Inliners International Forums General Discussion Hi Performance 302 jimmy

For Ron, here ya go:



Snazzy, no?

panic, yes, that was my understanding, though in a somewhat more simplified sense. thanks for the detailed information as always. i was trying to clarify wilbur46's statement that a mushroom tappet could somehow affect lift.

Thanks for the picture. I sure don't want to be bench-pressing 6 of those mothers!
What is the pin size on the Hudson rods?
RE: Mushroom lifters. Much has been written, but to simplify a much larger lobe can be ground on a larger dia lifter. It is a technique first used (hot rod style) by the NASCAR boys. For a quick comparison, check a VW catalog for the differences in the grinds available for the stock/ larger diameter lifters. The big catch with the jimmy is cam cores. As those who have done it will attest, you gotta bust out some bucks or have a lathe/cnc plus heat treating quipment. Maybe CNCDUDE could whip up a few nodular iron blanks for experimental poipuses. The difference in flow rate-intake vs. exhaust is the absolute limitation anyway. Regards, Wilbur

Panic, re your last post.
I think your expertise (or terminology) may exceed mine, but I think what you are talking about is the increase in potential acceleration of the lifter on the ramp, whereas I'm still talking about a big ol lobe base circle affording a lot more lift/duration. The low lift acceleration of the lifter moving up the ramp is a newer idea of the Crower or maybe Comp Cam "High intensity" grinds. (is that right?)
I quit reading the mags 20 years ago, except maybe McFarlanes stuff in Circle Track.
What happened to tech editors with degrees in mechanical engineering????? Again, thanks to all who contribute and Regards, Wilbur

Certainly preferable to have a large base circle, but there still has to be clearance for the "foot" above the lobe under the tappet gallery. This is a slight disadvantage to the VW or any other mushroom - the base cannot almost disappear up into the block at full lift. I'll bet that since there's no oil pressure (unlike later stovebolt) the bottom of the gallery could be cut back to get clearance if needed?
Anyone have ideas as to how much spring pressure the cam will stand?

panic, the Empi 31mm lifters have a .024 oil feed hole in the center of the foot to increase spring pressure capacity

Erik, Thanks for posting the picture for me.

You'll notice that the Hudson rod isn't as "beefy" as the stock GMC. However,each JE piston/Hudson rod/pin assembly is more than 1.25 pounds lighter than the stock GMC and the net results is a stronger combination. It also takes a lot of load off the crank.

We turn the engine 6000 RPM without any problems. By the way a SB Chevy harmonic balancer fits perfectly. We use a Fluidamper balancer.

The wristpin is stock Pontiac. The small end of the Hudson rod can be honed to fit the Pontiac pin.

Ron

Thanks very much Ron.

How are you going to add oil pressure to the lifter galley? They have gaps between the lifter bores, so you can't drill a long oil passage like the 235/261's and no provision for rocker arm pressurization. External line? There are only four bearings supporting the camshaft, how will you keep it from deflecting?

I agree that pressure would be nice, but other engines with flat tappets have demonstrated longer life with just a simple hole that slowly bleeds drain oil from above (some always follows the pushrod) onto the lobe/tappet mating surface.
Is the VW tappet oiled from an annular groove (like a hydro), or is it perforated top down?

Erik & Ron, Thanks for that picture. It is clear that Ron has found something there. I'd like to see a shot of one of those Pontiac rods beside a GMC rod.
As far as oil to solid lifters goes it is a common practice in Studebaker V8s to plug the oil holes in the lifter bores and rely on the free oil slopping around. It forces the oil to go where it is needed. Those engines like to put all the oil into the valve covers.

the vw lifter has two narrow annular grooves around the stem about 5/16" apart. upon inspection, there is no galley or oiling holes to the lifter bores in my 248 block. i think the GMC must oil the lifters simply by splash & drainback, so i guess ordering the drilled lifters would be a moot point.

Increasing the drain-back volume is simple: increase the height of the existing drains, or relieve the tappet bores down onto the cam.
I'd consider drilling the VW tappet from the pushrod socket down to intersect the existing face hole.

the intersect hole is already there in the lower groove of the vw lifter, from what i can see in web images. looking at the block again, i see no reason why the bottom of the lifter bores could not be fully relieved for the lifter foot.

Garagepunk, there is nothing wrong with the mushroom tappet idea, but many times we look too far outside the box thinking we are gaining a lot, when we are actually no better off that if we used tried and true methods and concepts that have been proven to work and function well. NASCAR used the mushroom tappets in the late 70' and early 80's with good success, but changed to the conventional style flat tappet lifters afterwards with even better results. Cam technology has advanced so far and rapidly, that lobe profiles that weren't able to be had without the use of the mushroom tappets, are now way beyond what could be done with them, using standard tappets. Roller cams have been available for the GMC's since the 50's, so using this type of lobe profile instead of a flat tappet style will even take you to a much higher plateau again.
Flat tappets are more sensitive to lifter bore misalignment than a roller lifter is, so just installing a bushing into the exsisting bores can magnify this problem unless you have precision lifter truing tooling like BHJ offers to do this competently. Plus the additional machining required to install a mushroom tappet into the block, where the bottoms of the lifter bores have to be spotfaced with specialized tooling to allow the lifter foot to recess for clearance presents more challenges. I think you would be money, time and performance ahead by just upgrading to a Chrysler lifter, and having a custom lobe profile ground on your cam to get you where you want to be.

cnc-dude, those vw lifters can be had for $29.95 for a set of 8, so 2 sets would be required. that's still only $60.00; and i CAN have my existing n.o.s. iron cam ground with the vw profile for well under $100.00. that's bang for the buck that the rollers just can't hold a candle to. i have access to a CMM and we can plot the locations of the existing lifter bores and write a cnc program to bore them accurately once the block is bushed; that can't be any less accurate than the standards that GMC actually machined them to originally. i have actually seen the lifter bore bushing mod done to a vw waterboxer engine fitted with type 1 tappets, so it's not completely out of the question.

the block may or may not need spotfacing with my reduced base-circle cam. tooling would not be a real issue as i can make or modify most anything at school.

i'm also after valvetrain mass-reduction, and these fit the bill nicely.

Any tappet smaller than .990", including the "normal" Chrysler .904", requires the bore to be sleeved. The only big cam that will run on the .990" tappet is something designed for the Chrysler .970" mushroom.
AFAIK, the reason for a precision tool to spot-face the bottom of the tappet bore is tight conditions in a V8 valley area - the GMC should have room to get a bigger tool in there. However, I'm a little nervous about how much metal there is above the cam. To fully recess the VW std. 31mm tappet, the bore radius is widened by .115". On the outboard side, the skirt wall looks like only 3/16" thick.

I should have been more specific, I was meaning the 1" diameter lifter, this doesn't require bushing the GMC blocks to use them, only honing the existing bores. We have discussed this in the past and I thought everyone was on the same page, as far as which Chrysler lifters to use for the GMC's when going to a roller setup.

Maybe I'm missing a point here but, lifter oiling is almost always just oil being slung off the crank and what drains back from the valvetrain area. My GMC has flat tappets with 100# on the seat and 300# open and shows no sign of wear and never needs valve adjustment. I'm also lifting the valve more than 0.600".

I made sure the oil has lots of ZDDP to combat wear associated with flat tappets.

I don't think you need to reinvent the wheel without seeing a significant gain in performance or reliability.

Ron

Yeah Ron, that was my point also, but it sounds like he has already made his mind up on the subject....

I think your right. Maybe we can help someone that needs help.

Ron

the 1" diameter lifter

Nope, not familiar.
Replacement for the RB hemi?

Yeah, its newer Top Fuel and Funny Car technology stuff. You can pick them up used dirt cheap. I just thought this would be a simple roller lifter fix for the very hard to find application specific GMC roller lifters you can never seem to find anywhere.

Ron, Panic & CNC-Dude, all very good info and all of it is taken into consideration, as i'm not committed to anything yet. it's all in fun to talk shop with knowledgeable folks. thanks again

Ackkk - senior moment!
I already had data, but not recorded as GMC, duh.
The center-to-center tappet distance (between linked pairs) of the KB etc. hemi roller tappet is 2.000", which is (almost?) correct for the 235/261 stovebolt (the "normal" hemi and B/RB tappets are 1.800" apart). The GMC distance is probably slightly larger, so the slots etc. in the link bars will need elongating, etc.

Find the 1.00" roller lifters used if you can. We just had a custom set made (Crower)for a SB Chevy that we're building and they cost over $1200 for the set.

Ron

CNC-Dude , I will send dirt, please send lifters!!!

The big boys use larger than 1" now, for us the hot ticket is the .987 Jesel keyway lifters but way too spendy for this hillbilly.

On the VW lifter thing, my main worry would be the side load on the lifter itself. It might work just fine with the right bushing. The only way to know, is do it!

Unless there's something else, a fairly common bushing material is 660 bronze.
The stem area vs. tappet forces shouldn't be any worse than they are in the VW - it should work.
You'll have to plug the hole in the annular waist area to make a drain from the pushrod cup feed the contact surface hole.
The TF tappets can be rebuilt by the manufacturer - new axles, needles and rollers, polish the body, etc. so they need not be perfect. In a GMC (or early stovebolt with no hydraulic tappets) the tappet's oil feed area is harmless, but in a late 235 you have to measure where this is vs. the tappet oil gallery to make sure it's open front to back, and no leaks.

[quote=Armond, II#298]CNC-Dude , I will send dirt, please send lifters!!!

I wish they actually were that dirt cheap, but used they are not likely to break the bank like the Jesel stuff will. I have a guy local to me, that all he has done for the last 10 years is buy out Top Fuel and Funny Car teams for pennies, and build entry level racers for guys looking to jump into the sport. I'll stop in and talk to him about this more and see what he has to offer as far as cost. Most of the billet cranks he sells for those engines only have one pass on them, and he sell for $300-$500 bucks. He is fairly reasonable on this stuff.

Another consideration about engine size is the relative sizes of the ports, the bigger the engine, the more relatively restrictive the less than optimal porting is.
My research of the 383 Vs 440 Mopars shows that using the same magnum heads the 383 makes more Hp.
I also prefer the shorter stroke in that it should allow the engine to safely wind farther.
Roar

dual weber 38's or holley 390 4brl