LT1Z28

Hey guys just a quick question on a engine dyno i ran last week with my motor. Couldnt afford to finish up all my efi stuff in time so decided to slap a carbed lt4 manifold on for some break in runs on the engine dyno. Basically a stock lt4 manifold i port matched it and that was about it. My questions being the motor started to lay down at 6300 RPM. I was presuming that it would pull to 7000 esentially with my cam and head setup. My question being is how much would the dual plane be holding it back over a fully ported LT4 fi manifold. I know dual planes arent the best for higher RPMs and predicted it to run out of breath but does anyone know where the LT4 carb manifold tends to max out as far as rpms. Also will the fuel injected version suport 7000 RPM. Power ran out at 6300 RPM @494 FWHP TOURQUE @ 4600 was 479. I have the table on the link if you need to see a more detailed run http://rufidlz.cz28.com/dyno.jpg there is also a video of the run in the vids section of the site.


I was estimating to be atleast in the 550fwhp range so i am just more so curious if it still has it in there with the efi setup and a good tune.

The motor is a 383 with
LT4 AFR 210s with a mild compresion of 10.4
Intake .200/153 .300/211 .400/237 .450/265 .500/276 .550/282 .600/295 .650/303

Exhaust .200/111 .300/168 .400/196 .454/203 .500/208 .550/211 .600/214 .650/216

custom grind solid roller with crower 1.65 shaft rockers
Duration 256/260 Intake lift .646 exhaust Lift .614 Lobe Seperation 112

Anyways just some insight to if i am on par and the power will come or if something seems weird snd i need to do some hunting. All input is appreciated
Later
Mike

Denny McLain

Mike

I can’t really help ya, but thanks for sharing the information. Everything looks in order including your fuel/air but with that much cam duration, I’d expect it to peak a little higher also.

The only thing that stands out to me is your dynamic compression must be real low with only 10.2 static compression and a lot of cam duration. That has to be hurting ya some. The LTx stroker motors that I’ve seen perform the best with the AFR 210 heads had more compression and less duration in the cam.

Question….. whose 1.65 rockers are you using? Any problems with valve cover clearance

LT1Z28

crower shaft mounts and the valve covers are modified morosso valve covers that have been chopped and hacked for my DP and clearance. Compression was something that i ended up fubbin on my end of things changed my setup a few time and then just stuck with it. I know it would like it a little higher but thats just were i ended up when the smoke settled .

OldSStroker

I did a little EA Pro simulation on your engine with interesting results.

Using 14% driveline losses and 300 rpm/second acceleration I got 494 hp @6300, but peak was 502 @ 6800. Torque peak was 428 @ 5300. I need to work on the manifold simulation to get the peak torque higher. I'm guessing something in the valvetrain (springs?) is letting you down about 6300.

The "bad" news was a DCR of about 7.1, even with 4* advance in the cam. Straight up I got 6.8 DCR. To get DCR into the high 8's, you'd need 13:1 static CR with that cam. The good news is 13:1 SCR/8.8 DCR gave 30 more hp and 20 more lb-ft.

A good single-plane with EFI was worth an additional 35 hp (559 @6800). Remember this is predicting rwhp with 14% overall driveline losses.

I didn't play with cams: I get help for them.

Less cam duration would help DCR and probably power, IMO.

LT1Z28

The reason i am questioning the LT4 Carb mani is due to the fact on the initial runs the shop owner had a el cheapo dual plane that he had converted over for break in runs on a lt1 with that manifold i peaked out at 460 FWHP at around 5600 RPM . Covertinting over to the lt4 dual plane i picked up another 40 horse and essentially 700 RPM. My curiousity more so lies on how does the carb version of the lt4 compares to the efi version for upper RPMs. I would love a single plane setup but my damn Direct port is too pretty to scrap now and if i sacrifice a bit of power na i will make it up on the squeeze. By the way stroker interesting advice on the DCR. My piston choice was my limiting factor on my SCR it has been a slow build financially. Originally my direction was welll lets say in a differnet direction. However for the time being i will be running it as it is. Heads were all dissambled and springs all checked out up for the battle. So i dont know really where i am lacking and am just hoping that i can gain some going to the my manifold.

tjwong

I am not all to sure that the low DCR is the reason that he is not where he wants to be. The reason I say this is because we run a NHRA stock eliminator car which is a 95 Transam. In the NHRA rules we have to run stock appearing heads meaning no port work, stock compression ratio, stock rocker arms, stock 48mm TB, stock stroke cranks, and unported intakes. In our car we can run 10.70s uncorked. The engine dyno'd at 525hp and we use a cam ground by Bullet Cams with specs like: 256/262 but with stock lift numbers. Our cams are typically ground on either a 106 or a 108 which means even more overlap than LT1Z28's choice. In our car of course our chassis is setup correctly and works extremely efficient to get the 1.30 60 foot times that we do. All of that equates to quick ETs as well.

I do agree in his case especially if he is planning on driving this car on the street that less duration will certainly help. Our car is not streetable, we run a 5500 RPM stall behind a TH 350 tranny with 2.75 low gears. Not to mention a spool in the rear end which don't help going around corners much I couldn't imaging driving a car with that much duration as a daily driver, streetability would be lousy.

LT1Z28

Car is to be mainly a track car with occasional cruises on the street. Hense the full manual TH400 with tbrake diff is a 9inch with locker and 3.89s for now but spool and different gears may be going in depending on how traction out of the hole is with the the tbrake and juice. So streetability isnt much of my concern however the motor was idling quite nicely at 1000 rpm on the dyno.
But regardless still more into the concept of the dual planes effect if any on my motor. As storker said i would benefit alot from a single plane but am more so curious as to the benefits of my intake over the dual plane lt4 manifold used on the runs

OldSStroker

Your initial idea was FI? That's my guess.

Try dynoing with your ported LT manifold. I'm not predicting anything, but you might be surprised...one way or the other.

Pretty manifolds sell well.

LT1Z28

I wish i had the money right now to redyno it with my setup however i am tapped. Plus still need to get my speedpro setup for a distributor order a dizzy for the intake and a crank trigger drill a hole for the dizzy and a list of other crap before my intake goes back on. Just consider me the poor racer with a lot of time and not a lot of money so things take even more time
But thanks for the input guys if anyone has any more feedback that is great otherwise we shall just have to wait and see how thing go for me.
Later
Mike

Denny McLain

Old Stroker.........

This is not meant to be offensive as you and Bret are very knowledgable, but I have the same software and it doesn't match the dyno sheets of combinations I've dynoed.

I may be a bit more salty regarding dynoing different combinations than most give me credit for. If fact, I'm thinking about deleting it completely from my computer as it simply does not match my "actual dyno" sheets.

I kinda love playing with it, but real world is........ real world. I believe in software to get ya in the ball park, dyno tuning to get ya on base; but track tuning gets you to home plate.

NJLT1SS

Hey Mike, I used the GM LT4 dual plane carb intake on my 396 to run in on the dyno. I didnt have the funds to get an EFI setup on it for the dyno, but all I was lookin to do was get it running, rings seated, and make sure nothing leaked. I am running a fully ported/welded/epoxied LT4 intake on the car, and will be going for a chassis dyno session in a few months. Here is a little more on my set up: 396, AFR 210's Comp port heads hand finished, flow numbers similar to yours, Comp hydraulic roller, 242/252, .580/.580 LS 114, 11:1 compression. It was run in on the dyno with the GM LT4 carb intake, 750 HP carb, 1 3/4 headers, MSD HEI ignition, total timing set at 36*. This set up made 506 HP at 5900 RPM, and 496 FT TQ at around 4400 RPM. I was very pleased with this outcome, as I didnt think it would make over 470 HP or so with the dual plane choking it, not to mention the air quality sucked that day, 75* outside, and it was pouring rain all day. My builder said that with the LT4 intake there is at least another 20 to 30 HP waitng to come out, as my cam should have peaked around 6300 RPM. I hope this info helps you out, as far as your combo being on par or not.



Nick

Denny McLain

I happen to have a good friend running NHRA F/S. Regarding the stock unporting of heads and intake....... you don't happen to know anything about acid do ya? Just wondering.

Seen his dyno sheets and the powerband really is amazing consider such low lift. Still wondering how you guys figure out these things.

I agree...... with that much duration even with lower compression, it should be peaking at a higher rpm. Could even be the rings are not seated yet.

LT1Z28

NJLT1SS I would be extremely interested if you could keep me informed on your chassis runs when the time comes. Also out of curiosity sake do you happen to have your engine dyno graphs so i could glance over them. It would be greatly appreciated.
Later
Mike

tjwong

Denny, I do know about acid porting. But even with acid porting you can't ever acid etch enough metal out of the ports to even come close to say a set of AFR CNC ported 195's. Sure there is some gain, but its not as much as one may think. Too much etching and its pretty obvious that they are not stock. The NHRA tech guys are not that dumb Not to mention that they have gauges to measure TB bore size and intake bore sizes as well. There comes a point where the overlap helps performance by improving scavenging in the exhaust system to help evacuate the exhaust and at the same time to help draw in the fresh intake charge. But the Hp curve peaks at a pretty high RPM. We typically trap the car at around 7000 to 7200 RPM. 500hp isn't a lot of Hp, the rest of what makes the car fast is the chassis setup that is at least 50% of what makes it so quick.

NJLT1SS

Hey Mike, I will see if I can scan it sometime this week and e-mail you the graph. I will definitly keep you posted on my results with the chassis dyno session, I would like to hit close to 450 RWHP.



Nick