928 Supercharger question... | Page 2 | FerrariChat

928 Supercharger question...

Discussion in '308/328' started by mike996, Nov 20, 2019.

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  1. ferrariowner

    ferrariowner Formula 3

    Feb 21, 2014
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    Ron
    Jim, I really don’t want to talk you out of supercharging your car. I would have probably sold my car years ago for something more powerful if I hadn’t more than doubled the power. Mine has been very reliable, but it requires that you build the engine for turbo/ or supercharging for reliability. Lots of help here if you want to go that route.
     
  2. Mike C

    Mike C F1 Veteran
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  3. mk e

    mk e F1 World Champ

    Oct 31, 2003
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    For what its worth I ran a roots blower on my QV at 10psi (no cooler, inlet air temp about 260F) for about 15k miles with no issues. Internally the engine was stock other than slightly stiffer valve springs, externally I added EFI since my CIS system was already having issues and was part of the reason I decided to work on the engine. It was right at 300 rwhp and its hard to over state the difference in driving experience the extra power made, there is no way I could EVER go back to a stock 308, I just couldn't.

    I later upgraded to a screw type blower with cooler at 24ish psi that ended up around 450rwhp. Still no changes inside the engine but it made very short work of the clutch. Really fast but honestly didn't give as much additional WOW as the 1st blower did and I found I tended to drive at much lower rpm most of the time....kind of felt like driving an old big block....even from near idle you push the throttle, the engine starts to shake and the car just goes....really different feel from the stock engine.

    My setups both had a bypass valve that unloaded the blower at low power so it only made noise on boost and highway mileage was actually better than stock if I stayed off the throttle....that was the efi I guess.
     
  4. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
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    Weren't you having head gasket problems with the second configuration?
     
  5. mike996

    mike996 F1 Veteran

    Jun 14, 2008
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    24 PSI? WOW!!!! I can't believe an unmodified engine could stay together at full boost. :eek:

    That would increase HP by around 150% o_O
     
  6. Rifledriver

    Rifledriver Three Time F1 World Champ

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    F40 makes 500 as I said, with the same parts.
     
  7. mike996

    mike996 F1 Veteran

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    Well it would seem that contrary to much "common knowledge," these 3x8 motors were dramatically overbuilt!!!!!!! :)

    If a 250HP (more or less) motor can be boosted to produce nearly double that with no issues, that's SERIOUSLY good engine building.
     
  8. mk e

    mk e F1 World Champ

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    Yes and no.

    It was never leaking but when I eventually tore it down I found the flame rings missing in a couple cylinder and some light damage from when they must have exploded years ago.

    On the 1st setup the day I was on the dyno 1 cylinder shut down....the injector was dead and the plug gap was 0. I replaced the plug and injector and all was well again until some months later during a hard pull on the highway something happened....again injector dead and plug gap 0. This time I switch injector brands, retuned to get the mixture back where it was and never had another problem. I could never figure out how the plug gaps got to zero.....fast forward to the tear down and it was pretty obvious how it happened. I since learned the stock gaskets HATE detonation...I guess the injector started to fail, the cylinder went lean and detonated cause the flame ring to fail. That was the 1st blower though.
     
  9. mike996

    mike996 F1 Veteran

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    I'm a little confused, in an earlier post you mentioned not having any problems (other than clutch with 24PSI) and the last post you mention broken rings/issues with the spark plugs/injector problems with the 10PSI boost configuration. So the posts seem contradictory or am I misunderstanding something?
     
  10. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
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    As I read it all the issues in the 10psi configuration were caused by an injector failure, or rather 2 injector failures. I think he had an EFI system.
     
  11. mike996

    mike996 F1 Veteran

    Jun 14, 2008
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    Right!

    Of course, if the supercharger hadn't been there, an injector failure could not damage the engine! ;)
     
  12. ferrariowner

    ferrariowner Formula 3

    Feb 21, 2014
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    I would wager the engine detonated and destroyed the injector and not the other way around.
     
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  13. mk e

    mk e F1 World Champ

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    #38 mk e, Dec 4, 2019
    Last edited: Dec 4, 2019
    Maybe...but I'm not sure how that could happen? The injector is in the port not the chamber but who knows. I do know a new set of injectors with the mixture and timing unchanged fixed the problem so I just assumed it had started with the injectors , could be wrong though.
     
  14. mk e

    mk e F1 World Champ

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    No, you're right. The injector failures (efi injectors) happened early in the de-bugging/tuning and I never thought any more of it. I drove it about 15k miles with that setup and it was basically my daily driver for a couple summers. Then the second blower which at the time was literally the largest blower made then they came out with a bigger one and I got to thinking they wouldn't be making it if I didn't need it and maybe with a bit port port and cam work I could get an even flatter boost curve..which led to me pulling the heads and realizing what the issue had been years before.....which led to pulling the engine to rebuild it....which led to a V12 ;)

    but I never knew there had been any issue with the first setup until years later.
     
  15. mike996

    mike996 F1 Veteran

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    FWIW, If I decide to purchase a supercharger, I would limit the boost to 5 PSI on the stock engine. Although I have not seen the instructions that come with the 928 kit, I ASSUME the wastegate can be adjusted for whatever pressure is wanted. If it's not adjustable via a bolt/knob, an appropriate change of spring should be able to accomplish that. Based on my experience with engine mods/reliability, I wouldn't be comfortable with any more boost than that without making changes specifically to accommodate forced-induction. But a 60-70HP (more or less) increase in power would be very noticeable. Putting it in acceleration terms, it would make a 328 a bit over a second quicker in the 1/4 mile - from low 14's (based on magazine tests) to low 13's.

    Since the stock car can hit 160MPH, the whole point, IMO, is for increased acceleration, not additional top speed. Low 13's would enable it to out-accelerate most of those pesky soccer-mom SUV's that can currently best it in acceleration. ;)
     
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  16. mk e

    mk e F1 World Champ

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    Supercharged systems normally adjust boost with pulley ratios choice but I guess some centrifugal systems also use a flow restriction on the blow inlet to let you get more boost at lower rpm without over boosting on top to make them act I little more like a positive displacement blower ( my screwtype blower setup made 12psi at idle and settled in at around 18 by like 3000...then swung up starting at about 6k toward the 24 redline number iirc)

    I ran my first setup at 5psi for a bit while breaking in the engine and waiting for new pulleys....it is a big difference form stock. I was using an eaton roots blower that made a lot more heat than boost above 5psi.....the higher boost was a net gain but I'd bet 5psi was 80% the total gain 10psi gave.
     
  17. mike996

    mike996 F1 Veteran

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    OK - I didn't realize superchargers used pulleys to adjust the boost rather than wastegates - I only have experience with turbochargers/wastegates. I like the wastegate method because you can have boost at fairly low RPM but the WGate ensure it never rises above the desired boost. It seems to me (again, no experience) that if you have a pulley to deliver the max boost in the peak power range - say 7000 RPM - you have very little boost until you get up to that range. Maybe that's not the case?
     
  18. mike996

    mike996 F1 Veteran

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    To answer my own question - I just found that 928 MotoSports has what they call a Boost Limit Valve (BLV) to do exactly what I was concerned about. For some reason they prefer calling the device a "BLV" ads opposed to a "Wastegate." ;)
     
  19. Rifledriver

    Rifledriver Three Time F1 World Champ

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    #44 Rifledriver, Dec 5, 2019
    Last edited: Dec 5, 2019
    With a centrifugal blower that is pretty true. The pressure to RPM curve is pretty bell shaped. A positive displacement blower is a far flatter curve. Both have their advantages. I prefer a PD blower exactly because you can have so much available at low RPM.

    Their BLV is more like a pop off valve used in racing like Indy. Just lets off output air. Thats fine if the blower is upstream but more typically it is just regulated by pulley size. A waste gate lets off exhaust gas for a turbocharger so the pressure is never made in the first place.
     
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  20. mike996

    mike996 F1 Veteran

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    Ahhh, right! good explanation, Thanks RD!!!! (glad to see you back on a regular basis).

    BTW, where are you (your shop) located in TX?
     
  21. Rifledriver

    Rifledriver Three Time F1 World Champ

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    Lakeway. West of Austin.
     
  22. mike996

    mike996 F1 Veteran

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    Thanks; found your website. Next March, when we're back in TX (my 328 is in San Antonio), I'll contact you about doing some maintenance! In March I'm having some minor surgery and one of the "recovery requirements" is 45 days of not lifting more than 10 lbs! So I can't do much in the way of car work. Feel like installing one of those 928 superchargers (in addition to checking/adjusting valve clearance)?
     
  23. Rifledriver

    Rifledriver Three Time F1 World Champ

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    Sorry but I don't do modification work.
     
  24. mike996

    mike996 F1 Veteran

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    Oh well. :(

    I won't be able to do the work while we're in TX next year so I'll put off the supercharger for the 4th or 5th time and do it in '21...unless I lose interest again! :)
     
  25. jim rosenthal

    jim rosenthal Karting

    Sep 10, 2006
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    Mike, we are about 2w away from getting mine on the road. It's boring up here in the winter as you know. Come up and supervise me installing a blower on my 308 :) LOL

    Actually, I expect there will be some sorting out to do of various systems. But I hope to be driving it between Xmas and New Years' with a bit of luck. Would be nice to see you all soon, too.

    I also have to rebuild the Webers on the GT40, they sat too long. :( That's on the winter list, too.
     

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