.090 length, and the crank is a stock 5.0HO as well with a 3.000" stroke. that should put the pison top .009" over the deck, .003" if I dont need to deck the block. The head gasket should be at least .030" thick compressed if not more, so I should be OK right?

Wrong. The height of the piston is determined by where the manufacturer places the piston pin. You can't figure it by adding your stroke and rod length and comparing them to your deck height. (Deck height is measured from the crank centerline to the top of the deck. Your crank's rod journal only rises 1.5" from there, the other 1.5" is below the crank centerline).

If you add your rod length of 5.09 to the 1.5" of rise above crank centerline, you get 6.59". The rest of the distance to the top of the block is made up by the distance from the piston pin (top of the rod) to the top of the piston.

Except for the dome - if any - the top of the pistons are usually kept at or just below the deck to keep them from hitting the head under high rpm stretch.

Also, I would never use someone elses used pistons. But maybe that's just me.

Steve [img]graemlins/red.gif[/img]

[MJN]

Power Forged Pistons #TRW-L2488F30 with a 1.619 compression height

Steve.

He did list the piston compression height. This is the distance from the center of the pin to the top of the piston.

block deck measurement from crank centerline - (1/2 stroke + rod length + piston pin height) = piston deck height

8.206-(1.5+5.09+1.619)=-.009

[Rickster]

I think I calulated it right, I used the same method Mike described above. I've found the compression height varies slightly from manufactureer to manufactureer. 289's and early 302's usually have a nominal piston compression height of 1.605 compared to the later models 1.619, but that tends to vary by a few .001" depending on manufacturer...I'm pretty sure the two types are close enough that some creative machining or component selection will negate any problems using the later model pistons in an earlier block.

[Porxter]

I apologize for missing that small, but vital, piece of information!!
However, my math is coming out different than yours, but it matches Ricksters:

Undecked:
(1.5+5.09+1.619)=8.209-8.206= +.003 above deck

Decked to 8.200:
(1.5+5.09+1.619)=8.209-8.200= +.009 above deck

Sorry again for missing the original compression height.

Steve

[Rickster]

No problem! It's a good thing to make me double check my methods...thats what were here for.

Anyone with experience using the small base circle retrofit cams?

[Mustang Medic]

Rickster,
I used the Keith Black hypereutechtic pistons in my 289. (0.030 over 0.0022 average clearance).
I don't plan to use "juice" and will run one single 4V 1850 Carb with my "P" heads. I will be getting back the assembled long block from Riebes this week. Stop by and I'll show you the pieces and give you some black carpet.
Best regards,
Chuck

[MJN]

Sorry just can't add in my head that well I guess. 0.003" is correct and I think you could get away with that on a street motor that stays below 6500 rpm.

I set up my pistons to zero deck and have run the motor to the rev limiter more than a few times with no evidence of intimate contact between piston and head when I changed head gaskets last year.

[Mac1]

Rickster,
By now I assume that you have gone to the COMP CAMS web site. They posted an article on the31-442-8 cam you referenced earlier. Article covers a retro-289ish engine destined for a Sun. Tiger. 301 h.p.286/tq. might not sound that impressive on paper, but this engine doesn't seem to be where you are going. (old manifold,carb,heads). Love the spec's on both cam you referenced, right up until you add a blower. They'd both be loppy little buggers. If your heart is set on a blower, there would be a lot of better split/overlap blower specific cams. If you are going for a more traditional 289FIA .544L/229Deg (31-452-8)...love it....love it. As long as you check piston/va.
Mac

[FordManDan]

There is nothing wrong with a Hyperutectic piston as long as you gap the top ring correctly. Lean conditions are what cause the trouble with pistons. Power adders (especially No2) increase the chances of an inconsistent air fuel ratio and add more cylinder pressure. I wouldn't have a problem cramming 8psi of boost on top of a hyperutectic piston, but since you haven't bought them yet why not just go with a forged? The forged piston will give you more of a margin of error or better tolerance to a less than desired air fuel ratio--especially if you add more boost in the future. --dan

[Rickster]

Mac1,
have you used or experienced the 31-452-8? Thats kinda were I'm leaning right now...any idea how it would sound and mind itself in the skool zones?

I've been pracicaly living on the CompCams and Crane sites, but don't have any real world experience to back any of my theories up...

Chuck, I might stop by and shake you windows this weekend if the weather is right...if not I might stop by anyway..

[Mac1]

Rickster,
No, I don't have any experience with that specific cam. The sort of information, I'm sure as you have figured out will have to be with someone with a 289-302 in a Cobra built the way you are going. My background comes from being an NHRA stock/SS guy...Mopar, no less. We did pull around with a bunch of Ford guys and one guy in particular campaigned a "genie" Shelby. One of the sweetest sounding engines I've ever heard.

I do know with lift/duration there will be a nice lope to it, but sound and how it will act will be application specific ie:Tri-Y's, cross-over's, light-light flywheel, with a lot of effort to get the right gear-set in the trans are not usual fare in the Cobra world. As far as sound goes, are you planning on doing anything different on the side pipes?

[Rickster]

Just the standard FFR 4into4 fare for the pipes, and anywhere from 3.75 to 4.10 rears with an auto tranny...stall will depend on what is recomended, but I'm thinking in the 2800-3000 range. I'm hoping for a cam that will make decent power, sound mean, but not leave me looking the fool through town...

[Mac1]

Auto tranny??...nothing against them, but educate yourself, if you havn't already on converter choices. Published stalls are based a lot on curb weight so published figures will be asscue. I'm guessing that T/C will start off life as a 10", but some mfr's. might want to go smaller with the kind of stall your looking at. 10" based can definately be set up for what you're looking for, and the larger surface area gives a lot more surface to furnace braze the fins, etc. and should just last longer.

Just my oppinion, but the cam(s) you are looking at should be really good with a loose(r) converter. They seem to give it up a little bit on the bottom of the RPM curve which, in your case looks to be a good thing. If you've ever been in a light street rod with a semi-stock trans. and a healthy engine, you know the feeling at a stoplight where it's trying to pull you through the intersection.
Mac