How To Build a MONSTER HP GMC 302?

Ok, guys, help me out here. I've searched, and found some info, but not enough.

Let's theoretically build the perfect blown,alcohol 302 GMC, punched out to 322CI

We'll run a Skinner 12 port head, with Fontana injectors.

Should we use the Sissel pushrod setup? Crank girdle? Tell me what you think.

I know nothing about these engines so please educate me!

 

I think you should set it on a shelf for a few years and develop the Flat Cad. While you are at it develop a close relationship with Joe. He knew everything there is to know about GMCs before I knew which way to Bonneville.

 

Haha!

That's pretty much the plan. Dollars dictate it must be so!

In the mean time, I'm talking to everyone I can, and gathering information and ideas. I just got off the phone with Don Ferguson. He has a billet cam blank.

 

Between Doug Robinson, Don Ferguson, and Joe Fontana there must be all the information about big power GMC engines that exists. Since you are in contact with all of them, I would say, Listen to what they say. How many HAMB guys with their experience? Doug's blown motor has always exemplified the all out GMC to me. But Joe must know more than anybody about running a Skinner head. And Don has a 300mph GMC. Don't hear a lot of people saying that. Plenty of good advise in that group.

 

Point taken!

I like that avatar better than the plane....

 

Shiga Maru. That was the name of that brand new DC8. Sitting in San Francisco Bay on my way to work. He was going to the same place but didn't quite make it. Towed it in on a barge two days later and flew it out after some months and of lots of overtime.

 

That's pretty ironic!

The Shiga Maru was also a Japanese ship sunk during the war.....

 

id like to pick up the flatcad and Jimmy torch as well... but my pocket book would kick me in the nutts repeatedly. although im real curious to see what your motor will do this year, its going to be interesting!

 

Oh, mine does that too!

....and then there's still the wife to worry about!

 

It was explained to me that all Japanese ships are Maru. It means fish or some such so only the first word changes. Then for some reason when airplanes came along they still called them Maru. I would guess there have been several Shiga Maru's. This one flew for at least another 20 years after landing in the Bay. No one got wet. Not even their baggage. It ended up in the drink just off the San Mateo Yacht Club. And the Yachtsmen there powered out and brought the people back to the bar. What a deal.

 

Hey Buddie, you have the best form of ADD!
TP

 

That, or I'm just a glutton for punishment!

Anyone know the rod journal size? I'm just wondering if there's enough there to offset grind the journals and gain .1 stroke?

 

When you get inside your 302 look and see how close the rod big ends come to the cam. If the cam isn't timed right the rod will hit the lobe. Now start thinking about racing rods, even with smaller journals. Moved out .050. Talk to Doug before going forth with that idea. I know it's been done but at what cost?

 

Ummm... I thought to GMC 302 was a torque Monster. Better to use a 270 for hp??.... Most the Bonneville guys I know are using 270's.... But what do I know, I'm building a 302 for roundy rounds... not sodium.
http://s1185.photobucket.com/home/speakfordadead/index

 

PS.... I have 248 cranks... you'll need the shorter stroke!!!

 

Why would a 302 be a "torque monster" and a same but smaller bore 270 be a horsepower engine? I set my share of GMC records on the dirt and salt. I started with a 270 but when I got a 302 I ran it. As far as most of the records I think you will find 302 engines holding them. None that I know with 248 cranks.

 

Rich,

As usual, you bring up good points. We are going to continue to work on the FlatCad, and try and get the most out of it that we can.

In the mean time, I'll continue talking with Doug, Joe, and Don, and collecting parts, until the time is right for the engine build.

 

Maybe I am applying V-8 technology, but I am possibly under the wrong impression that a shorter stroke allows you to spin at a higher RPM. 270's can runout .125 over bore. 302's can run .125 over bore as well. Which is obviously larger, but how do you spin it faster with a 4 inch stroke??? Straighten me out!!! 248 crank is shorter, spins faster.... do you not de-stroke for higher rev's??? Pop's liked putting 305 cranks in .010 350 sbc's. Those roundy round cars lept out of the corners.... reverse cams helped too, but now are no-no's....

 

OK, yes a 270 actually can and often does run a +.156 overbore. which with it's 4 inch stroke makes it a 292 cid engine. The 302 at +.125 over and with the stock 4 inch stroke is 320 cid. The extra 10% displacement should show greater power. The thought behind shorter stroke, higher power is that you will get more power strokes for ant given period on time. And if your heads will support unlimited RPMs this may actually work out But in real life, most of the time a good running small engine will become a better running large engine. That;s why we are not all blasting around in 1 liter Corvettes and Mustangs. 427s are faster.

 

305 and 350 are the same stroke it's the bore that changes but there are some lighter weight 305 cranks

 

Point taken.... thanks for the schooling. I guess attaining top speed is different theory than left circles. On and off the pedal requires torque and hp curves to turn on at lower rpms. When you have a few miles to crank it up it's all about displacement and how high you can rev it.

 

ok heres the recipe for a killer gmc 6
#1 you need a flow bench whether its a stock head or 12 port get instruction manual from superflow in colorado springs anything can be used as a flow bench like a big shop vac or grainger sells vacuum motors thats whats in the superflow
when don ferguson sr and i built the first stock head gmcs he bought every cyl head we could buy that was run at drags or bonneville i flowed them all intake would only support 220-250 hp wihin a week w were up over 400 hp cast iron welding was required not easy but can be done ( i didnt say it was easy)
next make yourself a honing plate and use it
use a steel cam core or billet
i dont care if its a 270 or 302 big horsepower can be made
we have been over 300 mph with stock cranks leave a little extra clearance as they flex we now use carrillo rods but have gone fast with stock ones with big block chevy bolts some polished beams some boxed
do yourself a favor and make or buy some decent rockers
you cant put enough bolts or pin in the flywheel to crank
i got in the el mirage dirty two club with joe fontanas skinner and it runs pretty darn good
we use big mgs now but had good results with gm hei from late 250
there are no old intake manifolds that will feed this combo so make your own
with a little learnin and a bunch of hours youll have a kick ass gmc, if it was easy everybody would be doin it (quote from don ferguson jr)
jellybean

 

dirtdeville, thanks!

I've got a couple of questions, if you don't mind?

Did you have to do port work on the Skinner head, or was it good?

Didn't you guys use a 7 main girdle in your 300+ mph engine?

What kind of lift and duration are you using on those monsters?

Did you use the two piece pushrods (think Sissel) with the additional lifter in the head?

Oh, and I talked to Don, and ordered a billet cam core!

 

can't wait to read more on the 302. i want to recreate my g-pa's hot rod from the 60's. it had a 302 in it. so i want to learn all i can. but i want mine to still be a streetable car.

 

Can anyone provide the GMC 302 bore centerlines?

 

This is a little OT but you might like this drag car i put one if those 302s' in. The engine isn't complete here, it has a lot of clifford research stuff.

 

Oj, that's pretty cool!

Any details on the engine build?

 

...here's some inspirational eye-candy....go forth my son...

 

I don't know much about it, it is roller and has some serious componants - it was built by less than knowledgable persons and when dyno'd they bent pushrods etc, the owner replaced the bent stuff and sold the engine to the current owner for literally pennies. While here i had the valve cover off it for fabrication purposes and saw that the roller rockers were bottoming out on the shoulder for the rocker studs. He pulled the head and i machined to bosses down .200 or so and that free'd everything up. I believe it has venolia rods and pistons, roller cam, crane gold roller rockers etc everything looked to me like it was sbc stuff but i didn't verify. I heard that it was built for N2O and belonged to a DC street racer and was in a 1st generation camaro that he'd sneak into big-purse street races. After-all, its only a 6cyl right? give me a car length and we'll run your mustang for a big one.

 

OK,, You have me hooked,, I need input,,