Turbo with a big cam?

[broncr]

I ran a quick post the other day on running a turbo with high(er) compression (10.5) . I quickly deleted it out of respect for those who tire of rookie questions and opted to do more homework (picking up the McInnes book today). From my homework I've come to realize I'm chasing/flirting with the early turbo disaster - detonation & meltdown. I should have probably waited to read the McInnes book before posting this - but ignor it if you prefer...& my appologies in advance - Turbo talk should be on the prescription drug list - it's very addictive 8).

'made a quick reference to my Q in the Winter projects and am still pursuing my dream (thanks Whit, JP)...

It seems one can "still run a turbo with higher compression if the cam has at least 218* dur. @ .50" " excess compression is bled off at lower rpm & natural loss of VE comps. @ high rpm." The tradeoff - "soft low end torque -then good at 25-2800 rpm through 5000". In a way that answers my Q - do I want to sacrifice some low end torque for turbo power at the upper end of MY normal rpm (daily work truck)?

Any thoughts/insights? Thanks, again Broncr

btw - I LOVE the pic in "Turbo...250" - 54Ford's 223 I-6 Turbo - I can work with that...

 

[BB6Mustang]

IMHO, you will probably be happier with a close to stock-size cam on a turbo motor. A well sized turbo won't start building boost until about 2000 RPM, and won't have full boost until about 2500-3000 RPM, so you want a motor that is strong down low where the turbo can't help you. Plus turbo motors don't like a lot of cam overlap; they tend to run better (even on the top end) when the overlap is kept to a minimum. Usually RV/towing cams work best. They usually have a modest duration (200-208° @0.05"), high lift (0.44"-0.48"), and a high LSA (112-116°). a well matched cam-turbo-motor combination should get good power from about 1500 RPM to 5500+ RPM.

 

[Anonymous]

Broncr, I have had 4 vehicles with turbocharged engines, including a high performance gasoline powered one (Eagle Talon), so can speak from some experience. The contrast between my turbo VW TDI Golf and the Talon couldn't be greater. The Talon doesn't make full boost until 3500 RPM, so even with its 9:1 static compression engine, it can take quite a while (speaking subjectively) for the boost to come on. The TDI, on the other hand, makes usable boost from about 1200 RPM, and hits max boost by 1700 RPM. This makes the VW drive like it has a small V-8...nice usable torque from right off idle.

Since your truck is your daily driver, I suspect that you will be much happier with a turbo that builds usable torque from right off idle. High performance turbos are fun to drive, but one has to keep them buzzed to keep them on boost, and I doubt you drive around all the time with your engine buzzed above 3500 RPMs.

Okay, so much for that. Now to your original question about big cams. I am going to venture out on a limb here and guess that your truck already has a high CR and a big cam in it, right? Well, not to worry. It IS true that you can run this combo with a turbo. It's just that it's not ideal, especially with a carb'd engine (older engines don't have the sophisticated computers to watch out for the engine). There is no built-in detonation identification and avoidance, so it'll be easier to nuke your engine. The exhaust gases will run hotter at lower RPMs, possibly causing premature wear on the turbine section. And you will certainly have to run a boost-activated water/alky injection system to avoid detonation.

Oh yeah, be sure to continue your education at http://www.turbobuick.com/forums/forumd ... forumid=11

Have fun!

 

[Anonymous]

I think,
MSD makes a boost referencing ingition box, that will retard your timing.

MSD makes a Detonation sensor that mounts on the dash.

Use a Stainless Steel tank on your water injection and have it boost referenced also.That way the water flow will increase along with the boost.

For Heavens sake, set this thing up on a chassis dyno to dial in the ignition, water injection, and carb calibrations.

:!: But, that will be one wicked sounding engine. High compression crackle in the exhaust, with a lope of the long cam and a turbine whine

John

 

[broncr]

When I rebuilt my current engine, I was turbo illiterate. I had a really good shop do a good job on the machine work. Bored (min), ballanced, etc., all new everything - stock. I put the engine together myself since I like building engines. It took a bit longer than necessary (porting , etc. ), but I have a rebuild you can't get in a crate. The spare engine had flat tops so that's what I went with. Later it was Clif, Holley 390, EFI exhaust into 2 1/2' single, etc. mmmm mojo...

Soooo... , I have a stock cam in a 10.5 CR engine that is just getting broken in (30K now) and I've been bitten (again) by the mo'power bug. An Rv cam was/is high on my Winter Project list - quick, easy , fairly cheap and effective. But, a Turbo is right there too - as long as I don't blow up one helluva motor in the process. I know my CR is not what you would prefer to turbo, but it's what I've got. If I was patient enough, I'd cam this engine and turbo the original - it NEEDS rebuilding... BAAADLY.

I'm going back to the "library", there's just too much I don't know 'bout turbos. My speed shop didn't have the Mc Innes (sp?) book... drat. Thanks for the input.

 

[BB6Mustang]

As Floridaphatman alluded to, if you use water injection you can use your current engine and run some decent boost. You may also want to consider an intercooler (an air/water will work better than an air/air). You basically want to keep as much heat out of the intake charge as possible. Also, EFI will make tuning such a complex system much easier. You can definitely make this combination work. It will be hard, but should be well worth it in the end.

 

[Anonymous]

:!: I really hate to date myself here BUT that is exactly what Oldsmobile did on the 62-63 Jetfire 215 V8 turbo. It had 10.75 to 1 compression, 6-8 lbs of actual boost, water injection they called "TurboRocket Fluid" and 1hp per cubic inch.
While the reliabilty wasn't what we are use to today the performance was really good especially down low. The one I worked on and drove for 2 years was just as quick as the late 70's TransAms and Z28's.
As most of you have seen in my previous post I like to run the larger cams and have 10 to 10.25 to 1 compression in my 302.
Use of the MSD BTM is a must for timing control.
I havn't used my new water/methanol injection system on this one yet but its about to go on.
Moderate boost is the best way to go. I run 10lbs right now.
As Floridaphatman said "High compression crackel, the lopey idle and Turbo Whine" is DEFINATLY present in my 79 Cobra!
And man does it draw attention at the stop lights!
One thing for sure: Don't use cheep head gaskets!
BigTorque

 

[Anonymous]

How about swapping to a different thickness head gasket?? I know that Clifford Performance carries some that are in various thicknessess up to .100 thick??

Open up the combustion chambers a few cc's each to dump the compression slightly??

Just a thought!

Doug

 

[MustangSix]

The 215 Olds turbo had a high compression engine to alleviate the effects of lag by offering good power before the boost came on. But ultimately the strategy was not workable since it relied on water injection and very high octane fuel. In addition, because of the high compression, boost was very limited and the turbo didn't offer that large an increase in power.

A lot has been learned about turbos in the last 30 years and it's possible to build an engine that has very little lag, high boost, and runs on pump fuel. Electronic engine management, intercoolers, and advanced materials makes it possible even on cars with higher than expected compression ratios for a turbo.

Boosting a 10:1 iron head engine with a hot cam is probably not going to net you a lot of power. I think your boost levels are going to be limited to just a couple of pounds and won't gain you much power in exchange for the compromises you'll have to endure. The more usual low CR/mild cam approach really is a better approach and probably will yeild more power across the range.

 

[broncr]

That's kinda of the conclusion I've come to. Having a good spare block laying around that can be built with a turbo in mind makes it an easier conclusion to accept. Besides, then I can get a bit crazy knowing that - at worst - my fallback is my current 300. Back to the books - on building a turbo block...

 

[Anonymous]

Personally, I would not try to turbo charge an engine with a C/R that high. Sure, it could probably be done, but you would have to be soooooo careful about everything. You'd be skating on very thin ice. It's almost a guarantee that something will break.

Someone mentioned a thicker gasket. I don't know if there are copper head shims available for the I-6. Probably. Even if you put a .060" copper shim in there C/R would still be too high. Intercool and H2O or alcohol injection would help, but still not enough to be really safe. You've already confessed to being a power junky (aren't we all!), so it's unlikely that you will be satisfied with 5 psi of boost!

My thoughts on cams (from the turbo Dodge world): A little overlap is acceptable if you're not going to run high boost. However, as boost pressure goes up the need to have less overlap increases.