No Power Low RPM

[ryanc]

I just got my SVO back up and running after a complete tear down and something isnt right. It idles good and smooth and revs sharp in neutral, but when I try driving it, I have almost no power until 2800 RPM or so. Basically get it rolling an put my foot to the floor and it takes ~10 seconds to get to 3k or so. Just before it hit boost, it starts to feel alright and then once on boost, it seems like the power is there. I havent gone above 8lbs or so because it is a fresh motor and cam so Im trying to take it easy on her.

Ignition timing is set at 10* BTDC with the spout out.

Cam timing mark is at 0 with the crank at TDC. I did retard the cam timing by 4* and it helped, but still not right and I dont think I should have to retard that much so I didnt want to go any further. And at 4* advanced it wouldnt even start.

Compression check showed ~120 in all cylinders

Fuel pressure is at ~41 PSI and increases with boost.

The car has a ported head, Bo 1.5 cam, Racer Walsh cam gear, gutted upper/ knife edged lower, SC throttle body, Rods header, full 3" exhaust, LA3, and 75lb injectors.

Please help :p

[svobud]

The car has a ported head, Bo 1.5 cam, Racer Walsh cam gear, gutted upper/ knife edged lower, SC throttle body, Rods header, full 3" exhaust, LA3, and 75lb injectors.

Please help :p

75 lb injectors!?! Seriously?

The no low end power sounds like the Cam isnt right.

[ryanc]

Yes on the 75's...Id agree that they are a little big but from what Ive read you get the largest ones that you think you will need and its better to have too much injector than not enough because you can tune around that. And from my calculations, to make 350 crank HP, it requires a 71 lb injector... So that leaves room for the future.

Whats my best bet to be sure of the cam? Like I said, the marks line up correctly. But Im also thinking it cam related because @ 4* retarded (according to my marks) it felt much better than at 0.

[GAboySVO]

If Bo ported your head then he most likely surfaced it to bring the compression ration back to stock. This will make your stock timing marks not work. If you didn't have him do that then your compression ratio will be low and the engine will have no power without boost.

Read in the Compression ratio analysis section under Motor(air) link.

http://www.merkurencyclopedia.com/index.html

When you advance the cam, your power (peak torque) band should move down in the RPM range. When you retard the cam, your power band (peak torque) moves up in the RPM range.

I'm with Bud on this one. Your initial cam timing is not correct. Put a vacuum gauge on it and adjust the cam until the gauge is in the green portion.

Also, with the 75lb injectors on a stock computer, you are flooding it out and that could have an effect on the power. Reduce your fuel pressure to compensate until you get a J3 chip to set it up for the big injectors.

[svobud]

Yes on the 75's...Id agree that they are a little big but from what Ive read you get the largest ones that you think you will need and its better to have too much injector than not enough because you can tune around that. And from my calculations, to make 350 crank HP, it requires a 71 lb injector... So that leaves room for the future.

Way too big on a stock computer. I'm surprised it idles. BTW, plenty of people here making 300 rear wheel HP with the stock 35# injectors.

[ryanc]

If Bo ported your head then he most likely surfaced it to bring the compression ration back to stock. This will make your stock timing marks not work. If you didn't have him do that then your compression ratio will be low and the engine will have no power without boost.

The head was not ported by Bo, so I dont know if it has been cut down or not. But it does have the heart shaped chambers (which have been worked) so Id imagine that would bring the compression up a bit. And just to make sure I was clear with this, when I say it has NO power, I mean it has no power. Foot to the floor in 1st gear and it will take 10 seconds to come up to 3k.

And I do have a J3 set up for the injectors. Im pretty sure it wouldnt run at all with out it.

Ill try the vacuum gauge thing, But Im not exactly sure what you are saying to do. Id get the gauge and put it on a good vacuum source and take a reading. Then from there, just shut down and adjust a few degrees and take another reading?

[GAboySVO]

But it does have the heart shaped chambers (which have been worked) so Id imagine that would bring the compression up a bit.

Taking material away will increase the chamber volume and lower the compression ratio.

Ill try the vacuum gauge thing, But Im not exactly sure what you are saying to do. Id get the gauge and put it on a good vacuum source and take a reading. Then from there, just shut down and adjust a few degrees and take another reading?

The vacuum gauge has zones that indicate wrong cam timing and ignition timing. It will help you diagnose the problem. Then shut it down and adjust the cam sprocket accordingly. Rinse, repeat. I have Bo's 2.1 cam and had a similar situation when using the stock pointers as a guide. The vacuum gauge got me in the right ball park.

[ryanc]

Taking material away will increase the chamber volume and lower the compression ratio.

Yea, I got that... I was just saying that the heart shape combustion chamber should bump it up vs the stock D shaped chamber.

Ill pick up a vacuum gauge and see where that gets me. Thanks!

[ryanc]

Im borrowing a vacuum gauge tomorrow, Im not sure if its got a green section, or if it just has the numbers on it. If it just has numbers, What are my green numbers?

[GAboySVO]

My gauge says:

0-10 in Hg - Late valve timing
14-17 in Hg - Late ignition timing
17-22 in Hg - Normal moor

[ryanc]

Thanks, I should get it checked this evening and Ill report back.

[ryanc]

Let me remind you that Im not sure of my actual cam timing, but based on the marks, I checked the vacuum with my cam mark reading retarded 4* and it was reading ~10 inches at idle. So I advanced it to 4* advanced, based on this picture (my gear just has #'s but no +/-)

http://www.svoca.com/forum/attachmen...1&d=1135237900

And the car wouldnt start. I reset it to 0* and was reading ~8 inches of vacuum so I then set it to 8* retarded. Here Im getting 15 inches of vacuum. It felt a little better there, but still not right. So do i just disregard my marks and keep retarding it til I get 17-22 Inches?

[GAboySVO]

Let me remind you that Im not sure of my actual cam timing, but based on the marks, I checked the vacuum with my cam mark reading retarded 4* and it was reading ~10 inches at idle. So I advanced it to 4* advanced, based on this picture (my gear just has #'s but no +/-)

And the car wouldnt start. I reset it to 0* and was reading ~8 inches of vacuum so I then set it to 8* retarded. Here Im getting 15 inches of vacuum. It felt a little better there, but still not right. So do i just disregard my marks and keep retarding it til I get 17-22 Inches?

Yes. Advance until you get at least 17 then take it for a spin and report back. You could have it set 1 tooth off, about 9*, so you could just be getting to the correct setting.

[ryanc]

From where every my cam was, I retarded it 4 deg, and it felt better, then 8 deg and better still, and then maxed out the adjustment at 12 deg and it felt even better but still not perfect. I took the belt off and moved it over one more tooth and set the cam gear back to 0*. It feels pretty good and I still have 12* either way to fine tune with. Thanks for the help!

[gbeaird]

Yeah, getting the gears all aligned up right is a real PITA to me. I've done it about 4 times on two different SVOs and seem to spend way more time than necessary getting everything properly aligned. I HATE doing that job.