Milling the head = to pistons

AngleT

AngleT

Always more tuning to do
I'm thinking of milling my head to remove the combustion chamber "dish". I currently have 9.2:1 pistons installed and the block has been decked about .018-.020...

What compression ratio would you think I would be at if I shaved the head that much in combonation with to other mods? 10.5:1, 11:1, higher?
 
Assuming you have about 9.5:1 currently, milling the relief should put you around 10.5-11.0. These are real rough estimates cause we don't know if the head's been skimmed, if the pistons are true 9.2:1, gasket thickness you'd use, were the piston crowns at deck height, etc. Piston/valve clearance becomes more of an issue at that point.
 
What I'm debating...

is that I have a set of 12.5:1 pistons and total seal rings that I didn't use when the engine was being built. My father (RIP) didn't think the head would fit over the 12.5:1 pistons, so we didn't use them (I was in Iraq and he was building it for me). I know the head has been skimmed (probably .010)

That being said, if I put the 12.5:1 pistons in, if the fit, would I need to run race fuel? Or, should I just sell them and just shave the head down and up the compression that way?

If I sell the pistons and total seal rings, which sell for $780 at Vicks, I could get the head work done with a better cam and have a little money left over for some other "wants". It already has a PBS Big valve head with S-2 cam, racing cam springs, racing valves and an adjustable cam pulley.

I'm just not satisfied with the performance, and want the need to "hold on!" to be non-negotiable! LOL I don't need to lead the pack, just be fast enough to at least run with them.
 
Hold on the compression.

I tried running 11.5:1 years back but the detonation caused me to loose all of the top rings. With the way gas is now, I wouldn't push it past 10:1, cool days will be a fun ride, but the hot days will bring on alot of Ping when climbing a mountain. Be prepared to use an octain booster on those days.

TonyK.

Grimsby Ontario Canada.
 
I was able to run 11.1:1 on 91, mostly from Shell or Sunoco, but I did use it this way for years. Mind you it was on an injected car with programable fuel so that's likely the main contributor. But considering "those in the know" acknowledge injection is worth half a point, 10.5 may be around your upper limit depending on what gas you have in your area. This was also during the summer months with slaloms mixed in.
 
What kind of dyno numbers were you getting?

and what cam were you running? I've just been feeling a little disappointed with the performance considering the amount of $$$ I've put into the engine. I know that getting rid of the stereo equipment and loosing the bumpers would make a big difference, but that wouldn't affect the numbers I'm getting on the dyno. (95hp 85trqe)
 
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95 at the wheels?

Hi Tom,

If you're seeing 95 at the wheels with a street motor and normal induction, in my opinion, you're doing pretty good. That's about 110 at the crank, give or take.

In most cases, anyone who says they have a 125HP or higher normally aspirated street X is misguided, lying, or both.

-M
 
Should I...

To remain streetable (ie pump gas), should I just tune what I have or could I shave a little more off the head to up the compression a little more and gain a couple more HPs? Currently running a PBS S-2 regrind. Should I be looking at more cam? All my engine stats are listed on my profile.

PS Keep in mind my 4.54:1 final drive is a wash with my 225/50-15 wheels. With stock size tires on it, it's pretty zippy, but wound kinda tight for a trip down the interstate.

This dyno run was to get a baseline. None of the carb jets have been changed or cam timing have been played with yet.

X19Dynorun28July09.jpg
 
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Looks to me like you are doing pretty well, Tom...

The broad, flat torque curve is an excellent indicator of good streetability. It shows a well tuned and matched system. I bet it justs kicks you in the butt when you toe in to the throttle on a twisty road.

Going upward in horsepower normally aspirated at this point is going to entail some significant losses in driveability and convenience, as well as higher costs due to octane requirements.

If what you want to see is higher dyno numbers, why not fit NOS or a turbo? Either of those approaches will give significant dyno numbers at moderate further costs on the project.

Otherwise, my opinion is that you have a pretty sweet car as it stands. You are never going to be able to out drag a lot of cars out there. Just get them on a twisty road and show them your taillights!

Ciao,
 
A couple of thoughts Tom. Dynos don't all read the same so we can't compare. My 1500 made 113 whp, 101 lbs with what I had in it. It had the usual, big valve, compression, porting, seats, dual throttle bodies, programable fuel etc, etc, but I did have a 35/75 cam. I was looking at pbs, and the S2 does look a little tame. Good for drivability, but with my torque curve, I had an initial peak at 4k and a larger one at 5k. Not ideal for slalom, maybe, but it did pull. Maybe try a B3 cam if you can get one, you'll loose a bit below 3k, but it will pick up above 5k. YMMV:drink:
 
That's more like it

Those are the numbers I was looking at hitting. This car isn't a daily driver and may see some "auto X" this summer, so drivability isn't a MAJOR issue. I know a dyno only measures torque and calculates HP based on a standard figure. I also realize that all the reduced mass improvements, ie aluminum flywheel, lightweight rims, pulleys, etc. are not going to show up on a dyno but do make a difference on the street/track. I don't know if PBS is doing the cam grindings anymore but maybe I could get delta to grind a B3 up for me. The other cam I was looking at was the "SOHC 42-82 High-perfromance cam" at Vick's.

If a guy in a 78 Camaro told you that his 350cid V8 was pulling 430hp on the dyno, it sounds impressive. Funny thing is, a 92cid inline 4 in a Fiat pulling 113HP is the same hp/cid ratio. 1.23 HP for every cubic inch of displacement. That's the kind of numbers I want to pull.:excited:
 
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Just called PBS

They are still regrinding cams! It'll take them a few weeks, but very resonable price.
 
What is involved...

When replacing a cam what exactly is involved? Does the entire cam box have to be removed or just the end plate and then once new cam is installed is it a matter or adjusting the valve clearance accordingly to the chosed cam and that's it? In a carbureted X would the carbs need to be setup again due to the different cam specs?

'PeteX1/9
 
You have to remove the cam box

petex19 said:
When replacing a cam what exactly is involved? Does the entire cam box have to be removed or just the end plate and then once new cam is installed is it a matter or adjusting the valve clearance accordingly to the chosed cam and that's it? In a carbureted X would the carbs need to be setup again due to the different cam specs?

'PeteX1/9
Click to expand...

You can't just slide the cam out the end, in the first place I'm not sure there would be room in the engine compartment, and in the second place, it's not going to slide out when the valve springs are pressing against some of the lobes. You have to take off the timing belt and remove the cam box. It's a good idea to change your timing belt at this time.

As far as the carbs go, any change in the breathing characteristics of the engine (displacement, intake, cam or exhaust) is likely to require carb re-jetting or other adjustments to keep the mixture optimal throughout the rev range.

Edit: forgot to address any other changes:
If the new cam has the same "base circle diameter", it will likely be close enough that all you have to do is measure the clearances and re-shim where necessary. However, a lot of performance cams are "reduced base circle" cams, which will make valve adjustment outside the range you can handle with the stock adjusting shims. This is handled either by the use of "lash caps", which are hard spacers that ride on the end of the valve to add some space, or by milling the cam box to make the cam sit closer to the valve ends. When you buy a cam, it's important to find out if it's stock base circle or reduced base circle, and compare that with what you have, so you will have everything you need when it comes time to install it. If you install a reduced base circle cam where a stocker was and don't change anything else, performance will be in the toilet (you have effectively reduced your valve duration and lift), plus your valvetrain will eat itself with parts slapping against each other that are designed to ride smoothly on one another.

Pete
 
AngleT, I have almost the exact motor you will have if you mill the head, and get more aggresive with the cam. My block has been decked .015" and the head milled flat, approx. .070" from stock. I have the small valve relief (9.2:1) pistons * 87mm bore and a PBS BV head. If you do this, check valve to piston clearance very carfully as it will be close. I also have a PBS B-3 cam and adj. camwheel. Given your at 95 RWHP now, I have no doubt that if you mill your head flat and install a similar cam, you will be at or above 105 RWHP. But the extra compresion will yield a significant gain in tourque, which is what you'll feel when driving.
Will you have to re-jet carbs?.......to see max. potential, yes.
Will you be able to run pump gas?.......with carbs, not likley. I have not calculated my comp. ratio but it is for sure 10.5:1 at least and will detonate under load on 93 octane. I mix 110 octane racing fuel 50/50 with 93 octane premium and it works GREAT. Its's pretty easy, drive till I need gas, dump in 5 gal. of racing fuel, drive to the corner Chevron and top off with premium. I can get 250+ miles on a tank hot footin' around town. I have also run 100 octane low lead av-gas, works equally as well. If you use the deep valve relief pistons, you will be right on the edge of pump gas. Multiple members here have milled heads flat on stock 1500 FI motors and had good results with premium gas, with no block decking.
The most important factor here is piston to head clearance, you want to run that down to .035"-.040". Which will require decking the block also and letting the pistons protrude out the top of the block. This tight squish area around the combustion chamber is what generates tubulence and an efficient burn of the intake charge. If I recall corectly, there is some .090" to .120" of material to remove from the head/block surfaces to get the piston/head clearance right....when you factor in the .050"-.065" head gasket thickness.
A better/easier solution might be the pistons Matt at Midwest/Bayless offers which have a raised compression height to optimise piston/head clearance and yield 11:1 with no milling/decking/cam timing changes.
http://www.midwest-bayless.com/stor...l.aspx?sid=1&sfid=208227&c=193056&i=250926645
I am concidering a bigger cam for my motor as the B-3 is quite streetble with my setup.
 
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