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View Full Version : Highest Safe Compression ratio running on 87



pipnit
02-24-2011, 09:32 PM
Hey guys, so what would be a very SAFE compression ratio on 87 and where do I start to stand next to the edge of the cliff? I'm thinking 9.2:1 right now but figured I'd ask you guys for your opinions.

THX

mrfixxall
02-24-2011, 10:14 PM
Hey guys, so what would be a very SAFE compression ratio on 87 and where do I start to stand next to the edge of the cliff? I'm thinking 9.2:1 right now but figured I'd ask you guys for your opinions.

THX

8.5-1,,9.2 go tp 89 minimum..

BUIZILLA
02-25-2011, 07:29 AM
iron or aluminum heads?

MOP
02-25-2011, 07:31 AM
I am running 9:125 on my 383 for about four years now, I have tried higher grades and experianced loss of performance. "Griz" God Bless his soul explained how higher test fuel in lower compression engines degrades performance, I can attest that mine runs noticeably better on 87. I have run ignition as high as 34 degrees with no ill effects, I am currently running 31 degrees due to concerns with alcohol content.

LKSD
02-25-2011, 08:01 AM
Id recommend the better fuel as well..

Carl C
02-25-2011, 09:24 AM
There are other variables such as what Buizilla asked and is it EFI or carb. Combustion chamber design is no doubt a factor. The 525 EFI is a surprisingly low 8.75:1.

CHACHI
02-25-2011, 09:39 AM
I am running 9.7 and using 89 with no issues on the street in a BB Ford with iron heads.

Ken

Fishermanjm
02-25-2011, 10:01 AM
9.8-1 in my 1998 2500 ram truck with a mild cam, ported , blue printed, i haul a good size slide in camper with it an run the cheepest fuel i can get. No issues at all,,, a mopar engine that doesnt ping,,, when u get up higher than that with a comp cam or somethin like that thats when u will run into issues marine engines seem to run cooler not sure if that is entirely true butt they seem too

pipnit
02-25-2011, 10:11 AM
Guys,

I have a constraint here, that's why I'm asking the question. Of course I don't want to run 87 but that's ALL I can get at the two gas docks and towing the boat to the pump isn't an option for me. If I could have my druthers, they'd have 100 octane at the pump and I'd run 11.5:1, no brainer but that's not the case, all I can get is 87 and I'm not going to be mixing Toluene or anything like that.
Also, it's not a car motor, it's a boat motor, unfair comparison. How often do you run WFO with your street car for extended periods of time? Probably not very often, if ever.
I'm going to be using Aluminum AFR heads with Inconel valves, diamond pistons (-18) full seal rings, stainless marine manifolds and bring the pipes almost to the transon. If I get a set of 75cc combustion chamber AFR's and mill them to 70cc, that'll bring me to 9.17:1 with this setup. I'm thinking 9.5 might be getting me to the hairy edge. Thoughts?

pipnit
02-25-2011, 10:13 AM
BTW, the cam (Marine Kinetics) and the carb (Nickerson) are going to be built around the motor. I imagine we'll add a couple degrees to the exhuast side to try to expell heat the best we can.

Carl C
02-25-2011, 10:41 AM
What kind of engine? I agree with fixx. I think you will be too high and should keep it under 9:1 if you want to run hard on 87 octane. JMO, there are others who know a lot more about this but I think we need to know what engine we're talking about since there are people here who know a lot about a particular set-up.

Fishermanjm
02-25-2011, 10:43 AM
so the marine engine doesnt really run cooler,,,, u sound like u have it well under control,,, nope deffinantly don't run the truck WOT at all but the engine is under tons of strain haulin the camper

mrfixxall
02-25-2011, 10:48 AM
BTW, the cam (Marine Kinetics) and the carb (Nickerson) are going to be built around the motor. I imagine we'll add a couple degrees to the exhuast side to try to expell heat the best we can.

I think you should ask bob @ marine kinetics..

pipnit
02-25-2011, 10:54 AM
I think you should ask bob @ marine kinetics..

Oh yeah, I'm picking his brain to the point where he's going nuts. What a nice guy, too, man, a fountain of knowledge too! I just wanted to throw the question out here too, fun conversation and wanted to see what people think and what they've experienced themselves, first hand.

mrfixxall
02-25-2011, 11:03 AM
Oh yeah, I'm picking his brain to the point where he's going nuts. What a nice guy, too, man, a fountain of knowledge too! I just wanted to throw the question out here too, fun conversation and wanted to see what people think and what they've experienced themselves, first hand.

my opinion,,Dont mill the heads,surface the deck of the block,, have it Zero decked and leave the cylinder heads alone,moving the piston closer to the combustion chamber will give you a more complete burn..If you have not bought the pistons yet i would ditch the diamond pistons idea,,go with SRP which are made by JE pistons or ROSS pistons,you may spend a little more but they have been out their far longer then any piston mfr and have been proven to last..

pipnit
02-25-2011, 11:11 AM
Thanks Fixxall,

M.K. reccomended the Diamond Pistons and I got them ordered already.

Fishermanjm
02-25-2011, 11:17 AM
fixx,,, the guy that did the engine in my truck builds drag engines, he told me the same thing,,, dont mill the heads zero the deck it will bring the compression up slightly but give u a clean burn,,, it worked well in my 360 mopar engine

Pismo
02-25-2011, 12:33 PM
The aluminum heads save you. You will be fine at 9.2 or 9.5 and 87 gas.

HallJ
02-25-2011, 12:55 PM
Thanks Fixxall,

M.K. reccomended the Diamond Pistons and I got them ordered already.


Nothing wrong with Diamond pistons.

Jeff

mrfixxall
02-25-2011, 01:06 PM
Thanks Fixxall,

M.K. reccomended the Diamond Pistons and I got them ordered already.


oop's,,my bad....I was thinking diamond but i ment probe:bonk:

Diamonds are good too :wink:

MOP
02-25-2011, 03:57 PM
I am running 9:125 on my 383 for about four years now, I have tried higher grades and experianced loss of performance. "Griz" God Bless his soul explained how higher test fuel in lower compression engines degrades performance, I can attest that mine runs noticeably better on 87. I have run ignition as high as 34 degrees with no ill effects, I am currently running 31 degrees due to concerns with alcohol content.

Add on I am running Dart Iron Eagles, the engine is in a 22 putting more load than an 18. With the lighter load and aluminum heads you should be fine with a little higher compression.

joseph m. hahnl
02-25-2011, 07:13 PM
so the marine engine doesnt really run cooler,,,, u sound like u have it well under control,,, nope deffinantly don't run the truck WOT at all but the engine is under tons of strain haulin the camper

marine motors use a lower temp thermostat 140 to 160. Raw water setup or,a 1/2 cooler run cool, a full cooler runs hot at wide open throttle .

raw water will run 140 to 170 Degrees

heat exchangers will run 160 to 195 degrees

optimum efficiency is 195 degrees and is the standard for automotive

pipnit
02-26-2011, 08:54 AM
9.17:1 it is! Figured we may as well play it safe and make it bomb proof. Aside from that, this engine is going to be so powerful compared to what I have been running that I'll be all smiles anyhow. If I were to have bumped it up to 9.5, I would be lucky to even see a 15 hp gain.

mphatc
02-26-2011, 09:34 AM
I have three set of AFR heads in marine applications. Allow me to suggest you send them to Dart Coatings, talk to Omar there and get them coated, internally and externally to prevent corrosion. He also coated my exhaust runners in the heads to protect against corrosion from humidity in the exhaust when the boat is not in use.


As to the recommendation to not run the Diamond Pistons, there isn't anything on their website as to the materials or technology they are using . . forged , alloys, hypereutectic etc . . . that raises a flag for me.
You might seriously reconsider that selection.

Mario L.

pipnit
02-28-2011, 10:36 AM
As to the recommendation to not run the Diamond Pistons, there isn't anything on their website as to the materials or technology they are using . . forged , alloys, hypereutectic etc . . . that raises a flag for me.
You might seriously reconsider that selection.
Mario L.

All sorts of info on thier website, here is the short of it:

Lightweight 4032 forging - Great for a street replacement piston!
Designed for N/A & small boost applications
Designed to fit most 23 cylinder heads
Will also work with 3.500 stroke
Standard 1/16 x 1/16 x 3/16 ring package
Premium 8620 wrist pins included
Standard 1/16 x 1/16 x 3/16 ring package
Top ring down from piston crown = minimum .190
Valve relief depth = .295 intake and .200 exhaust

HallJ
02-28-2011, 01:26 PM
I have three set of AFR heads in marine applications. Allow me to suggest you send them to Dart Coatings, talk to Omar there and get them coated, internally and externally to prevent corrosion. He also coated my exhaust runners in the heads to protect against corrosion from humidity in the exhaust when the boat is not in use.


As to the recommendation to not run the Diamond Pistons, there isn't anything on their website as to the materials or technology they are using . . forged , alloys, hypereutectic etc . . . that raises a flag for me.
You might seriously reconsider that selection.

Mario L.

I have a set in my pressurized Toyota and am quite happy with them.
Smidgen Too used to work there back in the day!

Jeff

pipnit
05-25-2011, 11:07 AM
Ran the motor on a bench today. One whack of the throttle, hit the starter and she jumped to life! She sounds MEAN!

Now to put her in the boat, finish the measurements for my new exhaust and finish up with the hydraulic steering.

I'm guessing I'll be in the water in three weeks or so. Woot woot!