[pa140flyer]

Building this for a 1967 GTO using a tremec 5 speed with .68 5th gear, 3.55 rear gears.
I want to keep the 670 heads and was planning on using ram air exhaust manifolds (if I can even get them!). I want to make this a reliable cruiser and I would like to burn 87-89 octane. I want to get as much performance as I can but in reality I know that will be limited as I want reliability and economy over brute horsepower!
Now I need advice on camshafts. I was going to use a flat tappet hydraulic then 2 Pontiac businesses said basically there is a 50-50 chance these days that a flat tappet cam is going to fail. I have read all about the correct oil to use and correct break in practice but there are still those out there that say in the world we are in quality is suffering. I don't want to go to the complications of a hydraulic roller either.

So what recommendations do you have for a camshaft manufacturer and specifications? I was looking at the comp cams xe268 any recommendations?

I was looking at keeping compression in the 8.7-8.9 range, any recommendations?

Piston manufacturer and specifications? I was looking at maybe Ross forged 22-24cc dish pistons, recommendations?

Do I need to rebalance? My machine shop says it isn't necessary, recommendations?

Do I need hardened seats? My machine shop says they aren't necessary since I won't be towing or racing, recommendations?

Can I use the existing cast rods? Do I need ARP rod bolts?

Any vendors out there that you would recommend to supply components?

Any other wise advice would be appreciated as there seems to be a lot of knowledgeable members out there?

[Rar_421]

Im doing a 350, hydraulic flat tappet cam and hylift Johnson lifters

[b-man]

Stick the factory 068 cam (Mellings SPC-7) in it, less likely to wipe a lobe due to the slow acting low-lift lobe. A performance cam that was designed to last through the vehicle warranty period and beyond.

If you want your engine to tolerate cheap low octane gas a cam with a lot of seat timing like the 068 should be your saving grace, the XE268 would be the opposite of that.

Toss the stock cast rods in the trash and buy some decent offshore forged rods.

Ross custom dished pistons or Icon custom dished to your specific compression target are a go.

Balance the rotating assembly and use hardened exhaust seats along with all new stainless steel valves and bronze guides. Do it right.

Honestly you shouldn’t build it to run on cheap low octane gas, the added efficiency of an engine with slightly higher compression that runs on premium will more than offset the added cost of premium fuel. It’s a win win situation, you get the same overall cost per mile and more power at the same time.

[pa140flyer]

b-man what do you recommend for forged rods? The one reason I was after running 87-89 octane isn't because it is cheaper but because I plan on driving this car on long trips a lot and the way things are going I was concerned about even getting 91 octane fuel! I know I am probably being paranoid! What is your opinion on CR for 91 octane?


Rar_421 How far are you on your 350 build and what company are you dealing with to get parts?

[tom s]

FWIW,about 3 years ago I built a street 421 engine.I did the 068 with a NOS set of GM lifters.Factory cast crank,custom Autotec dished pistons.Factory cast 69-70 rods with ARP bolts.The car gets driven pretty much every week,sometimes as far as 100 miles each way.It does not get beat on 2.68 rear gears so 1800-2000 on the freeways.Having experienced a dropped valve in. 400,seeing a cast rod bend without catastrophic failure I chose to use a set in the 421.Tom

[wakesupremo]

I use Tin Indian for all my parts. Good service and very knowledgeable.

[b-man]

Originally Posted by pa140flyer

b-man what do you recommend for forged rods? The one reason I was after running 87-89 octane isn't because it is cheaper but because I plan on driving this car on long trips a lot and the way things are going I was concerned about even getting 91 octane fuel! I know I am probably being paranoid! What is your opinion on CR for 91 octane?


Rar_421 How far are you on your 350 build and what company are you dealing with to get parts?

Nothing wrong with being a bit conservative with compression when you might be stiuck using 87 or maybe even 85 depending on what state you’re traveling through. Your 8.7 to 8.9:1 should be fine in that case. Somewhere between 9 and 9.25:1 would be pretty safe I’d say.

I built my 421 HO at 8.8:1 intending to run 91 octane premium. However my car is a heavy and highly optioned Le Mans convertible with factory A/C, automatic transmission and a 2.56 rear end so it’s a bit less octane tolerant than a lighter weight 5-speed stick shift hardtop GTO.

Forged rods in whatever price range you can afford are available at most any established Pontiac parts vendor like Butler’s or even through one of our forum members Paul K (Paul Knippen) who also builds some nice engines as well.

[steve25]

Forged rods besides aiding longevity add to performance and fuel mileage long term.

They are far lighter then the cast rods and this allows the motor regardless of its compression ratio to rev up faster.
The different I found on one build I did for myself was interesting.

I had planed on going from 2.93 rear gears to 3.23 like I had helped a buddy do the year previous .

I found that with the lighter internals of my new motor that it’s acceleration even with still keeping the 2.93 gears was so close to what I had found with a swap to 3.23 gears that I ended up just staying with the 2.93 gears.

Both of the motors I have discussed here where making within 5 to 8 psi of cylinder pressure of each other and basically weighed the same .

It takes note worthy less Hp to keep light weight internals spinning and since you plans are to drive the car far & wide your fuel savings will pay for the cost of the new and better Rods.

Since your going for new pistons and have to get a rebalance job done anyway, that’s not a issue to consider.

In terms of pistons you should not consider any forged replacements that use the stock high friction 5/64” ring size, you should be only looking at 1/16” or even .043” rings, and they should be of the gapless type .

This change will make for a nice reduction in friction, lower oil and engine temps and added fuel mileage.

In short everything your going to do to rebuild the motor which has to be done either way needs to be optimized by thinking thru carefully.

[i82much]

Originally Posted by steve25

Forged rods besides aiding longevity add to performance and fuel mileage long term.

They are far lighter then the cast rods and this allows the motor regardless of its compression ratio to rev up faster.
The different I found on one build I did for myself was interesting.

I had planed on going from 2.93 rear gears to 3.23 like I had helped a buddy do the year previous .

I found that with the lighter internals of my new motor that it’s acceleration even with still keeping the 2.93 gears was so close to what I had found with a swap to 3.23 gears that I ended up just staying with the 2.93 gears.

Both of the motors I have discussed here where making within 5 to 8 psi of cylinder pressure of each other and basically weighed the same .

It takes note worthy less Hp to keep light weight internals spinning and since you plans are to drive the car far & wide your fuel savings will pay for the cost of the new and better Rods.

Since your going for new pistons and have to get a rebalance job done anyway, that’s not a issue to consider.

In terms of pistons you should not consider any forged replacements that use the stock high friction 5/64” ring size, you should be only looking at 1/16” or even .043” rings, and they should be of the gapless type .

This change will make for a nice reduction in friction, lower oil and engine temps and added fuel mileage.

In short everything your going to do to rebuild the motor which has to be done either way needs to be optimized by thinking thru carefully.

would it be even more imperative to find a shop with a pontiac torque plate if you use thinner rings?

[steve25]

Yes, that’s a given to me even if staying with 5/64” rings.

[android 211]

If you are using a mild street cam that is done by 5500 then factory rods, resized with new bolts will get the job done and cost half what new forged rods will cost. New forged rods sometimes have to be resized too. Quality control isn't perfect. The Summit 2801 cam works very well with 8.5:1 compression in a 400, I have personal experience. I've had engines rebuilt with the factory balance and I've had them custom balanced and the difference in smoothness is noticeable. Use a thin head gasket, go for a .030" piston to head clearance to reduce pinging. Pontiac used a .027" head gasket and the piston was not down in the hole. In a perfect world with high octane gas an aggressive advance curve would give better response but a factory advance curve is probably a good compromise between power and knock prevention. Get a repro Ram Air pan and open your hood scoop. Cold air is your friend. Use new valves. Install bronze guides. If you really think you'll put 50,000 miles on the car then hardened seats too.

[Rar_421]

Originally Posted by pa140flyer

b-man what do you recommend for forged rods? The one reason I was after running 87-89 octane isn't because it is cheaper but because I plan on driving this car on long trips a lot and the way things are going I was concerned about even getting 91 octane fuel! I know I am probably being paranoid! What is your opinion on CR for 91 octane?


Rar_421 How far are you on your 350 build and what company are you dealing with to get parts?

I'm loading my block to take it the machine shop tonight
As far as parts I try to buy from Pontiac specific vendors if I can,many are members here,and I use eBay as you can still find some of the USA made stuff from retired shop owners etc,I've also bought from jegs,summit competition products and direct from companies like Crower etc

[chiphead]

Autotec for the pistons. They are fully customizable for what you want to do. Buy them through Paul K.

The trick is to have the heads CC'd after all the machine work is done, that way you know the head CC for sure. Then order pistons. I once had a set of Ross pistons done with a 20CC dish for a set of 670s. The machinist assumed they were 72CCs. Turns out they were 76CCs and the compression was lower than it should have been.

If the valve seats are ate up, it needs seats. The stock valves are 50+ years old, replace all of them. Guides often need inserts. Cost it out, often the cost of a full iron head rebuild can approach speedmaster aluminum heads.

For cam, use a slow ramp cam like a factory cam or a Summit 2801. I use the 2802 at 9.8:1, 2801 would be good for less compression and stall. The proper valvespring pressure and valvetrain geometry is key to cam life.

Ditto on forged rods. I beam forged rods 6.625/2.250 are about $390. Cheap insurance. Balance any time a rod/piston/crank is replaced.

[77 TRASHCAN]

Originally Posted by chiphead

Autotec for the pistons. They are fully customizable for what you want to do. Buy them through Paul K.

The trick is to have the heads CC'd after all the machine work is done, that way you know the head CC for sure. Then order pistons. I once had a set of Ross pistons done with a 20CC dish for a set of 670s. The machinist assumed they were 72CCs. Turns out they were 76CCs and the compression was lower than it should have been.

If the valve seats are ate up, it needs seats. The stock valves are 50+ years old, replace all of them. Guides often need inserts. Cost it out, often the cost of a full iron head rebuild can approach speedmaster aluminum heads.

For cam, use a slow ramp cam like a factory cam or a Summit 2801. I use the 2802 at 9.8:1, 2801 would be good for less compression and stall. The proper valvespring pressure and valvetrain geometry is key to cam life.

Ditto on forged rods. I beam forged rods 6.625/2.250 are about $390. Cheap insurance. Balance any time a rod/piston/crank is replaced.

Who sells these $390.00 I beam rods?

[chiphead]

https://www.lmperformance.com/150015...BoC7M4QAvD_BwE

[77 TRASHCAN]

I started a thread here, years ago about a higher compression 400 build. I just brought it to the top, if interested.

[pa140flyer]

This is still an active build but it is moving pretty slow. My machinist got back to me and said we would probably do a .030 bore. Now I have been researching the Ross custom forged pistons and was looking at a -24cc or -26cc dish but Butler is saying these pistons will not work with the stock cast rods without narrowing the small end of the factory rod to fit the ross pistons. Can anyone chime in and let me know if they have used the ross custom forged pistons with stock cast rods?



Are there any other pistons out there one could use with this amount of dish? I did contact rock and roll engineering and apparently he has some custom JE pistons that he says will work with stock cast rods but from what I have read he may not be the most reliable person out there.



I didn't want to go the route of forged rods but yet I don't want to have to narrow the cast rods either. I know this is being silly but I really didn't want to put China forgings in my Pontiac block!



I was looking at using the Melling SPC-7 cam as that looks like an exact copy of the 068 cam. Any opinions on using that cam and what would you suggest for lifters. Could I get by with the stock valve springs or should I still replace them?



Thank you all!

[Jay S]

I am going to suggest a couple different directions than what has been suggested.

If you are wanting to rod stock cast rods, I would absolutely stick with a stock type pressed fit speedpro L2262F piston. No rebalancing, works perfect with your rods, and way cheaper than the other aftermarket options.

Next your probably think that puts my compression to high, I calculate it to be 9.8:1 if it has 72 cc heads, with a .045” thick head gasket, 6.7 cc valve reliefs and the piston down .020” from the deck. Plus I think your engine has big cylinder scallops, so it is probably closer to 9.7 SCR all said and done.

You most certainly will get the argument the 9.7 is to high for 89 octane. But there are ways to manage it. I run 11.2:1 on 91 octane on my iron head Pontiac, I currently do not even have a Pontiac with less than 10:1 compression, at 9.7 to 10.5:1 compression we are running 87 octane, and all 455 cid or larger engines, which are more prone to preignition than your 400.

When you drop the compression a point down to high 8s your really hurting the efficiency of the engine. Which is ok, there is nothing wrong dropping the compression to meet conservative fuel octanes, the 068 regrind would like to be around 9:1 for what your goals described.. Lowering the compression is not always necessary though, sometimes you can design the engine to manage it better. It depends on what your willing to change to get there.

At 9.7 compression, I would use a Summit 2802 camshaft, 224* intake, 234* exh, .465” and .487” lift, 114 LSA, degreed in at 109* or 110*. If you kept with the stock 2.11” 30* intake valve it would run on 91 octane. If I was building it, I would actually change out the 30* intake valve to a 45* intake valve, it will make less peak tq and a little less power than the 30*s valve, but at low end cruising it will make more power, and be more efficient and get a few mpg better with your overdrive. It will also seat the intake valve a little deeper and gain a couple cc on the heads. That combination will knock the VE down at your peak tq, and spread the power out more. That simple change on the valve angle is like widening the LSA of that summit cam to 116 from 114, and it would end up dropping the octane requirement of the engine down a few points. With some port work and headers, it would actually run on 87 octane fine. With stock ports and manifold it probably would not quite get there, but it would be noticeably more tolerant to fuel than if it retained the 30* valves. I run one of my cars on 87 octane that has iron heads and 10.5:1 compression with over 500 cubes.

For lifters I would either search for NOS HFT lifters, old stock from the 80s Johnson lifters, have your old lifters machined and resurfaced, or buy new Hylift Johnson lifters which often run just under $200 now. Butler sells them. My first pick is NOS lifters or a old set of NOS Johnson’s.

Keeping the compression higher by close to a point the engine will make more power and be more efficient than it would be with light weight internals and a point lower compression. My 11.2 compression iron head combo makes a lot of power (550+), sports the factory q jet, looks stock except it has headers and get’s around 20MPG with 3.23s and no overdrive. For your exhaust, honestly, you have a huge hurdle finding anything but log manifolds for a 67.

[JLBIII]

I'm running KB Icon pistons with a 30cc dish. Heads are stock '68 #16. The combo has a 9.4 CR with a custom Comp cam.

[Jay S]

Originally Posted by JLBIII

I'm running KB Icon pistons with a 30cc dish. Heads are stock '68 #16. The combo has a 9.4 CR with a custom Comp cam.

That sounds like a stroker engine if you still have 9.4 SCR with a 30 cc head and 16s.