1.6 to 1.7 roller rocker swap... net gain on my combo?

[IndyBlk5.0]

im 8.6:1, running the f 303 with 1.6 fms stud mounts, with a tmoss ported gt40 intake, bored intake opening to 75mm , 75mm accufab, full cai with 75mm pro m, protopline 180cc heads (flow more than afr 185's) ....

i was wondering if i would net a nice gain from the added .035 from the cam?

im at .512 right now, which would sit me at .547 lift (my valve springs are good to .550)

also, i have probe pistons w/ valve releifs, the valves are 2.02 1.60... suspect any ptv clearance issues?

THANKS!

 

[Maryland Stang]

You say you are using a TMoss ported intake... Which intake? HO, Explorer, Eddy, TF or what?

 

[IndyBlk5.0]

sorry i forgot to say that... it's a gt40 intake (tubular)

 

[Maryland Stang]

This is just my opinion but I think you've gotten about as much out of that combo as you can. If the Pro heads can outflow the AFRs then the intake is holding you back. I would yank the heads and have them milled to raise the compression and put a higher flow mainfold like the Eddy RPM II on it before I worried about spending money on a rocker arm ratio change.

Additionally, I wouldn't assume that those springs are actually good to .550. Have you taken them out and verified them? .547 is really too close to .550 to use. If one or more springs is out of spec you'll be floating the valves.

 

[04sleeper]

Every combination is different and will net different results.
I have tried this swap with an e-cam back in the day and it slowed the car down 2 tenths in the quarter so we switched them back. We also tried the old 1.6 on the intake and 1.72 on the exhaust ad didn't gain anything from it either. I'm not saying it won't work but in my experiences with it we did not gain anything.

The best thing you could do to maximize your combo would to be to go with a custom grind cam from Buddy Rawls or Ed Curtis.

 

[Rick 91GT]

Every combination is different and will net different results.
I have tried this swap with an e-cam back in the day and it slowed the car down 2 tenths in the quarter so we switched them back. We also tried the old 1.6 on the intake and 1.72 on the exhaust ad didn't gain anything from it either. I'm not saying it won't work but in my experiences with it we did not gain anything.

The best thing you could do to maximize your combo would to be to go with a custom grind cam from Buddy Rawls or Ed Curtis.

I had similar results to this, now when a cam is designed for the mix of rockers you can see some gains. I also think the intake is too small even with porting the upper will hold you back. As far as springs, check the installed height and pressures before making any adjustments. If you go custom and it is a healthy asymetrical lobe design, most likely you'll need springs.

 

[IndyBlk5.0]

they are dual valve springs, the valve train has been upgraded and built professionally to .550 lift. From the sounds of it, I don't want to take the chance of wasted time / possible ptv clearance problems

ps. my combo when it was dynoed only had 300 miles on it and still very tight with a crappy tune. I have a feeling i'm making more now... I do have a feeling my intake is a restriction though... =(

 

[tmoss]

Your lower compression will not net the same power as a 9.0-9.5 compression motor too. Your torque says your getting good VE. Might be worth a new pull to check the A/F and numbers.

The intake is a restriction if you want to make power over ~5,500 rpm based on the length of the runners. If you change intakes your average power may not change much but your power will shift up in rpm.

 

[IndyBlk5.0]

im going to make another dyno pull this summer with a few more added mods... just getting rid of my 10 year old flowmasters, and doing race bullets or another straight through muffler, mac underdrives, and a full msd ignition... we'll see I guess...

 

[Michael Yount]

Indy - what was your p to v clearance?

 

[IndyBlk5.0]

Indy - what was your p to v clearance?

wasnt documented

 

[Michael Yount]

In that case you don't know what your clearance is now -- so know way of knowing if the rocker replacement is gonna cause a problem unless you measure your p to v. The good news is that it won't likely cause a problem. You need to know what the valve lift is at the minimum clearance point - and then you use the ratio of the rocker ratios to calculate how much you'd lose with the change from 1.6's to 1.7's -- with most streetable cams in these engines it's usually around .005-.008". So unless you're right on the edge of clearance, it's usually not a problem.

 

[IndyBlk5.0]

i just dont want to invest the time and money to be dissapointed on a performace gain (if any)

 

[Michael Yount]

I've seen dyno numbers on rocker swaps (1.6 to 1.7) where no power was gained; and numbers where up 15HP was gained at peak. I don't think there's anyway to no unless you 1) do it, then tell us what happened; or 2) pay one of the cam designers to model your set up with the 1.6's and 1.7's. I'm with Tom -- I think the biggest way to help your combo is to get the static CR up -- that combo would REALLY like some more compression.

 

[IndyBlk5.0]

that's not going to change... it is going to see a blower. I also don't want to have to do internal work

ive talked to a very reputable engine builder in indy, and he didn't THINK I would have ptv clearance problems... but not to hold it to him of course.

 

[Maryland Stang]

that's not going to change... it is going to see a blower. I also don't want to have to do internal work

See now, there you go changing the scenario. In this case I'd ditch the GT40 upper and go with the Summit box upper. Take the money you were going to spend of the 1.7s and get a custom cam instead. It doesn't cost that much more then the RRs and it will be tailored to your needs.

 

[IndyBlk5.0]

See now, there you go changing the scenario. In this case I'd ditch the GT40 upper and go with the Summit box upper. Take the money you were going to spend of the 1.7s and get a custom cam instead. It doesn't cost that much more then the RRs and it will be tailored to your needs.

I'm thinking about this, especially when I see how the f303 reacts to an auto.

 

[Michael Yount]

Well - knowing that, I'd skip any changes until you get the huffer on it. See how it strikes your fancy then.

And any truly reputable builder should've smacked you around a bit and told you that you have to measure if you want to know what the clearance in your engine is. Consider yourself smacked again -- with all due respect of course.

 

[IndyBlk5.0]

Well - knowing that, I'd skip any changes until you get the huffer on it. See how it strikes your fancy then.

And any truly reputable builder should've smacked you around a bit and told you that you have to measure if you want to know what the clearance in your engine is. Consider yourself smacked again -- with all due respect of course.

he did.. he even told me what i need to get and how to do it...

I agree about what you just commented on.. I'll just do things i'll need for the combo... i definitely need ignition, and a straight threw muffler if i want to run a 2 1/2'' dual setup. underdrives are 60 bucks new, something i'll think about for the time being... thanks guys... great advice.