Matt Marks

Hi all - being relatively new to boxsters - I wanted to throw my dyno sheet up for discussion.

• Motor is original to the car (99), and has about 130,000 street miles and maybe 10 track weekends (DE and Race) on it.
• It runs on all 6 cylinders
• I'm not concerned by the low numbers (it's been mid-170s since I bought it a couple of years ago), as I have a new motor build build in progress.
• I see cars in the Nasa GTS and ST5 compliance databases that look to be SPB in the 195's - is that a high number? or in the middle of the competitive range

So primarily, I'm just trying to get an idea of what might be going on for personal knowledge.

Other items that may be of note that I haven't done as it's not worth spending a lot of troubleshooting money when I have the new motor coming in the summer.

• Compression has not been checked,
• Fairly certain that the injectors are original to the car.
• Fuel pressure not checked
• I'm not a variocam/varioram expert but it sure looks like something wonky is going on at 3800 to drop 25 HP over a 500 RPM range. Also peak HP seems to come relatively early at 5700 RPM vs. 6000 or 6100 on the charts that I've seen.

Looking forward to your thoughts.

Matt

trygve

In my observation and interpretation:

190 - 195 = typical
185 - 189 = below normal but not uncommon
175 = engine trouble
196 - 200 highly unusual
200+ = cheater

(with the caveat that every dyno is different, etc. -- if you pull 10 SPBs off track and they all dyno 195-200 then that's normal for that dyno that day)
(also what I consider "normal" assumes you have an underdrive pulley and some kind of race exhaust, each of which is good for a small number of hp, so if you have neither then 175 is probably close to normal)

Matt Marks

Thanks trygve - you are correct. Motor has a race exhaust and the underdrive pulley.

Streak

Depending heavily on the dyno the 195+- is a legitimate number.

Every time mine has run in the 170's it's due to a bad MAF.

Matt Marks

Do you see the MAF issue as something that often occurs? Or something like - just swap it out once/yr to be safe kind of thing?

C4 Pazzo

Only replace the MAF if it is bad. You can easily test it by disconnecting the electrical connector to the MAF and then drive the car. It will use a default MAP that will perform fine and if the MAF is bad you will notice a marked improvement. It won't hurt anything to drive with the MAF disconnected.

Matt Marks

Thanks C4 - will give it a try. That would also be a quick method to reduce overall car mass

Streak

All the time.

I spend $1500 year on MAFs!

txhokie4life

What's killing your MAFs -- blow by? AOS?

Matt Marks

Update from a a day at the (mustang) dyno. Did a baseline pull that showed same shape and relative number as the Dynojet.

Performed the following updates

New:

- MAFs
- Plugs
- Coils (originals from 1999)
- checked for vacuum leaks

Re-ran the pulls and gained about an HP

Then purely in the interest of science, we rigged the solenoids so that they could be manually triggered anywhere from 2000-3500 only result of interest was when we tried it at 2500 and 3000, we were able to drop the dip in the graph about 500 to the left. However, this dropped total HP to the 160s and the dyno pull was much longer. In retrospect, this sort of makes sense, as the DME is really smart with the solenoids....it doesn't care that RPM they are at - it just won't advance the timing/fuel etc when its parameters of RPM, throttle and whatever are met.

But at least I have some newfound knowledge and new coils to transplant over to the new motor next month!

Streak

I was mostly joking but I have replaced the MAF several times over the years. I do not know what fouls them up.

sbelles

I've gone for stretches where I needed one every race. Then it goes a year without blowing one. Beats me.

RennPart

I never dynoed either of my old SPB's but when I was at Watkins Glenn in 2018 I was getting pulled on the backstretch and it really bothered me because I knew I could run up front. After talking with the normal suspects I found that they all ran their oil level at around half on the dipstick hot, I was filling mine to the top then when the car was hot it was technically overfilled. After making a huge mess and draining a quart out of the car I was no longer getting pulled on the backstretch. Was this a loss of 20+ HP, I don't think so but it helped!