To change pistons, or to not change pistons... |
Post Reply |
Author | |
72BoB
Senior Member Joined: 25-January-2011 Location: Atlanta Status: Offline Points: 248 |
Post Options
Thanks(0)
Posted: 31-January-2012 at 2:03AM |
...that is the question...
So yeah, when I bought the engine that I am currently about to put in my car the builder said it should have about 11:1 compression. Me of course being as zealous as I was at the time said "sure, I can work with that." I might have been a little starry-eyed looking at the parts list considering all of the parts used in the build are really good parts, and everything was balanced and blueprinted, and it had worked C9 heads. So now, as the time gets closer and closer for me to drop the engine in the car (which I was planning within the next month or so), I have become more and more nervous about that 11:1 compression with iron heads, considering that this is a street car that sees about 5000 miles per year. I have talked to people and they are all saying that I can run it on premium as long as I back off on the timing, but is that really that safe in the long run, or am I just going to install a ticking timebomb that is going to detonate and blow chunks all over the place? Plus, how is backing off the timing enough to make 11:1 survivable going to affect performance? Should I just risk it and install it and run it? Or should I fork out the dough to have the pistons changed out for a CR around 10:1?
Edited by 72BoB - 31-January-2012 at 2:06AM |
|
1972 Torino
|
|
ilyes
Senior Member Joined: 09-January-2010 Location: Philadelphia PA Status: Offline Points: 3782 |
Post Options
Thanks(0)
|
Pistons are not everything, it depends of the cylinder bore, piston relief, gasket thickness and head volume. The cheapest way to go is to buy a thick gasket, it will drop compression a little, some valve notching would help as well
|
|
Rockatansky
Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6059 |
Post Options
Thanks(0)
|
i've run 11.4:1 before, you can't back off the timing enough to make it work
you might want to 'pump' a cylinder to find out exactly what you have before doing anything else. this is how the tech guys determine if a race engine is legal or not for class without taking it apart, they fill a cylinder with liquid with the piston at either top or bottom then turn the engine 180* and measure both the pump volume and how much it took to fill the chamber at TDC
your cam also has a lot to do with whether or not 11:1 will work, i had a lot of cam and still misery. it sounded like Orville Redenbacher was blowing the lid off my piston tops with ping & detonation... but if you don't mind filling up with LL100 at the local airport... mine loved that LL100, or you can buy it by the can for about $60/5gal, some stations pump 100 octane for about $7/gal
possible you can have some of the domes milled off and still use the same pistons
|
|
72 GT Ute
|
|
Regul8r
Admin Group Moderator Joined: 26-December-2007 Location: Sarasota FL Status: Offline Points: 6624 |
Post Options
Thanks(0)
|
11:1 is EXTREME for s street car.
Going to cost money to run the HIGH Octane gas it wants in order NOT to detonate badly! Many things you COULD do to lower the compression ratio. After ALL the work that has been done to it... IF you want a little less compression I would make a deal with the machine shop... they take this short block in exchange for a milder built short block. About the same money. OR put the motor up for sale and have a milder one built. No concerns/worries about the heads though.
|
|
Carl Corey (Moderator/Event Coordinator) Contact ANYTIME!
1976 Ford Elite "Lola Mae" 97 Suzuki Intruder 1400 US Army Retired |
|
madmaxtorino
Moderator Group Zombie Killing Training Instructor Joined: 04-August-2010 Location: Lawrenceburg Tn Status: Offline Points: 971 |
Post Options
Thanks(0)
|
my 429/466 was 10.5:1 had no problem on 93 octane. also my 2012 5.0 is 11:1
ENGINE:
466 ci
10.5 comp ratio
TRW forged pistons
Arp Rod Bolts
High Flow Aluminum Water Pump
Pro Comp Harmonic Balancer
Cobra Jet Baffled Oil Pan
DOVE heads ported polished
Cobra Jet titanium valves
procomp full roller rockers
CobraJet/Police Interceptor Exhaust
Manifolds
comp cams custom grind camshaft
Cobra Jet valve covers
Weiand stealth intake manifold
fast EZ EFI Fuel Injection
serpentine belt conversion
2.5 inch exhaust with X pipe and
Dynomax VT Mufflers and High Flow convertors
all hoses and belts new
Roush plug wires
MSD 6A ignition
MSD Pro Billet Distributor
Aluminum High flow 3 core radiator
Aluminum power steering cooler
140 amp 3G alternator conversion
Edited by madmaxtorino - 31-January-2012 at 2:03PM |
|
Allan
Revelation 6:8 When there is no more room in Hell, the dead will walk the Earth. |
|
steve
Senior Member Joined: 22-January-2006 Location: new hampshire Status: Offline Points: 243 |
Post Options
Thanks(0)
|
Hi, I plann on high octane fuel with my build. Then detonation shouldn't be a problem. The oil should have a zinc additive as well. This is all new to me but I don't plann on any long rides !
|
|
72 gts fst bk in 1982 !!
currently building 73 fast back with a dove-a 429. |
|
Rockatansky
Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6059 |
Post Options
Thanks(0)
|
modern computer controlled cars running high CR have knock sensors to pull out timing several times a second to control detonation, no comparison to old school
72BoB, do you have the cam card info? if you know the intake closing point you can calculate the Dynamic CR and you'll have an idea if it'll run on pump premium or not, but you'll also need to be accurate on the static CR for the calculation
i'd call local speed shops and ask if they have the equipment to 'pump' a cylinder to find the CR Edited by Rockatansky - 31-January-2012 at 9:03PM |
|
72 GT Ute
|
|
bigblocktisdale
Member Joined: 26-September-2010 Location: wisconsin Status: Offline Points: 99 |
Post Options
Thanks(0)
|
i have found that by doing a compression test, if you stay around 180psi or below 93 octane works fine.
|
|
1972 Gran Torino Sport : 10.30 @ 131 mph NA
1991 mustang : 11.38 @ 123 mph sold 91 and bought a 67 mustang |
|
stuck
Senior Member Joined: 23-December-2007 Location: michigan Status: Offline Points: 279 |
Post Options
Thanks(0)
|
I am finding E85 interesting ,but i,m not sure yet what the minimum CR needed is[12:1?]. you will need a carb and fuel pump for it.+ in the winter they change the formula a little so you might have to reset timing. sorry to hear what a pain in the a. Or maybe with a thicker gasket and cam timing+ ignition timing. i'm not sure about boost in a bottle. It would stink to machine and rebalance $$$ouch.
|
|
michigan
|
|
Rockatansky
Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6059 |
Post Options
Thanks(0)
|
yeah you could run it on E85 and run all the timing you want!
|
|
72 GT Ute
|
|
72BoB
Senior Member Joined: 25-January-2011 Location: Atlanta Status: Offline Points: 248 |
Post Options
Thanks(0)
|
Sorry for the late reply... This is a 460, bored to a 472. I am looking for the ideal solutions, or close to it. I have some money that I can play with, I just wanted to find a good compromise. Options I am not looking into is running aviation fuel, switching the E85, or just trying super thick head gaskets. First off, the builder didn't have too much information on the specs of the cam, but he said it had .530 lift. I haven't taken it to a shop to have them check the actual compression, but I'm looking into doing that right now. I have a set of Kaase Super Cobra Jet heads that I can put on, but they're currently bare and I know that won't be the end-all fix. Once again, I know I was pretty stupid getting an engine without knowing the full spec details of it, but it was a really good deal. Even if I have to pull the pistons out and change them I will still come out ahead than compared to if I built the engine myself. |
|
1972 Torino
|
|
Post Reply | |
Tweet |
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |