High Compression 2.8

[rvbilly]

Hi to all , I am wanting to know of anyone running a 2.8 with over 9.5 to 1 compression, I want to run mine at 9.88 to 1 and don`t know what octane I could get away with, I`m hoping I can use 91 or less, I know the 3.4 crate is supposed to be around 9.66 to 1 but don`t know of it`s octane requirement, thanks for any feed back,, Bill

[Superdave]

Hi to all , I am wanting to know of anyone running a 2.8 with over 9.5 to 1 compression, I want to run mine at 9.88 to 1 and don`t know what octane I could get away with, I`m hoping I can use 91 or less, I know the 3.4 crate is supposed to be around 9.66 to 1 but don`t know of it`s octane requirement, thanks for any feed back,, Bill

you'll be fine with 89 on that...


i run 89 in my 10:1 SBC w/o problems. How do you plan on getting 9.88 exactly?

[geoffinbc]

Actually the best way to determine what octane you will require is by finding your cranking pressure. This is because cam profile along with compression and other less major factors (like quench area, chamber shape, operating temperature, air charge temp) is what will determine your ocane requirement.

For instance wilh aluminum heads you can easily run 1 compression point higher with all other factors the same. Or a 272 crane cam would allow for more compression than a crane 260 cam.

[rvbilly]

2.8 High Compression

Hi SuperDave, my block is getting bored 30 over, the block is having 24 thou. shaved off the deck , ( will give me a .040 Quench ) and the heads are getting shaved .010 thou. I have a cam with 112 LSA , 202 intake 210 exhaust @ .050 .420 intake .427 exhaust lift with a 109 intake centerline , am waiting for my Hedmon longtube headers, I also have a new Eagle crank going in it, I`m hoping for aleast 170 HP and 180 Torque. should be doable with the parts and high compresion, Bill..

[sil]

im running about 9.7:1 right now(according the cr calc on this site), had to use felpro's gaskets instead of my copper ones. i have a 2.8/3100
im using the lowest octane gas which is 87 octane. on the stock timing tables i had no knock counts, so i was able to get a few more degs here and there

you will be fine if your motor is mechanicly sound

[rvbilly]

2.8 high compression

Hi again , that is good to here, my block is in the machine shop now, the engine will be a complete overhaul, I`d like to use that 89 , gas is almost $5.00 a gallon here, I am useing the HO iron heads, didn`t want to go aluminum because of the intake setups, I can go with the 4.3 TB with my injectors later down the road for a little more boost in power & torque, mayby I should it up to 10 to 1 . thanks Bill..

[geoffinbc]

10:1 might be much on iron heads. You can help your situation further by pilishing the combustion chamber and radiusing all sharp edges. Run the coldest plugs you can that will still resist fouling.

[rvbilly]

10 to 1 to much..

Hi betterthanyou, in other 2.8 iron head threads you state to go up between 9.5 - 10 to 1 , if 10 to 1 is to high then they should read go up to between 9.5 - 9.8 to 1 or something of that nature , I`ve been very greatful for all responces I have gotten from all, including you on this board and am building my engine on that imformation that I read , my heads aren`t shaved yet but the block is now zero decked, if I shave my heads 5 thou that will give me 9.82 to 1 , if their shaved 10 thou that`ll put me at 10.03 to 1 , I want the most I can use without problems , sure I`ll polish the chambers and use a cold set of plugs , but what happens when I want to change the chip out and the chip advances the stock timing table , I think then I`d run into pinging problems without the 93 octane even with my 40 thou Quench, the highest octane I want to use is going to be 91 as this is still my daily driver , after searching last night I`m also swapping out the 3.08 `s and putting in the 3.73`s , will still only bring my RPM up to 2100 at 60 mph but will be alot of fun with the shift kit in town, so what do ya think I should settle on ? The 9.82 or the 10.03 thanks Bill...

[ignoreance]

Just do this invest the next money in some 1.6 roller tips. that will open your cam to more profile increasing both duration and lift. That is an easy topside fix. If you do go to to the 10.03 then the lifters will drop that back down but If i were you and the current cam you have I would run the lower of the two.

[rvbilly]

2.8 high compression

Hi thanks so much, I`m gonna go with the 9.82 as you suggest , it`ll be safer as you say , I could add the roller rockers later, do you know if the roller rockers are the same as the small block Chevy v8, would they interchange, v8 stuff is alot cheaper, I think the biggest gain will be the 3.73 rear axle gears, will also allow me to tow my small boat easier, thanks for your reply , Bill..

[ignoreance]

They may be but I'm not sure they look pretty damn close to a v8 style. They sell the roller tips in the 60degree store 170 look at the banner above then go to the tab with the Gen 2 stuff on it. But I don't know if you have to run a different push rod. Most just bolt em on. Somebody correct me if I'm wrong but the splayed heads use the same rockers as the straight?

[SappySE107]

Yes, they use the same rockers. We use the gold race rockers that were meant for the iron heads. You could use those as well to reduce friction and get the 1.6:1 ratio.

Im not sure how lifters reduce compression though, and im not sure that 10:1 should be a limit for iron heads. We run 12:1 on aluminum head on pump gas but I am not familiar with iron head 60V6s and what they are capable of. I know you have to run more spark advance on iron heads so perhaps backing off the spark timing would allow you to go to 11:1? Also, are you sure .010 off the heads is a .2 increase in compression?

[Blue89rs]

Wouldn't putting 1.6 rockers on a 1.5 rocker cam increase lift, duration, and overlap? And since you would have more overlap, wouldn't that decrease compression?

[rvbilly]

2.8 High compression

Hi Sappy , I`m really worried about Detonation, I wouldn`t want to bump it up to 10.03 to 1 and find out I have that problem after it`s done, this is my daily driver and we are paying $ 5.35 per Canadian Gallon right now for 93 Octane, there is a huge difference between it and 91 or lower Octane, I would like to put a chip in it later on which would advance the timing as well and might put me in that detonation zone if I was way up on the compression, I wan to keep it as high as posable for 91 or less, my machinist told me that .0045 thousandths of shaving will amount to 1 cc of less combustion chamber on the Chevy head, thus my block which is the HO 2.8 with .030 over iron head pistons , + 1.496 crank throw + 1.598 piston pin height + 5.70 rod length = 8.794 deck height - the deck height of the block which is 8.818 inch`s would give me .024 piston deck height , so I had block machined to obtain a 0 deck ( which gives me a 40 thou Quench using stock head gasket ) my head gaskets have a .038 compressed thickness , so it`ll put my Quench at 38 thou , now if I shave the heads 10 thou that should equal 2.25 cc`s less on the combustion chambers , I`ve used your Compression Calculator and that will all work out to 10.03 to 1 compression , I`m trying to get as much as I can out of this engine NA . I`m hoping for 170 to 180 HP , better than the stock 125 HP, with 3.73 `s in the rear axle it should all work really well , I`ve got 3.08 `s in this thing now and at 60 mph the engine can`t hold it in overdrive very well , I `ve only been able to find the Jet or Hypertech chip for this truck ( OBD 1 ) and I know their shit from what I`ve heard , do you think if it`s possable that I set the timing at 14 degree`s before TDC base if it`s possable without pinging it`ll do pretty much the same effect as a chip ? The other thing I`ve found out to be very restricting is the stock 2.8 TB- it only flows 235 cfm , so the 4.3 with my injectors will flow 400 cfm , thankyou all fo your help, If ya think mayby I`m wrong on any of my calculations or theorys let me know, thanks Bill..

[fivepointhustla]

I could have sworn that the GM 60V6 power manual says that they had pistons for the 2.8 that increased the compression to like 13.1 or around that. If so then the iron heads will be fine with 10.1.