HIPO manifolds VS Long Tube Headers 289 65 mustang

[synthartist69]

Hey everyone,

I just got the HIPO manifolds on today. I installed them on my 65 fastback shelby GT350 clone. It has a 289, Weiand aluminum intake, Holly 600, 268 comp cam, electronic ignition, 4 speed manual, 373 gears. The heads are completely stock as is the block. It originally had long tube headers on it which were a pain in my opinion. Exhaust leaks, warping, noisy, just a nightmare all the way around.

After switching to the HIPO manifolds I feel that I have lost about 10% of my upper power. The engine doesn't seem to want to wind out as high. It feels like I have gained just a tad bit of torque. These seem to perform somewhere between the factory logs and the long tube headers. They are worth the sacrifice in upper end power.

 

[2+2GT]

So you didn't convert to the 289HP clutch equalizer and engine side pivot. I had to do a little blacksmithing to the lower arm when I switched to the manifolds.

Even on "real" K codes LH manifold clearance was an issue- I have seen dimples worn on the bottom of manifolds by the motor mount.

 

[synthartist69]

I was suprised that I didn't have to do more to make the LH manifold fit. However, it could be that someone else did some blacksmithing when they installed the long tube headers on this car 18 years ago.

 

[JonK]

Not surprised you lost some top end and gained low end torque as I've read that's the difference between shorty's and long tube headers > shorties - bottom end, long tube - top end.
Jon

 

[2+2GT]

Not surprised you lost some top end and gained low end torque as I've read that's the difference between shorty's and long tube headers > shorties - bottom end, long tube - top end.
Jon

Look at it this way- Unless you drive like a wild man, where are you really going to need power? 2000-3000 rpm, or 5000-6000 rpm?

 

[JonK]

Look at it this way- Unless you drive like a wild man, where are you really going to need power? 2000-3000 rpm, or 5000-6000 rpm?

Agreed and understood that the low end is more useable in DD but apparently his 'seat-o-pants' meter tells him he's down 10% on the top end and this agrees with design & scavenging properties I would guess. The OP must have been a wild man enough times to notice the difference. That 5-6K really matters at the strip and open track probably but if you don't have it there it's very apparent. I would guess that long tube headers on the street at 2-3K will be less apparent of a 'loss'. He also has stock heads which would have hampered the long tubes full potential?

synthartist69, is the upper end loss more apparent than the lower end gain? I llike to read opinions when drivers switch setups, especially when it's only one item chaged.
Jon

 

[2+2GT]

I would guess that long tube headers on the street at 2-3K will be less apparent of a 'loss'. He also has stock heads which would have hampered the long tubes full potential?

synthartist69, is the upper end loss more apparent than the lower end gain? I llike to read opinions when drivers switch setups, especially when it's only one item changed.
Jon

No matter what exhaust you have, if you still have OE iron heads and you haven't port-matched the horrible stock ports to your manifolds or headers it'll be brutal on performance. When I port-matched my iron HP heads to my HP manifolds, I had to drive 400' out a gravel drive to get to the street. I could tell the difference before I ever got to the street. Smoother, better throttle response, better exhaust sound.

 

[synthartist69]

Jon,

Thank you for your input. The loss of top end was not worth the gain at the low end. The gain at the low end is very small, and I mean very small, if any. The loss in the upper rpm is very obvious. I don't have a tachometer yet so I can't tell you exactly what the rpm is at when it starts to give out. If I had to guess I would say at 5,000. With that said, I am still glad that I ditched the headers.

The longer term plan is to go with a 331 stroker for the street. I also plan to put a higher geared rearend in it. I like the 373's through 1st and 2nd but they are way to low for the highway, especially above 65mph. Hopefully by going with the 331, I will be able to make up the loss and then some, of going with a higher gear. From what I have seen on youtube, I really like the way the 331 screams! My 289 really gives out once I get to third gear, around 50mph.

I thought that the stock 289 heads were already matched to the hipo exhaust manifolds?

 

[2+2GT]

If I had to guess I would say at 5,000. With that said, I am still glad that I ditched the headers.

My 289 really gives out once I get to third gear, around 50mph.

I thought that the stock 289 heads were already matched to the hipo exhaust manifolds?

The 289/302 exhaust ports are crap. I port-matched mine, and now it's still getting interested above 5000. Power curve has nothing to do with cubic inches- Just look at Shelbys racing vehicles- The Cobra started out with the 260.

Power at rpm is all about the camshaft profile. I'm using the C3OZ-6250-C cam, with 310°/310° & .477"/.477" (228°@ .050). I could go another 1000 rpm if I switched to the C7FE-6250-A Cobra LeMans, 318°/304° & .510"/.510".

Your proposed 331 stroker will be a dog if you choose the wrong cam, and long stroke engines have a disadvantage at high rpm, since the short stroke engines move the piston less vertically, it's easier to build a high-rpm short stroke than a high rpm long-stroke. Nature of the beast.

Getting back to the exhaust, this is a stock 67 exhaust port. There is a huge but typical amount of excess metal around the opening blocking good flow (marked by shading), and this particular head has the internal smog bump, placed where a Chevrolet spy might have put it to kill performance. Both must be removed for performance. If you don't, you could use long tube heaters and 3" exhaust and your power will still suck.

 

[JonK]

Synthartist69, as you may notice in my sig I'm about to install my 289 stoked to 333ci (had to go .040" over) 9.7:1 comp. with MAC long tubes, AFR 165 heads port matched to a Weiand Stealth (dual plane/highrise), 3.50:1 gears and a built AOD (2200-2500 stall). As mentioned by 2+2GT the heads are probably the weakest link on the sbf.

Based on my pieces and driving intentions 90% of the time I used CompCams free program CamQuest and discussed the engine with my builder, we narrowed it to ~3 cams and settled on the CC XE262 (tallest cam ~.500 lift that still has plenty of vac for my PB and AC). The CamQuest program was nice to fiddle with, change rear gear, compression, etc. and see what it does to the cam selection suggested.

I hope to have this in and running in the next couple months to give a report on power feel and driveability. I'll be doing a lot of DD driving so the AOD is a must and will make it hwy friendly, weighs more than a C4 but I'll trade that for 2200-2500 80mph RPM's and > MPG. Should be quite a change from my <200hp stock 289 2 bbl.....
Jon