[GoneNova/406]

i am having some machine work done soon on 406 parts and was just wondering how much milling or angle milling the heads should have?.say i have 9.4 now.i am looking to increase to what ever 87 octane will handle.i have been seing people here saying they have 383's and the like using 87.i had a 10.5 406 but never tried 87 and could kick myself now but that was before the price increase too.i can also go with about .010-.015 block decking if it were needed but i am thinking that would be overboard.i am looking for your help and points of view on this and any help as always will be appreciated.thanks
its for a 406 and the heads have never been touched accept for porting. iron bowtie heads with 2.05/160.

[nitro_baller4692]

You should check to make sure that end to end both heads and blocks are square and parrelel.i've seen brand new crate motors from gm performance parts with as much as .012'' from end to end and side to side on there blocks.the best thing to do if in the budget is to have it decked and squared by a good machine shop.don't ever let someone resurface a block or heads on a belt type resurfacer,it won't be flat and the finish maybe wrong for the head gasket sealing.yes it makes a differance.
also on the heads you might want to have them cc the chambers,once again this is the best way not the most affordable but you will end up with the best results and compression ratio will be a known factor if the machining would give you to much compression you just run a thicker head gasket to get the desired results.any good engine machinist will know how to do this work but it comes with a price.the saying go's,HOW FAST DO YOU WANT TO GO AND HOW LONG DO YOU WANT TO GO THAT FAST?OH YEAH HOW MONEY DO YOU HAVE?that will be how they deturmin what you will get for your money

[machine shop tom]

Personally I wouldn't run 87 in anything over 8.5 to one unless it was fuel-injected with a good knock-sensing system.

tom

[GoneNova/406]

well thanks for replying i welcome most any attempt cause you just never know what someone might come up with.i just don't have all the math square in my head right now but do not want to use thick head gaskets.zero decking or close to it will help with detonation and i have the motor out and have the opportunity to try.thanks for your help.

[Rick WI]

Gene, there is a lot to this story but I'll make it very short and to the point. May relate may not. I can go into all the details later if you want.

We did a build late last year, 406, L98 aluminum heads, RPM manifold, Edelbrock carb 10.5 compression. When we build a motor, as I am sure folks like Tom and others do, we blueprint everything. We know if a motor like this was tested for compression it would test 10.5, in otherwords there are no assumptions.

That motor would NOT run on pump 87, no way no hell not a chance in gods green earth would it run on 87. It barely ran on 93 without detonating itself to death. no amount of timing, carb tuning nothing would help. Bottom line, customer pissed.

TODAY I just took the vehicle out for a tuning session with the customer. What I/we did was convert to a TPI with large Edelbrock runner and a FAST XFI EFI controller. On PUMP 93 the truck runs fantastic. BUT, the fueling map and timing map are not like anything you'd be able to do with a carb or distributor, not a chance in hell. It was a fine line between running 40 degrees of advane at cruise with 14.7 and then 500 RPM later with harder throttle needing to dial back timing to 23 with an air fuel of 13.5 scaling down to 12.6 under wide open throttle. You'd be hard pressed to do that with jetting and air bleeds and springs and weights. I had it all done and doing burnouts in an hour. Even with The EFI I still had to keep "total timing" at wide open throttle at about 27 degrees. On the dyno with race gas, the engine liked 30-31.

As to your specific question I'd take as little off as possible to square up the heads front to back and side to side. Measure the CC of the chamber and verify deck height of the piston and see EXACTLY where you are. When you blueprint these heads what you will find out, unless it's a Brodix, All Pro, AFR or something of that quality, the chambers will all be different CC's. Most likely there will be a variance. Now your going to have valve work to equalize the cc's.

I'd not consider going any higher than an actual 9:1 trying to run 87. Tom is right where I'd be if someone said they have to run 87.

I know, first hand, no questions asked, a carbed L98 aluminum head 406 at a real 10.5 compression will not work on 93 unless you are silly enough to want to run 15 degrees of total advance. It's not going to happen.

[k-star]

Man Rick after a week of fighting everyone on all the sites i visit it's nice to read a reply like that....

Everyone that reads this please go back and read Ricks post again... There are some excellent points made..

Real compression. Not some body that guessed that there engine was a 10.5:1 and they ran 87 octane, when the engine was in fact a 9.0:1 because it was not checked....

If you get anything over 8.5:1 static on a iron head engine and 87 octane you better be able to tune it....Chances are if you have to ask your probably going to have problems with it...

Keith

[1bad18]

First post and all, so howdy....

guess you could say i do a bit of this kind of thing as a second job / hobby to keep myself sane.... mostly sbc / sbf marine stuff...

a few more things to keep in mind... about compression... camshaft choice, combustion chamber design, piston choice, quench distance, cylinder head material and engine operating temperature and intended usage all play a very large role in just exactly what an engine will tolerate as far as fuel...

todays gasoline blends... just seem to deteriorate in quality every year... unfortunately...

Jamie

[Rick WI]

You know what it's like Kieth. If you start with raw castings and true EVERYTHING up so compression is as correct as it can be across all 8 cylinders, THAT's A LOT OF WORK,and makes a huge difference compared to what you thought you had start with. Even when you go through all the effort to square things up on the block and give all the data to someone like JE or Diamond to set the pin height you mock it up and can still end up .005 below the deck when you wanted to be at zero. Cause.........who the hell knows, it just happens from time to time.

Your right Jamie, all those things affect how an engine will tolerate octane levels. On our particular application "I think" if we would have run a head like an AFR or E-Tec, if we could have worked on the cooling system so it ran lower than 195, and didn't have that front mounted air filter on the TPI setup right in the air stream of the radiator we might have been able to get a tad more agressive with the tuneup. It still though would not have run on 87 pump, not a chance in heck.

It makes absolutely NO sense to push the edge of compression only to have to detune it to run. In the end you loose overall power and economy. It takes an excellent head, great heat management, lot's of tuning to get a higher compression motor to work welll on the street. Even the concept of running a big camshaft with high compression to "lower your dynamic" is a misnomer. Think of it this way, what exacty is so DYNAMIC about dynamic compression calculators. Not one friggin thing is dynamic. A MUCH better term would be net compression, since it's compression based on intake valve closing.

What is dynamic is as a larger duration camshaft comes into the powerband the volumetric efficiency of the engine increases, it it's a correct cam for an engine. This increases cylinder pressure which increases the chance of detonation. So, unless the combination is set up correctly instead of having detonation at 2500 RPM you moved it up to 4000, which means it will hole a piston almost twice as fast.

So, in my world I take the dynamic compression and will it work on pump gas with a grain of salt. As Jamie said, there are lot's and lot's and lot's of factors that will give me a feel for what will work and what won't.

Sorry Gene, we kind of kidnapped your post here. Basically when you take the heads to the machine shop they will square them in the milling machine and I'd simply have them flatten them to the RA spec you'll need for your chosen gasket. I'd suspect your going to trim .010 to .020 off the head.

[k-star]

Welcome Jamie,

IMO the 2 biggest things that go along with your points are quench and keeping any and all oil out of the chambers. This with a proper chamber design will get you some results, but like Rick, i am not sure there is any awards to be won just to get a bigger compression engine to run on 87 octane... For what 15 hp????maybe??? after you factor all the differences...

Keith

[machine shop tom]

We can thank the Hot-Rod style magazines for hyping up the high-horsepower on "pump gas" engines. So many time we see these builds but they don't always tell the whole story or the wannabe engine builder doesn't read between the lines or do his homework.

To start with, 87 octane gas is sub-regular. In the "old" days, regular was 89 octane and you couldn't run a built engine on THAT, much less 87.

Next, most guys aren't top-notch engine tuners like k-star and others. Even with the 93 octane available today, there isn't much room for error in timing or jetting, even with mild motors.

Then, how long do these magazine builds really last? So they make the "power tour". Big deal. Most guys' engines have to be reliable for a few years. Running on the ragged edge of detonation is not conducive to a long-lasting, reliable engine. I would bet that a lot of the "pump gas" magazine engines are in rough shape after a good summer's hard driving.

As was stated by wiser people than me before in this thread, trying to build a performanc engine to run on 87 octane is really an excersize in futility. You can have a performance engine or you can have an engine that runs on 87. Getting one to do both is a hard trick to accomplish.

tom

(I feel better now)

[GoneNova/406]

maybe it was something i said!it is a nearly new 406 with 9.4 speed-pro hyper.'s with a 12.5cc dish with .025 deck clearance and the heads are nearly new iron bowtie's never touched with a machine except to change the 2.02-2.05 intake.1 3/4" x 3" exh..professional products hurricane andcustom 3310 holley and msd.it has 1.6 rockers and right now a magnum 280 comp. cams.there should be some of you who could venture a ball park guess how much compression would change if i decked the block all or half.and again the heads are nearly new so what type of decking should be done here, angle or straight and how much?now between the two of them or only one of them,how much could one expect to get from it.i am guessing that i'll be looking for 2-3 full points so what would all or some of this do for me.i am not going to run right out and do it.ball park.thanks guys