Today I took my car to the dyno. It is a 1975 280z with an ls1 stroked 383.
The car flatlines on the dyno once it gets up into the 5000rpm range. My first pass was 386hp and final was 401hp. This is very low considering when I was a 346ci I made 408hp 405tq with a 225/229 580/591 114+4 cam and patriot predator heads 63cc 205cc intake.

The new mods. I am using the same heads as before with patriot dual gold
BLOCK
Lunati 4inch crank
lunati connecting rods
mauhle pistons gapped .018 1st .022 2nd
HEADS
patriot predator heads 2.02intake 1.6 exhaust. 63 combustion, 205cc intake. stock deck. Manton 7.57 11/32 pushrods. ls7 lifters.
INTAKE/EXHAUST
ls6 intake ported throttle body
saunderson shorty headers (only option)
dual 2.5inch to 3inch single

Like stated I am running everything the same except the new MS4 cam and 383 stroker but I was making more power with the stock cubes and small cam. I did increase lifter preload to .0825. Do you guys have any Ideas? I just ordered BTR extreme dual springs that are rated for .660 lift instead of .650 and 25lbs more tension than my patriot dual golds. I have been scouring the web since I got home and cant really find the info Im looking for. If you guys need more info Im sure I have it.

 

Why did you change the preload? Do you have a dyno graph you can post up, that would help.

 

The MS4 is pretty tight on a 346, did you check PTV when you installed? Have you done a leak down check?

 

I changed the preload because I had lots of valve train noise. I only had .062 on the ls7 lifters. It was loud.
The MS4 is not installed on a 346 this is a 383 and yes I have plenty of room on the ptv. I have done a compression test and leakdown both with great results.
I am sorry I dont have a copy of the dyno sheet. It looked like it just stop pulling once it got near 5000. It would dive slightly then raise slightly then dive slighty for nearly 1200 rpms

 

Never seen valve float look like a flat line, normally its all over the place on the sheet, and it sounds awful if you were at the dyno.

 

I was at he dyno. It wasn't perfectly flat it was fluctuating and just didn't gain anymore power after 5000

 

So you put a rather large aggressive cam that specifically states in it's description it needs a on used springs?
If so you put it on a used spring with 135lbs on the seat new 375lbs open and now they are somewhat worn.
where the recommended spring is 145 closed 450open.
The specs for the springs you say you ordered are .
160 lbs @ 1.780", 380 lbs @ 1.180", 400 lbs @ 1.130
That is a step in the right direction but still 50-60lbs less over the nose, still not the same specs as what the cam calls for. I might call Texas Speed and see if they think that spring will do the job long term. Even if it works today as the springs "break in" it might soften enough to cause problems a little valve loft isn't always a bad thing but I wonder if being 50lbs shy of spec pressure over the nose will loft too soon and not land well.

Oh and your belief of 25lbs more tension is based on different installed heights.


You really need to choose someone you trust and let them sell you the right complimentary components. You liked that Texas Speed cam so why not get springs from them too.

 

How long have you been running those patriot dual golds, was the seat height set to the recommended height, and what rockers?
What trans A4 or M6?

 

Ok I see what your saying about the springs. When I purchased their cam I asked if my springs would be able to accommodate the new cam. The said yes considering the valve train had only 2156 miles on them from the 346. I just got off the phone with them now and they told me they were surprised that those springs didn't hold. They also said I would be fine with the btr extremes I purchased.
The trans is a t56 from an fbody

 

So hows your clutch, any slipping issues(that would also kill your power if it was slipping some while on the dyno)?

 

the clutch is 2156 miles new, it is a spec stage 2. i dont think its the clutch. i say that because the car continued to rev the same speed and mph climbed in accordance with rpm and no smells

 

Post an image of the dyno chart.

 

Valve float at the end of my graph.. Is that what yours looks like?

 

Do you mean at 6,400 RPM? Valve float won't recover. From the curve it looks like it was starting to recover.

 

I assure u it wasn't recovering

 

Well for one you have shorty headers. That holds you back big time especially with big cams.

 

yes that is exactly what mine looks like on the dyno above. My shorty headers I know are holding me back but with the same build with the same headers on other 280z they are making high 400and close to 500hp. I only have so much space on the sides of my engine bay. I am currently modding some longtubes. but yes I almost thought that you somehow got ahold of my dyno sheet. My pushrods are also 11/32 7.57. I wonder if the extra weight may be putting extra stress on the springs...next time i go back to the dyno Im going to go with my 7.55 5/16 pushrods as well.

 

Get the best pushrod you can, some 3/8 would be great. The extra weight vs deflection is worth it.

 

Im running the Manton 11/32. They are ridiculous sitting next to the regular hardened ones I had from patriot.

 

I have my dyno graph. I just installed the btr springs and no change...any ideas
how do i upload the graphs