I haven't seen any install pics or fitment comments on TGO about the new Holley Hi-Ram for small blocks, so wanted to share some thoughts.

Overall I'm happy with it, but here's some direct-experience and info for posterity.

• It fits under the stock Firebird hood. I'd already cut bracing 20 years ago to fit the HSR, but it's possible that the Hi-Ram would fit even with stock bracing intact.
• At the highest contact point of the HSR (throttle body), the Hi-Ram is about an inch shorter. The middle is nearly identical, height-wise.
• The injector mount angle on the Hi-Ram is strange and seems stupid. The injector is angled at the intake port floor, almost backwards, whereas the HSR is more pointed into the head port. I'm not sure why Holley designed it this way, but maybe there's a reason. Can see this pretty easily in the last photo.
• If you're running a non-electronic transmission, the height on the TV cable mount is problematic. It's still doable but took a good amount of modification to make it work.
• Overall the design looks superior to the HSR. The runner placement and spacing is better and the plenum is better-designed. You can tell this is a purpose-build design versus adapting an existing mold.
• There aren't enough vacuum ports if you're using an external MAP sensor, but you can solve by using a bolt-in to barb fitting adapter.
• This is subjective but it's kind of ugly. The HSR is much better looking under the hood.

Here are some comparisons to the HSR. I wish I had an apples-to-apples comparison but replaced the intake at the same time as other changes so don't have good data on power gains.

 

What I have found is injector line of sight at the intake valves makes a HUGE difference in your transient fueling. If the injector is not pointed at the back of the valve with a clear line of sight it creates signifigant work for you as a tuner to get the transitient fueling correct. I had to make a lot of changes tuning wise going from a stock L31 truck manifold that had the spider injectors pointing directly at the valves to GM L31 Marine crossram style intake that has the runners layed flat from one bank with their inlets on the opposite side and injectors pointed straight down much less backwards. Replaced that intake with one that now has a direct line of sight to the valve because it has tunnel ram like ports (Indmar MCX). Suddenly nearly stock transient fueling values work exceptionally well again. It might not be as much of an issue with a batch fired setup but with full sequential setup it makes a tremendous difference and creates a big headache either way you want to look at it. With sequential the fuel os sprayed on the back of a closed intake valve at idle and low loads that helps heat and vaporize said fuel. I feel like alot of the drivability issues of the Proflow 4 4150 setup like used on the ZZ6 come from the injectors pointing straight at the port floor rather than at the valve on that setup as well and it is further compounded by Edelbrock not having a decent calibration during starting and cold warmup.

Just a WAG but my money is on the HSR making more low-midrange torque due to increased port velocity and better air/fuel mixture quality. That newer manifold would probably be great with big cube engines, high rpm and boost but I do not see it performing better on the average street engine. I wish Holley had done some A to B dyno testing on both a fairly stock SBC maybe even a 305 and a larger engine like a 427.

 

Whats the port dimensions at the plenum entrance? Definitely seems like more area than hsr and seems like it would be a great choice for street 383-400+ inch sbc’s. It can actually feed the heads those engines need

the injection angle i can see being an issue depending on what system you are using. With a Holley hp/dominator, you can play with the injection timing end angle and possibly could improve your drivability. Some guys dont spray on a closed valve at any time and it works well enough. I believe my current bbc is setup like this with a custom end angle table, id have to go back and look at the low speed low load areas to see what timing i had in it but i believe injection starts well after valve opening but this is with large injectors with low pulse widths and low cycle duty.

 

While a cam with a lot of overlap negates the benifit and often run better at idle and low loads delaying the start of injection until the exhaust valve is closed on split overlap, on cams with a smaller or near stock overlap triangle spraying on the back of the closed intake valve tremendously helps idle quality and off-idle drivability especially immediately after a cold start. The valve itself will always be the hottest part of the intake tract. The intake valves temperature increases much more quickly than the rest of the intake tract due to the fact the valve is exposed directly to the heat of combustion in the chamber. I am not a fan of overly large injectors for a given power goal. I prefer to see 70-80% duty cycle at WOT. The smaller the injector the better it atomizes the fuel and the longer you spray the fuel during the intake event at higher mass air flow conditions the better the fuel is mixed into the incoming air and distributed around the combustion chamber giving a more uniform, even, fast burn during combustion. There is a reason most factory injectors are sized near the upper limit of their flow ability and in some GM engines it is not uncommon to see 100+% reported duty cycle at WOT on a stock engine and stock tuning. Think early LR4/LM7/LQ4/LQ9 and L18 where GM was pulling out all the tricks to keep them clean emissions wise and get as much fuel mileage as possible. It sucks having to buy injectors when you modify them but there was a reason GM used those.

While it is not the biggest, baddest engine ever built, this is my 383 that is probably making 475+ hp now with the milder 219/219 @ 0.050 on a 112 LSA cam running on 70% Ethanol pump E85. On the highway rolling 75 mph, it is getting 16-17 mpg on E70 and 20-21 mpg on E10 93 octane in a 7,000 lbs Express van. It burns very clean and has stock GM like drivability. Perfect cold starts, great throttle response, pulls smoothly in overdrive from 1,100 rpm with a locked torque converter and just all around a great cruiser. The injectors I chose seem perfectly sized for the combination too on pump E70. My normal end of injection timing is set for about 30° BBDC. The makeup injection used for like adding AE fuel can continue to BDC which is a Boundary setting of 6.5 in a Gen3 LS controller. The PCM calculates the start of injection timing based off the RPM, Pulsewidth and End of Injection values.

 

They're actually sized really close to the lower openings, which measured out to about 2 1/4 x 1 3/8. I'm running Bosch 210s...duty cycle is only 30% at WOT, and that's with 35 lbs of fuel pressure. So may be an option.

Pretty much the exact scenario Fast was warning against below.

I was wondering that too. And especially with the poor physical injector angle, you're not even getting the benefit of atomization when fuel is spraying directly at the port floor. I don't understand why Holley designed it this way.

 

Yeah what oems do for sizing they have to take into consideration a lot of factors most of us performance enthusiasts dont need to worry about.

injection atomization will vary depending on fuel pressure, air intake temps and air port velocity, and injector spray patterns. I guess its a compromise for that intake design, runner positioning and height and where the injectors have to be. While not ideal i dont think it will be too much of a problem.

 

I think you are downplaying it a bit. It will flat out be a pain to dial in the low pulsewidth areas near idle and the off idle transients especially when the engine is cold. It will be an epic tuning disaster drivability wise without a lot of tuning time and effort to make it somewhat work. Even manifolds with injectors pointing straight down much less backwards are extremely finicky. The GM L31 marine manifold comes to mind as I ran one with an 0411 and later P59 LS controller. It took a lot of work to make it run right. Edelbrocks 4150 PF4 manifold especially running their garbage ECM is flat horrible on cold start. The Chevy ZZ6 crate engine has that same garbage on it and has the same issues plus some because the controller is locked. It tends to have a massive lean bog, even backfires and it will stall when you drop an automatic transmission into gear unless you hold it up around 1,000-1,200 rpm. I ultimately ended up maxing out their accelerstion fuel adjustments and richened the cold start AFR considerably but it was only a minor improvement to the situation and still has the stalling issue unless you warm it up first like a chokeless carb in cold weather. Literally a chokeless carb would run better in my experience. I will say the absolute worst combination I have ever come across was a LSA blower on cathedral port heads using adapters and the oversize injectors in it only made the issues with it worse. Since it was a 6.0L talked the owner into swapping the heads to rectangle ports and ditching those adapters in addition to putting suitably sized GM injectors with good data available into it vs the injector decaps Sloppy promotes and is a straight up hack thing to do anyway. It drove like an OE vehicle after. That one was especially bad because it had a 6spd manual behind it vs an automatic that has a torque converter that temds to absorb some of the drivability hiccups that expose themself far worse in a vehicle with 3 pedals.

 

This was when I first got the marine manifold running with a P59 on my 383. Even though it had about 140-150F of coolant temp in it in this clip, coming off idle it had a massive hesitation/lean bog coming up off-idle that took a ton of transient fuel adjustments some that are only defined in open source and not HPTuners software to sort out. Without using the added transient fuel tables available in open source for the P01/P59, I never would have been able to get it to run correctly. As I mentioned previously it is a bigger issue at low flow rates. As you see in this clip once the engine is turning some RPM it accelerated fairly normally. At the time this would have been fairly undriveable had it had a manual transmission. You would be trying to smoothly let out on the clutch and the engine would just hesitate and bog. This was the exact issue that LSA setup I mentioned above was having too. This is also the issue the Proflow4 4150 and ZZ6 crate engines have. Excuse the perceived valvetrain noise. My phones microphone latches on to the roller rockers and guideplates and makes them sound much louder than they are in real life. In real life it sounds about like a stock LS6 valvetrain.

 

It's already got some startup and low-speed/low-RPM drivability issues compared to the HSR. Has to be directly related to the injectors and intake.

Nothing detrimental, especially with an auto and pretty loose converter, but annoying nonetheless.

With smaller injectors and/or a smaller cam it may not be as noticeable, but as it is it's going to take some tuning time to get it sorted out.

 

It will definitely require that. Depending on what you are running ECM and tuning software wise will dictate just how accurate you are able to dial it in as well.

 

possibly injectors but also possibly flow characteristics from the runner design/shape and plenum volume. Doesnt surprise me it may need some tuning over the hsr

 

Do you feel you have gained or lost anything since the change?

 

Unfortunately I don't have an apples to apples comparison. The new intake went on at the same time as a supercharger.

I can tell you that the RPM range was extended with the new setup generally. The HSR is the red graph. Note the peak at 5,500 and the odd kink down before 6,000. This kept happening after numerous other changes (coil on plug, lifters, springs, etc.) that eventually lead me to believe it was the intake choking the engine in the upper Rs.

What I don't know is whether the supercharger could have also extended out the RPM peak (blue), versus just making additional power on the same curve. So hard to tell if the intake contributed on it's own.

 

I have a pro Flo xt intake on my zz430 clone. The Gm dyno sheet showed the engine running out at 5800-6k. When I put the blower on mine the it continued to make power up to 6500. I wasnt ok w spinning it that high so I have a limiter at 6k. So my experience is similar to yours as far as rpm range.

 

What did your boost curve do? Usualy centri have increasing boost with rpm so it always is rising and that can extend powerband peak since boost is overcoming losses.

 

Boost was still rising after the engine rolled over - maxed out at about 8.5psi at 6,400-6,500. Few hundred RPM past peak HP.

 

Yeah i tuned a blown tpi car that basically had flat hp from 5000-6000 where we stopped cuz it would throw belts, alignment issue. Boost rose to 12. Was 8.5 at 4800-5000 ish and that 4 psi basically extended the hp curve out a bit past where it normally would peak. But a short runner intake would have made another 75-100 hp i think lol

 

Interesting. Good examples here. Seems like boost will commonly extend the usable RPM range.

Also means that I don't have any reliable, apples-to-apples on potential Pro-ram gains over the HSR.

 

what is your throttle cable setup? I'm almost at the point of installing the hi-ram into my bird

 

I used the Lokar universal LS cable. Had to adapt to the firewall hole and pedal, but wasn't too difficult.

https://www.summitracing.com/parts/LOK-XTC-1000LS1