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purple72Gremlin 
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Charter Member Joined: Jul/01/2007 Location: Illinois Status: Online Points: 16610 |
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 Posted: May/02/2019 at 5:11pm |
Id put a fuel pump gauge on it and see if you are losing pressure
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WesternRed
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Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5796 |
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Posted: May/02/2019 at 5:15pm |
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Bigger cam will kill a little torque down low, that might explain the drop in 60' times, what sort of numbers are you seeing.
1/2 pre-load on the lifters sounds pretty normal, shouldn't be a problem, could try backing it off to maybe 1/8th turn or even just contact, if the problem goes away then it would indicate that the lifters are pumping up. Could also be a dud lifter that is not holding up at higher RPM. With the ignition, make sure you have a full 12 volt supply. Cam RPM ratings are pretty vague numbers in reality since the RPM potential will depend on how the whole combination works together. If for some reason, your heads/intake combination flows really badly then that will limit the RPM potential of the engine, particularly with a high lift short duration cam, which is sort of where the Comp XE series sits, but the XE274 is still a pretty decent cam.
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I've finally given up drinking for good...........now I only drink for evil.
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WesternRed
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Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5796 |
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Posted: May/02/2019 at 5:32pm |
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Bit of follow up since my 360 is fairly similar to yours.
Comp recommends the 986-16 springs with that cam, which requires some sort of machining to the heads, I am running the 926-16 springs, which are a step down from yours. All other valavetrain componentry is similar. My cam has similar duration at 0.050", slightly less lift and more total duration, I have no trouble turning it to 6500 RPM in all gears, I feel that is pretty much the limit, but I have seen as high as 7000 RPM with the odd brain fade moment. I am using the Crane anti pump up lifters: https://www.summitracing.com/int/parts/crn-99278-16/overview/ Maybe that is helping. Still running stock pressed steel rocker arms to although they have been converted to adjustable with new studs and polylocks. I did find the exhaust was initially holding this combo back, but that was with factory free flow manifolds and 2" pipes. Some headers and 3" piles really unleashed it's potential.
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I've finally given up drinking for good...........now I only drink for evil.
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PROSTOCKTOM
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Joined: Jun/20/2010 Location: Indiana Status: Offline Points: 2450 |
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Posted: May/02/2019 at 6:49pm |
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From what I am reading I'll bet it's either an ignition box or a fuel supply problem. Having dealt with both of these issues in the past on my first strip only race car. My first guess is lack of fuel since it's pulling fine in low gear and RPM limited in the others. Sounds like fuel bowls running dry. Have you checked the float bowl levels with the bowl plug out? A blue pump should supply you with adequate fuel delivery if the pump is working 100%. I ran a 5-gallon rear mounted cell with a #6 Earl's braided stainless hose up to a Holley regulator on my first 100% strip car long ago. It had a Holley Blue pump that fueled a 7500 RPM 306 CI Ford, Holley 650 DP ,250 @ .050" solid cam, 5500 converter, 538 gears, and never ran out of fuel running 7.50 1/8th mile, 11.85 1/4 mile times while puling the front wheels 18" off the ground, so unless you have a pump problem your blue pump will feed a lot of engine.
I really think it's a simple problem, but it can be frustrating tracking it down. Tom
Edited by PROSTOCKTOM - May/02/2019 at 8:16pm |
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WesternRed
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Posted: May/02/2019 at 8:03pm |
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He is running a MSD 6AL box, that should be up to the task unless something is wrong with it or the power supply.
My combo above is working fine with the old Pertronix Ignitor. Stick the fuel pressure gauge up on the cowl so that you can see it while you are running. Might be something as simple as the fuel line sucking flat and restricting flow, I have had that before.
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I've finally given up drinking for good...........now I only drink for evil.
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PacerLarry
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Joined: Aug/02/2010 Location: New Lenox, IL Status: Offline Points: 103 |
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Posted: May/03/2019 at 7:44am |
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WesternRed:
To clear up some confusion, when I said my 60' is down, I meant numerically (faster). I went from 1.96 average to 1.79. I am very pleased with how the car is launching. I am running the 986-16 springs as recommended. Based on what I am hearing from everyone, that is not likely the issue. Tom: Yes I have checked my float levels. I am also running jet extensions in the back. After going through just about all of my wiring, verifying connections, trying replacement parts, etc, I am leaning toward a fuel issue. After talking with Dad, we realized when I went from the 650 to the 750 carb, all I changed was the main body. Metering blocks and bowls were transferred. I borrowed a set of larger diameter needle and seats, as well as metering blocks off an HP carb. Going to be playing around with the fuel system this weekend.
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5918 |
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Posted: May/03/2019 at 11:10am |
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Is it a dead-head type fuel system with a Holley Regulator? Is the fuel pump mounted lower than the tank?Is there a fuel line routed somewhere that might get a hot spot? Is the intake manifold choke stove crossover blocked off? Big bucks option, an O2 Sensor and Mixture gauge would show if it's going lean.
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xfactor
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Joined: Sep/09/2012 Location: Port McNeill BC Status: Offline Points: 478 |
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Posted: May/03/2019 at 11:46am |
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Just a shot in the dark but you said the engine won't rev over 5900 rpm . Is it possible your rev limiter has slipped down to 5900 rpm . Mine is built into my tack and have this happen a time or two when working around the tack when I inadvertently moved the setting down
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Ray Harper 69 AMX 401
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PROSTOCKTOM
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Joined: Jun/20/2010 Location: Indiana Status: Offline Points: 2450 |
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Posted: May/03/2019 at 11:54am |
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I don't think the metering blocks or needle and seats are going to end up being the cause of your problem, but it won't hurt to look at them. As Red mentioned already, having a mechanical fuel pressure gauge is really handy to have on the engine. However I still think it's a supply issue and the reason I say that is, your car is doing the same thing my friend Jody's factory stock 67 427 Caprice did. It took off great in first, but it half way through second the car would nose over and rpms would not climb just like it had a throttle stop on it. The problem ended up being that the fuel bowl on a 67 Quadrajet is really small compared to the later versions and the mechanical pump could not pump fuel fast enough to keep the bowl full with wide open exhibitions of speed. He added a small flow through inline electric fuel pump in the back of the car and a toggle switch. Now he can leave the pump off in normal driving, but when he wants to drag race all he has to do is flip the switch and it never runs out of fuel. His problem sounds exactly like yours and this is why I think its an issue from the tank forward. Be interesting to see what you find out. I always like to learn about the root cause on problems like this since it helps educate us all when we run across similar issues.
Tom
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PacerLarry
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Joined: Aug/02/2010 Location: New Lenox, IL Status: Offline Points: 103 |
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Posted: May/03/2019 at 12:25pm |
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Just to clarify, the car pulls real hard up to 5900 in first gear. Second and third is where it hits a wall at 5000. Just like its on a rev limiter as some have said.
The pump is below the tank. It is a Holley deadhead regulator (also have a backup to try) The only spot where the line would see head is when it crosses from the fender wall to the intake manifold Exhaust crossover is not blocked. My 6al box has the rev limiter built in. it was set at 6500, I upped it to 7000, then 8200. Aside from sending the box to MSD to test, I have to imagine that is not the case. I found that a blue pump should flow 70 gal at 9psi. I am going to flow test right at the carb inlet to see what I have. That should eliminate the possibility of a line restriction (as well as a visual inspection). My thoughts on the needle and see are along the lines of what Tom mentioned. I have standard needle and seat right now. Theoretically, I could have all the volume in the world at the carb, but if I can't flow enough fuel through the needle and seat, the bowls will empty. I appreciate everyone's ideas. I know there is something right in front of me that I'm missing
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PHAT69AMX wrote: