Can you go 10 to 1 on pump gas with iron heads?

[supserdave]

Trw 2355's, Stock 71 440 block .030 over that hasn't been decked, and 915 closed chamber heads. I'm still waiting to get the heads back from the shop to get a true volume number. I just want to ask you guys to see if you think it will work on pump gas before I buy the pistons. Right now with the calculator I come up with 9.75 to 1, that is with the 78cc heads and the pistons .04 in the hole, and .04 thick composite gaskets.

It's going to have, 3.55 gears, with a stall converter. Don't have the converter yet but will get it built when we get the engine done. The car has no power brakes, so would going with a bigger came help the cause? How about the Lunati 60303 268 cam be a good choice? I would use a custom grind, but the engine will be going together very soon so I need to get one off the shelf. The car will be 90% street use.

So to sum it up, would that be a good cam choice, and am I heading the right direction?

[i c e b l u e]

im sure chryco and firefighter will chime in with more info. From what i have discovered with a iron closed chamber head the limit is around 10 to 1 static compression ratio, and about 8.3 dynamic to run on 93. However these are( or at least what i consider) to be the limits and staying a few tenths conservative won't hurt you on a street engine. If it were my engine and were to be street driven i would stay right about where you are at now, just to play it safe from detonation

heres on online comp ratio calculater that will also figure in your dynamic compression ratio with your cam specs

http://www.kb-silvolite.com/calc.php?action=comp

Marcus

[supserdave]

Thanks for the link Ice blue.

With my specs, I come up with 9.75 Static compression, and 9.01 for dynamic with the Voodoo 60303.
With the 60304, the dynamic goes down to 8.85, is that to much dynamic compression for 93?

[jg68]

Thanks for the link Ice blue.

With my specs, I come up with 9.75 Static compression, and 9.01 for dynamic with the Voodoo 60303.
With the 60304, the dynamic goes down to 8.85, is that to much dynamic compression for 93?

8,85 is still too high i'm sure, 8.5 is much better, closer to 8.2 is were you really want to be with iron heads & pump 93 from what i've been told, but i think you'll be fine with 8.5, what is your Altitude?

[Chryco Psycho]

with 9.75 compression typically you will be on the ragged edge , using a higher stall converter I slightly longer dduration cam & playing with the timing curve & depending on the rear quality of the pump gas where you are you "should" be able to make it work
I used the Mopar solid .590 cam . 2355 pistons Zero decked , closed chamber heads milled .020 with a .035 gasket & it never detonated with pump premium , but I never put load on the engine below 3000 rpm & it was a 4 spd car

[firefighter3931]

  I prefer to keep it in the 9.3:1 range with iron heads.....much safer. 


Ron

[68chargerboy]

i have a 10.2 to 1 compresion motor with iorn heads and use it as a daily driver everyday, with no detonation

[supserdave]

Altitude is around 1000 or so above sea level.

[jg68]

Altitude is around 1000 or so above sea level.

Ya might as well call this sea level really, there are ways around this by picking the right cam, even though you don't here it, there is such a thing as silent detenation, it will still damage parts over time, your pushing the envelope with the iron heads IMO, your on the right track trying to calculate the dynamic compression, you really need to stay in the low to mid 8s on this, it can be achieved with a 11.5.1 engine picking the right cam, your static comp. is in the neighborhood of 10.2-10.4, i'd say you'll be safe with a MP .590 solid no question, but is this cam ideal for your needs, most likely not, i had a 446 with FTs & milled some irons to closed chambered (meassured 68cc), i didn't quit understand all the dymatic comp. thing, still don't really , but the static comp. on this engine was 12.2 , i was at 3700 ft., ran a .509 cam, i'm sure it had dymatic comp. in the high 9s easy, but at this altitude, i still had to run at least a mix 50/50, at sea level, this engine had 200+ lbs. of cranking pressure, with total timing at 30*, it didn't just ping, it rattled, now lets take my 451 low-deck build, it had FT ross pistons, 906s at 90cc, .039 gasket, it static was 9.73, i ran the comp. XE284H, at 800 ft. alt. the cranking pressure was 190-195 all around, it wouldn't run on 93, popped in a comp. solid with 250/256 dur. @ 50, a tad more lift but ground it on a 108 LSA vs. 110, cranking pressure dropped to 180-185, i tried it on 93 just to see, i didn't hear any pinging, but it showed on the plugs , so just be careful in cam selection, get one on a 112 LSA, no lower, talk with some cam companies also & get there input. having closed chambered heads will help with better quench, but there still irons.

[supserdave]

I really wish we would have measured deck height before we took the motor apart. I guess we can assemble the short block and get the distance the pistons are in the hole, and cc the heads and see where we are from there and try and correct with the head gaskets.

The block is a virgin 71, never decked, any guesses how far down the 2355's will end up?

[firefighter3931]

The block is a virgin 71, never decked, any guesses how far down the 2355's will end up?

The 2355's are usually .020-.025 in the hole depending on how close the block is to the 10.725 factory spec. Mine needed .020 to get to zero deck.

Cranking compression in the 150psi range is safe for iron heads, inmo. More than that and it's a crapshoot. 

With the closed chamber heads you might be better off with a 2266 speedpro piston. 



Ron

[supserdave]

Ok, so I tried the numbers for the 2266's, Looks like they are about .07 shorter than the 2355, so that puts them about .090-.095 down the hole. With the Lunati Voodoo 60304 cam, and its 43 degree intake closing point, that gets me to about 9.3-1 static, and about 8.35-1 dynamic compression. But, my quench with those pistons and the closed chamber heads is .130 with a .040 gasket. Is this cam to big for this much compression? This is option number one.

Option #2
If I go with the 2355's, and they end up .025 in the hole, plus .04 for a gasket, gives me a .065 quench. The compression works out to 10-1 static, and 9.1-1 dynamic. Would the better quench numbers overcome the higher compression enough to make this work? Is there a better cam for bleeding cylinder pressure? I guess we need to stay hydraulic, so that is a limiting factor.

Sorry for all the questions, i need to get this all ironed out by the weekend in order to get parts coming.

Thanks a bunch everyone!

Dave

[supserdave]

Ended up going with the TRW 2266's. Ended up .099 in the hole, came out with 9.1 static, and 8.5-1 dynamic. Should have it fired up for break in on the dyno onMonday!

[firefighter3931]

Ended up going with the TRW 2266's. Ended up .099 in the hole, came out with 9.1 static, and 8.5-1 dynamic. Should have it fired up for break in on the dyno onMonday!

That will run fine on pump gas....good work ! 

What's the rest of the build ; cam, intake, carb, headers ?

Looking forward to the dyno numbers 




Ron

[supserdave]

Voodo 60303, 69.5 six pack setup, Undetermined headers, probably cheapy's for now. It should run good.

[supserdave]

Just got off the phone with my brother, and they had it running today! Bad news is the dyno at the college where he's building the engine won't bolt up to a 440 I guess. So they can only run it on the run stand. It had good oil pressure, didn't get hot, and sounded great!

They had to break it in with an Edelbrock they had laying around. Tomorow they will bolt the 6 pack on and see how that works. Thanks for all of the advice everybody, nothing better than putting it together yourself and having it work!

[firefighter3931]

Congrats Dave on the successful fireup 



Ron

[Chryco Psycho]