kalli

Hiya all,

i was wondering. I have a 289 from 1966 and from what I see the CR seems to be 9.81:1 (according to a few sites). as well they mention to have 54cc heads stock. I can't for the life of me find info about piston cc and underdeck clearance. But if I let's say drop in 61cc heads wouldn't that dramatically drop compression to ~9.0:1?
in what way would that affect me? anyone any ideas?

urban_cowboy

Decreasing CR will lower horsepower some. It is not much, but it is less.

Not sure if you have a 2v or 4v motor, but according to my trusty book, the 289 2v in 1966 had:
200hp@4400
282ft*lbs@2400
9.3:1 CR
52.5-55.6cc Combustion Chamber Volume
.016 Piston to Deck Clearance
1.6 Compression Height Pistons
5.155 Connecting Rods

If you need 4v 289 specs, just holler.

FYI, my trusty book is Ford Performance by Pat Ganahl Published by SA Design. SA Design make a bunch of excellent books. I have a big library of them that are great for reference stuff like this.

kalli

thanks a million for that. exactly what I neded to know (original 2v)
with that and and 54cc and my current head gasket i calculate 9.55:1
with 61cc heads that will go down to 8.75:1
according to desktop dyno that will be only measly 5%-10% max. since i was asking because of (still maybe) new heads (225hp->300hp at flywheel with my current setup) i needed that for my calculations. cheers for that. very much appreciated. i'd prefer 58cc but could get a deal on 61cc.
I guess that means as well less problems with 92 octane and engine not running as 'loud' in idle. that right?

kalli

looks like i'm missing a lot of low end torque though

MIL1ION

2V's are better for bottom end torque than 4v's

4v's are better for top end performance than 2v's

urban_cowboy

Lower CR such as 8.8:1 should allow you to run 87 octane with the proper timing. That is close to what every stock 351W EFI was.

What do you mean by missing a lot of low end torque? Compared to what?

Remember that the 289 is not a high stroke motor. 2.87 stroke is pretty small which you look at the 302, 351, or strokers. It will make power at rpm, not down low. If you get some heads that flow well and are not crazy low compression (which high 8s to low 9s is not), the power band is dependent on what cam you choose.

kalli

i quickly checked my 289 with 570cfm carb, stock heads, stock cam and small tube headers with mufflers. I compared the exact same engine (no cam mod) with AFR165 (reduced down to 8.75 CR because of 61cc). AFR results in brackets

rpm HP TQ
2000 106(103) 278(271)
2500 132(131) 278(275)
3000 159(160) 278(279)
3500 190(197) 284(295)
4000 215(235) 282(308)
4500 225(270) 262(315)
5000 216(296) 227(311)
5500 204(315) 195(300)

from this I'll loose tq and HP under 3000 and only then they start screaming

if I'd get the 58cc AFRs I'd be at virtually the same values at 2000 and then increasing from then on.
I don't dare spinning the engine to 5500 maybe that changeswhen it actually makes power up there),. it seems currently above 4500 is a waste of time.

I do understand that I should match all that with a camshaft (XE262 would bring me to 350HP/340TQ@5500)but I'm probably to scared to **** up something else ;-)

again: this is all a maybe situation, so don't waste time on that

my77stang

you can always get those heads milled down a little to help bring your compression back to where it should be.

just food for thought.

kalli

the idea is correct and very valid but I rather live with less compression than bringing the head to paddy the farmer to have it milled down ...

MBDiagMan

I doubt that this much CR loss would result in more than a 5% power loss, but if it did 5% is significant.

What will not show on paper is that a higher compression engine, all else being equal will feel snappy. It's nothing you can measure, but it just does.

8.75:1 may not get into the mushy area that I'm talking about, but it might. In the seventies, they built Beaucoup engines with 8:1 CR. Granted there were MANY other issues that made those engines low performers, but when compression gets that low, the engine gets a mushy feeling, even if everything else is up to snuff.

My $0.02,