 Any HP gain for early 1.7 heater boxes and Bursch muffler vs late 1.8 system? |
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| 914rrr |
 Jun 21 2025, 11:09 AM
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#1
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Senior Member  Group: Members Posts: 1,908 Joined: 1-July 03 From: Knoxville, TN Member No.: 874 Region Association: South East States  |
I have a 75 1.8 with the OE heater boxes and a Bursch muffler w/o cat.
Is there any HP gain if I were to switch to an earlier 1.7 heater boxes and Bursch muffler? Another alternative is to use a Supertrapp muffler with the late 1.8 heater boxes. |
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Replies(1 - 5)
| brant |
Jun 21 2025, 11:30 AM
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#2
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914 Wizard Group: Members Posts: 12,010 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains 
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If you have the late style where the short header points to the front of the car and then does a 180 turn to go out the back
That 180 is resrictive The 1.7 being straight to go back is less restrictive and will give you a couple of hp The 2.0 (or SSI brand for a 1.7) has bigger diameter tube and will give a couple more hp over a stock original heater box |
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| 914rrr |
Jun 21 2025, 04:01 PM
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#3
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Senior Member Group: Members Posts: 1,908 Joined: 1-July 03 From: Knoxville, TN Member No.: 874 Region Association: South East States |
Thanks! Are we talking 2 HP add or 8 HP added, worst case to best case system?
That also begs another question: Is the early system lighter than the late system? If so, by how much? |
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| bdstone914 |
Jun 21 2025, 07:25 PM
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#4
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bdstone914 Group: Members Posts: 5,031 Joined: 8-November 03 From: Riverside CA Member No.: 1,319 |
1974 1.8L stock heat exchangers have the same size pipes as the 73-74 2.0L.
SSI all use the larger pipes. In theory yes. How much? Had to be tested. I would not expect much difference on low HP engines If you switch go with SSI or 2.0 73-74 or 1974 1.8 stock. I am not a fan of SSIs. Especially with the Dansk Kuality. They were better when made in California |
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| rick 918-S |
Jun 22 2025, 10:02 AM
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#5
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Hey nice rack! -Celette Group: Members Posts: 21,011 Joined: 30-December 02 From: Now in Superior WI Member No.: 43 Region Association: Northstar Region
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The other issue is heat from the case manifolds. Harder on the heads from heat cycling. At least that is hypothesis. (IMG:style_emoticons/default/idea.gif)
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| Dave_Darling |
Jun 23 2025, 11:56 PM
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#6
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914 Idiot Group: Members Posts: 15,196 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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The official power figures are the same for the 74 1.8 and the 75 1.8 . I don't buy that, personally.
On the 2.0 cars, the 75 has 7 fewer HP than the 74 does. 95 HP -> 88 HP. The 75-76 2-liter cars used exactly the same exhaust as the 75 1.8 cars did. I would expect between 4 and 7 HP difference on the 1.8 motors (the 74 1.8 was rated for 76 HP), but I don't have any actual data to back that up. Or, come to think of it, any back-to-back experience. --DD |
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