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Old 06-07-2013, 09:30 PM
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Benefits of an H pipe on a 305 TPI?

I have a stock 1991 Z28 305 TPI engine that I'm putting in my '57 Chevy pickup.
I am going to keep the internals of the engine bone stock and am going to use a set of repro Corvette 2 1/2" ramhorn exhaust manifolds with it. I intend on setting it up with a 2 1/4" dual exhaust system and turbo mufflers.

My question is whether I would see any benefit from an H pipe in this particular setup. It wouldn't be that hard or expensive but I don't want to waste time and money if it would make no difference.

Thoughts will be appreciated.

Just for interest,
Here's the mock-up of the install:
After I get everything fitted I'm going to remove it all and do a cab-off restoration.

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Old 06-08-2013, 12:47 AM
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the sound is preferred by most people.
2 1/4 is quite small for any exhaust system
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Old 06-08-2013, 05:37 AM
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In my opinion there is only one good reason for not installing one - more work. The reasons for installing one are many : it is the best place for you put your O2 sensor, otherwise you should run two; exhaust balance; sounds better, less exhaust vibration, etc....

I've done it once and will never leave them seperated again. It wasn't that much more work and the benefits definitely outweighed the time it took to hook them together.

Looks like a nice build - good luck
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Old 06-08-2013, 05:55 AM
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Quote:
Originally Posted by vinniekq2 View Post
the sound is preferred by most people.
2 1/4 is quite small for any exhaust system
The 'H' pipe is a good addition for balance and sound.

This is what I used to design and build the exhaust for my 5.0 moderately warmed over engine. Sorry the table looks confusing so I also added the link:

"Quick and Dirty Exhaust System Math

Easy Way To Estimate: Your intake system needs to flow 1.5 CFM per engine horsepower, and your exhaust system needs to flow 2.2 CFM per engine horsepower.

Good Way To Estimate: Take engine RPM x engine displacement, then divide by two. This is the intake volume. Use this same volume of air for the exhaust system, but then correct for thermal expansion (you need to know exhaust temps to figure things out).

Exhaust Pipe Size Estimate: A good section of straight pipe will flow about 115 CFM per square inch of area. Here’s a quick table that shows how many CFM each common pipe size will flow, as well as the estimated max horsepower for each pipe size:
Pipe Diameter (inches) Pipe Area (in2) Total CFM (est.) Max HP Per Pipe Max HP For A Dual Pipe System
1 1/2 1.48 171 78 155
1 5/8 1.77 203 92 185
1 3/4 2.07 239 108 217
2 2.76 318 144 289
2 1/4 3.55 408 185 371
2 1/2 4.43 509 232 463
2 3/4 5.41 622 283 566
3 6.49 747 339 679
3 1/4 7.67 882 401 802
3 1/2 8.95 1029 468 935

NOTE: These numbers are just estimates. All pipes are assumed to be 16 gauge steel.

The table above is probably over-estimating pipe size, but you can see that a 400 hp vehicle with a dual exhaust system only needs 2 1/4 – 2 1/2 inch pipes. Anything larger is overkill." How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos
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Old 06-08-2013, 06:59 AM
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RE:I.C.,,,QUOTE;
Here’s a quick table that shows how many CFM each common pipe size will flow, as well as the estimated max horsepower for each pipe size:

what about that stupid muffler in the system and all the non mandrel bent pipes?
2 1/4 exhaust is likely too small for a 283 if you use mufflers or bend the pipes
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Old 06-08-2013, 07:09 AM
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Quote:
Originally Posted by vinniekq2 View Post
RE:I.C.,,,QUOTE;
Here’s a quick table that shows how many CFM each common pipe size will flow, as well as the estimated max horsepower for each pipe size:
what about that stupid muffler in the system and all the non mandrel bent pipes?
2 1/4 exhaust is likely too small for a 283 if you use mufflers or bend the pipes
Since this is a truck, I don't need tail pipes. I'll just put on short turn-downs on the back of the mufflers. The exhaust pipes will only have one 90 turn coming down from the manifolds. I could get a mandrel bend for this one.
The other thing is that this is a 305 TPI and is a low rpm engine. Probably around a 5000 rpm redline. My experience with TPI engines is that the shift point on full acceleration is best at about 4,800.
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Old 06-08-2013, 07:10 AM
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Wow! Thanks for all the feedback here.
I'll go with an H pipe.
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Old 06-08-2013, 07:39 AM
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post a video

Quote:
Originally Posted by roger1 View Post
Wow! Thanks for all the feedback here.
I'll go with an H pipe.
look forward to seeing/hearing your ride,,,
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Old 06-08-2013, 08:16 AM
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You will need a higher shift point than 4800rpm.

A cross over, balance or H-pipe will give you a mellower, quieter sound and will only bolsgter low rpm torque with no power improvements. The TPI engines are not short on torque.

2 1/4" is more than big enough, esp. for a stock 305. The IROC TPI exhauist manifolds had 2 1/4" exhaust manifold exits which were larger than other Fbody manifolds. The 2 1/2" Ramshorns are overkill.

The TPI 305 all else equal will have a higher power/torque band than a 350. All depends on which stock cam your 305 cam with. The auto cams were wheezy, the 305 manual would run with the 350's.
The 1985 IROCZ TPI 305 would cetainly be limited with 4800rpm WOT shiftpoints.

The TPI 305 will work excellently in your application. Your truck wouuld look pretty cool with a TPI/dual filter air intake system that the Chev's used. WHat yoiu are using is just fine though, plus you are running SPeed density that dont run those horribly restrictive 85-90 MAF's.

I had a manual trans TPI 305 installed in my 1984 reg cab longbox GMC truck. With 3.08 gears and 315/70/15(33") tires it woudl run low 17's trapping in only 2nd gear, but running 84mph. Same trap speed as the stock 454 SS trucks.
Stock 1985 IROC Z auto would run 15.3@88mph.

peace
Hog
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Old 06-08-2013, 08:57 AM
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Thanks Hog.

I'm building this truck for my wife to do errands with. I want it to be a good smooth running truck for her and I thought the 305 TPI would be perfect for that. I found the engine/700R4 transmission on craigslist. It was in a creampuff '91 Z28 with 63K miles and I got to hear it run before it was removed.
My wife has no interest in hotrodding the truck. She just wants it to run well and be dependable. It had the original 3 on the tree and a 235 6 cylinder in it but she would just not drive it without power steering and A/C.

You can see the new power steering box I got in that photo. It is a CPP 400 series box. I've got the Ididit shift steering column too. I'm also going to put in power disc brakes (front only). I've already bought the Vintage Air A/C for it too.

Btw, here's the air filter that I'm going to use for it. It will fit inside the fender well behind the headlight really easy.





Here's the truck right after we got it for her:





Also just for interest, here's my Bel Air that I just completed last year. This one is my car so we're doing the truck to call hers. I'll try to make her truck just about as pretty.



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Old 06-08-2013, 11:46 AM
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that is a fine looking shoe box.I hope the boss enjoys the truck,,,
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Old 06-08-2013, 12:16 PM
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Thanks. It was a bunch of work.

Here's the day I brought it home in Sept. of '09: It was much more rough than the pickup is.





Same shot now:

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Old 06-08-2013, 12:22 PM
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manually operated gear shift selector,very nice.If you have an album?post some build pics,,,
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Old 06-08-2013, 12:32 PM
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It's a T56 Magnum 6-speed.

Yes, I have an album with a boatload of pics. They aren't sorted that great but you can get the idea.

roger1 Gallery - Hotrodders Photo Gallery
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Old 06-08-2013, 12:44 PM
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album

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It's a T56 Magnum 6-speed.

Yes, I have an album with a boatload of pics. They aren't sorted that great but you can get the idea.

roger1 Gallery - Hotrodders Photo Gallery
looking at the pictures,job well done and nice choice of colours. Probably looks nicer now than when it was new.
Thanks for sharing,,,
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