Inliners International Forums General Discussion Blown and Injected GMC with boost...vs headgasket...

good day gents, I haven't posted here in quite awhile so figured I would throw question out there. For some reference I'm building a blown 270 GMC street motor for my '53 chevy truck. It was a built motor when i got it, sans blower, so i'm finally getting around to finding out what is in the inside. It was supposedly a 'race' motor( I know how many times have we heard that) from back in the day with a Fisher head and lots of other goodies. the head unfortunately did not come with it, with it does ahve some old , read heavy, Jahns forged pistons, Isky solid cam and other small things. The head is a run of the mill small port GMC with some very minor port cleanup and double springs with damper, stock valve sizes. I haven't pulled teh cam yet but seems to have appx mid .22x lift at the cam, so nothing too hairy.
SO, my first question mainly dealing with head gaskets...I know there are some on this board and other( I frequent the landracing.com forum as i'm a racer out there, not with a GMC) that have some very good knowledge of the GMC so was wondering when I should worry about blowing head gaskets due to boost...what exact type is recommended. Right now it has a FElpro 7391 installed. The problem(well not for me with a supercharger) is the flat top pistons where used with the special head which had to have those form what I have been told...but with a conventional 819 head which cc'd at 94.8cc you end up which a CR of about 7.24....and the previous owner said he had blown head gaskets recentyl in the front engine dragster....somethign doesn't compute there...or he just overheated it...this is not going to be a race motor(I've said that before) but just a very strong motor going in from of a WC T5 and 3.73 rear gear in my truck. Torque is of utmost importance, which the blower should provide. I know the head is a weak point but the blower can fool the head into thinking the intake is more efficient than it is and some bigger valves in teh exh and as much porting as allowed should make an OK driver.Would really like some roller rockers...hint hint Supercharger of choice is an Eaton m112 off a Jag. I have set up in my head a 5000 rpm max for the motor and 10psi max boost. this gives a pressure ratio of 1.68 and spinning the 112 to 10000rpm it is not near its max and should live a long time., but still in a fairly efficient area(85%, maxes at 90%). No intercooler, might impart some methanal injection at boost.

ANy comments questions or suggestions welcome.

Hans

Has the head or block ever been milled? Might not be straight.
Even if straight, something as small as not counter-sinking the bolt holes to prevent thread pull-up (or shortening the bolts) will blow the gasket.
Was the water circulation path tampered with? Block filled?
What's the actual bore size?
Not that familiar with the Fisher, but the pictures I have show an open chamber, vertical valves, with no quench - a flat piston would have knocking and turbulence problems.
That's really small for a cam, how identified as Isky?
Nothing available in a rocker.
What carb for the Eaton, mounted how?

bore is .020 over(3.801), no water modifications that i know of, he was running a electric pump to some sort of wasted setup, no mech water pump, just flowing cold water through from a tank to a reservior catch. I agree and will look at teh deck. I think i might get it surfaced and threads countersunk to be sure while its on the bench. he did have the rear head port hooked up to the thermostat housing which should be good for helping the rear cyls stay cooler.
I meant .295 lift on the cam...my mistake. The only reason I have to believe it is an Isky is teh previous onwer swore by it, I will pull the cover maybe tomorrow and see if i can see some markings then degree teh cam to get some accurate numbers. I know it's oldschool, but thinking of a 650 holley draw through for now, maybe Megasquirt later. It has a McGurk 5 carb intake on it now, so its either make a bolt on plate/plenum to mount the blower to that or for teh same amount of work just make a new intake. there would be an adapter fabbed to mount the carb to the blower as it is rear inlet.

your cr of 7.24 is not much at all for an engine. but put 10-15 pound of boost in there and your going to probibly have gasket problems. on my 270 i ran a small port 270 head that cced out at 104 with gasket.i ran about 8 pounds and i did lose 1 head gasket. i'm now runing a 302 head with valve work and i'm not sure about ccs on it. but i upped the blower speed to 15 pounds. one thing about the gaskets is i think you need to retork the head maybe 2 times. my cam is fairly mild at.442lift,270 duration and 112 lobe sep.if your cam is an isky mine has isky and the grind no. on the back end of the cam. my ride is a 53 2dr. with a 471 and a 700r4 with a 9in and 370 gears and 25 in tires. its just a cruzer but it has really shocked several large v-8s for a big old 6 banger it really gets it on!

Hans, O-ringing the block will be a big help if you plan to run high boost like that. Also, copper head gaskets will be of a huge benefit when doing this.

The 819 is a closed "D" chamber which can definitely stand some improvement, especially more relief radius around both valves at the bore edge.
The quench distance is going to be important here, how far below deck is the dome @ TDC now?
I've seen some (other) manifolds where the original aftermarket manifold's multiple carb inlets were used as entries for a blower discharge. I think the idea was to balance the flow volume between the front and rear cylinder groups - but I'm not sure it worked. You'll still need a big transition piece between the Eaton and the manifold.
Remember the Eaton isn't position-sensitive, and can be mounted on end (rotors top and bottom) so the discharge is pointing sideways and can use a big 90° "L" into a conventional manifold (instead of having to be above).
Does the M112 turn the right way (I'm wrestling with reversing the rotors on my M45)?

Alrighty then, tried to make some progress on crutches...got teh cam pulled....not suprisingly it's not an Isky...but it is a Howard. On the front is the stamped Howard(pretty sure anyway) and F6..and the back is stamped Z77...i checked the piston to deck and without having a degree wheel on there and good estimate is about .010 under the deck. These pistons have no dome at all, perfectly flat at the outer edges then machined inward in a slight dish. I'll try to get a couple pics up later tonight.

-.010" is very good, but it limits your gasket choice somewhat since you want no closer than .035" no greater than .050" (IMHO).
Your quench area is limited to the flat surfaces (unless you weld the chamber in), which isn't as much as I would like. With some luck, the dish will be entirely under the chamber.

The engine was run with the Fisher head and this cam, yes?
I have a strong suspicion that the cam won't work with any GMC factory head. My Fisher ad says "billet Howard cam", and this was because the lobes are placed to line up with the new valve positions, either:
In-Ex-Ex-In-In-Ex-Ex-In-In-Ex-Ex-In, or
In-Ex-In-Ex-In-Ex-Ex-In-Ex-In-Ex-In
which is not in the same sequence as GMC (and 235):
Ex-In-In-Ex-Ex-In-In-Ex-Ex-In-In-Ex
Perhaps Howard can confirm the ID stamp as to which head?

I am skeptic now that it had the Fisher head, maybe another 12 port, but this cam has been run with the stock 819 that is on it now. It is a billet cam and I have seen reference(in the last hours since finding the F6) several times, mainly in the California BIll book, about using the F6 with the Fisher head on more than one occasion...of course teh F6 is more than likely a somewhat genereic grind they used on all manufacturers. I have seen articles with a Howard F6 in a flathead Ford and 50s Olds V8 as well. I haven't found any specs on the cam, but all motors referenced with this cam where more of the full race variety .

I looked up teh Howard website and they have no Emial to make an 'easy ' inquiry. I might try to call after teh kids are in bed.

It's kinda fun tearing an old hotrod motor apart that you have never seen the inside of before...it's abit scary as well, this is the first time i have ever bought a used complete motor that has supposedly been hopped up in the good old days....at least i didn't tear it down and find a bunch of stock wore out crap...bore looks in excellent shape, one minor vertical scratch in cyl 1, but i can live with it for a street motor. the motor is still on the running stand, I might try to get it up onto a motor stand so i can flip it over and better inspect the bottom end. I'm curious about the pistons. If they are Jahns, they shoulve have thier name on the inside of the skirt. Oil pump looks new, but still has the swinging pickup, I didn't realize these had those....I assume you can get ARP bolts for teh stock rods or modify some others???

Hans

Another question...I know the SBC balancer will bolt on. I have a fluidamper off another motor that never got built that i will rob, but are the keyways and timing marks in teh same spot as well or do you need to turn the outside and re-degree?

And yes, Panic...I paniced a bit myself when you asked the question on the blower rotation...I though i had checked that 2 years ago when I first started piecing this together....but luckily it still is the correct rotation...;) I was thinking about that this morning, although it gives more rotating parts and more noise for sure...you could machien a little raotation reverser using a pair of quick change gears, which could you could use to help any offset on your belts if you need it and while your at you might as well design it to be able to swap the gears easily without taking the belt off....I wonder what those suckers sound like at speed...of coure you can slow them down with you belt pulley choice.....blower whine and QC gear whine under your hood, could turn some heads...;)

The Howards Camshaft company is no longer owned by the Johansen family the started it originally, so you might or might not find the answers you need by calling them. It was purchased by Competition Products and is now in Wisconsin.

Ahh yes, you think Donny? Johnasen still has the figures since he's still grinding cams? I know there where a few getting him to grind cams for them...any contact info?

Try Patrick Dykes for contact with Donnie Johansen.

http://www.patricksantiquecars.com/chevrolet.htm

God's Peace to you.

d
Inliner #1450

thank you kind sir, I just emailed Patrick.

Hans

couldn't open pictures let us know how the fluid damper fits i have a fisher on mine but been thinking about building a 302 and want to keep the 270 in one piece[img=http://img88.imageshack.us/img88/461/ebay1487.th.jpg]

A floating pick-up was used on some engines.

I took a quick measure with caliper on the cam comparing base circle(90DEG TO LOBE) and lobe itself and subtracting..I know very crude and doesn't work well on cams with tons of duration, but came up with a lift at cam of exactly .320 .

Donnie has also sold the equipment portion of the Howard Cam company also, no affiliation with Competition Products, so he is unavailable most of the time. You can reach him thru Chet Herbert in California, but you may have to call and leave many messages before he responds back. I have his cell phone #, but same deal, out of 200 calls to him he might answer once. But i'd say he knows those specs of top of his head.

I have not seen an original GMC oil pump installation, but the GMC oil pump in my 261 has a swinging oil pickup. It was bought from Bob Toros in 1960. In 1954 Harry Warner was selling GMC oil pumps with either a fixed or floating pickup.

yes sir mr hoyt, i've disasembled 5 or 6 270s and 302s two had floating pickup tubes

This is very interesting. Any ideas what the purpose was? certainly not extreme acceleration!
Coping with odd angles as found in 4 X 4 military stuff?

Not sure, but I will be ridding of it, in my opinion it's just another way to aerate my oil.

If anyone has one still in place, I'd certainly examine the swivel mechanism very carefully - this is a major cause of engine failures in race cars.
A worn seal or O-ring causes a big air bubble to enter the line, but only at severe pick-up angles (which is why the gauge looked OK). Result: big OP drop, and bearing failure.

I'll chime in here.

ALL my GMC's using the stock oil pumps had swinging pickups; I've had 20. I never, repeat never had an oil problem with this setup. If you are going to use the stock pan I suggest hinged flappers over the drain back holes in the braces as all the oil wants to go to the timing cover on deceleration and I guarentee you will loose pressure especially at Bonneville without them. I would also suggest a welded angle scraper on the side of the pan if you are not going to make one which will attach between the engine rail and pan. There is a 12 quart pan and a 7 quart pan; the bottom of the pump are the ony difference. This does not include the military 4X4 pan.

The 270 has a lot more "meat" between the bores so it is a possibility you may not have gasket problems. Check with "Best Gaskets" for your 270 it may be the answer. I have tried everything to hold back high compression on my .060" over 302's with only one thing working. Remember high compression is like a blower both putting strains on head sealing. The best for me was a .040" o-ring in the head and a.040" o-ring in the block pushing against a stock gasket. I promise you I tried every other comination of gaskets and o-ring/reciever groves without success. O-ringing a head is time consuming and needs a custom fixture unless your machinist is really good using a head gasket.

The only time a copper gasket worked for me was with the Skinner 12/port and it had a .050" o-ring and a reciever groove and .060" copper gasket. The only reason it work was we added 2 more head "allen cap screws" in the water jacket between our problem cylinders.

Doug Robinson went to 9/16" head studs to hold on his blown stock heads. Oh yeah head studs are a must. APR will package them up for you. They MAY now list them for a GMC 302; when I first asked for them they didn't. Remember the hardened washers and nuts.

Stock rods will be plenty good but make sure you have enough side clearance to let out the oil and change the nuts (ARP again). My stock pumps, when I ran them right at 50 psi with a little bypass work. Remember to oil your distributor gear.

If the head you are going to use has two 1/2" water plugs near the back, the front one is for your water temp guage and rear one is to be plumbed back up to the left side of the thermostat neck. This is a must for hi-comp and blown GMC's that back cylinder head and block gets mighty hot and that flow back hose is stock on military 302's to control this.

Roller rockers are hard to come by (I made my own) and if you go over .500" lift at the valve you can have the stock rocker continually pushing the valve back and forth causing valve guide wear if you don't have the geometry just right. Working with the rocker stands and lash caps can help with this. Smith Brotheres and Manton can make push rods; I have used both.

I hope this helps. Just stuff I've learn with GMC over the last 50 years......Good Luck JD

here they are up and down[img=http://img52.imageshack.us/im[url=http://img687.imageshack.us/my.php?image=ebay1499g.jpg][img=http://img687.imageshack.us/img687/3803/ebay1499g.jpg]g52/2044/ebay1500.jpg][/url]

up[img=http://img687.imageshack.us/img687/3803/ebay1499g.jpg]

Sorry for the error - I don't have a GMC, never saw a reference to the pick-up, even the pump pictures don't show one, but the literature does refer to a "floating inlet screen".
However, the picture is confusing.
It looks like the pickup is designed to pivot inside the cover plate, but what's that cotter pin doing? if it secures something, the part it's holding is the outer sleeve for the pick-up tube, but what seals them?
The only way that's going to be air-tight without a seal is if the pump cover itself is always submerged.
The original purpose may have been as simple as allowing the pick-up head to track small changes in oil level due to long service interval or minor leak.
This explains why hard braking will break the siphon - the pick-up head can't move to follow the oil volume since it's travel is pretty limited, and even if it did once the tube entry into the pump cover is exposed you have an air leak.

panic your right! it looks like and air leak look'n for a place to happ'n. the swivel part is just a lose (as in real lose) fit in the tube on the cover plate the cotter pin is what holds it together. i never could see any benifit to this (must be a militry thing)

Assuming you don't want to modify the pump itself, and the baffles are not doing everything you want (pick-up still gets air on hard deceleration), you can just squash an O-ring in between the tube and the fitting on the cover, then attach a strap from a pump cover bolt to the head to prevent it from swinging and eating the O-ring. Just large enough to stop free movement is probably enough, doesn't have to be a press fit. If I had to, I'd use a piece cut from a bicycle tube!
I would guess that the cotter pin operates in a slot long enough to permit the tube to swivel, but not come out? If you can close up the slot (weld) you control where the pick-up can get to.
Is there enough pan depth to lower the pick-up by splicing in more tube between the swivel and the head?

My pan is huge, one long sump on the bottom and even with the swing it's failry close to the bottom. I'll rigid ount it at proper height if it's not there now and create a series of trap doors to control to oil with windage screen as well...roadrace style..;)...if a '53 chevy pu with a antiquated blown truck motor can have that phrase in same sentence...this pan has so much oil I think if you slammed on the brakes you would fill up the front two cylinders with oil from the bottomside.

huffin53: The long non stepped pan is NOT that huge. The stepped one hold 12 quarts. With a little work you can mount a shield/tray/baffle to the the divider plates and a brace near the front. You need to calculate how far above it to make the plate. As I remember it's about 1/2" and mine just misses the crank and rods as it spins You can louver, slot or screen it to catch the oil as the crank spins just like any other trick baffeled pan. Make the baffle about 1/8" from the front edge of the pan. Cut an opening to get the oil pump thru as you are putting it on. You can also add a solid plate at the rear of the pan parallel to the bottom sticking out 2-1/2 to 3" out from the back. This will keep the oil from shoshing up to the #6 rod during acceleration. Find the level for this by setting the pan flat and putting 7 qts of water in the pan to find the level of the oil. I make this plate pretty tight to the pan sides and back.

If your going to make the oil pickup solid I put mine 3/16" off the bottom. I use an external oil pump and figured out what pick-up to use by looking at the Moroso catalog for oil pans.

A lot of HP can be made or saved from being lost with an oil pan even at 5000 RPM. I've refind mine over the years and always saw gains.

The pan I use today was designed and made by Stan Shamura, better known as Oil Pan Stan, who designed and made countless pans for Ed Pink and Keith Black

Good Luck

Jimmy, thanks a ton for the detailed info, just what I need. Even though i'm not building a 500-600hp jimmy the 'free' hp is the best kind at whatever level you are running. I used to have a big sheet of that thick diamond screen for making pan screens but it is gone now, so I'll have to serach for more. Have you fabricated shields to mount in your block to keep drainback oil from landing on your cam ?

The cam isn't directly under the bore, so it doesn't get any direct drain from the cylinder walls. It's shielded from splash a bit by the hanging cylinder wall.
The head drains into the pushrod compartment through the pushrod clearance holes, and this oil reaches the lobes through the annular tappet clearance. The amount of oil passing through here can be somewhat regulated by counter-sinking and enlarging the small drain holes located between the tappets, but I'm not sure this is helpful.
A pan scraper will block crank throw-off from reaching the cam from below.

Personally I don't block any of the oil from the lifer gallery because I run a flat tappet cam and feel I need the oil on the cam and lifters. I control the spinning crank oil by the use of a custom scraper, the pan baffles, and right side extention.

One competitor I know has blanked off all of the holes in the gallery and drained the oil from the side plate in the back corner along with the front one that leads to the cam gear cover. You need a -8 or -10 hose for this. He runs a roller cam.

You also need to consider controlling the flow of oil to the rockers. There are many ways to do this. Remember the valve springs make a lot of heat and need oil for a coolant so don't block it all off. Also I run true roller rockers and they need far less oil so I contol mine at the fitting entering the head. The stock rocker system needs more oil.

You may consider running a vacuum pump which also helps but can be a little plumbing and baffel problem until you find what works for you and your engine. I now run between 7 and 9 inches of vacuum with a wet sump system....Good Luck

PS: personally I don't like screening in a pan. Louvers and slots in a solid panel have been my choice. Stan also.

The solid sheet-metal tray, as found in some stock pans, controls oil sloshing forward & back from climbing up and getting caught in the crank, etc. but has a few flaws for high performance use.
It interferes with drain from the walls, since the oil has to "find" the open area by running across the tray surface, and the droplets tend to bounce back up from a solid surface and strike the crank.
A solid tray can be improved by punching (not drilling) 3/8" holes through from the top using a gasket punch and a 3 lb. hammer with a block of wood as a back-stop. This makes a slight funnel in the upper surface to promote drainage, and a small lip underneath to prevent oil from passing through the wrong way. Yes, you'll have to re-sharpen it a few times, I heat-treat mine with Kasenite.
A tray should always point down from the pan rail, not only to promote drainage but to prevent oil from splashing up. The area at the ends should be solid (no holes) for about 1" wide to block as much splash as possible.
Vertical baffles are annoying to attach, since the pan rail doesn't help much here, but they can also limit front to rear wave motion and keep oil close to the pick-up head. The height of the baffle should be slightly above the normal oil level, the width matches the pan, but the entire height isn't solid - there should be a generous hole pattern near the bottom to allow oil to flow back to the pick-up head at all times. The total hole area should be at least twice that the pick-up head. An obvious shape is a simple vertical cylinder at least 2" larger OD than the pick-up head, vented all around with big holes near the bottom; the side is slotted to install the pick-up tube. I've seen what looked like a coffee can used - the bottom was riveted to the pan bottom, then soldered for sealing. Vizard suggests that simple 10-32 nuts and bolts are fine if soldered in place.
Remember that all shapes must clear the pick-up tube, discharge tube, pump body (enough to permit installation), and the entire rank counterweight path.

Wow, some very good input here. I as well think I will leave the oil dripping on my cam as I too am runninga falt tappet with some lift and since it's a street driven motor the extra oilon the cam is probably worth the minimal HP loss. I too will have rollers by the time I get this thing together I hope and had planned to run oil sprayers on the springs even though again, not comlpetely necesarry in my application, but it can't hurt. After I had mentioned the screen for the oil pan I started reading some of the latest thoughts on oil control and testing done on the screens vs louvered sheetmetal. The last custom pan i made myself the diamond screen was the new hot ticket...not so much anymore....scrapers, louvers, holes and pan kickouts will be used along with trap doors/baffles and such to control the oil once in the pan.

The starter is going to limit the size of a kick-out, especially if you need to service either one (leave room to reach the pan bolts, and drop the starter).
If you just need more oil volume without less ground clearance, you can add quite a bit to the left side (although it doesn't allow windage off the crank to escape due to CW rotation). A piece of 4 or 5" 16 gauge exhaust tubing, slit in half, can be attached to the wall as far down as you can parallel to the pan rail. Use a 1" hole saw on the pan side wall as low down as you can get. A 24" length of 5" adds about 4 quarts.
To figure out the best shape, get the length just above the sump. Now the height from the sump to the pan rail, subtract 1" for working room. If you have enough width, use the full 1/2 circle of whatever diameter is equal to the height (5", etc.). If there's less room, use less than the full diameter.

An idea i have had in the past but never implemented on anything is a system of oil 'catcher plates'. To explain, on the right side you have your kickout of a couple inches or more if you lucky , or dont mind having additional leak paths of plugs in your pan to access internal pain rail bolts. Lined up parallel(almost) and in line with you oil being slung of your crank you have flat sheets of metal angled slighty off parallel, perpendicualr to your wall of your oil pan. My unproven theory is that the oil being slung to the right side of the pan will hit these very slightly angled pieces of metal and due to the low angle the oil is slowed down gradually along the plane of the piece and in doing so it doesn't get hammered into a falt wall of your oilpan and at teh same time would still allow the extra 'air space' for some windage to escape the crank. The one thing in the back of my mind is wondering if the windage from the crank itself would try to push up the oil clinging to the metal pieces to the tops and try to throw it up into the crank throw area negating any positve effect....this is when you need a prototype and a high speed camera inside your crankcase...with tiny winshield wipers on the lense...

"Stock rods will be plenty good but make sure you have enough side clearance to let out the oil and change the nuts (ARP again)."

JD, just a question on an earlier post...notice you just said change the nuts and didn't say rod bolts. I would assume to change out both bolt and nut without any thought of keeping the stock bolt..or is there somehting I'm missing here ??
Hans