Exhaust size
 

I had planned on running 3 inch exhaust on my Tempest and my muffler shop has advised me against it. My shop who I have been using for over 20 years says he has a customer running in the 9s on 2 1/2 and that 3 inch will only make more noise in my car which is to be my daily driver. I dont want to give up power but at the same time I dont want to have the **** annoyed out of me. Is 3 inch a waste of money or can I get by with 2.50?

For a daily driver, I would stay with 2.5". It will be quiter and easier to fit, especially the tail pipes. If you wanted to eek out that last couple of HP (which you will likely not even notice via seat of the pants), you could do a 3" mid pipe and cross over, finished off with 2.5" or even 2.25" tail pipes.

I have mentioned this in another thread, but my exhaust is full 3" back to the last 12" section of tailpipe, which is 2.25" in order to provide better clearance between leaf spring and qtr panel on my qtr exit system.

Anyway, I did back to back tests at the drag strip with and without the 2.25" tail pipe, and noticed zero difference in ET or Mph in a 600hp engine running 10.5's.

My suggestion is to go with 2.5" and dont look back.

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One more thing... have them install the longer case mufflers if they fit. I had 20" Ultraflows in my 73 and 14" Ultraflows now in my 68. The 14" is a little more obnoxious. Not bad, but noticeably louder than the 20".

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The guy running 9's with 2.5" might be running 8's if his exhaust was sized properly.

My super-mild 7.8:1 455 with stock iron heads, mild HFT cam, Performer & Qjjet. It had a hodge-podge exhaust system that comprised of 2.5" pipes feeding into 3" FlowMasters, into 2.25" tailpipes, behind the headers. I replaced it all with 3" pipe to 3" Borla ProXS mufflers, into 3" tailpipes.

Granted, I did not expect to gain ANY power. This system was more in preparation for adding more power down the road, but I put the car on the chassis dyno before and after, just for giggles.

After changing secondary metering rods to correct the AFR (it leaned out more than expected), I gained 15rwhp and 10rwtq. Possibly it was ALL in just the mufflers, but even though I'm not a FM fan I expected their 3"ers to be WAY more than enough for such a mild motor.

I disagree with leeklm on pipe sizing, I think you should use the biggest pipe you can. I would urge you to talk to a different muffler shop, it may be that your old guy isn't able to install anything bigger than 2.5" with his equipment.

I agree with leeklm on muffler sizing though, the larger the case the less the noise. I've used the AP Xcelerators on a 11 second and a 10 second street car, and they were surprisingly quiet.

i was debating on 2.5 vs 3" when building my 500+ hp 467 & did lots of reading here & other places, read lots of guys say they went faster with the bigger exhaust at these power levels. the tail pipes can be 2.5 due to exhaust gasses cooling off so much that far down the system. if its only a daily driver & you dont ever plan to race the car or uprgade the engine for more power then the 2.5 will work fine, but then again if its only a daily driver & you dont care about power loss, why build such a powerful expensive engine? a stock'ish iron head 455 would be more than enough for daily use & fun street driving.

i followed what cliff advises: garden hose for fuel line & sewer pipe for exhaust!

I do not think there are any "wrong" answers in the suggestions here. I am sure many forum members do this as well, but we tend to get to know each other through our various posts, questions, results, etc.

I have a tendency to make recommendations (from my experience) based on my impression of how the member in question will realistically use their car, and what seems to be most important to them.

For example, I will strongly suggest iron manifolds over headers for anyone that seems to only own a set of wrenches from Home Depot- and their idea of working on the car is changing oil. More power to them, but again trying to keep the recommendation in line with the customer's needs.

In the case of 64speed, I have the impression he is building a stout car, wants to put a smile on his face when punching the gas pedal, but also wants to carry on a conversation or listen to some music cruising down the road in relative comfort. I do Not have the impression he will be hitting the dragstrip every weekend looking for every 1/10 second he can eek out like some of us. I apologize if I am off base here 64speed :)

Not trying to get too philosophical here, but had a few minutes inbetween conference calls :)

From what I know of the OPs build, I doubt any of us could feel a seat of the pants difference if he installs 2.5" or 3", assuming either system is well built with smooth bends and free flowing mufflers. His tires will be well up in smoke when punching the throttle regardless:)

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Thank you this is just the answer I was looking for and you are right. I dont want every last HP I can squeeze out of it at the sake of comfort not that comfort is in the forefront but I do want to be able to carry on a conversation or hear the radio if I am so inclined. I am only running a 255/55/18 tire so I will never get traction. Boys just wanna have fun

I'm going to hang with Lee on this one. My 78 TA running NMCA we could run 3" head pipes, mufflers and had to run 2.5" tailpipes for class. O had 3" head pipes, H pipe 3" 2 chamber resonating SOB Flowmasters and mandrel 2.5 tailpipes. Kept it on the car initially when I put the 455 roller motor in the car. When I swapped to a 3", 3" X 3" Ultralflows and 3" mandrel Torque Tech tailpipes it was quieter and ran as fast as the car did open headers even with the extra weight.

Mike Cooke a Texas racer had his 73 Firebird in the old HPP magazine and said 3" exhaust made a world of difference in his car's performance and Mike could squeeze performance out of anything! This was a high 10 street car. He and I ran fender to fender at PSN with him one time trials.

I forget... is 64speed running headers or RA iron manifolds?

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How will this affect my low end torque/driveability? I have Dougs headers with 3.5 inch collectors Edelbrock round port heads ported to 315 CFM. Holley Sniper fuel injection with timing control. Cant remember my cam specs right now but Paul Carter specd it. 1.7 BBC roller rockers. Torker II intake with one inch spacer.

Since you do have headers, would be easy enough to order the 3" mid pipe with X from Pypes. Your exhaust guy could easily install that into a set of 3" long case ultraflows and then bend up 2.5" tail pipes. This will give you the best of both worlds plus additional comfort you are getting the max benefit from your system. And, your local exhaust guy can do the work. This is exactly what I had in my 73 GTO and the heavy car was turning ETs in the low 11's and still sounded great on the road (maybe a little loud fornsome) At the track, it was the quietest car out there short of someone running a stocker or a new model muscle car.

Or you can go 2.5" the whole way, lose a few HP, and still be very happy with the amount of ridiculous quiet street power you will have :)

For comparison, my 66 4SPD GTO had a 455 with SD Performance KREs and Stump Puller cam. RA manifolds with 2.5" all the way back through the more restrictive Turbo mufflers. The car still had more power than I could put to the ground, and was definitely more pleasant driving around town if you do not want to wake up the neighbors.

You have good options :)

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My car is relatively quiet inside at 70 mph with 3 inch exhaust.
From what I've tested at the track with a low 11 second car just 2.5 inch full length tailpipes was a restriction. I'd assume a full 2.5 inch exhaust even more.

A 455+ Pontiac is not going to worry about low end TQ!! My 78 has a "tight" Continental Convertor and a 239/247 HFT and has perfect street manners. Weighing 3750 in good air(rare in Houston) can run 10.90s more weight and 100 degree Texas weather 11.50s-which is good for the tracks that are strict on roll bar rules.

Correct, these builds make for ridiculous "street" engines and TQ will be the least of your issues. I would have been in a lot of trouble with this kind of power in high school. The slant 6 with 3 in the tree kept me in check.

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If you want to see a comparison of 2.5" vs. 3" exhaust on the same engine with dyno and discussion, watch this Engine Masters video: https://youtu.be/_PVXvHkr-Vs

Personally, I wouldn't bother with a 3" exhaust on a street car, but that's just me.

Off topic..but still relates ..What are the specs of the camshaft?

I like that one!

As I've said in your exhaust threads before, I wanted my car loud and asked the muffler shop to run 3" all the way back. They said that they couldn't get 3" over the rear end, so it steps down to 2 1/2 there. With a big cam and headers, it certainly is loud! If I have my foot on the floor, and there's a brick wall on the other side of the sidewalk, it sounds like one of my headers broke free.

I love it, and it's exactly what I wanted. Even as a high school kid, I thought loud pipes were annoying on a daily driver - but that's why I don't commute with mine. It's a "fun" car.

With stock iron "66" heads, 8.4 compression 3.08 gears, stock torque converter, a FAST XFI Sportsman throttlebody efi system with timing control, and my 3" exhaust system, my tires will spin at 1/4 throttle. Cruises great at low-rpm, never lugs.