How much good are Tri-Ys with my set up?

68conv4sp · Sep 19, 2007

My '68 has a stock 289 (8.7:1 Comp.) and the smog bumps in the heads, a Edel Performer 289 intake, Edel 500 cfm, and dual exhause w/ log manifolds. Two questions about Tri-Ys. 1. Will they help low or top end more now? How much? 2. If I can afford a crate 347 later, will the ports shape/size match most crate motor heads? Thanks.

SoCalCruising · Sep 19, 2007

Your 289 requires 1 1/2" primaries, max, for best performance. A stroker will need 1 5/8" or 1 3/4" primaries - assuming street use. Well-made tri-ys make mid-range power and often good high-end power. This seems to be due to the short primary tube, especially if the secondary tube is large. If you are going to do a zippy 347, I'd wait and get what that motor needs.

That said, I installed 1 5/8" primary, 2" secondary tube Tri-ys on my car before I built the 331. I gained some performance on the stock A-code motor (I had more compression than yours, though) and I didn't regret doing it. There was a s light fitment difference, however, when the exhaust system was bolted up to the AFR heads later. Not too bad, but the fit was different. Wait if you can.

D.Hearne · Sep 19, 2007

I've run Tri-Y's on my 331 in the Ranger. If they were a bottleneck, you sure couldn't tell. Canfield heads on the 331. I welded the outside of the tubes all around then ported the insides to blend them to better match the head ports. This motor is making around 400+hp. The Ranger weighed in at 3800 lbs. With the Toploader 4 speed & 3.73 rear, 275/60's on it, it ran 13.70's @ 102 in the 1/4. Top speed was 140 mph.

68conv4sp · Sep 20, 2007

Interesting that both of you guys chose 331s. I know there have been lots of threads on this, but I will face that decision next. Perfect rod ratio? (whatever that is). I would gladly trade 16 cubes for longevity, and am somewhat concerned about applying too much torque to a convertible. It has Global West sub-frames, export brace, and Monte Carlo, but I often wonder if that would be enough with a torque monster.

How important is the port shape? I beleive the stock heads have rectangular ports. Do the tri-Ys?

D.Hearne · Sep 20, 2007

I went with the 331 also due to the fact that it will last longer. The Canfields have rectangular ports as do the Tri-Y's.

jb1dsl · Sep 20, 2007

I run into a issue with my 66 Cali. smog heads and the tri-y's. The headers would not fit with the air nozzles in. I did not have the emissions on my car anymore so I plugged the air nozzle holes up on the heads and all was well.

Vinyl66 · Sep 20, 2007

The tri y's will work great with what you have now. A 347 will need larger tubes.
Either 1 5/8" for a milder build or 1 3/4" for a higher HP build. Go with the 347. There are no problems with the current 347's on the market. Extra hp, extra torque, for the same price as the 331.

S-Car-Go · Sep 20, 2007

I bought the car had stock manifolds with dual exhaust (2" to flowmasters, dumps), no H pipe on a stock 289. I did the exhaust before pulling the motor, because I didn't want to tow it to the exhaust shop. Easier to remove a new exhaust system and bolt it back in.

I used FPA step headers 1 5/8 to 1 3/4, added an H pipe and tailpipes (2 1/2, dynomax). I figured I'd loose a little bottom end or stay the same. I was shocked at the seat of the pants improvement with a stock 289. More power from off idle all the way up.

SoCalCruising · Sep 20, 2007

I had a nice face-to-face talk with the tech guy at CP Pistons about 331 vs 347. He said that most guys run into trouble when installing the ring support on the oil ring land. It gets tweeked and then the ring looses some of its oil sealing properties. If installed expertly, he said that the 347 should not have oil sealing issues. We didn't talk about side loading of the pistons or longevity. Since I was building this motor myself, wanted to eliminate as many sources of trouble as I could. So, I went about finding 331 pistons that didn't require the oil ring support (some do, btw). I eventually bought Mahles and am very happy with how things turned out.

As far as longevity is concerned, there are good short rod motors around (Chevy 383, 400, and 454, for examples). What I did not see, however, were a lot of high mileage 347s that were still making the same (or close to the) power they made when new. That may only be that most people don't put a lot of miles on their cars with there 347 motors (neither do I with my 331). I would be happy to hear from people who have high mileage 347s that are still making the power. That would go a long way in dispelling the idea that these motors don't last.

68conv4sp · Sep 20, 2007

Going from a stock 289 to any high performance motor is going to be an amazing change. Since I don't need to squeeze every last ft. lb. out of the block, I'll be going the 331 route. Because of my conservative nature, I'll want to verify that any crate 331 that I buy doesn't require oil ring support. Do you think that CHP, or some other specific manufacturer are using that type of piston (or not)?

SoCalCruising · Sep 20, 2007

CHP uses Probe slugs. Check with them, but their older pistons don't use the support. Otherwise, specify Mahle pistons with your supplier.

mikethebike · Sep 20, 2007

D.Hearne said:
I've run Tri-Y's on my 331 in the Ranger. If they were a bottleneck, you sure couldn't tell. Canfield heads on the 331. I welded the outside of the tubes all around then ported the insides to blend them to better match the head ports. This motor is making around 400+hp. The Ranger weighed in at 3800 lbs. With the Toploader 4 speed & 3.73 rear, 275/60's on it, it ran 13.70's @ 102 in the 1/4. Top speed was 140 mph.

Have to agree with you. I've run them on stock head 289's since 1967. They just plain work! Why else would Shelby have used them?
The short tube feeds directly into the long tube that then feeds into the collector. This creates a low pressure in the adjacent short tube and evacuates that cylinder better. And this in turn causes an increase in your volumetric efficency. Which last time I checked was an effective increase in your cid and torque and h-p across the entire rpm range.....unless you plan on living above 6500 rpm most of the time.....which I doubt he is.
On a street motor they are hard to beat. Just look at the new hi-po cars out there and the exhaust manifold design.....tri-Y on most of them.

mikethebike · Sep 20, 2007

68conv4sp said:
My '68 has a stock 289 (8.7:1 Comp.) and the smog bumps in the heads, a Edel Performer 289 intake, Edel 500 cfm, and dual exhause w/ log manifolds. Two questions about Tri-Ys. 1. Will they help low or top end more now? How much? 2. If I can afford a crate 347 later, will the ports shape/size match most crate motor heads? Thanks.

Why not build a long-rod 302? They use a 400 SBC rod that gives about a 1.86/1 ratio. You gets lots of dwell at tdc, you reduce your rod angle at 90 degrees and elimnate a boat load of side loading on the piston and cylinder wall. The Speed-o-Motive guys said it's good for 6500 forever and if you get the Crower rods and special bolts you'll break the stock crank and block before you break the rods/pistons. Crower quoted somewhere north of 8000 if you have the block/crank to hold it.
But, if you do that you'll need long tubes.

68conv4sp · Sep 20, 2007

Sounds like good advice so I just bought some used tri-ys to play with. Next question: since '68 heads have the smog bump (I have not looked inside but think they are the orig heads) is there some way to remove or reduce the bump without removing the heads? Probably a stupid question. I think I know the answer...

Vinyl66 · Sep 21, 2007

Certainly the best way to smooth out the exhaust ports is with them off the block in front of you on a bench. But if I were going through the trouble to do that I would just bolt on a better set of heads.

I used to have an '89 Mustang with stock E7 heads. I used a Dremel with flexible shaft and removed the smog bump in each exhaust port while still bolted to the block. I just stuffed a rag in the port to keep metal particles out of the exhaust port. Then cleaned up each port with some brake cleaner afterward. It takes a little while because you have to grind, check your progress with your finger or little swivel mirror, and grind some more. You can increase the exhaust flow a good bit by doing this.

How much good are Tri-Ys with my set up?

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