Where did my HP go?

Last season my motor got hungry and decided to eat the cam. This is an SVO block, 4.5 stroke and had 4.5 bore, but due to having to get rid of a few scrapes we took it another 80 over and comp specd the same cam, so that's what went back in. I have SCJ heads worked as much as they can be worked, 13:5 comp.

My problem is I can actually feel a loss in power. Went from a 4.8 sec 320' to a 5.1, and NOTHING else has been changed.
Any ideas on how to get more power out of her? The last time I had it on the dyno it was 4.5 with 4.440 and was over 900 hp, and 871 torque w/over 700 of that at 3100 RPM (AWESOME LAUNCH off the trans brake in the sand, but kept super heating the oil) so I had it squared up. (which did take care of the oil temp issues) Did not dyno it after that build though.
Have I maxed out these heads capabilities?

This is a 4,200 lb full size Bronco, built for just playing in the sand with the occasional trips to the drags. I used to be the fastest on the dunes and REALLY want to get back to the top.  

ANY ideas would be appreciated

Thanks, Ray

Did a guy named Les build all that power for you?

If you went another .080 on the bore from 4.440 that would give a 4.520 bore your heads may not be up to the task of tjat many cubes. That is alot of cubes and HP for a SCJ head

The current bore is now 4.582, the 4.440 was a few years back. What would be the next step for heads, and how much of my current configuration can be reused? IE/ intake, headers?

Motor was built by Babbits Performance and Pierce Race Engines up here in MI. and the heads were done by Roush way back in the day
Thanks

Did you degree the cam? What about gaskets? When you parked the intake, are you sure your gaskets aren't in the runners? Did you deck the block? Shave the heads at all?

Aluminum heads don't tend to stay straight when used, and taken off. Should have had em milled a hair to true the deck face again.

You shouldn't have lost anything, about the only thing that should have happened everything else equal, is the power peaks would have moved down the RPM range a few 100 RPM.

P51s would help some over the SCJ and won't have to change headers or intake. Maybe some of the head guys will chime in.

69F100 wrote:P51s would help some over the SCJ and won't have to change headers or intake. Maybe some of the head guys will chime in.

Sad part is, somebody talked me into selling a set of them 2 years ago, because they were just sitting on the shelf collecting dust waiting for me to need a rebuild I said sure!

If I could pick up quite a bit more power with a new set of heads, I wouldn't have a problem with changing the intake, but my headers were a royal PIA, and I would hate to have to do them again.

Hoping some head guys chime in also!

Thanks!

I'm with Kim on this one boys... It shouldn't have lost that much on the strip by just changing the bore size...

kim wrote:Did you degree the cam?  What about gaskets?  When you parked the intake, are you sure your gaskets aren't in the runners?  Did you deck the block?  Shave the heads at all?

Aluminum heads don't tend to stay straight when used, and taken off.  Should have had em milled a hair to true the deck face again.

You shouldn't have lost anything, about the only thing that should have happened everything else equal, is the power peaks would have moved down the RPM range a few 100 RPM.

Yes, they were milled the minimum, new gaskets were used and the cam was degree'd back to match original build, because it was working perfect and running consistent.

If you are looking to change heads, I'd go A460 all the way especially at your cubic inch...has the transmission started doing anything funny?

460bronco wrote:If you are looking to change heads, I'd go A460 all the way especially at your cubic inch...has the transmission started doing anything funny?

I changed to a Coan Pro-Glide 6 or so years back, I couldn't find a c6 that would last a weekend. By far one of my happiest investments

you should'nt have lost any power.i'd think a big bore would help the heads flow more if anything. where you got the timing set?

The 4.585" ring set is not available in as of a low tension as the 4.500"/4.530"/4.560"/4.600" stuff. May not be "the" issue but could be an issue.

Did you spec. the new pistons up to keep the same compression ratio?

Just thinking of course, camshaft timing could add to the loss of performance and as Lem wrote, the ring package could contributed as well. Put the two of them together and you may have the answer to your concern.

Dave.

Are you running a vacuum pump on the engine? If you are do you have a vacuum gauge on it? If the vacuum is going down that could be a problem.

Did u do a compression test on each cylinder to see if they are all close to the same?

How much bore did you go up since the loss in power? might not have enough carburetor for the added cubes.

When you went to the 4.582 bore who speced your pistons? Did you keep same C.R?

I think something else might be wrong. You should have not lost much power (if all is the same) with just a bore change. Yes the bigger ring tension will hurt some but not to the point of loosing 0.3 sec!!!! Also was the camshaft degreed back in correctly?

Your power is still there, like someone else said on here. What has happened is your probably running the engine out of it's happy place, all of your power now is at a lower rpm.

Take some converter out of it and some gear, and see what happens. With that small of a head , you need to be loading the crap out of the engine during the run to make it work.


The hp you making tells me that your heads are probably flowing as good or better than a set of P-51s with a smaller cross section that's why the torque is so high on your engine.

With the combo you have , you will need to cam it like you do a 440 dodge (6-8 more degrees of duration @ .050). It is short on head big on cubes.

JMHO

"super heating the oil" could you explain that a little? Trans or engine oil?

Lem Evans wrote:"super heating the oil" could you explain that a little? Trans or engine oil?

When I had the bore at 4.440 with the stroke at 4.5, the motor would make 6-7 runs and overheat. I did EVERYTHING possible to alleviate it; 55 GPM mez pump, biggest radiator Howe makes w/sealed shroud and w/ dual fans, external oil cooler, keeping the front clip off, etc., all with no success. Put a oil temp gauge on it and found the oil was heating to above 320* before the water temp even reached 200*, so we figured that could be the issue. I dealt with it for one summer and tore her back down. Found massive friction wear on the piston skirts, so we took the bore to 4.5 figuring it would square it up and eliminate that possibility.
And it worked. She can sit there and idle now and all the temps stay right around the 180-210 range, and I can run back to back non stop w/out any overheating.
I am NOT an engine builder by any means, and I try to pick the brains of anyone who is before I rush into things. But I do help with the shops doing my work to learn and know what I have.
This rebuild was 100% done to mirror what it was previously other than the overbore; pistons same CR, cam degree'd and set the same, etc.
That's what is really bugging me. Any of you who have driven the same set up for years know you CAN feel a difference, and that's where I am at.
Could I make a significant gain with a new head and bigger cam Lem? With the rings not being as tight, would that mean I am getting some blow-by, hence losing a little compression?
I REALLY appreciate all the input and ideas guys!!
Thanks, Ray

bronco911 wrote: I used to be the fastest on the dunes and REALLY want to get back to the top.  

IDK about the fastest, but for the first 50-100' you have alot of us killed.  That is a pretty big drop in ET though, didn't seem much slower racing you this summer. Have you attended a few T&T to be sure of these results? Being we race on 300' of dirt, things aren't always written in stone as far as ET/MPH from what I've found. Maybe you had a separate issue and don't see it?  Tires, converter woes, anything else?  What is the MPH on the latest passes?  Maybe since the season is over, best to go dyno and verify where your power is.

And I'm still confused why making the bore/stroke square would cool the engine down? Was the piston/wall clearance just too tight, hence the scuffing?

J.Toney wrote:

bronco911 wrote: I used to be the fastest on the dunes and REALLY want to get back to the top.  

IDK about the fastest, but for the first 50-100' you have alot of us killed.  That is a pretty big drop in ET though, didn't seem much slower racing you this summer. Have you attended a few T&T to be sure of these results? Being we race on 300' of dirt, things aren't always written in stone as far as ET/MPH from what I've found. Maybe you had a separate issue and don't see it?  Tires, converter woes, anything else?  What is the MPH on the latest passes?  Maybe since the season is over, best to go dyno and verify where your power is.

And I'm still confused why making the bore/stroke square would cool the engine down? Was the piston/wall clearance just too tight, hence the scuffing?

Good to see some other duners on here! Yeah, got a few T&T's in. I'll look at the slips when I get home for the mph. The tires are new, and are a different brand. Hoosiers vs goodyears. I did notice a much stiffer sidewall on these, may be an issue since I was having issues hooking down on the flats with these, where the GY's hooked at 7lbs these I have to take to 5lbs.
I do want to do some dyno time this winter, but I want to be prepared; try to get some different head and cam combos to try, etc. (I am trying to build another motor also, so spare parts would be a good thing) I want to get as much as possible out of her, trying to at least look respectable with the Bad Company jeep and beat Bracketts old Chevy. Real hard when they have 2000lbs+ less than me and I am SO close. (I just picked up a 66 bronco chassis I want to put together as a two seater 1500hp to give them a big surprise next year) But I want the old lead sled to stay respectable also.
The machine shop told me the odd angle is what made it so tight ( but I almost think they ordered a piston with to tall of a skirt and were covering their azz by the way they looked) The only thing I know for sure is that it worked, so?
Thanks, Ray

Ummmm...Ben is running a good clip better than 4.80's:shock: . Sorry, but the bronco is down here with us sportsman. Still, 4.80's is quick going NA. 5 teens something ain't right, my 4800-ish # wood hauler runs there all day on motor and it made 700/650 when it was fresh in '09. Keep us posted, interested in seeing where it's at right now power wise.

J.Toney wrote:Ummmm...Ben is running a good clip better than 4.80's:shock: . Sorry, but the bronco is down here with us sportsman. Still, 4.80's is quick going NA. 5 teens something ain't right, my 4800-ish # wood hauler runs there all day on motor and it made 700/650 when it was fresh in '09. Keep us posted, interested in seeing where it's at right now power wise.

Yeah, thats why I said look respectable, not beat Ben. (thats the goal with the new build) Ok, before the rebuild I was pretty consistent at 4.89ish, 1.87 60' and 61-63 MPH. Now, she's right around 5.04ish, 1.92 60' and 62.44 MPH. Looking at these now, looks like I am missing some of my low end torque.  

Or some starting line bite......