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Built, boosted and tuned, but slow

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Hi all, hoping someone can give me an idea of where to look as I don't think my tuner has the right idea.

I've got a 2.5 swapped NC MX5 (auto) with a built head (kelford cams, springs and valves done) and Rotrex SC on E85.

Stock ECU flashed with ECUTek

I've been working with the same tuner by email and logs for a while but I've only just added the head and we're both perplexed by how slow the car is. It's going between 12 and 15 seconds 0-100kmph. It should be in the sixes at ~250rwhp. He wants me to check boost leak, compression and try to get a standalone wideband on it.

The logs don't indicate any sort of boost issue, it keeps increasing with RPM and does not drop off until RPM decreases so I would think boost and compression are fine... and then there's the knock, on E85?

The only other change is I've taken out a high stall torque converter (was around 2400) and put a stock one in. Anyway, log attached, if any of you gurus could think of anything else I could do to work this out I would appreciate it.

Attached Files

i would be guessing you should start with the mechanical issues like cam timing being a tooth out

Regards Ross

Yeah sounds like cam phasing.

Not sure how much you can glean from logs, the tuner should be able to see if it isn't consuming expected fuel VS boost.

Does it have a catalyst? Blocked exhaust can do similar things.

The MZR is a not keyed in production, so the diamond washers need to be replaced whenever the crank bolt is loosened -- and you need the correct crank alignment tool to make sure the crank is at TDC with the cams being held by their alignment tool as you tighten the crank bolt (which should also be replaced at the same time). It takes a lot of torque on the crank bolt as well. I seem to remember 75 ft-lbs plus 1/4 turn (90 degrees).

Diamond washers replaced on crank and cam sprockets. With the tool in place aligning cams timing chain installed so cams are in phase and crank at TDC with timing peg in place for bolt initial tightening. Timing tested multiple times before final torque (as David said above) so I'm happy timing and cam phase is correct.

It does have a cat and considering the beater motor I was running before putting this one in it could be fouled... I have another mid pipe I can put in so that's a good way forward. Thanks for the help thus far!

Thank you Michael Howes! Blocked CAT was exactly the issue. Swapped it out this morning and the difference is chalk and cheese. I thought it was quick before the head work was done! Thanks again for the input!

Check it isn't running lean in the top end now.

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