Ok I have been hearing from some people about how they are getting some pistons for their 400's custom made from manufacturers such as JE, Ross, etc. I am really attracted to the idea of higher compression on the same fuel, as in the case of properly set up aussie heads. However, "properly set up" entails having the flat surface of the piston being within .050-.060 of the flat surface of the cylinder heads. Slight problem, deck clearance on a 400 is about .047. Add to that a head gasket that is .041 thick and you are nowhere near getting this magical "quench effect." I was about to give up on the idea until I heard that you don't have to run flat-tops, so long as they are "reverse-dome." This means that the dish in the piston is the same shape as the combustion chamber. So this just gives the effect of having a bigger combustion chamber instead of a dished piston. Anyways, my idea now is to get some custom pistons made. After getting my block and heads squared up I would take all neccessary measurements and order me a custom set of pistons. They would have a custom compression height that would bring the piston to practically zero deck. I would then have them put a reverse dome in the piston that would bring my compression down to about 10.5:1. And since the quench effect would be working (hopefully), I'll notice no ping on 91 pump gas. Does anyone forsee problems with this idea? The one thing I am worried about is that I also want to run a hydraulic roller camshaft with about .562 lift on the intake side (.580 on the exhaust side. Now with the pistons at zero deck I am going to need some HUGE freakin flycuts, aren't I? Please put your 2 cents in, especially you, Blu93GT! Any questions, comments, advice, or alternatives are more than welcome!

 

We're starting to overlap topics a bit, but new ideas keep coming. The better candidate for the Aussie 302C heads is a 351M.

It's essentially a bolt on because the piston is much closer to the top of the block than the 400. .017 deck + the .041 gasket will retain some of the quench benefits of the Aussie head, just barely.

Compression will increase from 8:1 to about 9.5:1 and still run on pump gas. The valve train can be re-used with the Aussie heads if you bought a bare set.

8:1 to 9:1 point compression increase will give you 2% more power.
8:1 to 10:1 point compression increase will give you 3.7% more power.

The hardened valve seats are another issue, but I'm not going into details right now.

The deck clearance on a 400 is .057". Way too much for quench heads to have any benefit.

A D-shape piston for the 351C looks like this.

KB148
C.I.D. 351C
CYLINDER V-8
BORE 4.000"
STROKE 3.500"
ROD LENGTH 5.778"
MIN. CLEARANCE .0015"
COMP. HT. 1.670"
PIN DIAMETER .9122"
HEAD TYPE 13cc D-cup
CRANK CL TO DECK 9.206"
WT.PISTON/PIN 597/143g

1)Designated as O.E. replacement for engines manufactured in years 70-74.
http://www.kb-silvolite.com/kb148pic.gif

My custom JE piston looks exactly the same except the dish is deeper and measures 23cc. I bought these second hand so I don't know how much they cost new.

The stock round dish is 3.5" and easily fits inside the D-cup reverse dome. The stock piston dish can be enlarged to the D-cup shape if you want to lower compression.

Have you ever heard information about "static vs dynamic" compression?
How about thermal coatings?

 

I think I agree with the first respondant. I'm running the setup you describe except with 2v cleaveland heads at about 170# static on 91 octane. If I had used the Aussie heads I would have had to set the piston farther down in the bore to keep comp. ratio within reason. I'm probably about 10:1 but couldn't stand anymore. Giving up 50 cubic inches to get better quench wouldn't make sense for me.

So.......the aussie heads seem me to be a conundrum as to how to employ them.

 

[updated:LAST EDITED ON 19-Aug-02 AT 06:00 PM (EST)]beartracks - i'm wondering how far compression can be pushed with open chambers on 91 octane... what altitude are you at? do you know your duration and lobe separation specs, or a part# ?

this will be for a mildly warmed-up 400. cam will not be real wild, maybe crane energiser (272 duration, 216 @ .050, 110 LSA, .524 lift), 1-5/8" headers, and an aftermarket intake with EGR hookups. car is a '77 cougar, with stock converter & 3.0ish gears. just want to pep it up a bit. it won't be used for towing, or racing, so basically just looking for strong mid-range power, and reasonable economy - which is the reason for 91 octane instead of 93...

i was thinking i'd have to shoot for about 9.2 to 9.6 compression - but if you're running 10.0:1, then maybe i could go a little higher than 9.6 - of course the air down here in houston is pretty thick, so that is going to be a factor - but that maybe offset by different cam...

brian - here is some info on how cam timing affects compression:

http://www.jr333.com/pontiac/compression.htm

and a pic of one of the coolest station wagons i've ever seen...

one thing i notice is that a gasket thickness of .042" is mentioned. i recently tore down a 2v 351C motor that was given to me, and measured the gasket thickness. i got a very consistent .035" - i don't know how those gaskets compare to the ones commonly supplied in full gasket sets, it IS something to consider. i noticed that one intake valve was different from the others, so these weren't the original gaskets...

 

Thanks for the "compression" link, but I was asking Jdawg78 if he knew about the subject because he mentioned the cam he's using.

The Feb Car Craft had a very good article explaining how camshafts affect compression. It's hard to explain in few words, so I scanned it and sent it out to people.

I haven't found much info about head gasket thickness. Usually they range from .035-.047. The thickness listed in the Ford Motorsport catalog is .041 so that's what I normally use for the compression calculations.

I didn't get back to the other guy yet about his .040 thick gasket for his 351M. He was thinking .030 when compressed but I don't think it will be less than .035. Just guessing.

 

Pretty much the only gasket thickness I have ever seen for a 351C/351M/400 is .040-.041. Fel-Pro, Mr. Gasket, Ford Racing, they all seem to be that. In fact, the only engines I have ever seen that you can vary the head gasket thickness on (without a custom gasket) are the SB and BB Chevy. Maybe the cause for his .035 351C gasket was excessive torque or reuse of the gasket. All I am really prepared to say is that I am just gonna buy a full gasket set from Fel-Pro, who inarguably uses a .041 gasket for the 351C/351M/400. I believe one of you wanted to know what kind of cam I am using so here are the specs:

Crane PowerMax HR-216/325-2S-12 Retrofit Hydraulic Roller
Adv Dur - 278 int 286 exh
Dur @ .050 - 216 int 224 exh
Gross Lift - .562 int .586 exh
112 deg lobe seperation
8.75-10.0:1 c/r advised

After reading the compression articles, I have found that this camshaft should build considerable compression. I think I am going to run 10:1 c/r with aussies and custom pistons. These custom pistons should make excellent quench within the aussies. Detonation should be virtually nonexistent with the proper timing and should provide excellent power. Thanx for all the help

 

[updated:LAST EDITED ON 19-Aug-02 AT 11:56 PM (EST)]>...bring the piston to practically zero deck. I would
>then have them put a reverse dome in the piston that would
>bring my compression down to about 10.5:1. And since the
>quench effect would be working (hopefully), I'll notice no
>ping on 91 pump gas. Does anyone forsee problems with this
>idea? The one thing I am worried about is that I also want
>to run a hydraulic roller camshaft with about .562 lift on
>the intake side (.580 on the exhaust side. Now with the
>pistons at zero deck I am going to need some HUGE freakin
>flycuts, aren't I?
>

your cam's timing really has a lot more to do with piston/valve clearance than the maximum lift does. when the valves are fully open, the piston is further down in the bore. what you need to look at is when the exhaust closes, when the intake opens, and how aggressive the open/close rates are. with a hydraulic roller it's going to open & close faster than a "flat tappet" cam, so you definately need to be careful.

there are 2 ways to "be careful" that i know of:

one is to put playdoh on the piston tops, put the heads on, assemble the valvetrain, and turn the motor over by hand a couple of times. then pull the heads, slice through the playdoh and peel off a strip by each valve, and then see how thick the part that's left is.

the other way is to assemble the heads & valvetrain, but put some really weak springs on in place of the valvesprings... like SO weak that you can push the valves open with one finger. then you turn the motor by hand and look at an exhaust valve. the valve opens and then starts to close... when it is about halfway closed, push down on the roller tip of the rocker. it will probably go all the way until the spring binds. then turn the crank a little more and do it again. you will get to a point where the valve taps the piston when you push it down. keep going, turning just a little at a time. the piston and the valve will get closer and closer until you can just push the valve down a little bit before it contacts the piston, then the gap will start to open up again. go back and find the exact point where the valve is closest to the piston, then use a feeler gauge to measure between the rocker and the valve tip. you want to have .100 or more for the exhaust. do the same for the intake, except it should have .080 or more clearance. it's a good idea to repeat the test for more than one cylinder - especially if the clearance is pretty close.

with either method, you have to eliminate lifter compression or else you won't get the correct action at the valve, and it will look like you have a lot more clearance than you really have. one way is to let the lifters bleed down, and then adjust the rockers so that everything is "tight" (zero lash) with the lifter compressed. another way is to take the lifters apart, pour out all the oil, and put them back together without the springs in them. then adjust to zero lash. make sure the main part of the lifter has a positive stop on the inside to keep the plunger part from going down too far and crushing the little valve part. another way would be to borrow some solid (non-hydraulic) lifters.

anyway, those are the 2 ways i would do it. there are 2 other ways though. one is called the "money" method - you pay somebody to build you a motor. the other is the "lucky" method - you put it all together and turn it over by hand. it nothing seems wrong, then start it up. if nothing bad happens right away, then you are lucky. if nothing bad happens within a year or two of driving and racing, then you are VERY lucky! the lucky method is notorius for trashing valves, pistons, rods, heads, cranks, and blocks - and pushrods of course. it usually happens on the track, so a bunch of people will be very mad at you for oiling it down...

oh yeah - there's also the "call a friend" method - if you can find someone else with the exact same setup as you who doesn't seem to be having any trouble. i dunno though - this one is pretty close to the lucky method. there are probably a dozen different things that could make just the hair's worth of difference between a good running motor and the ultimate PCV setup!

 

[updated:LAST EDITED ON 20-Aug-02 AT 00:09 AM (EST)]sorry, i'm a slow typer! that looks like a fairly healthy cam.

i'm not a cam guru by ANY means - but just looking, my guess would be that there is some overlap on that one, and the "powermax" series probably has the most aggressive ramps of all the crane hydraulics - so i would definately measure the piston/valve clearance if i were you!

i assume you're also using roller tip/roller fulcrum rockers? are you getting the rocker pedestals machined for 7/16" studs, like the boss 351?

 

Well I was really hoping I could avoid those damn stud mounted rocker arms. I really don't like getting the lash adjusted with them. I found some nice aluminum roller rockers by Ford Motorsport that use the stock "bolt-on" type system. Other than that they are full roller rockers. They include a pedestal shim kit to adjust lifter preload so I thought those would be okay. Otherwise, yes I am going to have to use stud-mounted. If I do go to studs I will probably just use those cool conversion kits by Crane. Take all the hassle and machining out of it. One other question. With double valve springs (req'd for roller cams) I notice you have to use teflon valve stem seals. I heard from someone that they are bad for street engines. What's your take on these things? Thanx for the help. Oh yeah, when I get the motor put together, can I just take it into a maching shop and have them check the clearance or are they going to want to build the motor from scratch to do that? I want this thing to run fine at 6000 rpm (I'll hardly ever be there) so I don't want it to "work until 5000 rpm". My main concern is that I am going to lose effective quench by putting big @$$ flycuts in the pistons, which are going to be expensive forged customs by JE. Oh BTW, can I just tell them when they make my pistons and know what to do? Thanx for all the help

 

[updated:LAST EDITED ON 20-Aug-02 AT 02:01 AM (EST)]if you're getting custom pistons, then just get big valve reliefs in them anyway - that will cut down on how deep they'll have to make the dished part, since the reliefs will be adding a few cc's.

i don't think you have to use teflon seals, you just can't use the big fat stock umbrella type. try the ones that come stock on a 5.0 mustang. you'll probably have to get the tops of the guides cut down for them, but you'd have to get that done for the teflon ones anyway. i've heard the teflon ones don't let enough oil in, unless you have silicon-bronze valve guides (which don't need as much oil).

i've seen the crane setup (or was it comp cams?) and i'm not real impressed. you're still using a little 5/16" bolt to hold it all. you're going to have some stout springs on one side, and a meaty cam on the other, and they'll be flexing that skinney bolt back and forth 100 times a second. the nice thing about a 7/16" stud is that it is STRONG!

last time i looked, those kits were kind of pricey. even though the machine work for screw-in's will cost a little, the studs and guideplates themselves are pretty cheap - you can get them anywhere, made by anybody, so pricing is a lot more competitive than a one-of-a-kind item like the conversion kits. same thing on the rockers - a few companies make the pedestal-mount rockers, but everybody makes stud-mounted ones - you can find stronger ones for less money. the extra cost for regular screw-in's may not be as much as you're thinking when you add it all up.

the adjustability is nice too. you're not exactly talking about a stock valvetrain, so pushrod lengths are going to be tricky. shims will work if the pushrods turn out to be a little long, but they aren't very good for taking slack out!

besides alowing you to tweak your final setup for precise lifter pre-load, the adjustables are also good for checking piston/valve clearance. from what i've heard, the poly-locks do not slip - so if you're runing hydraulic, you can pretty much just set 'em & forget 'em.

i used the crane pedestal-mount roller rockers (same as ford racing) in my mustang. the heads had never been off the motor, it had the original lifters, original everything except intake and cam - and the cam was from ford too and had no problems with the stock rockers. but i wanted to spice it up with 1.72:1 instead of the stock 1.6:1 ratio, and i wanted rollers. so i put them on, and about 1/3 are within the specified preload range. most of the others had less preload than they were supposed to, but at least they had SOME - there were a couple that barely got to zero lash when i torqued them down, and a couple that even still had a little slack in them after torqueing down. these things were MADE for exactly what i had! i guess there was enough variation in the head and/or block castings or in the machining so that it didn't all fit quite right - who knows... all i know is that from now on, any non-stock rockers i bolt on will be adjustable, even if they're pedestal-mount with the adjustment on the pushrod end. and if i have the heads off and there's a "viagra" cam going in, then i'll get the heads set up for 7/16" studs before they go back on!

 

Thanx for the input on that. I am going to go with the 7/16" studs. I have a feeling that you just saved me a pricey rebuild a possibly even an engine. The only thing I was worried about with the pedestal ones is the fact that you can't adjust them. I just hate getting all oily when you adjust them with the v/c's off. Is there some other way to do it? Thanx for all the EXCELLENT help.

 

Hey Blu, I just got on the Crane website. Good news. Their rocker arm pedestal conversion kit uses a 7/16" stud! They even come with inserts that allow you to use non-heat treated pushrods with the system. But wait, it get's better. They even make custom pushrods made to the correct length for use with their conversion kit and their retrofit hydraulic roller camshafts. Pretty slick for a custom set-up, if you ask me. The only thing I don't like about the system is that those inserts I talked about earlier are not an integral part of the guideplate. That is, they are like pushed into position on the guideplate. It just worries me because I am afraid that won't be sturdy enough to hold up to high RPM's, for which guideplates are implemented. And when I say high, I don't mean incredibly high. My springs and valves and all that are capable of 8000 rpm but my cam redlines at around 6000. All in all, I think it will hold up to 6 grand but I don't want to be over confident and drop a valve on my new custom pistons. Tell me what you think.

 

with hydraulic, you can adjust them with the engine off - cold even (no burnt fingers!) in my opinon, it's the best of both worlds.

as far as getting a shop to build it - i don't think regular (aka affordable) stock engine rebuilders want to mess with custom performance stuff. they make their money by volume, so they don't want to spend the extra time. and they probably don't have anybody that would know how. they just bolt 'em together & ship 'em out...

the performance shops aren't much better - there is no warranty on performance stuff! true, they will have one or two guys there who know what they're doing, but most of the actual work is done by young guys without much experience. also, those places make their money by selling high-dollar parts. you don't get a $200 set of roller rockers, you get a $450 set of roller rockers... basically, they'll say that to make 600HP, you need a $1500 SVO block, $1500 aluminum heads with $500 of extra porting, the aforementioned rockers, a $750 steel crank, $450 rods, $600 pistons, and so on. labor cost is added on to all of that!

they're looking for "blank check" type people...
estimated cost: $4500 - $5000
actual cost: $9675

and they'd laugh you out of the shop if you said "performance" and "400" in the same sentence!

 

Yeah it is too bad that nobody thinks of the 400 as a performance engine. Sure, it won't rev as fast as a small block (or any other engine for that matter) but it'll torque the frame right off the axles. It's sad that everyone immediately thinks performance when you mention 351 Cleveland, but nobody puts it together that a 400 is a BIGGER cleveland. It works for you though because no one thinks you can beat them until they are looking at your taillights. Regardless of what people say, I'm putting a 4-bolt 351C with ARAO 32-valve heads and a blower in a 1967 mustang. I am thinking like 600 hp. But let them say what they will. No one has to convince me that there is massive power in a 400. I know that all you have to do is unlock it. And as for convincing other people. I'll put some cheesy sticker in my rear window so they have something to do while they are getting smoked by my "low-performance" 400. That's all the convincing I'll ever do.