I have an '89 5.0 engine. After 5 years of racing this engine, it was time to freshen it up. I run in a spec class so the engine must remain relatively stock. As the subject says after doing a rebuild/refresh, I go to the dyno and the numbers are worse than before. Any thoughts would be appreciated. Below is the before and after specs.

Before rebuild:
Bone stock 5.0 with underdrive pulleys and 1-5/8" headers
Dyno'd at 214 HP271 T

After the rebuild:
normal machine shop stuff with a 0.030 overbore.
new 30 over pistons and rings
slightly higher compression ratio
heads redone to stock configuration.
swapped in 1.7 roller rockers for the stock stamped.
swapped in adjustable fuel pressure regulator
swapped in 1-1/2" headers for the 1-5/8 ( should increase torque)
Stock Injectors sent out to be clean and rebuilt.
Everything else replaced with stock OEM parts.

So now I go to the dyno and after 13 pulls with varying tunes, I end up with 190HP/240T as best. We checked most of the obvious things. We were all over on timing and fuel pressure but nothing helped. Engine sounds stout and revs up just fine. With the changes I made, even with a bad tune, should be better than the original. This one has me scratching my head.

Thanks in advance for reading this and providing suggestions.

 

I wouldn't think a switch to a bigger header would increase torque. Can you switch back to the old headers?

As for the power loss. You may have lost compression ratio with the new pistons. You'll need to do some measuring to see that one.

I minor loss in horsepower might be from a new timing chain. New = advanced, relative to old which = retarded. Retarded cam timing will make more hp but that doesn't explain your huge loss in torque.

Hopefully other can offer some more ideas.

 

your choking the engine, with restrictive heads(in stock specs) and smaller exhaust. Smaller exhaust only increases torque if the exhaust was too big to begin with, as I have seen happen in various 5.0s

 

Who built the shortblock?

 

this maybe a stupid question .. isnt stock bore 4.000 .. if you went from 4.000 to 4.030 and used the same stock pistons wouldnt they be to small .. and whenever i look for pistons they always say 4.030 .. do pistons not come 4.00 ? i dont get it .. will someone so kindly explain please

 

Were the before and after dyno numbers done on the same dyno? Is there anything the dyno operator may have done to change the numbers by setting something up differently?

Go back to the 1 5/8 headers see if anything gets better.

Also, you are dealing with a new, tight motor and it may need to loosen up a bit before you get top power out of it.

 

with all the mods in my sig im making 217hp and about 285 tq. with just pulleys and headers you making just as much as me wtf.

 

and yea you should check out to make sure you cylinder walls arnt bigger then ur piston rings

 

the motor needs to break in, and i'd like to know which pistons you used. alot of rebuilder pistons are "destroked" and sit lower in the hole to compensate for milled heads and block, but in reality just end up dropping your compression.

 

Jfsram, 86 5.0L

The switch was from the larger 1-5/8 to 1-1/2. I made this switched based on others in our series who found this mod to make better torque. Belive me, this is something I've been considering and will probably switch back to test.

My compression ratio is actually a little higher....It was measured.

nmerrill

I was the builder, this is my 25th engine that I've built.

ponyboy302

Stock bore is 4.000 so 0.030 over is 4.030. Ithought people would read in that I went to larger pistons and rings.

capri debris

You have hit on something that I am hoping for. The dyno I used this time is a new one the guys at the local speed shop put in. I'm not confident they have things set up right. At least I'm hoping. My plan is to take the car to my usual dyno that I have used numerous times. I hope to do this in the next week or so. I'm not going to change anything until I get the first pull on that dyno.

Yes, I know a tight motor will be slightly lower but I'm not going to get 30 HP after break in.

crocop

I stake my making those good numbers on my engine building skill. there's actually cars in the series making better than me in stock configuration.