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Old 06-01-2014, 11:08 AM   #1
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Default Did compression test: Turbo this engine as it sits?

I ran a dry compression test on my 150k '94 engine and got 170, 170, 180, 170. I picked this engine up last August after spinning rod bearings on my last one. I just grabbed the first I could find to get the car running again.

Now I'm trying to decide whether to turbo it as it sits or upgrade to a fresher, newer VVT motor first?

Seems like the numbers are pretty good, but y'all are the experts. Thanks.

Also: engine was tested cold, I've been researching this on here and I should have tested it hot. I assume hot would just improve my results though? Or do I need to go back and do it again
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Old 06-01-2014, 01:41 PM   #2
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It would change the results, although as is I'd definitely turbo it. You're not really looking at the numbers so much as the consistency between them. You're within 6%, and that's plenty good.

Read a proper write up on how to compression test, they can tell you a lot. Everything from his many cranks (5 is the norm I believe), to the difference between crank 1 and 5, it's all telling you something.
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Old 06-01-2014, 07:55 PM   #3
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Thanks! I appreciate the sanity check.

I was figuring with the age and mileage I'd definitely be looking at putting in another one, but with that response in mind, I think I'll just pull it to do some refreshing (clutch for the turbo, RMS, VC gasket, WP, timing belt, coolant reroute).

I'll also look up more info on compression testing, thanks for the tip.
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Old 06-02-2014, 10:55 AM   #4
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you could do it either way bro, if it were me i would sell the engine you have, only reason I say that is because the VVT engine is a little more robust, also it will be newer, more than likely it will have better comp numbers, and you'll have a little more headroom to grow power wise. unless you dont want to deal with the complexity of the VVT engine, but either way you'll be happy with it, your car your decision.
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Old 06-02-2014, 11:13 AM   #5
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The VVT motor will blow up at the same power levels as the 94.
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Old 06-02-2014, 11:21 AM   #6
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Naw, it's relative, both engines, power wise are the same, although when not taking all factors of both engines into account you get the answer you gave me,,,
the difference will be in the newer engines as i said will more than likely have better comp numbers, equaling more power. plus the VVT motor has the crank location plate, which keeps it more lacated when changing load or RPM rapidly. So if he can offset the cost, for a VVT engine, that's newer hopefully better comp numbers, and is a little more robust than the engine he has, that equals more power, will last longer assuming it will be taken care of. Go Vtt, you'll be glad you did.

between the 94, and the introduction of the 01 VVT engine, thats an engine that's 7 years newer, try and find one with documented miles if possible, under 80k would be a great find, but as low of mileage that you can find and afford will do you good.

Last edited by curly; 06-02-2014 at 01:43 PM.
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Old 06-02-2014, 11:28 AM   #7
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I like VVT motors, but you're really just making posts for the sake of making posts with no real meat to them.
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Old 06-02-2014, 11:31 AM   #8
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No meat? he's asking what motor he should go with, I simply gave my opinion, that's hat he's here for other peoples' opinions, it's ultimately his decision, do a dry comp test, do a true leak down test, and if the 94 is in good shape, then he can use that one

plus the VVT has a bump in compression ratio, he can make the same power with it, with less boost on that 94.

Last edited by curly; 06-02-2014 at 01:44 PM.
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Old 06-02-2014, 11:36 AM   #9
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Quote:
Originally Posted by derakbell View Post
plus the VVT has a bump in compression ratio, he can make the same power with it, with less boost on that 94.
So? Who cares?


The higher compression is a DOWNSIDE of the VVT motor, and not because it makes the motor weaker.
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Old 06-02-2014, 11:43 AM   #10
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here's some meat, 94 cam lift intake 0.318 exhaust 0.338
01+ VVT engine cam lift intake 0.370 exhaust 0.350

VVT flows more air, with addtion of a little higher compression ration, and being newer with less mileage, VVT engine doesn't require as much boost pressure to make power.

The VVT is more robust, just an educated answer.
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Old 06-02-2014, 11:46 AM   #11
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You need to define robust, as both motors will blow up at the same power levels.


Less boost pressure to make power is ricer BS. It doesn't matter, and nobody on here will care.
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Old 06-02-2014, 11:47 AM   #12
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I am not trying to argue, I simply said what I thought, what's wrong with making the same power at 9psi on a VVT, than a 94 engine at 10-12 psi?

unless your wanting to run 11+ psi. the lower cmpression would be better, so you would be able to say yea i run 12 pis, as long as your making the power you want, an it's set up right. I also said he could do it either way, are you trying to make a point here? I have 15+ years experience with miatas, i don't know everything, but i do know what is fact. if i didn't know i wouldnt comment,
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Old 06-02-2014, 11:49 AM   #13
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Quote:
Originally Posted by derakbell View Post
I am not trying to argue, I simply said what I thought, what's wrong with making the same power at 9psi on a VVT, than a 94 engine at 10-12 psi?

unless your wanting to run 11+ psi. the lower cmpression would be better, so you would be able to say yea i run 12 pis, as long as your making the power you want, an it's set up right. I also said he could do it either way, are you trying to make a point here? I have 15+ years experience with miatas, i don't know everything, but i do know what is fact. if i didn't know i wouldnt comment,

What the **** does PSI have to do with anything? Repeat after me: "PSI doesn't mean anything."

What you just said is that if you want to run 10.99psi, the VVT motor is better. 11.00psi, the 94 is better.

I mean, do you realize just how retarded that is?


This is what i'm talking about. You're making posts that don't mean anything, have no meat, no real information, and is just a bunch of vague BS. It's great that you have 15 years of experience with Miatas. I have.... 3? Why aren't you teaching me awesome ****?
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Old 06-02-2014, 11:54 AM   #14
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I don't know, why dont you make a sandwich and think about it.
He asked about a 1994 engine and a VVT. these are answers to his post, you must be bored, MY OPINION was i would go VVT. he has a 94. he hasn't yet completely inspected his engine fully.
what if someone wants to run 10.99 psi,? I feel like I'm responding to a teenager that thinks he knows everything. what are you trying to say there brother?
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Old 06-02-2014, 12:01 PM   #15
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I'm trying to say that if you had just left it as "VVT is more gooder," i probably would have left you alone. Pretty much everything else you said is either irrelevant or ricer talk.

He ran a compression test. Motor is fine. If he wants to swap out a perfectly good motor before boosting, all power to him. I wouldn't bother, i'd boost this one until it blows, then build a VVT or BP4W at that point.


But at what PSI do you think this motor would blow? You said it's the best choice for 11psi or more. How much is too much PSI?
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Old 06-02-2014, 12:07 PM   #16
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you'd make good power on a VVT at 9psig. ricer talk? also iwas taking other things into consideration like if he uses the VVT engine, get a standalone and learn how to use it, i don't know it it was read wrong, i simply said....

VVT needs less pressure than a 94 and will make the same power, it's newer. and probably in better shape if he looks for a low mileage example.

saying something is more gooder is something a clueless amateur would say.
I apologize i didn't say 'more gooder'.

it's not about psi if it will blow, it's how well the tuning process has been implemented.

although there is still a power limit, on point tuning will save an engine on the threshold of that (power limit).

Last edited by curly; 06-02-2014 at 01:46 PM.
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Old 06-02-2014, 12:13 PM   #17
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Quote:
Originally Posted by derakbell View Post
you'd make good power on a VVT at 9psig. ricer talk? also iwas taking other things into consideration like if he uses the VVT engine, get a standalone and learn how to use it, i don't know it it was read wrong, i simply said....

VVT needs less pressure than a 94 and will make the same power, it's newer. and probably in better shape if he looks for a low mileage example.

saying something is more gooder is something a clueless amateur would say.
I apologize i didn't say 'more gooder'.
Who gives a **** if it "needs less pressure?" Pressure doesn't mean anything! Holy hell.

And why does he need a standalone with the VVT motor and not anything else he would boost?

Quote:
Originally Posted by derakbell View Post
it's not about psi if it will blow, it's how well the tuning process has been implemented.
If it's not about psi, then why are you flapping your mouth hole about it?

Quote:
Originally Posted by derakbell View Post
although there is still a power limit, on point tuning will save an engine on the threshold of that (power limit).

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Sure is Miata.net and/or Florida in here. Which of the 4 Miatas are you going to post for sale today?
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Old 06-02-2014, 12:40 PM   #18
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Whoa, I didn't mean for this to get all inflammatory. Thank you for the input guys. Derak, I agree that the VVT motor would be preferable, although some of your specific points seem debatable.

However, as Ben pointed out, even though a new motor would certainly be nice, I started the thread to see if I can keep my motor as it sits. That's a whole lot cheaper than the time and money to upgrade.

Thanks guys, I think I'll just turbo this one. It'll probably fail sooner than a newer lower-miles engine, but if it does I can do the swap at that point.
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Old 06-02-2014, 12:42 PM   #19
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Its not inflamatory. The silly n00b just wants to bump his post count by posting some borderline ignorant info.
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Old 06-02-2014, 12:44 PM   #20
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Quote:
Originally Posted by jspadaro View Post
Whoa, I didn't mean for this to get all inflammatory. Thank you for the input guys. Derak, I agree that the VVT motor would be preferable, although some of your specific points seem debatable.

However, as Ben pointed out, even though a new motor would certainly be nice, I started the thread to see if I can keep my motor as it sits. That's a whole lot cheaper than the time and money to upgrade.

Thanks guys, I think I'll just turbo this one. It'll probably fail sooner than a newer lower-miles engine, but if it does I can do the swap at that point.

If it helps at all, jmuse on here boosted his BP4W with like... 250k miles on it. The Begi tubular manifold is the only thing to have failed so far (SURPRISE!). Motor seems strong.

And no, it's not an inflammatory subject, i'm just white knighting on your behalf in an attempt to keep the dumb away from you.
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