Ignition and prop Questions

Yeah, those computer geeks know nothing about motors! Gee, I wonder how he got his 96 impala ss to run 11.9 at 115 mph in the quarter mile on pump gas and without stripping the car down? You'd think a computer geek wouldn't have enough common sense to know how to install his own cam or port his own heads.

But he does. Go figure.

 

The optimum cam design is closely dictated by your head specs. I doubt the earlier cam would work much better than the stock one. If you follow the links I posted above for the power curves for the truck and marine versions of this engine, you'll see that the marine cam gives up some torque down low in order to gain some horsepower higher in the rpm band. Unless you change your prop, this is only going to make your hole shot worse, of course. Once you do, though, the higher revving marine cam should give you most of your top end back. Knowing how much R&D GM puts into their powertrain products, I'd say at a guess it's probably going to have better overall performance than the truck cam once you get your prop issues sorted out.

If you're going to change cams, you might look at this one. I'm running the V8 version of this cam (same grind, just two more cylinders) in my iron headed LT1 impala and it works incredibly well. It idles so smooth at 650 rpm you'd never know there was a hotrod cam in the car - yet it pulls all the way to 6000 rpm, and the car still gets 22 mpg on the highway. Passes the tailpipe sniff test, too.

 

does anyone know if the 2bbl roller cam is the same cam as the 4bbl roller cam in the earlier OMC engines?


BTW I changed the edelbrock 600 with a 500 and as I thought would happen, it gets out of the hole much better.
Will have to try and slalom behind it now.

With a lot of people in the boat it now gets on plane in about 3 seconds.( counting one one thousand- two one thousand- three one thousand..)

however it lifts the bow of the boat pretty high initially, and has to overcome this.(putting 2 people on the bow helps of course)

top speed now with the 500 carb is:

fully loaded -45mph

2 people in the boat- 50mph

(had to jet the carb richer for boat use.)

 

Seeing is believing. Since it is the season for drag racing, tell me where and when you are running your car and I'll be there.

 

I can do better than that. Here's a whole mess of impala ss timeslips. I'm #49 on the list, as well as #102. Every car on this list is either a 94-96 impala ss or a caprice, and there are even a few buick roadmasters and a fleetwood or two. I'm not even close to what some of my more dedicated friends have done.

We know our stuff. You better recognize, b.

 

Those times are not super impressive; about average for the type of car. It doesn't mean you did any of the work anyway or that you can drive it. For that matter that you own the car. Tell me when you race and I'll show up.

 

In the 70s I had a big American type ski boat with a mercruiser 228--it was a very poor pullout for skiing. I changed props,messed with carbs, all sorts of stuff, untill one day the Yankee motor parts man said put in an Edelbrock 2001 intake manifold ( I think it was )for 4 wheel drive vehicle?? Well they were 99 pounds and I couldnt afford it. Finally I bit the bullet and bought it.

Man-- that was the best 99 pounds I ever spent. I just could not believe the extra torque --possibly 25% increase over your wonderfull so called marine manifiold.

He wanted me to fit the cam and manifold package, I was qite happy with the manifold!!!.

 

Those high rise manifolds are great if you have the deck clearance. Volvo makes an intake very similar to the Edlebrock but with brass inserts at the water passages.

 

Gateway raceway in St. Louis. Tuesday night, August 15. Bring your pink slip.

BTW, this doesn't distract me from the fact that the 4.3 truck cam makes more torque below 3000 rpm than the 4.3 marine cam.

 

I went out yesterday and skied behind the boat with the boat fully loaded as it was previously.

Absolutely no problem at all getting up.

The difference between the carburetors was amazing.


Also,
I have a set of the older style 4.3 heads with edelbrock intake if anyone is interested.

The heads have less than 3 hours on them since a complete valve job with 2.02 x 1.60 stainless valves was done.

The intake also has less than 3 hours on it.

Im in California

 

Glad to see you solved your problem. However, everyone on this forum has been telling me that automotive carbs are a fire hazard on boats, because of the fact that boat engine compartments can't vent spilled gas the way a car can, and marine carbs have a different design to make them safer.

As far as the '87 4 barrel cam, I seriously doubt you would see any improvement in performance by swapping it out with your current cam. There has been a HUGE amount of research done in the last 20 years in cam design, what with CAFE and all. In particular, I suspect your current cam probably has higher lift, less valve overlap, and shorter duration than the older cam. All of these things make it a much better performer below 3000 rpm, right where you need it with your heavy boat, and the higher lift makes up for lost duration at higher rpm.

 

the only difference in venting was a single tube coming from the top of the secondaries. Which I drilled on the other carb, now they vent the same.

peak torque on this motor is at 2800 rpm, but when I throttle it, it goes right past peak torque to around 3200 rpm or so.

Maybe even a tighter prop would work better with this engine.

Now peak torque at 2800 is with the factory efi. With my carb setup, im sure peak torque is at a higher rpm.

 

Yeah, I remember them saying it had to do with venting. I'm not much on carbs myself, all my hotrodding has been with fuel injection. We had a time of it a few years ago trying to make the old heads understand that the size of the throttle body doesn't affect the fuel mix the way a carb's throat size does. You just have to reprogram the fuel injector and transmission line pressure tables in the engine computer to reflect the different flow numbers of a bigger throttle body and/or different injectors.

Have you thought about swapping to a bigger cam and running Rhoads lifters to keep the bottom end?

 

With my automotive background its,---- well pathetic that I have never been to a drag strip. St Louis is a bit far for me to go ( dont even know where it is) but I wish I could go as well. I would enjoy something like that so much I --I --might even buy the beer, yes i will buy you one too Gonzo, but not for Stonebreaker though-- hes driving!! I suppose it will be that crappy Budwieser stuff,-- whats a pink slip?

 

Come on down - after we drag race, we can tour the Budweiser brewery and get the beer for free! A pink slip, btw, is racer slang for the title of your car. I suppose because back in the day they were printed on pink paper or something.

PS - don't go to the drag strip unless you're looking for a new hobby to pour money into. It's worse than boating - you can bracket race in the sportsman class all night for 20 bucks at most places; but then you get tired of being the slowest guy at the track, and the mods begin...