Can this really be possible???

tpiini · #1 (**permalink**) 07-16-2004, 10:54 PM

Okay guys, I need someone to chime in here and tell me if I'm halucinating. I bought a completed Cobra a few weeks ago. It has a 289 that is obviously built for top-end power. It can barely get out of its own way below about 2,000 RPM, can just about maintain a cruise down to about 2,800 RPM, and just rips from about 3,000 RPM and up. I spoke with the guy who put the car together. He says he bought the engine from a guy that built it for a road racing Mustang and says that it should pull well up to 9,000 RPM. The only thing he knew "for sure" about the internals is that it has a 12.5:1 compression ratio.

WTF??? I took it out this evening and accelerated to roughly 7,500 RPM and sure enough, it was still pulling strong. I couldn't find the nerve to keep stretching it, however.

Now what puzzles me is that it will idle at 1,000 RPM with a nearly-dying lope, but its not like it's the most radical idle I've ever heard.

The car has 4.57 gears and a Tremec 5-speed so it has plenty of acceleration. I just find it hard to believe that ANY engine can idle somewhat-decently and still have so much top-end power. And to top it off, I'm running 91 octane pump gas without any pinging.

So... for those who have built 289's, is this really so out of the ordinary? I'm just having a hard time believing my eyes here.

Thanks for any input,

Tom

Excaliber · #2 (**permalink**) 07-17-2004, 12:10 AM

Pretty radical cam and 12 to 1 comp on my 427 side oiler. It will idle at 1000 rpm, but it doesn't like to, 1500 is better. Plugs start to clear out about 2000 rpm and from there on,,,,, well hold on 'cause it explodes with power! I find 6000 is about the best shift point for low ET, but it will easily rev to 6500 and beyond. Thats a lot for a BIG block (bore/stroke over 450 cubes).

I reduced the base timing to about 8 to address the "ping" problem and run 92 octane. I dare NOT EVER lug the motor, I MUST keep the rpm's up to avoid a dreaded "ping" condition. As long as I'm careful, no problem with pump gas! My best ET to date is 11.90 on pump gas, retarded timing, a burned clutch and a lousy hole shot, there is certainly more speed there!

So I would say your idle and 2000 rpm situation is "normal". 9000 rpm? Hmmmm,,,,, maybe, but I wouldn't take it there. It will "live" forever if you keep it under 7000. Go to 8 and plan on a "freshen up" every year. Take it to the 9's and figure on a "freshen up" every few months! I think I'll start shifting at 5800, heck thats still fast enough for me! And from 2000 to 5800 rpm is a VERY quick trip.

tpiini · #3 (**permalink**) 07-17-2004, 08:42 AM

Okay, buried deep in a pile of papers for this car I found a copy of a cam card for a Blue Racer cam. I'm wondering if this can really be what's in the car. The spec's are as follows:

Cam lift, .330 INT. .330 EXH
Valve lift, .528 INT, .528 EXH.
Lobe centers, IN, 102, EX, 112. Lash Hot .020 INT .020 EXH
Advertised duration 318 INT, 320 EXH.
.050 duration, 251 INT, 252 EXH.
Adv. Timing BTC 52. ABC 86. BBC 88. ATC 52.
.050 timing BTC 23. ABC 48. BBC 58. ATC 14.

From my engine performance description, could a knowlegable builder out there chime in and give me their opinion? That profile sounds way too radical to idle as well as it does.

Thanks some more,

Tom

Mike Simard · #4 (**permalink**) 07-17-2004, 12:11 PM

Compession effects idle smoothness, a higher compression will have a less lopey idle.

tpiini · #5 (**permalink**) 07-17-2004, 04:32 PM

Quote:

Originally posted by Mike Simard

Compession effects idle smoothness, a higher compression will have a less lopey idle.

Well, maybe it does make sense then. 12.5:1 will certainly have enough pump left in it after that radical cam bleeds off a significant portion of it.

Thanks for the replies,

Tom

Excaliber · #6 (**permalink**) 07-17-2004, 07:39 PM

Hmmmmm,,,,, that may well explain why my motor WILL idle at a 1000. It's doesn't "like it", but it will do it. BIG compression.

Anthony · #7 (**permalink**) 07-17-2004, 07:47 PM

I'd be careful with 92 octane. I think you can have detonation , engine destruction, without ever hearing any pinging, especially at higher rpms. I'd talk to a reputable engine builder.

Excaliber · #8 (**permalink**) 07-18-2004, 01:24 AM

Actually I would think the detonation would be LESS likely at higher rpm. Ping is not just a function of high compression. Running lean, hot or "lugging" the egine is much more likely to lead to ping than a high rpm condition.

I recently had the heads off my engine. Looks pretty good inside, well, except for that blown head gasket on #3.