Go Back   986 Forum - for Porsche Boxster & Cayman Owners > Porsche Boxster & Cayman Forums > Performance and Technical chat

Reply
 
LinkBack Thread Tools Display Modes
Old 05-21-2019, 11:12 PM   #1
Registered User
 
Join Date: Jul 2017
Location: Los Angeles
Posts: 12
Compression & Leak Down Test Results

I have the following numbers for my 1998 2.5L Boxster that is for all intents and purposes a spec Boxster race car (no engine modifications). Would appreciate any insights as to the meaning of these numbers. I have a suspicion that the engine is not exactly healthy. But would it affect how well the car accelerates? Car was dyno'd with 2 runs at 178.74 and a run at 180.58 but with stock exhaust so horsepower numbers might actually be within range of other spec Boxsters if it had a full race exhaust set up.

Compression Test in psi
1. 135
2. 130
3. 145
4. 145
5. 140
6. 130

Leak Down Test
1. 8% past rings
2. 9% past rings and intake
3. 5% past rings
4. 5% past rings
5. 5% past rings
6. 9% past rings and intake
Andy804 is offline   Reply With Quote
Old 05-22-2019, 05:05 AM   #2
Registered User
 
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 5,067
Quote:
Originally Posted by Andy804 View Post
I have the following numbers for my 1998 2.5L Boxster that is for all intents and purposes a spec Boxster race car (no engine modifications). Would appreciate any insights as to the meaning of these numbers. I have a suspicion that the engine is not exactly healthy. But would it affect how well the car accelerates? Car was dyno'd with 2 runs at 178.74 and a run at 180.58 but with stock exhaust so horsepower numbers might actually be within range of other spec Boxsters if it had a full race exhaust set up.

Compression Test in psi
1. 135
2. 130
3. 145
4. 145
5. 140
6. 130

Leak Down Test
1. 8% past rings
2. 9% past rings and intake
3. 5% past rings
4. 5% past rings
5. 5% past rings
6. 9% past rings and intake
Several of the leak down numbers are approaching the upper limit, suggesting that you may need to plan for a rebuild.
__________________
Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
JFP in PA is offline   Reply With Quote
Old 05-22-2019, 05:40 AM   #3
Certified Boxster Addict
 
Join Date: Nov 2010
Location: Los Angeles
Posts: 7,368
I'd call this a somewhat "tired engine". Nothing is hugely out of whack, but the compression should be somewhat higher (more like 160) and the leak down numbers somewhat lower (more like 5%). And yes. this could affect acceleration.

Most Spec Boxster's dyno in the low-to-mid 190's at the rear wheels. The stock exhaust might account for 5-7 hp. Do you have the under drive pulley installed? If not, then that might be another 3-4hp especially if you still have a/c. Do you still have the cat's? There is probably another 2-3 hp there.

If we use the upper range of those numbers: 7+4+3 = 14. 180+14 = 194. Which is about right. If we use the lower range, the you might be down a couple of hp compared to a stout SPB engine..

I also sent you this info via FB messenger.

Here are the compression and leak down numbers for my last engine just before it failed. It was clear that cyl's 4 and 5 were not happy. The engine still made decent power but the engine felt "off", like it wasn't its old self.

__________________
1999 996 C2 - sold - bought back - sold for more
1997 Spec Boxster BSR #254
1979 911 SC
POC Licensed DE/TT Instructor

Last edited by thstone; 05-22-2019 at 05:44 AM.
thstone is offline   Reply With Quote
Old 05-22-2019, 08:57 AM   #4
Registered User
 
Join Date: Jul 2017
Location: Los Angeles
Posts: 12
Thank you for the explanation, Tom. A/C is out and under-drive pulley was supposedly installed per the build sheet when I bought the car as a BSX. In your opinion, would having the lighter flywheel provide a noticeable improvement in acceleration as well?

My suspicions about my motor came back recently because I was looking at a partial lap video of a beginner driver in a spec Boxster at Willow Springs this past weekend. The driver was completely lifting going into turn 8 and feathering the throttle through it, braked earlier into turn 9, then turned in a lap time not much different than mine. If I had done the same thing, I certainly would have been at least two to three seconds slower if not more if you extrapolate that over the entire lap. Then I thought about a few instances when I would get a run on another Boxster ahead of me coming out of turn 9 but it didn't matter once we got going down the straight.
Andy804 is offline   Reply With Quote
Reply

Tags
compression test , leak down test


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -8. The time now is 08:43 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page