Engine and Transmission Tech

From what I'm seeing about the LT4 Hot springs, seated pressure should be around 125 and open pressure around 315-325lbs. So I projected pretty close to the mark with 125/350. The PAC-1231X springs are going to fall short by about 50#.

The actual specs on my cam are a little different and the only reason I can think of for it is that Tim at TA chose an in-house grind that was the closest and was designed for the Buick engines. I bought two cams, one a solid and the other a hydraulic. My motor gets the solid cam. They are Grind # 69005 and 69005-B. The -B is the solid grind.

69005
TA 272-82RH
LS: 112
Dur: 272/282
Lift:.525/.550

69005-B
TA 264-74R
LS: 112
Dur: 264/274
Lift: .544/.544
Lash: .016/.018

Lt4-Hot
LS: 112
Dur: 279/287
Lift: .525/.525

So anyway, the Pac 1231X falls short of the Lt4 springs by about 50# which is not enough to make up by shimming the springs. It means the redline will be compromised. Also those springs are spec'd for a hydraulic cam with a redline around 5800 rpm. Going higher means stiffer springs. How much stiffer? Good question and I don't have the answer. But I don't even know if any stiffer springs for the GT500/Cobra Jet engine are available.

Jim



Edited 1 time(s). Last edit at 12/19/2022 12:24PM by BlownMGB-V8.

Jim B, What is duration @ .050?

Jim, IMHO, one of the advantages of the beehives over conventional springs is you don't need the high pressures to prevent valve float. Installed height pressure of 100-120 for flat tappet and 120-140 for roller performance cams is pretty normal. The PAC GT500/Cobrajet springs are an upgrade over their stock springs.I don't think you would have any issue @ 7,000RPM. Sounds like your cams have a little less duration and higher lift than the LT4 hot cam. I would cut the seat low enough to add a shim and have a lip around the spring to locate it. So. you need a cutter just slightly larger than diameter of the spring.



Edited 2 time(s). Last edit at 12/19/2022 01:37PM by mgb260.

I'm now liking the look of the comp 26981 springs with the 795 retainers.
(again, assuming the TA 10-degree retainers are indeed compatible)

Springs:
[www.compcams.com]

Retainers
[www.compcams.com]


I will revisit my sectioned heads tonight to verify how much can be dug out of the spring seats. Per my notes, the Stock 10-bolt heads have an installed height of 1.579" as a reference and the spring pockets in the head are 0.93" ID and 1.23" OD..



EDIT. I totally missed the post by Jim on December 17, 2022 12:55PM

The PAC-1231X springs could work pretty well. The ID at the top is shown as 0.636" vs the 0.645" of the Comp retainers linked above. IO reckon that .009" could easily be tweaked with a dremel on the ID of the spring.
[www.racingsprings.com]


(again, assuming the TA 10-degree retainers are indeed compatible)



Edited 6 time(s). Last edit at 12/19/2022 02:23PM by turbodave.

Dave, I figure with the chamfer on the retainers and the springiness it's likely you could just seat the retainers in the top coil easily on an arbor press, then they'd just stay like that. (Or maybe just with the spring compressor)

I don't have the .050" specs, they aren't on the cam cards. On the LT4-Hot it is 218/228. I know there's a pretty fixed relationship between advertised and .050 duration but can't remember what it was. Looks like about 60 degrees though and I'd expect that carries over to the TA cams though it looks like some of their cams fall more in the 40-60 range. So yeah, I really don't know.

Jim

Quote:

"...and the production conrods and pistons remained weak."
Do the Rover V8 engines not use a forged connecting rod? I know that the Buick/Olds 215 does.

Dan LaGrou sez the Rover rods are also forged.

"You can use the Buick/Olds 215 rod or any Rover 3.5, 3.9 or 4.2L rods. They all have similar dimensions and the required 5.66" length. Surprisingly, all of these OEM connecting rods are forged, thus making rod failure very rare."

Dave, These retainers are a better fit for the Pac-1231X springs. Strangely same part# though.

[www.summitracing.com]



Edited 1 time(s). Last edit at 12/19/2022 09:31PM by mgb260.

Here's a spring that has a bit more load but is rather expensive:

[www.lethalperformance.com]

I just fired off a Design Request to PAC springs, let's see what they say. Can't imagine they would really have any problem with running off a beehive spring for the Rover V8 but it'll probably come down to quantity and price. I'm asking for a 350lb open load.

Jim

Jim, Those retainers won't work. 7 degree 3 ring. I think 350 is a bit much. Probably 280-300 would be fine for a beehive. Conventional springs require much more to stop valve bounce from harmonics. That is where the beehives excel. I bet the PAC racing springs are all tested to 7000RPM on the Spintron.



Edited 1 time(s). Last edit at 12/20/2022 01:07PM by mgb260.

Jim, the Comp Cams springs Dave mentions above, instead of 1.7, how about 1.65. installed height. How much room to coil bind and how many lbs more open and closed. You would want to cut the guides down also when you open up the seat. The Modular springs are meant for overhead cam engines and require less pressure due to no losses from pushrods and rockers. You could do an experiment and see how the Buick keepers fit on the Rover valves with Rover retainers compared to the Rover keepers.



Edited 1 time(s). Last edit at 12/20/2022 02:54PM by mgb260.

>Those retainers won't work.

Probably not, I guess you mean the ones with the Lethal springs? Was only looking at the springs.

You could be right about the spring load, but we'll see what PAC says when they answer the quote request. I told them 7000-7500rpm. Due to the lack of pushrods etc I doubt the spintron results would cross over for the mod motor. Doesn't do to get in a hurry I guess, we're learning more almost every day.

Dang it Jim, seems like every time I turn around I'm having to pull the spring back off that end valve on the 300 head! ;-) But the good news is that the keepers seem to do just fine with the rover valves and retainers. No rock, no play, feels good and I'm convinced they will lock up tight. Good catch on that one. Should be no reason why the TA 10 degree keepers wouldn't work with just about any 10 degree retainers.

On a side note, looks like a set of 9-3/8" Smith's pushrods from my parts cabinet will work fine with the stud type rockers on the TA heads. Just get lucky sometimes. I'll see how they look with the valve open.

Jim

Jim, We appreciate all the work you do! Besides I know you have fun doing it!

Gives me something to do during the dark days of winter.

Anyway I think this makes for a pretty potent SBB/Rover package for the MGB and I'd like to get it finished out. As it stands it's now pretty reasonable to build a pretty potent 5.7L engine based on the 300 block, 350 crank, ex-nascar rods, roller cam, 4.6 heads, and even roller rockers while putting the extra $400 or so of savings from the bellhousing into the engine and then using the RV8 headers and a set of inexpensive home fabricated engine mounts. If you figure the bellhousing savings pay for the cam then the only significant added expenses are the forged pistons and the crank work. And it opens the option for the TA heads later on if desired. I think it's a build that just makes sense. This is really the last piece that is needed for the complete package. You could forgo the 350 crank but then you'd need to come up with a different set of pistons.

I like the fact that it lets you stay in the SBB/Rover engine family while not limiting the performance potential or the option of modern engine upgrades.

Jim

Jim, it looks like your current plan is exactly what I am planning. I too will use the 350 crank and will need custom pistons and plan to use the 4.6 heads (at least for now). Any idea what intake and carb (or EFI) you will use and what the resulting horsepower target is?

Eric, I'm actually building a couple of engines here, neither of which exactly match that formula but both of which are close. The engine that gets the Rover heads is the Buick 340 long rod motor with Scat FHF rods and modified Venolia pistons. (Venolia is no longer in business)

I do NOT recommend the 340 for the MGB. The 300 is a much better choice. But since I've already made the mods that one goes back together with the Rover heads and roller cam as my backup engine.

The stroker 300 has a set of TA heads with beehive springs and titanium valves. Ex-nascar Carillos and Wiseco pistons.

That leaves me with my iron head 2bbl 300 (in the car now) to play with later if i want or sell it if I don't. It will eventually be getting the alloy 300 heads and runs an alloy 4bbl intake and custom Enderlie throttle body with port injectors and COP. Stock valve springs and 4800 rpm redline.

In that configuration the 2bbl iron head 300 which has 9:1 compression probably puts out around 250hp. Just a guess, it could be a little less than that but the torque output is very good. That's with the stock cam. The iron heads also have larger ports and valves. The engine is no slouch by any means and the car seems to keep up with the 302 cars pretty well.

The configuration posted above is obviously going to be more powerful. For one thing the potential redline is going to be in the 7k range so clearly the numbers are going to go up and that doesn't even count the displacement increase. How much really doesn't matter, the power level will be adequate. It should be no problem whatsoever to exceed 300. Beyond that I pretty much stop counting.


The part number for those Wiseco pistons is WD-12883, they work with the Rover heads, 350 crank, and 6.2" rods with .827" wrist pins and use the modern thinner rings.

Jim

Thanks for the information Jim, I appreciate it as always.

Eric

PAC suggested either the PAC-1276X beehive at 1.67" installed height or the PAC-1202 dual spring at 1.7" installed height.
Either one is going to take some work but should give enough spring pressure to get a decent redline out of a roller cam with around .500 lift. I'm new to roller cams so not really familiar yet with the level of pressure required to follow the lobe profile at a given lift and RPM, but my machine shop guy says he likes to see spring pressure equal lift. In other words 500# at 1/2" lift, 600#@.600" lift and so on. He didn't say what target rpm that was suitable for and I didn't think to ask but I suspect we were in the 7-8K territory.

So with that said, the PAC-1276X @ 1.67" gives 200# seated and 427# @ .550" lift. They require opening up the pockets to 1.300" and making up .110" of height somewhere, maybe with offset retainers and cutting the seats deeper. Coil bind is at 1.070" so these numbers give .050" of free play, I think that can be shaved probably about .020" leaving .090" to make up. A .050" offset retainer will work and a .100" one might. I expect cutting .050" deeper pockets would be OK and they might be able to go .100" but I haven't taken any measurements. I'll have to check with Dustin on that unless one of you can do it. This seems like it might be a viable option.


The dual springs at an installed height of 1.7" have 187# of load and 484# open. I do not know what the coil bind figure is for that one but it might be usable at a lower installed height. Coil bind is at 1.100 so that installed height again represents .050 of free play and these springs need .140" made up. Probably possible, not necessarily easy.

Jim

Jim, Wow! Those spring pressures will snap a flat tappet cam in half! Those pressures may work good for racing roller cams but for the street 120-140 closed and 300-350 @ .550 lift would be good for a hydraulic roller and 100-110 closed and around 300 @ .550 for a hydraulic flat tappet cam. Check out these PAC beehive springs for a Dodge Viper V10. If installed at 1.7. Also perfect for the bigger, longer 75-76 Oddfire V6 valves.

[www.racingsprings.com]



Edited 3 time(s). Last edit at 01/25/2023 01:58PM by mgb260.

You would add 20-30lbs closed and about 50lbs more than above for solid lifter cams.

From Alex's Parts:

Hyd Flat Tappet, High Performance Street- 110 Lbs Seat Pressure.
Hyd Flat Tappet, High Performance Marine and Hot Street- 120 Lbs Seat Pressure
Hyd Roller, Mild Performance Street- 120 Lbs Seat Pressure
Hyd Roller, Mechanical Flat Tappet- 135 Lbs Seat Pressure
These are considered general "rule of thumb" pressures.



Edited 1 time(s). Last edit at 01/06/2023 01:26AM by mgb260.

The rate on those PAC-1283 springs is 363 lb/in so wouldn't you divide that by 20 to get the increase for .050"? And then wouldn't that apply at both ends? I get 18lbs so if installed at 1.7" it comes to 128/346 if my math is right. (Actually looking at the chart in the PAC catalog it would be 146/346 installed at 1.650" with .550" lift but that only leaves .020" before coil bind, with my Procomp rockers it'd probably be fine. Have to pick up .090" or more somewhere on the installed height. Waiting to hear back from Dustin on how deep the pockets can go.

The price is a bit better (about $60 less) so here are two options, one with higher loads. If the heads were cut to accept the 1276X but the 1283's were installed a simple spring swap later would be easy enough if more rpms were needed. Since the 1.290" spring is LS size it might make sense to go that route.

I'm a little more concerned with what are considered standard loads at .550" lift and how it affects max rpm. Love to see a chart on that. (I'm aware that valvetrain weight is a factor) BTW I'm pretty much done with flat tappet cams. Seen way too many lobe failures.



Jim