Hoping the throw the motor back together quick and easy, so hoping there's some wisdom that I want on the board here.
Would like to know if a Schrick-ish 292 will go in without additional machine work to clear the pistons.
It's an E21 but will have the 9:1 pistons from an e30 M10, figure stock thickness head gasket, if need be I have an adjustable cam sprocket (the one from IE).
Anybody here run a 292 in a 1.8 on a throw it in and forget about it basis?
I can't say anything definitively, but I've never heard of any issues with a 292 and higher compression pistons. The only thing might be if the dome shape is not matched to the head, or if you've got larger that stock valves. I run a 300 Motorsport cam with ~9:0 pistons and have zero issues, and I've heard of lots of others with up to a 304 and stock or other factory pistons with no interference problems. I've always had the impression that there was a fair bit of leeway in the M10 for more lift/duration until you start getting into track builds (316 or 324 cams, 10:1 pistons, etc.).
I've seen it both ways in what I've searched.
And, having posted the question on 2002faq, a guy had a 292 touch his pistons, but he said the head had been shaved quite a bit. What I can't tell from his response is whether or not retarding the cam helped with stock pistons, or whether he retarded after he went with some higher compression pistons (that probably had valve reliefs anyway).
Late E21 have a bit of a dome, and the NOS pistons I took a flyer on are supposed to be for the E30 M10, so a little more dome.
I will of course check when putting it together, but I'd rather not order the cam if it's never going to fit without machining (not sure how much I could notch the pistons if I had to even so...).
I've got the IE "adjustable" cam gear, and am not opposed to altering cam timing if that makes a 292 fit comfortably.
If not, I've heard that retarding the cam timing moves the powerband a little higher in the rev range, so I'd throw the 284 back in it and do that.
That said, I'd like the bit of extra lift & duration.
Have you checked the height of the cylinder head to determine if it's been skimmed, and if so, by how much?
I'll check when home - the head I'll be using looks pretty original in all respects.
I ignored conventional wisdom on the current/existing motor, floated the valves, and voila! Bores look good, but one piston is ugly, another is dinged, and #1 cc on the head is just toast. Sad part is, the car was running to perfection, and it let go about a block from home, just cruising at 2500 rpm....
I'll be using components that will live safely at the rpm range I want going forward (turns out I had a spare E21 2.0 head with the good rockers, and IE's upgraded valve springs are cheap...)
I had just started auto-xing the car, and I want more oomph between the cones, thus the reason for asking about the 292.
What RPM range are you planning on using most? What else are you doing to the engine to complement the cam?
I have a set of the IE upgraded valve springs that I was planning to put into a spare head I'm going to rebuild, but I've read some accounts that suggest they aren't really needed until you start getting over 7k on a regular basis, and that they increase cam wear. My current engine rarely sees 7k (though I think the exhaust is holding it back at this point, so it doesn't feel like there's much to be gained) and I haven't had issues with the valves floating, so I haven't decided whether to use them or not.
I was turning 7k. Weber 38 (140 & 145 mains, I think 50 idles, 195 air correctors, 284, header/exh, hotter coil, low ohm plug wires, lightened flywheel, crank scraper, stock 3.91s.
Pulled so easily in first and felt like it could keep going. I put a rev limiter in it to keep it from going past 7. It ran well enough in second that I'd routinely run it to 7 there, but it was pretty well done at that point, and as often as not I would shift before hitting 7 (and everybody says that cam is done at 6500 anyway).
Several mentioned I should keep it under 7, as I was probably experiencing valve float. They were right, obviously.
IE literature says 292 will make power over 6500, but I'll guess probably not past 7, so, we'll keep that as the target RPM max.
And since I broke stuff by going to 7, and I don't want to do it again, I'll get parts to try and run it there reliably.
If you're on the stock valvetrain, DO recommend you max at 6500.
Have you worked out what the dynamic compression ratio would be with the cam and piston combo?
I have been around a lot of motors that were ruined with big cams and not enough compression to back it up.
There are a lot of online calculators out there. You will require a cam card to work it out though.
https://www.396maro.com/home/performance-calculators/compression-ratio-calculator/
I usually shoot for a dynamic CR of 8.5-9.5
In reply to Trent :
Cams for these are a pretty known quantity, 292 has been used on a lot of 9:1 motors, have not read any sour grapes on that front if they're not whacking valves (as noted above).
All the 300+ duration cams everybody runs compression to match.
Using incomplete numbers, that calculator says you lose half about half a point compared to static, so ~8.5 dynamic.
It might be a case of not finding out until I order the cam, which is extra time fixing the car that I didn't feel like dealing with.
If I can do it easily enough, I'll go for a little more cam, if it's a pita, I'll be throwing the 284 back in it. I'd just rather have a little more cam all things being equal.
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