Questions about a mild build for a 350 in a Jeep

I've done a few builds in other vehicles but never a Buick.

First, I'll describe my intended use.

I'm going a little bit against the grain here since most people are looking for street/strip performance or more out of their builds. I'm going a different direction. My goal is to have a good, solid, reliable powerplant in a 1969 Jeep Wagoneer. It will mostly be a driver. Occasionally I'll load it up with camping gear and head up to the mountains. I may even get a camper to tow behind it but it will probably be fairly light weight. Certainly not over 5,000 pounds. So I need good low and midrange torque and I can sacrifice top end. I may do some light trails off road but nothing really major. I'm not going to do any serious crawling in the Wagoneer. I have my Wrangler for that.

So I don't have any hard numbers but my goal is "good low to mid range torque balanced with acceptable fuel economy".

I'm still deciding between keeping the stock TH400 or swapping in a 700R4. I looked at a 200-4R but no one makes any adapters to have a transfer case hanging off the back. Besides, the Jeep really is a truck so a truck transmission like the 700R4 is more appropriate. Also, a 4L80E is overkill for what I'm doing and it's more expensive.

I can gear the axles any way I want. So my first question is what a good target freeway RPM would be for my SBB? With the setup I'll be running for axles and tires, the TH400 puts me at around 2,250 at 70 with the tallest gears I can have (2.73). Though I'll be more likely to get axles with 3.31 gears which puts me around 2,700 at 70. I can split the difference with 3.08s which put me at 2,500. With the 700R4, I can take the freeway RPMs down to well below where I would think they're reasonable for a heavy SUV but going up from there is merely swapping out the ring and pinion on the axles. So what say the experts? What's a good target cruising RPM for the SBB 350?


Next question has to do with what benefits I'll get from upgrade parts when I rebuild the engine. I will be tearing down the engine to completely start over. I'll be having a shop do a full set of machine work on the block. Bore (or just hone) the cylinders, line hone the mains, deck the block if it needs it, etc. So when I start putting it back together I can keep the existing parts or upgrade. I don't mind spending the money on upgraded parts but only if they actually buy me something.

I figure at the very least an aluminum intake is a good idea so I've looked at the TA Performance stage 1 dual plane manifold. That looks like it's good for my mild/moderate build. It looks like a perfect foundation for a TBI throttle body.

I know aluminum heads shave weight and that's never a bad thing. But given my target build do I gain much beyond weight by going with the TA stage 1 heads? I know airflow is better on the Stage 1 but I'm not really pushing my build so how much benefit would I really see?

From what little research I've done so far I'm assuming that the SBB has the same lack of choice when it comes to off-the-shelf pistons and that I can either choose stock dish with stock ~8:1 compression ratio or jump right to a flat top which pushes my compression way past my desired 9.0-9.5:1. Have I missed the "moderately dished" piston somewhere or am I out of luck? I'm also assuming the factory crank and rods are fine for a moderate build as long as they pass inspection. Anything to look out for there?

As far as the cam, I always have trouble picking the right grind. Last time I chose a cam it was for an AMC engine and I have no doubt that the numbers for a SBB would not exactly line up. I'm leaning towards the TA 112 cam or something close to that since it's a driver. Are there better choices? Is a roller cam and/or roller rockers worth the extra money in a moderate build?

I know I'll be having the shop do any oiling mods. And, having worked on AMC engines, I'm familiar with the drawbacks of the pump being built into the aluminum timing cover. I'll keep my eye out for excessive wear. Anything else to think about as far as oiling mods?

Anything else that really stands out when building a SBB 350?

Thanks in advance.

 

Not much advice from me, and you will get the good replies soon from the ones who know what they are talkin bout! Lol.
But if I remember right from what I've read, good head work is where it's at. The TA stage1 aluminum intake doesn't seem to flow much better than the iron intake. So it seems its more of a weight reduction than a big power increase. I just installed a Ta212 which seems to be a good all around cam for the 350. Good head porting, Distributor recurve, Larry has a great write up here about power timing the buick. Could shave a little off the heads to bring compression up some.
350 likes to breath so a good exhaust system will help. I like a nice built quadrajet personally. The 350 seems like a nice reliable potentially strong motor. been driving mine for 90,000 miles now and it's been great.
Again, I'm not very knowledgeable on the subject but this is what I seen to remember from my research over the years. Good luck

 

I'm not in favor of the TA 112 because of the relatively short 260 advertised duration.
The short advertised duration will force you to use a lower static compression ratio than you want which cost fuel mileage and some loss in torque.

You will get votes for the Crower 50258 level 3 cam which is a good choice if you stay with the TH400 tranny.

If you end up with the 700R4 with overdrive and lockup converter then I suggest the Erson E650101 cam.
It has a 208/208 duration on a 111 LSA for excellent low end torque and fuel mileage and a 280* advertised duration that will let you use over 9:1 compression.
The mild ramp rate will help with longevity.

Paul

 

Look at the Crower level 2 cam for bigger lower end torque for truck/rv use. It will limit top end rpm some. Also the 2.73 effective gear is for a 26 inch tall tire. Depending in tire size you need much more gear and you should have the rpm closer to the torque band for best mpg and power. So 2200 at 70 will be inefficient ,worse mpg,and worse for a truck use say in mudding as equivalent torque isn't where its needed. New jeeps with v6 run 4.10 gears and 29 inch tires. Most gm trucks run 3.42-3.73 gears now on LS engine. If your using stock pistons from 68-75 pistons. They have a 1.835 compression height. Mill .025 off block to get piston closer to deck. Then mill heads to get your compression to desired . I assume 9 to one is good for your purpose so it will be like .020 off heads. Avoid pistons with 1.805 or less compression height. Stock intake is better for low torque then ta intake

 

That's what I'm looking for.

Stock Wagoneers in the 1980's came with 2.73 gears and 235/75R15 tires (28.8" advertised OD). The towing package was 3.31 gears. This was with an AMC 360 and TF727 transmission. They seem to do pretty well mileage wise for a brick on wheels without overdrive.

Should I take it that the Buick wants to run higher in the RPM range?

Most Wranglers come from the factory with 3.21 gears and 255/75R17 tires or equivalent (32.1" advertised OD). Only the absolute base model Sport wrangler comes with 225/75R16 (29.3" advertised OD). 3.73's are an option. Stepping up to the Rubicon gives you standard 3.73's with optional 4.10's on the same 32" tire.

The 3.6l Pentastar makes crap for torque below 2,000 RPM. They make up for the 3.21's by having a transmission with a very deep first gear (3.59:1 in the auto and 4.46:1 in the manual) and a higher stall torque converter in the automatics. When mine was stock with the 32's and 3.21 gears, I basically couldn't use 6th gear in my manual because it dropped the RPMs below 2,000 and it couldn't hold speed unless I was going downhill with a tail wind. It now has 35" tires and 4.56 gears though I wish I would have gone to 4.88's.

My intention is to run on the lower octane pump gas if I can so I don't want my compression ratio too high. Somewhere in the low to mid 9.x:1 ratio would be as far as I want to go. It's good to know there's room to shave off the deck and heads to bump up the compression. Is it good to assume that there is no interference issues with the valves and the dished piston? I know most flat top pistons have reliefs for that purpose. At what point do you have to worry about it?

 

The valves should not contact Pistons. It's not a huge lift cam and Pistons will sit down hole between .030-.060 down hole in most cases that's even with .030 shaved off block. Build for torque and you will be good. You don't need much for compression . 9 to 1 would be fine for this cam and most others. If you have a bone stock 68-75 engine and shave heads .030 you should have 8.8 compression. The crower does increase cylinder compression for more torque. So compression doesn't need to be high and retarding cam timing without loosing low end is possible. I know the new v6 is weak but I was talking about the earlier 2.8 I believe. Had nothing but gear. I see your doing the math just saying to a little rpm is not bad at cruise. I run 3.42 gears with a 28.8 tall tire. Still pulls super hard and 22-24 mpg depending on how hard it's driven on highway

 

Use the Crower level 2 with 9:1 actual compression. T400 is over kill, adds weight and cost power to operate.

 

TA needs to update their catalog!

The current TA 212-350 cam differs greatly from those old specs.

Last I saw (and they could have changed it since then, who knows right?) It was 280/285 @.006 and 218/230 @.050 with .454/.456 lift @1.55 rr on a 110* LSA, ground 'straight up' (0*/0*), which would put IVC @ 70* at that position.


Gary

 

Good to know. Thanks for all the help.

Yeah, the 3.8 minivan engine from 07-11 was a terrible engine for the Jeep. But, and I got this directly from the head of the Wrangler product line, they went to a V6 mostly to make it easier to pass crash tests. A big long straight 6 makes that a lot harder. The 3.6 Pentastar they've been using since 2012 has a much better top end but it's still gutless below 2,000.

For the Wagoneer, I figure with the 0.70:1 overdrive in the 700R4 and 31x10.50R15 tires I can probably get away with 4.10's easily. That would give me around 2,200 RPM at 70.

 

Good choice for a jeep.

Remember though that with a 58* IVC point and 9:1 SCR, DCR will be in the premium fuel zone.

This combo will produce some serious low-mid range torque.


Gary

 

HI Roy here is my 2 cents:

1. I would keep the th-400 it is strong, reliable and easy to rebuild or find another if needed.

2. I would use a 3.08 gear, 2500 is a good RPM for the Buick 350, and no matter what it is not like you are going to get 30 MPG with this thing. The 700R4 and other trans options are okay however it would be a big pain in the but to swap over as both the driveshafts would need to be modified as well as cross member modified. Not worth the hassle in my mind. If going to that much work might as well swap in a 5.3 and 4L60E.

3. Before picking pistons get the engine torn down and have the machine shop measure what needs to be done. You may be able to re-use the stock pistons if the block is within spec. If you do need new pistons then just get a set of the 10:1 rated pistons and you will end up with about 9:1 compression as the pistons sit in the hole from factory. Many people think that it is very important to have the pistons sit at zero deck however with the open chamber head design I do not think kit is worth the hassle. If you can afford the $ a great idea is the nice forged pistons from Diamond or other people such as "buyracingparts.com", then you can get a custom piston that sits at zero deck without milling the block.

See this pic to see where the valve reliefs are in my Diamond pistons and why even dished pistons need valve reliefs for big cams when the pistons are at zero deck. Notice how the reliefs are at the edge of the piston so dish does not effect the valve reliefs much.




Doing a mild build without a huge cam valve reliefs are not going to be needed, so its a mute point.

I agree with the others. 9:1 and a mild cam is good... I would do 9.5:1 and a TA212 cam... I would not spend the $ on a roller cam or roller rockers for this application. The crower level 2 cam is also a good option for you as stated above.

 

Thanks everyone for all the good advice. It's really helpful.

 

Thanks Larry

The Crower Level 2 cam is also a good choice but as Gary pointed out the compression ratio needs to be lower than 9:1 unless you plan on using premium pump gas only.
In order to run regular grade pump gas the compression ratio is restricted to 8.5:1 with this cam.

If you need new pistons this can be accomplished with KB S1749H hypereutectic pistons, no head or block milling except what might be needed for surface cleanup.

It may be extra work but the 700R4 will allow low gearing for the occasional off road journey and low rpm for highway use.
The other piece is; anytime the torque converter can be locked up, energy is no longer being wasted in the form of heat with converter slippage and fuel mileage increases.

Paul

 

So, assuming everything is kosher with the block and everything and I only need a few thousandths cleanup on the deck and heads, with maybe just an overbore, the stock dish piston (or an overbore with similar dish) would be right for the Crower Level 2?

That's my thoughts as well. While it's not necessarily a good car transmission, the 700R4 is very highly regarded in the truck and Jeep world, especially when you do some basic upgrades in the rebuild. And while the TH400 is stock and easy to keep, the 700R4 has quite a bit going for it and merits consideration. But I don't have to make that decision today.

Thanks again to everyone for the help.

 

The KB/Silvolite S1749H hypereutectic pistons sit .040" in the hole and have a 23cc dish which will give you around an 8.5:1 compression ratio with a .030" overbore.
The hyper pistons are stronger than the regular cast and use very tight piston to wall clearances
That's why I referenced those pistons specifically.

The Crower Level 2 cam closes the intake valve 58 degrees ABDC (if installed 4 degrees advanced) which gives the engine a 7.2 dynamic compression ratio when the static compression ratio is 8.5.
A 7.2 DCR allows lower octane gas use with a Buick 350.

I like the idea of a TBI sitting on a TA Dual plane manifold. No problems with off road extreme angle carburetor problems.
Which TBI are you looking at?

Paul

 

I'm running the Holley Avenger TBI on the 401 in my truck. I don't have a lot of miles on it yet but I do like the self tuning aspect, especially for trips over mountain passes. I'll probably get another for the Wagoneer. I'll have to see about getting a TBI compatible HEI distributor but that shouldn't be too hard.

 

Yes indeed, but it doesn't distract from the fact that TA's catalog needs updating because the cam specs there are incorrect/antiquated.

The 112 cam differs also, btw.

You can try to find some conflicting quotes on that too if you like.