Inliners International Forums General Discussion Engines 302 GMC questions

just picked up a 302 Military GMC engine want to know if there are any aftermarket parts for the engine and any thing suggested on improving design flaws like the intake needs to be supercharged to eliminate the fuel dropping out and puddling in intake runners > is there a retro roller CAM and lifter available or what info on a engine builder need to grind a billet blank and what will be needed to make the lifters is there roller rocker arms or will that need to be fabricated anything else to suggest I plan to bore out to 4.125" and use a 8" ish rod and keep the crank at 4.00" but use a 400 SBC piston

I don't think there is a design flaw in the intake ports requiring them to be supercharged. Aside from a few common speed parts like 4 bbl intakes and valve covers, most things such as roller rockers, roller cams and lifters will be have to be custom made and expensive. Even though you gain the use of a common piston by using that long of a rod, you will loose significant low end torque by increasing the rod length that long. And likely loose more than you gain by the piston.
What is your objective with this build? Are you racing or street driving?

I'll say it again. We need a modern GMC hop up book. Bill fisher's writings were done before there was a Small Block Chevy V8. A lot has changed. Ron Goldman used Hudson rods and Custom pistons ( I think ) and saved 1 1/4 pounds per cylinder. Some have used MOPAR rear main seals. Some use small block valves and springs. The bottom end is pretty strong. The stamped rockers are plenty good for street and some racing. Patricks has pistons for stock rods. There is a ;to on this site if you can find it.

I am building a 1957 pick up truck Hot Rod and want a strreetable engine the rods can be aftermarket the pistons was planing on useing 4.125" SBC I can have the crank off set ground but would like to keep the journal size the same less maby .010 " the CAM if a roller set up will gain the effect that the CAM will not wear so I do not lose the CAM profile with time and less rotating assembly rotating resistance the roller rockerarms will be stronger and if correctly made should reduce wear in the guids and reduce rorating resistance ...

The engine in my '53 Chevy pickup is a '57 270 GMC. I built it in 1978. It was my only driver for several years and is still used as a driver/hauler. It has never spent a night inside unless I was working on it. It has been all over the West from Nevada to Texas and all one California. I don't know how many thousands of miles are on it but none have been easy. I have freshened it twice with new rings and bearings and just lapping the valves. It has a cam from Clifford that has held up fine. It runs the later welded stamped rockers. I think it is bored .060". I don't remember what pistons I used. It has the small port late 270 head with bigger valves and a little clean up porting. I'm running an 500cfm 4bbl carb and Fenton cast headers. At first I ran Viper tube Headers and got higher rpm with them. The valves began to float at 6,200rpm. I still regularly shift it at 5,500. In the In the first 3 gears. It has 3.54 rear gears and a T-5. It will cruse at 70-80 mph all day. In 5th gear 3,000 rpm is 90 mph. (clocked with mile markers and a stop watch over three miles on the way home from Bonneville) At 65-70 it will get almost 18 mpg.My point is that you can build a great dependable driver out of these engines without too much trouble or money. The bragging rights of a 302 are substantial. Most people you run into won't know what it is. You can tell them anything you want and they won't know the difference. Build it to be the most fun and trust worthy.

A rollerized valve train is nice and if you have the funds by all means go for it, but as Beater said, a lot can be had by just keeping it simple. Here's a pic of the Hudson rod swap with a 400 SBC piston vs. the stock GMC rod and piston.

Just curious here, but the GMC rods are not known for being weak. I just put a set in my 261 chevy. Some come with .990 pins. So the question I am asking is why the push for offset grinding crank work and after market rods. You could go with the stock 302 rods, they can be rebuilt, big block chevy arp rod bolts are what I used I think, forged pistons from ross or venolia. Then its just a matter of grinding the crank and indexing the throws, sorting out a compression height and ring package for the pistons. Cam shaft, Why a billet roller? I am pretty sure roller lifters for a GMC are pretty expensive if you can even still get them. You could have schneider cams grind you a flat tappet cam that would be to your specifications. A little head work, some decent headers, intake and carb package, you should have a relly good runner, no?

my whole point to go with the 7.883" mopar rod or 8" is to add torque not sure why a lighter stronger longer rod would produce less torque ? I planned on using a Carrillo rod but not sure what a set of 6 will cost may need to go with SCAT or EAGLE as far a the CAM I want to longevity and not to need phosphorous and Zink in the oil

You are just not understanding the engine dynamics of how rod length affects the characteristics of an engine. Longer rods slow down piston velocity at many spots thru its travel up and down in the cylinders, thus reducing the torque, especially at lower RPM where it is more noticable. Many sources and books have been written on the subject, so its easily proven and verified and many dyno and track tests have backed up these findings. Longer rods are often used in racing engines for other benefits where the lose of low end torque isn't needed, such as high RPM operation.

You might need to contact Carillo for pricing, I don't think Scat and Eagle do custom rods. Along with the roller cam, roller lifters, roller rocker arms and aftermarket rods your looking to add around $3000 more to your build than is necessary for your intended use of street driving. Just trying to help you get more more smiles per mile out of your build and help you spend money where its needed.

Hi Ronald . . . panic doesn't come around here much more any more - but his victory tech paper on the effects of rod-ratio is quite instructive:
Rod-Raitos

ok the info is mostly a V8 setup where the pistons have thrust in two directions the flatter the angle will affect the torque of the engine build flatter = more torque and thrust direction or main barring wear surface is wider this is why the inline six has a longer rod length the characteristics of a single direction of thrust id different then a V engine this with shorter rods is why V engines have higher RPMs and Inline engines have higher torque and lower rpm's if you build a inline six with shorter rods and change the bore to stroke ratio with bore bigger then stroke you can have a engine that revs up faster but will lose torque threw out the power band I want to build a high torque engine and keep the longevity the reason the 302 is so desirable is the build is square 4X4 " and the rod is 7" this is a high torque engine known for longevity my reasoning for a 8" rod is to use a lighter 4.125" piston and not change the stroke to gain CID and faster spin up but want to increase the torque threw out the power band

let me add the info on the build the rear or final gear ratio is 3:70:1 ford 9" I plan to use a 30" tire with 15 " chromed wheel in a truck build that is a Dakota chassis modified to fit a 1957 GMC short bed truck with a flat bed built for this cab and chassis the weight will be around 3200 LBS I have a Allison 545 4 speed automatic transmission so the engine build I want to have at least a 4500 RPM red line preferably 5000 and be able to use mostly around town but can jump on the highway and run 80 MPH with out the engine running a high rpm to maintain the speed I am looking to build the 302 to this build to have good low engine torque and high torque threw out the power band and have a reliably long lasting build that performs well so the 4X4 with 7 " rod is good for that but wanted to increase the top end RPM and how fast it revved up but also have the low end torque My understanding was that ther longer rod in a inline six will add torque with less effort from the engine and help with fuel consumption and be able to maintain a automatic transmission at all speeds !

The difference between Inline and Vee configuration is largely about balancing of the rotating assembly. Rod Ratio affects the dynamics within each cylinder independent of layout - piston speed; side loading/slap etc. Some suggest that this variable is perhaps the last one worth worrying about:
QuarterMile
especially in a relatively slow turning street application.

Now when one is designing an engine from scratch to rev like gang busters (motor cycles, F1 , Indy) then long rods buy you piston dwell at TDC - useful on both compression and exhaust strokes

MotoIQ

But as the Victory Tech papers instruct - in a slow turning street engine the short rod is your friend. The added piston speed off TDC makes better use of multi-carbs and provides low end torque. One strokes to add displacement - why give it back with a longer rod?

I ap-reciate all your input and rethinking build however I am not going to use a multi carb setup was planing on 1.94 intake and 1.60 exhaust with a single 500 CFM holly 2 brl carb or 4 brl the engine top rpm isn't high enough for multi carbs IMHO a 4 brl I can go to like 600 CFM if needed with 302-320 CID I get the low end torque being higher somewhat the engine will have a lighter rotating assembly will use current stock crankshaft will need a custom forged piston to accommodate the use of stock rod as IDK where I can find a forged stock piston for a .125 over bore I know Egge has cast piston up to .090 over but want a lighter forged alloy piston with shorter skirts the problem is the cost of using a custom piston and stock rods or using stock rods from a Jaguar 4.2L or Mopar Inline six and offset grind with stock 400 SBC pistons the rod for the Jag looks like a good choice 7.75" and width close to the stock rod of the 302 will need to grind crank shaft to journal size and gain as much as I can on offset grind then deck block to .000 and use a flat piston should be around 8.4 : 1 compression then plane head like .020 and get closer to 9:1 the added .75" will lose some velocity on piston but lighter rotating assembly should regain the velocity back and less angle for rod will last longer as I was told

I had a 4.2L Jaguar XJ8 the rods are 7.75" the stroke is 3.0" so rod length = 2.5x the stroke and the car had plenty of low end torque this engine has 4" stroke and 4.125" bore the rod length will be less then 2x the stroke so I think the build will be fine with lighter rotating assembly ?

There are literally many dozens and dozens of parameters that engineers consider when designing an engine. And simply comparing only one or two of them between engines that might have one of them in common with the other is a common mistake that happens when someone is set on starting a build such as this. The parameters alone that the cylinder head brings into the equation are a big part of why one engine can have a long rod such as the Jag, and the GMC be better suited with a shorter one, even though they may have the same stroke or other similarities. The Jag also has a complex computer system that compensates for things such as timing and fuel curve that the GMC does not have that may make it "appear" to have a lot of low end when its really the computer system tricking you and manipulating things to make it seem that it does. Good luck with your project.

thanks everyone for your input I have taken in all the info and due to I just found out the engine is a low mileage almost new I plan to use a .030 over bore Build blue printed from Clifford performance then send them the CAM for regrind and the rocker arm assembly to be chrome plated and bushed ... keep the original rods and use new .030 pistons from EGGE and install headers dual Weber 38 carb intake ... this will have like 120% more torque then original build the HP I am not sure about but did want to convey thanks to all for your input it was suggested to not go more then .060 over bore and I have clean cylinders at Stock so could go with just new rings and barrings if I wanted the block is in that good of shape I may consider 7" aftermarket rods with new pistons to reduce the weight of rotating assembly as well as a new Harmonic Balancer and the flywheel will need to be replaced with one that will fit the torque converter for the 545 Allison that will bolt to the adapter plate that cam on the engine this should result in a heavy duty high torque inline six that should last a long time and not have a need to re-tune the engine much at all Thanks again !
rod possibilities:
http://www.sissellautomotive.com/engine%20parts.htm

with EGGE pistons and new Pro Street Harmonic Balancer 8Lbs the re Balancing should be a rotating assembly that weighs less and the duel carb setup Custome grind on CAM reworked rocker arm assembly should net at least 250 HP and over 400 FPT

Sounds like a good solid build. Keep us posted on your progress. And at a later time if you want to do a more involved build with the longer rods, you will have a baseline to compare it to.

What you are proposing sounds good. The link you posted is about 194-292 engines which are very different from your 302 and I wonder if that is where the .060" bore limit comes from. No matter your well built 302 will give you many years of fun. Please keep us up on your progress.

Egge called and said they do not have any pistons so far I can only find NOS on eBay for 4.020 pistons and cast rings for 399.99 looking for any .030 pistons there is a guy in town that will make a piston set for like 900.00 so that may be the only option EGGE wanted over 1000.00 for a forged set will raising the top ring help any ? the stock height is like 3/8" down and will having a set made I can set the height where I want like 1/8" down from top of deck and spread the ring stack will this have a good or negative effect ?

so far only Carrillo will make a set and all others BBC are too thin at rod end by like 3/8" the stock rods are like new would like a lighter rod if I can find one with 1.455" width

anyone have all data on connecting rods length = 7.00" width at rod end = 1.455 what is the rod end size 2.?? and pin size Carrillo are 335.60 per rod

The connecting rod bore is 2.4568" and it is available with a .990" wrist pin just like the BBC.

Here are some links to old 302 threads here. I don't know if you have seen these or not. Sometimes searches are easier to do on Google and then come back here.
#1
#2
#3

Have you checked with Ross Racing Pistons? www.rosspistons.com

They support Inliners by advertising in the 12 Port News.

Will Willis

They also offer Inliner discounts on the purchase of inline pistons, so another great reason to become a club member.

Not to mention that they deliver forged works of art:


hard to stuff them in a cylinder never to see them again.

If you drive them hard enough, they will come out and give you another look !

regards,Rod.

Patrick's can order custom forged pistons (from Arias I believe)
under $700 a set.

Order them from Arias,its easier. I had a problem with Patrick's.

Ditto with Patrick's. Found a set of .60 over Arias piston though.