difference between K-code and stock exhaust manifolds

Scott, The Hi-Pos are larger than the stock "log" manifolds. Plus, as you mention they look factory. They also should last longer than aftermarket headers, at least in the past they did. In this day & age of ceramic coatings that may no longer be true. I've heard of the Hi-Pos being compared to shorty headers. Note though that Shelby swapped them for Tri-Ys on his cars. FWIW the Hi-Pos I put on my '64 required an odd bend in the exhaust piping to get around the clutch fork/linkage probably negating some of their advantage over the factory logs.

bill

64.5: 260, 3 sp, a/c, SVO cam, Performer, Holley 390, Pertronix, Hi-Po exhaust, 1.5" front & 1" rear drop, Jacobs wires, Torq D's

66: '93 5.0, C4, a/c, ps, Performer RPM, Holley 600, Pertronix, bench seat

Colt SP1,Sig P220, Moss. 590A1, Marlin 70P

The purported reasoning behind C Shelby's switch in 1967 from the Header/Tri Y type to the HiPo manifold was due to the addition in 1967 to PS on all Shelby GT cars (less the SuperSnake) to add to the Touring Car mindset of a little more civility and increase the sales market. The header did not allow proper clearance for the PS. The HiPo manifold also sounds great -though not the roar of a header nor do they provide the performance increase. Although the 67 Shelby GT 350 retained the advertised 306 HP I doubt the exhaust flowed as freely as the previous models that used headers. A natural assumption to which I'm sure most will agree.

All things considered I really like the HiPo manifolds in reference to the more tamed exhaust noise. When I purchased my 70 Boss 302 in 1987 it was sporting headers attached to the original exhaust but the sale also included the original free flowing Boss manifolds. Within no time the headers were gone and the orig manifolds reinstalled. Sure there was a performance loss-especially with the Boss 302 power curve in particular-but no regrets on my part. It is far from quiet but I can at least hear a little better and makes for a little more pleasant driving.

J Burke

67 GT 350 70 Boss 302

Another alternative that many people have forgotten is the use of iron 351W manifolds. These take a different approach than the Hi-Po's. They actually get wider from front to rear, creating a progressively bigger inner port as each cylinder "adds on". Remember, they are made to work with 63 more cubes.

I used them in a '69 engine bay. They "should" work in a '66, but I really can't remember what the shock tower clearance is like in your car. But if you hunt around some junkyards, you might be able to score a set cheap. Mine were sitting in the dirt after someone had pulled the engine out of the car, and they cost me a whopping 15 bucks.

CobraJet

"CobraJet" wrote

Clearance might be an issue as you need special hedders for the 351 swap in the early cars. Although these would be going on a 302 and not the wider

351. hmmmmm.

So basically it comes down to some loss in performance, but quieter interior noise. Are we talking alot of power loss?? or not enough to really notice? I don't mind some top end HP as this will be a streeter, but I don't want to lose too much low-end torque, which is why I was thinking of the tri-y's.

Scott W. '66 HCS

Headers are different story altogether. The reason a separate swap header exists for the 351 is because it places the port exit higher and further out. A 289 header in that position could hit the floor pan or something else. The iron manifolds don't go down that far.

For absolute off-idle torque, it's hard to beat the stock manifolds and a single exhaust. I know, it sounds lo-po, but that's why they come that way. I went from this system to the 351 manifolds with a dual 2

1/4" exhaust. Off-idle torque decreased noticeably, but overall power increased throughout the operating rpm. The kitted C4 could still chirp second easily. This was a 302-2V with 100k on the odometer.

The Tri-y's will work well, and be noisier. Ultimately, you have to figure out the whole car as a package, and be very cognizant of your intended use. Shelby used Tri's, but his engines had upgraded cams, intakes, carbs, and usually more gearing.

CobraJet

How bout I tell you what I have so far and what I want to do?

It's a C8 cast .060" overbore 302 with a hi-po Melling cam (not an RV cam) similar in specs to the Edelbrock RPM cam. It has stock C8 heads with hardened exhaust seats gasket matched. It has the stock crank turned 10/10. Edelbrock Perf RPM Air-Gap manifold topped with a 600CFM Edelbrock Performer carb. It will have either an AOD or a T-5. I'm leaning HEAVILY to the T-5 as it was originally a manual 3-spd anyway. It has a 3.00/1 peg leg 8" in the rear. I'm not gonna drag race it, just cruise it. Take it to the local show and shines in the summer. It might be my daily driver for an EXTREMELY short period of time until I can get to work on another project which WILL be the daily driver ('69-'70 Sportsroof). What I want is alot of torque for the stoplights but have a nice cruising attitude at the same time. Handling is important, but MPG is more important.

I think I've got the suspension formed in my head. stock upper control arms, tubular lower arms. Front end disc swap. Upgrade the rear drums to the big boat brakes of the 70's, and 3.80's in the rear (I won't mind keeping the peg-leg 8"). 600-620 coils in the front and 5 leaf mid eye's in the back. Stock shocks or KYB GR-2's to smooth out the beefier springs.

Hints anyone???? Tri-Y and spend the money to have them coated or Hooker Super Comps or stock logs, or Hi-Po cast manifolds? Dual or single out the back? What size tubing? I'm thinking dual 2 1/4" would do well. I really wanted to use the GT valance on the rear, but the trumpets are only 2" pipes. Why go 2 1/4" just to choke it in the last 6 inches?? So I decided on the Shelby-style side pipe idea.

Scott W. '66 HCS

OK.

At this point I think the RPM equipment on unported heads with a

3.00 rear is a big ol' mismatch. For torque, you should have stuck with the Performer and possibly a Comp XE hydraulic. Edelbrock will be the first to tell you their RPM stuff was built for small-tube headers and massaged ports, an intermediate stage under the Victor stuff.

More rear gear is a must with your present equipment, but you've already got parts that will not optimize mileage. As the rated rpm range of an intake/cam combo goes up, the low end port velocity goes down. You have to pick one direction or the other. Buy a Trac-loc for the 8-inch.

If this were my car I'd toss mileage into the wind and go for Tri-Y's or street Hedmans with 2 1/4 exhaust and DynoMax mufflers. Forget the AOD; this combo with a short stroke will respond better to the T-5. The RPM parts will want a looser converter to keep out of bog territory, and that will cost performance. The stick has a lower first gear, too.

CobraJet

"CobraJet" wrote >

I bought the RPM air gap because it was a steal at the time and I could swap it onto another motor down the line when this one dies. At .060" overbore this block is shot after this build. I'm only keeping the stock heads for now until I can get some AFR's. My motor builder says it's not worth doing though and if I want to go with better heads to just start over and blueprint a new block. I was a dumbass when I started this motor and didn't have it balanced cause I couldn't afford it at the time and got ahead of myself. Hence my motor builder's advice of dumping this one and starting over instead of swapping externals on this block.

Which will give me more performance though? full dual exhaust out the back or side pipes? I didn't think traction loc would be worth it for just a cruiser. I know the advantages, but I'm not sure I'll need them. Explain to me otherwise and I'll reconsider it though.

I'm not worried so much about mileage on this one, but it's still gonna be a cruiser, not a bruiser. I've decided to go with the t-5 and the tri-y's. Should I still swap in the 3:80's into the rear? I want to make sure my power band is where the rearend will help instead of hinder. I'd like to be in the powerband in OD so the motor isn't lugging at 70mph.

Scott W. '66 HCS

I understand the allure of good deals on parts, but then you might wind up with a mismatch and a performance dilemma. As far as not doing the heads on this block; just how long do you think this engine will last? It might be years, and your driving a bottled-up situation in the meantime.

One trip to the strip and you'll be convinced. The change to a dropped trans ratio *and* steeper rear gears is going to be a shocker. Both to you and the rear suspension. Building more power will be a waste if you can't get it to the ground. Find a '68 and later centersection with the additional ribbing. Previous cases are not as strong.

Side pipes typically necessitate a tight "S" turn from the header collector to the front of the pipe. Whether that's any more restrictive than going over the axle is anyone's guess. I ran 2 1/2" pipe to 2 1/2" mufflers hung in front of the rear axle, and that's where it ended. No bends.

I hate to tell you this, but you are not headed towards "cruiser" status with this car. If you get this whole package together as we are discussing in a light '66 car, you will be having more fun than you bargained for. My car had 4.11's and some more rpm's up top, but it was doing 13.20's on street tires by the time I was done.

I forgot what the OD ratio is on the T-5 exactly. Let's go with .70 for giggles. 3.80's give you 2.66's, 4.11's gives you 2.88's, and

4.62's gives you 3.23's. The first combo is useless in OD for a small carb motor, the second will be snappy with good top end, and the third will put the hurt on the idiot next to you, and you probably will not be sacrificing any top end at all. With a dropped first gear, though, you may find yourself leaving in second in normal traffic with 4.62's.

OD transmissions really didn't grab center stage until EFI created some low end efficiency. With your setup, you really need to decide how much top end you want versus some giddyup on the local streets. If high speed is not a big concern, the 3.80's would work well with a 4-speed Ford Top Loader. It's much stronger than a T-5 and you don't have to deal with a hydraulic clutch conversion.

CobraJet

"CobraJet"

I know, I'm choking this motor with the stock heads. Maybe I can find a deal on used late model heads at a swap meet or salvage yard. Surely they would breathe better than the stock C8 cast heads. I am at least having the C8 heads gasket matched. I'm not going to match the heads to the intake though, especially because I'll reuse it with a different set of heads later on. I'm really only planning on having this motor for a few years. I'm gonna be looking for a good 289 block that hasn't been thrashed and blueprint it with only top quality parts.

I completely forgot to list originally that the motor is running flat top

10:1 pistons. With the altitude though (Denver) I guess it'll be more realistically like 9.3?? I'm hoping I won't HAVE to use premium.

I'm not planning on taking this car to the strip.

What about just moving the mufflers forward from the stock position a bit, or mufflers that enter and exit on the same end? Just curve the exit side into a side exit position.

What about running 2" all the way? More torque in the bottom end? or would it choke the motor?

I'd like to be somewhere in the middle. I drive from here to OKC and Kansas City on occasion and there's a WHOLE LOTTA NOTHIN' between here and either of these places. Top end speed is important. I don't mind giving up a little at the stoplight. My common cruising speed is between 85 and 90mph (and I'd like to have even a little more in reserve just for giggles).

Scott W. '66 HCS

A way to maybe cut down on the restriction of the pipe after the muffler would be to run larger tubing to make up for the tight curves? Does that make sense? Run 2.25" from the collector to the muffler, but run 2.5"-3" after it for the tight curve back to the side of the car. That shouldn't have THAT much of an effect I would think over such a short distance. From the header collector to the muffler then.

I know that the original Shelby side pipes didn't have a crossover (balancer) tube, but wouldn't it be advantageous to have one even for the shorter system? Tri-y's with an X into Magnaflows, then side exit them in front of the rear wheels? Or what about dumping standard mufflers altogether? Using Supertrapps' on the tips instead? That way there would be no necessity for funky tight curves in the exhaust pipe. Just angle out from the crossover into Supertrapps' with the tip showing in front of the rear wheel. It would look kinda "trick" with the different types of tips they have.

Scott W. '66 HCS

Nope.

True blueprinting involves squaring everything and dialing in the component stack, and a whole bunch more. Lots of shops throw that word around carelessly, so be forewarned.

Required octane will be depending on how quickly the camshaft builds cylinder pressure and, of course, your advance curve.

That was meant metaphorically. Ignoring the advantage of two driven axles instead of one is folly in this situation.

Well, now we're getting a liitle nuts here. Pick whatever you want to do. R-code Shelbys ran a glass pack a bit behind the header collector and then angled out to exit the side in front of the rear tire.

You're trying too hard to have it both ways. With a gear swap, low end torque will not be as much of an issue.

Run the 4.11's with 2 1/4" pipe. The '69 ran 112 flat out with a dead stock high mileage 302-2V, 2 1/4 duals out the back, and a 3.25 rear with G60-14's.

CobraJet

You're overloading me with stuff you'll have to figure out on your own.

CobraJet

"CobraJet" wrote

Surely they would

Damn

I know, I want a truly blueprinted 289 for this car eventually. I have an engine builder who'll do it right and I trust him. I also know he won't rape me on price either. Another thing I like about him is, you tell him what you want and he tells you what you have to have to do it. No candy coating it either. He's been building motors as longer than I've been alive, so he knows his stuff.

I'm not disagreeing with you, I'm just wondering if I need it enough to put out the money for a posi. advantage vs necessity vs $$$.

I don't want a loud exhaust, which is why I like the Dynomax sound. quiet but very definitely present when you step into it. It's also why I'm staying away from the stock Shelby R side pipes, too loud. Yeah I am a little nuts. :)

I want it all Dammit!! lol. I know, I know. I guess I'm trying to find the best middle of the road compromise.

You think that'll be the best middle of the road compromise?

Scott W. '66 HCS

I've had '70 351W heads on a 289 powered '65 for 20+ years so far. I've probably gone through 3 or 4 sets of headers since then. I've always bought the plain Hedman or Blackjack models for the 289 - I've never needed special headers. All this on stock, non modded shock towers too.

Cheers!

zëkë

Remember to keep track of the compression of your pistons as rated with "x" cc's in combustion chamber volume and compressed gasket thickness. Your builder should have supplied you with these figures. Other heads vary in chamber size, so you need to be careful about swapping parts around.

Good.

I had a 2.79 open in my '68 when I put headers and an intake/carb on it. It couldn't hook even with that. Then came the cam and the '65 heads. The choice is yours.

Does your brain melt down at Baskin-Robbins?

With a T-5, the 4.11's will work fine. My example was to give you an observed mph with a known combo. This was a C4 car.

Well, of course you did. It's the taller Windsor _block_ that makes the difference. The port exits in the same place whether 289 or 351 casting, so just a head swap won't need different headers.

CobraJet

My news server expired most of the original thread, so I thought the topic was 351W head swap and not block swap. You're absolutely correct about the taller and wider 351W block not fitting real well in a '65/'66 body.

Cheers!

zëkë