So we're in the process of putting together our first engine and have relied a great deal on the input of others as to what to expect and where we'll end up for engine performance.

I have a decent understanding but -ZERO- experience in terms of matching engine components, so I'm throwing this out there as a potential combo and seeing what the far more experienced masses have to say...

We've got a standard block 454 with the 8.5 : 1 compression I believe it is. Standard open chamber / oval port heads. Forget what the stock valve size is, perhaps you can help me there?

The engine is going to be bored .030 and the pistons will remain stock flat-top. A normal 3-angle valve job will be done as well, along with new performace springs. The cam we're being recommended toward by the machine shop's supplier for a fun street/strip application is a Magnum and looks like this:

RPM 1500-5800
Duration 270
224 @ 50*
Lift 510/510
LSA 110

It's then suggested we go with an RPM Performer intake and a Holley 750 carb. Hope to keep the stock torque converter attached to the TH400 and I believe we've currently got stock .273 gears in the rear.

What can we expect from a combo like this in terms of performance, weekend-only driveability, HP, torque, etc...? I'm hearing that a package like this will run pump gas with no problem, have a good low-middle performance curve and not be too much of a bear on the 2-bolt bottom end. It's not going to be a daily driver, but the

Would love to hear from someone with experience in a package like this !

Verify that compression ratio...Have everything cc'd and know what you have.

Here is an old combo I had with the same cam and intake.

Chevy 454 .060 over (468 CI) 8.9:1 Compression, Non-Ported Stock 1966 Oval Port 427 Closed Chamber Heads (100 cc +/-)
Comp Cams Hydraulic (270H) .510/.510, 224/224@ 0.050", 1.72 Roller Tip Rockers
Edelbrock Performer RPM Intake; Holley 750 DP
GM HEI, MSD Rev Limiter; Autometer (Gauges, Tach, and Shift Light) - Shift @ 5200 RPM
Sanderson Shorty Headers, 2 1/2" Flowmaster Series 50
Chevy TH-400, with B&M Holeshot 2400 11" Convertor (actual stall is approx. 2800 RPM)
Trans Cooler, Hurst 1/4 Stick, Chevy 12 Bolt, Powertrax Locker, GM 3:55 Gears.
Stock GM Suspension, Air Lift air bag in right rear spring
Stock 4-Row Radiator with Electric Fan to supplement Stock Clutch Fan
Stock Chevy Rallies; 15x7 Front, and 15x8 with 5" backspace in Rear
Weight = 3970 pounds

1/4 mile best - 12.65 @ 104.8mph
Consistent 12.70's and 1.74 60 ft's
1/8 mile best - 7.97 @ 84.9 mph

IMHO and experience,I wouldn't use a stock torque convertor..I run a B&M 2400 holeshot in my combo with 2.73's..works mint for me,no excessive slippage..you almost don't even know its there.Enhanced low end throttle response and quicker/harder launches are the benefits.

I guess the question mark for us (and I know YOUR 273's work great!) is how the total package will work out in car. Not having a lot (read: any) experience in putting such pieces together, there are some pretty big questions considering the time and cash investment. :confused:

Like everyone, we want tons of horsepower, lots of hookup and flat/detached eyeballs and expect to pay very little for it! :D So back to reality, with a 15" tire and relatively low gearing, would this combo work out and what kind of HP and torque can we expect?

I would guess 400-425 HP 500 ft/lb. tq
should run mid/low 13's I would guess w/2.73's
make sure you stick with a short 15" tire
add some gear,it could be in the high 12's

The combo I posted above made about 370 HP at best. Don't worry about HP, It doesn't matter, lose it from your vocabulary.

I am with Chris in saying 500 ft/lbs.

Do you have any comments on the combo I listed?

HP is really a secondary figure to me anyway - not worried about it truthfully...

More, we're looking for a fast car, one that will launch well and push you back in the seat while giving off that terrific BBC rumble and a nice lopey cam. Sounds like we're heading that way...

So if we go with that cam, intake and a 750DP, it sounds like an aftermarket converter in the 2400 range is a better bet and in the future getting some better gears will add to the fun even more.

I'm sure we'll have more questions and thoughts in the future, but at least it sounds lie we're on a good track for something fun to drive on the weekends!

A 3000 converter will give you more of a push you back in the seat feel. I would go with that to give you more of what you are looking for. I had very good luck with the BM 2400 Holeshot as Chris has mentioned, but a 3000 probably would have made the car quicker. Just install a good trans cooler to be safe

Thanks Tom - good tip.

We'll likely go with the cam that our machinist's cam guy recommended. Apparently he's considered quite the BBC authority (which scares the h*** out of me usually!). It sounds like the intake and carb will work fine with it too. We also were suggested to run the 750 with leaner jets or use a 650 during break in to allow the valves to seat properly before running a thicker (richer) mixture. He said once in awhile, with the hard seats, a thicker mixture will prevent the valves from ever seating properly. Hadn't heard that one before. Anyone else...?

A 3K converter eh? Sounds like around the high 2's it'll start feeling like a kick in the kazzoo! redface.gif Thanks!

-curt

I never heard of that before...I wouldn't worry about it.

IMHO that's not really enough compression for that cam.

Since you're buying pistons anyway, I'd lose the flat-tops, and get some low-dome ones. You don't need to go crazy on it or anything, but you need a bit more.

Your heads are probably 119cc open-chamber, like 781s, or similar. You want something like this piston right here http://store.summitracing.com/partdetail.asp?part=STL-H581CP30 with a .039" or .041" head gasket and stock deck height.

Having 2.19" and 1.88" valves installed in your heads, and mildly unshrouding and porting them to match, is another way to get more power without any penalty.

That combo will put your CR right at 10:1.

somebody here might be able to calculate the dcr on this combo, I bet it is very low with the 270 magnum and 8.5-1 compression. Compression might even be closer to 8-1 with composition head gaskets. 87 octane will probably work. I would think the 270 cam would like about 9.5 to 10-1 compression to run good.

So I'm hearing now that a higher compression may be the way to go. The shop already ordered and has the Master Kit in hand, but I could proabably tell him to swap pistons from it. Not sure what the cost difference would be to go to a low-domed piston, but how much of a difference are we talking about here? If we're only talking a 10th off in the 1/4 or something like that, then I wouldn't be too worried. If we're talking about a 14 sec car versus a 13 second car, then differences like that I would be worried about...

Realistically, what are the ups and downs if we sayed with the flat-tops and 8.x compression or went to the domed at 9.x compression?

This is EXACTLY the feedback we're looking for. Please keep it coming!!!


-c

The difference could be HUGE. Could easily be .2 off your 60', and several percent more pull all the way down the track.

A low compression motor with too much cam will tend to have too little leave, as its major inadequacy. Lazy down low, takes a while to get going. That's definitely what you'd end up with, with the combo you're about to build.

Double check things the best you can. My first big block was a over a full point lower than the machine shop guy said (turned out the compression was for a closed chamber head and I had an open chamber). I would vote for more compression also. If you decide later to add more cam, head work,etc. you won't have to tear into the engine to put in new pistons.

Bump the compression or add nitrous. Probably the same dollarwise and you can turn it off with a switch :D

Shoot for 9-1 CR. You can get pistons at near the same price for that too. Just make sure of the head cc first.

Speed Pro makes a .100 domed hypertectic piston..less than $200 for the set.With open chamber heads,you'll be around 8.5-9.0 to 1

Thanks guys - great feedback!
We'll look in to the cc's and then upping the CR
today.

Comparing domed that are .100, how much of a difference can one expect over the ones (Summit I believe) that were suggested at .340?
Cost-wise, of course there's a difference, but dollar:dollar how big of a low-end power increase and at what point does the increased dome-size and higher compression begin to make other motor-related changes neccesary?

Thanks again!

-curt

Okay, so now I'm confused.

I spoke with both the machinist as well as his supplier of heads and cams. I explained to them the concerns I've been getting and the thoughts on a higher compression to compensate for the cam we're using.

Both of them were strongly in agreement that the cam should be just fine with stock compression, especially since the manufacturer rates the cam at 1500-5200 RPM.

Both also strongly suggested going with shorter gears rather than the current 2.73's. Worst case, go with a higher stall converter they both chimed in.

The supplier said he'd be more than happy to take back the pistons we've currently got and make the extra money on the domed (.100 I believe) but he really emphasized there was no real cost-benefit here in the low-mid rpm range.

So what's the answer...? I'm concerend and obviously don't want to seal this motor into dog performance, but I've got folks on both sides of the fence here...

Is a 2400-3000 converter and say... 3.31's a good answer for the existing cam combo? Or do I keep the 2.73's, go with a 2400-3000 converter and up the compression? Combining all 3 up front means we keep spending extra dollars and wonder where it makes the most sense...

Somebody needs to write a book on combinations and expected performance... this topic is obviously regularly beat to death! :confused: :confused: :(

I would go with the .100 domes and shave the heads.Keep the 2.73's for now,and get a convertor.

Do whatever you have to do to get some compression in that dude. I played with one like that once many years ago and it was a stone. The 350 I pulled out would have spanked it all day long!

An 8.0 (likely really 7.75 with replacement head gaskets and stock replacement pistons that are usually shorter by .020 or so) will be slug no matter what you do to it short of a blower. At least get up near 9.7-10.0 compression.

Either change pistons or do some serious block/head milling.


JIM