brassplyer

ZZ4 crate motor in whatever their "stock" configuration is, Weiand 142 blower, 700R trans, 2200 stall converter, Holley Avenger 670 carb. He said he tried a 750 but had issues with it bogging. Amount of boost unknown, there wasn't a boost gauge. Do you see any potential issues, anything inherently inappropriate about this combination? Test drove it today - fires right up, idles smooth. Really quick - dang. I see the ZZ4's in out of the box trim are considered on the low end of performance but it seemed pretty healthy.

He says the trans was recently rebuilt by a well-known local builder, from the performance I didn't see any reason to doubt it. Trans fluid looks pristine.

cv67

was the carb set up for boost? Those little blowers can be lots of fun did he regap his rings or running as is from GM?

brassplyer

He says the carb has whatever jets were in it, he changed the springs some. The motor is as it came. I have -0- experience with blowers but it seems to work.

jackson

IIRC
ZZ4 motors come stock with right at 10:1 CR using cast pistons … I have NO blower experience but I'm under the impression that Hi-comp, blown motors without computer management ...or without expert manual carb & ignition tuning … may be flirting with detonation

brassplyer

This is the kind of thing I'm asking about - reading elsewhere I see detonation is of major concern with a blower. It has no computer management, he did the tuning himself. I didn't detect detonation but I don't know if going by ear is useful. I do know it runs silky smooth. It fired up without too much fuss when it was cold, once warm he just had to touch the starter to get it to fire.

Anyone else have info to impart on this topic?

Gunfighter13

The 142 blower has 5 to 7 lbs boost.
DETONATION ELIMINATION The increase in engine output with a Weiand supercharger does have the potential of causing serious engine problems (in one area), detonation, knock, or engine ping. The blower will increase the effective compression ratio of the engine. A 7 psi blower pressure will raise a 7.5:1 compression ratio to an effective 9.8:1 compression ratio. An 8.5 compression ratio will be raised to an effective 11.2:1, and a 10.0:1 compression ratio will be raised to an effective 13.5:1 ratio.

The ZZ4 has 10:1 compression. You would need to run race fuel.

brassplyer

He's running whatever the highest octane pump gas is around here - probably 91 - 93 octane. Would the detonation be audible like knock I've heard in other cars? I can tell you it ran really smooth - if there was any damage - cooking of the pistons presumably? - would it necessarily be evident?

Gunfighter13

Chances are it is not a ZZ4 motor. Here the link to the ZZ4.

http://www.gmhorsepower.com/350-ZZ4-Turn-Key.php

Gunfighter13

Sounds like you want the car. Blower motors rarely give any audible knock before they come apart. If the car seems sound then your not taking any more of a chance than you would with a non-blower car. Used cars are used cars expect to invest some money.

brassplyer

Certainly I'm interested but I don't want to buy a car with a damaged engine when a major selling point is that it's a fresh engine.

I have a boroscope, should a visual inspection of the piston tops be good enough to reveal any developing problems? I.e. if the pistons look fine they should be fine?

7T1vette

If the setup is all that good, why is he selling it? He might be having problems and wants to get our from under it....before it tanks. I wouldn't want to buy someone else's performance 'project', unless I knew the car and it had worked fine for a significant length of time. Sounds like a bunch of 'go-faster' stuff thrown together. Blower on a 10:1 compression engine seems "iffy" to me.

brassplyer

Yeah I wondered too - he puts all this time and $$ into it and then wants to sell it. It's even all primered and just about ready for paint. His story is that he needs a four-seater due to a growing family. He says he put the blower on it, it did seem a bit odd that he didn't know how much boost there is and that he doesn't have a boost gauge on it.

This Vette is very intact - nary a trace of underbody rust, power windows work, all the gauges except the clock (of course) work, new suspension stuff, the headlights even work. If there's no damage yet, I suppose I could pull the blower and look around for lower compression heads. Seems that ZZ4 is pretty stout even without a blower.

Or alternately I wonder if I'd be better off finding a clean example with a low comp factory motor and put a blower on that.

carriljc

Lets see some pictures. What year? If it's all in wonderful shape and the engine is fresh, then I would pull that supercharger off. But what year and how much and let's see it.

REELAV8R

Where are you at brass player?

could be at your elevation that a blower is fine on a 10:1 engine. Considering it’s a gm motor and advertised 10:1 cr it’s likely more like 9.2:1 Cr in reality anyhow.

Buccaneer

^^^THIS^^^ Absolutely!
Since you already admitted that you have no blower experience, you are playing with fire IMO. CR and tune are critical on this type of motor and if it has cast anything in it, I wouldn't even consider it. Again, just my opinion and playing it safe.

jackson

per ZZ4 compression … I respectfully disagree and Is about 10:1 CR because:
Its L98 aka ZZ4 heads have tiny 58cc chambers (Not efficient Vortec shape)
Its pistons are flat tops with 4 VRs

https://www.chevrolet.com/content/da...e-24502609.pdf

zz4 and x603 CT variant are still used in circle track racing & I've had my hands and eyes on several freshenings
AFAIK ZZ4 /L98 heads no longer in production and same for ZZ4 & x603 crates

brassplyer

Florida so essentially at sea level. Are the specs on GM crate motors notorious for being way off?

brassplyer

There aren't a lot of pics - all the exterior is going to show you is a primered albeit straight 'Vette. The undercarriage which I don't have any pics of is really the most impressive view currently, it's very clean.

Here's a few that show the engine bay and interior. There's also a front-facing scoop-type air intake, whatever the official name for those are.

brassplyer

What I don't know would fill volumes.

Besides the feedback I've gotten in here - which is appreciated - I've been exploring the 'net for info since encountering this car, I've picked up enough to get that there are lots of potential pitfalls. I've seen enough to question his competence, he apparently didn't adjust the ring gap which I find is considered crucial with a blower and the fact that he put a blower on this motor to begin with which I've seen stated in various places isn't a good choice of a motor for a blower without advanced detonation management which isn't in place.

Maybe there have been no ill-effects from this build but it's definitely a question mark.

REELAV8R

The production motors are always lower than advertised.

In the link posted by Jackson note that it says compression is 10:1 NOMINAL, meaning, approximately, so unless the head has been cc’d as well as the piston it is only an approximation.

my 8.5cr L48 was in reality 7.7 :1. That kind of variation is going to make a difference.

that being said I can’t speak specifically to the zz4 head as I’ve never cc’d one.